Singh et al., Afr J Tradit Complement Altern Med., (2018) 15 (1): 199-215
https://doi.org/10.21010/ajtcam.v15i1.21
A COMPREHENSIVE REVIEW ON THE GENUS PLUMBAGO WITH FOCUS ON PLUMBAGO
AURICULATA (PLUMBAGINACEAE)
Karishma Singh1*, Yougasphree Naidoo2, Himansu Baijnath3
School of Life Sciences, University of KwaZulu Natal, Westville Campus, Durban, South Africa.
*Corresponding Author’s Email: k1008.singh@gmail.com
Article History
Received: Jun. 01, 2017
Revised Received: Oct. 02, 2017
Accepted: Oct. 02, 2017
Published Online: Dec. 29, 2017
Abstract
Background: The genus Plumbago distributed in warm tropical regions throughout the world is the largest genus in
Plumbaginaceae. Medicinal plants are characteristic to the genus Plumbago and are cultivated and utilized worldwide.
Plumbago auriculata Lam. is common in South Africa and is often cultivated for its ornamental and medicinal uses
throughout the world.
Materials and Methods: A comprehensive review of the genus Plumbago with focus on Plumbago auriculata was carried
out and information was gathered using scientific publications, conference proceedings, the internet and books. Articles
based on the morphology, pharmacological and medicinal uses of Plumbago auriculata was analysed thoroughly.
Results: Plumbago auriculata plant parts posses a wide range of phytochemicals with plumbagin being the marker
compound showing various pharmacological activities. Different plant parts are claimed to be used for the treatment of
human and animal ailments, however they do exhibit toxic properties and need to be administered with caution. Salt
secreting glands and trichomes are characteristic of Plumbaginaceae.
Conclusion: This study reveals new insights on the genus Plumbago and the potential use of species in the genus as
medicinal plants. Plumbago auriculata possess the bioactive compound plumbagin and secondary metabolites, thus, it is of
high medicinal importance. P. auriculata is a poorly nor favourite studied species in the genus Plumbago and further
research needs to be carried out to explore specific details of the species.
Key words: Plumbago, salt glands, trichomes, pharmacological activities, plumbagin, micropropagation.
Introduction
Over the years, human health problems have been increasing at an alarming rate and are now becoming life
threatening. Conventional medicine used to control health problems is often too expensive and has many side-effects.
Therefore, many people have turned to the use of medicinal plants for the control and treatment of health problems. Plant
extracts have been used for hundreds of years to cure ailments (Balunas and Kinghorn, 2005). The vast resource of
thousands of medicinal plants and their contribution to human health are to be discovered. Exploiting traditional medicine
systems has served as a promising approach in an era of increasing demand for drug production and rising costs of western
medicine, globally.
It has been reported that many plants naturally produce secondary metabolites, commonly referred to as
phytochemicals or biologically active compounds which are essential for plant metabolism but play a great role in the
plants’ protection mechanism (Ascensao et al., 1997). In addition to plant protection, these bioactive compounds also serve
as precursors for the development of natural, environmentally friendly and low toxicity pharmaceuticals, flavourants,
fragrances, cosmetics and pesticides due to their therapeutic and aromatic properties. Bioactive compounds are either
produced, excreted or stored in small amounts in specialized cells, termed secretory structures in the form of salt glands,
trichomes, resin ducts, idioblasts, laticifiers, colleters and nectaries located in various reproductive and vegetative organs of
the plant (Thomas, 1991). In order to understand the biological activity and composition of the secreted exudate, it is vital
to know the morphology, distribution and secretory processes of the main secretory structures involved. However, these
structures vary in form, distribution, function and type of secretion across different plant families.
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The family Plumbaginaceae Juss.(a.k.a the leadwort family) has about 24 genera and about 400 species (The Plant
List, 2017). This is debatable because some publications reported that there are 700-800 species in the family (APG II,
2003; Simpson, 2010; Renner and Specht, 2011). Plumbaginaceae was first described in 1789 by Antoine Laurent de
Jussieu and it was the only family in the order Plumbaginales. However, in 2003 the APG system of plant classification
placed Plumbaginaceae in the order Caryophyllales due to certain species having carnivorous characteristics and is sister to
the family Polygonaceae (Kubitzki, 1993; Perveen and Qaiser, 2004; Simpson, 2010). Plumbaginaceae comprises mainly
herbs, lianas and shrubs, often occurring in saline habitats. The presence of secretory glands is characteristic of the family
(Wilson, 1980; Faraday and Thomson, 1986a). Species of the Plumbaginaceae are of ornamental and medicinal importance.
Plumbago auriculata Lam. an evergreen shrub is indigenous to South Africa (Figure 1) but is distibuted in other parts of
the world in tropical and subtropical regions (Foden and Potter, 2015). P. auriculata occurs in thicket and shrub valley
bushveld. It is often called Cape Plumbago or Cape Leadwort because it is widely found in the Cape regions of South
Africa (Batten, 1986; Kubitzki, 1993; Foden and Potter, 2015). P. auriculata is an easy to manage plant as it is tolerant to
high humidity, high temperature and diseases and can be treated as an ornamental as well as a medicinal plant as it contains
many potent bioactive compounds (Chen and Gao, 2013). P. auriculata bears a close resemblance to Drosera, a
carnivorous plant, which plays a role as an attractant as well as a repellant to many insects (Plachno et al., 2006). The genus
Plumbago comprises of 18 species, three commonly studied species that is Plumbago rosea L. syn indica L., Plumbago
zeylanica L., and Plumbago auriculata. In all these three species, P. auriculata is the least-studied especially in South
Africa. This review focuses on information about the morphology, biology, chemical composition, pharmacology,
medicinal uses and toxicity of the genus with a particular emphasis on Plumbago auriculata.
Figure 1: Distrubution of Plumbago auriculata in South Africa (After Fonden and Potter, 2015).
An overview of the genus
The genus Plumbago comprises 18 species distributed and utilised throughout the world in warm regions (APG,
2009; The Plant List, 2017). It is the largest genus in the family (APG, 2003, 2009). In Sourthen Africa 5 species are native
and 2 are cultivated (Glen, 2002). Species are cultivated and utilized worldwide mostly for their medicinal and
pharmacological properties due to the presence of plumbagin amongst other phytochemical compounds (Table 1) (Craven
and Craven, 2000; Galal et al., 2012; Jose et al., 2014; Saha and Paul, 2012, 2014; Omwenga and Paul, 2012; Purger et al.,
2012; That et al., 2012; Thamaraj and Antonysamy, 2013). The genus comprises shrubs or perennial herbs and the presence
of a hairy calyx is characteristic of the genus (Batten, 1986) The hairy calyx is associated with insect entrapment amongst
other functions. The most commonly cultivated and utilized species is Plumbago zeylanica with several publications
(Abera et al., 2008; Chauhan, 2014; Demma et al., 2009; Jeyachandran et al., 2009; Tyagi and Menghani, 2014).
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Table 1: Species List of the genus Plumbago (The Plant List, 2017).
Species Name
Common
Locality
Description
Name
Plumbago
Tanzania
Erect herb or
amplexicaulis
subshrub, with
Oliv.
glaborous stems
and bright deep
blue flowers.
Plumbago aphylla
Madagascar, Slender shrub
Bojer ex Boiss.
Aldabra
with erect stems,
Islands and
leaves simple,
Tanzania
entire, and
alternate. Flowers
white with hairy
calyx.
Plumbago
Cape
South
Bushy perennial
auriculata Lam
leadwort
Africa,
evergreen shrub,
Africa,
trusses of pale
America,
blue and white
Asia, India
flowers, leaves
have minute dots
and persistent
hairy calyx.
Plumbago ciliata
Engl.
Plumbago
caerulea Kunth
chileno
Common
leadwort/
European
leadwort
Plumbago
madagascariensis
M. Peltier
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Chile
Ethiopia,
Kenya,
Uganda
Europe,
Turkey
Kenya,
Tanzania
Plumbago
glandulicaulis
Wilmot-Dear
Plumbago indica
L. syn. Rosea L.
Pharmacological
uses
Used to treat
diarrhoea, mouth
infections and is
applied as an
eyewash for
cataract.
Anti-bacterial and
antifungal.
Has many
therapeutic
properties and can
be used for warts,
fractures, oedema,
headaches, skin
lesions, piles,
rheumatism,
diarrhoea and
malaria and as
emetics.
Antimicrobial,
antiulcer,
antimalarial,
antifungal,
anticancer.
Ornamental value.
Roots yield
plumbagin.
Used to treat
diarrhoea, stomach
ache..
Used for treatment
of blisters,
inflammation,
itching, toothache,
skin disorders.
Antimicrobial,
antimalarial
Tanzania
Plumbago dawei
Rolfe
Plumbago
europaea L.
Traditional uses
Scarlet
leadwort
Asia Africa,
India,
Indonesia
,Phillippines
Madagascar
Shrub, with erect
stem and blue
flowers.
Perennial herb
with erect stems
and white flowers.
Herbaceous half
shrubby,
multi=branched
plant with trusses
of pink or purple
flowers.
Herb, erect hairy
and sticky stem
with leaves
glaborous and
white flowers.
Perennial
herbaceous plants
with erect half
woody stems and
red flowers.
Shrub, erect stem
and variations of
blue, white and
Antimicrobial,
anticancer,
antifungal,
antimutagenic and
insecticidal.
Ornamental value.
Used to treat
gastric acidity, skin
disease,
constipation, ,
haemorrhoids,
rheumatoid
arthritis, paralysis,
also used in horses
to expel worms,
also abortifacient.
Anticancer, antiinflammatory,
antiatherogenic.
Ethiopia,
Kenya,
Tanzania
Namibia
Plumbago montiselgonis Bullock
Plumbago
pearsonii (L.)
Bolus
Plumbago
pulchella Boiss.
Plumbago
stenophylla
Wilmot-Dear
Plumbago
scandens L.
Cola de
iguana
Mexico
Kenya,
Tanzania
Louco;
caataia;
caapomong
a
Brazil
Plumbago tristis
Aiton
South
Africa
Darkflowered
leadwort
Plumbago wissii
Friedr.
Brandberg
Plumbago
Namibia
Plumbago
zeylanica L.
Ceylon
leadwort,
White
leadwort
Africa, Asia,
Australia,Et
hopia, India,
China
purple flowers.
Stout short
perennial herb
with pink flowers.
Erect shrub,
slightly branched
with pink and
purple- violet
flowers.
White flowers.
Small erect shrub
or woody herb,
white flowers.
Subshrub with
white flowers.
Perennial shrub,
dark-pink fowers
at the end of pink
hairy stems.
Multi-stemmed
shrub, with violet
to maroon purple
flowers.
Herbaceous
shruby plants with
climbing or erect
stems, petiolate
leaves and white
flowers.
Blank spaces= no available information.
Classification of Plumbago auriculata (Fonden and Potter, 2015).
Kingdom: Plantae
Division: Magnoliophyta
Class:
Magnoliopsida
Order:
Caryophyllales
Genus: Plumbago
Species: Plumbago auriculata Lam.
Common names: Cape Plumbago, Cape Leadwort, Blue Plumbago.
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Roots yield
plumbagin.
vesicant and
caustic effect, used
for body aches and
pains, skin
disorders, used as
veterinary
medicine..
Skin disorders and
orally for
hookworms.
Leaves used as
nape compresses in
mentally ill
patients also used
as local anastetic.
Soothes toothaches
and earaches.
Reduces joint in
flammation.
-.
Anticancer, antiulcer.
Antimalarial
Antimicrobial, anticancer and
antimalarial
treatments.
Roots yield
plumbagin.
Ornamental value,
used as a cure for
lead disease or lead
poisoning.
Used to treat
anemia, bronchitis,
rheumatism, skin
disorders, internal
and external
trauma, toxic
swelling, ulcers.
Antibacterial,
antimalarial,
antiplasmodial, antiinflammatory,
antiatherosclerotic,
antidiabetic,
hypolipidaemic,
antifungal.
Morphology
Plumbago auriculata is a perennial, bushy evergreen shrub (Figure 2a), up to 3m high with erect, climbing or
trailing stems that are glabrous below becoming pubescent above (Batten, 1986). The leaves are simple, elliptic to obovate,
slightly discolorous, greyish green beneath and often with whitish scales seemingly for light reflection (Aubrey, 2001).
Leaves are thin in texture (Figure 2b), having miniscule glandular dots, with a winged petiole at the base and auriculate.
The glands found on the both surface of the leaves are reported to be salt glands (Wilson, 1890; Sakai, 1974). P.
auriculata is covered with trusses of pale, sky blue flowers, however, there are variations of deep blue or white flowers
(Figure 2b) (Batten, 1986; Ferrero et al., 2009). Flowers are salver-shaped (Figure 2d), actinomorphic and grouped in
terminal inflorescences 2.5-3 cm long and flowering all year round (Luteyn, 1990; Aubrey, 2001; Ferrero et al., 2009).
Corolla is pale blue with the tube twice or more than twice the length of the calyx. Glandular and non-glandular hairs, often
known as trichomes, are found on the calyx (Figure 2c). Stamens are free from the corolla, included or exserted and style
exserted with 5 linear stigmas and superior 1-celled ovary. Fruit is a capsule, long-beaked, the valves coherent at the apex.
The seed one, dark brown or black, oblong 7mm long and slightly flattened (Luteyn, 1990; Aubrey, 2001).
a
c
b
d
Figure 2: Plumbago auriculata: a) Bushy evergreen shrub image captured at the University of Kwazulu-Natal, Westville,
Durban, South Africa; b) Variation of pale-blue flower and leaves (UKZN); c) Calyx showing trichomes; d) Illustration of
flower showing calyx with trichomes (After Batten, 1986; ICPS, 1986).
Secretory Structures
Secretory structures are specialized plant structures associated with the release of substances produced in the
cytoplasm and moved outside the cell (Cutter, 1978). Secretory structures appear in the form of trichomes, resin ducts, salt
glands, idioblasts, laticifiers, colleters and nectaries located in various parts of the plant (Thomas, 1991). It has been
reported that the primary function of secretory structures is related to defense responses against both herbivores and
pathogens. (Fahn, 1988; Lange, 2015). These structures have the ability to produce or sequester secondary (or specialized)
metabolites. Literature reports that salt glands occur sunken in the epidermis of leaves and are associated with ion secretion
whereas trichoms protrude from the surface of leaves or stems and are often responsible for the secretion of exudates
(Cutter, 1978, Fahn, 1988; Naidoo and Naidoo, 1998). Although some researchers report salt glands to be specialized
trichomes, based on available literature for the purpose of this review salt glands and trichomes are classified independently
as secretory structures in Plumbaginaceae (Metcalfe and Chalk, 1972; Faraday and Thomson, 1986b, Grigore and Toma,
2016).
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Salt glands
A major constraint to plant growth is salinity, which causes plants to adapt to saline environments via specialized
epidermal structures known as salt glands (Kobayashi, 2008). Salt glands are highly specialized organs consisting of several
cells intended to excrete salt or shift ions from mesophyll tissue to the leaf surfaces where a layer of salt crystals is formed
(Figure 3b). This serves an important role in regulating salt concentration in plant tissue (Fahn, 1988; Kobayashi, 2008;
Hasanuzzaman et al., 2014). Salt glands are known to secrete a wide variety of ions, especially metal ions which contribute
to metal tolerance in plants once these metal ions are eliminated (Fahn, 1988, Salama et al., 1999). The most commonly
secreted ions via salt glands in flowering plants are sodium, potassium, calcium and magnesium (Kobayashi, 2008). These
glands also secrete other salts in addition to sodium chloride that has a composition related to that of the root environment
(Storey and Thomson, 1994). Salt glands occur in halophytic species, which include several families that are not
taxonomically related, thus, providing a clear example of convergent evolution on a common adaptive device (Fahn, 1988;
Naidoo and Naidoo, 1998). Salt glands occur on any aerial organ of the plant but are most abundant on leaves and are
inserted in the epidermis (Fahn, 1988).
Salt glands function to eliminate salts to the outside of the plant or within the plant into vacuoles (Thomson, 1975).
Structurally there are three types of salt glands described (Thomson, 1975); the bicellular glands of the grasses, the bladder
cells of the Oxalidaceae, Chenopodiaceae and Mesembryanthemaceae and the multicellular gland found only in
dicotyledons. Regardless of the fact that the structure of salt glands varies greatly among different species, it is, very similar
in plants within the same family or genus (Salama et al., 1999). Salt glands of the family Plumbaginaceae are multicellular
and sunken in the leaf epidermal cells, consisting of basal and secretory cells with the cells varying in number from six up
to forty (Thomson, 1975, Faraday and Thomson, 1986b). Glands were first described in the 1800’s and were referred to as
chalk glands due to the presence of insoluble carbonate salts found above the gland on the surfaces of stems and leaves
(Grigore and Toma, 2016) . However, when it was later discovered that the glands of some species secrete sodium chloride
(NACl) these glands were then referred to as salt glands ( Faraday and Thomson, 1986a; Grigore and Toma, 2016). The salt
glands (Mettenius glands or Licopoli glands), as described by Grigore and Toma (2016), based on historical facts by
Metcalfe and Chalk (1972), occur inside the cavities on the inner side of stems and leaves, sometimes surrounded by simple
hairs or groups of elongated cells. The glands are made up of 4 to 8 epidermal cells arranged in palisade surrounded by
accessory cells made up of one or two layers (Figure 3a). Cutinized walls exist between the secreting cells and the
accessory cells. The salt-secreting glands of the species within Plumbaginaceae are similar in ultrastructure and
morphology and the primary pathways and basic mechanisms of salt movement through the glands is the same in all
species of the family (Figure 3c) (Faraday and Thomson, 1986a). These glands are able to secrete a wide variety of ions and
the secretions are similar in species of the family (Storey and Thomson, 1994). Salt glands are common in the family
Plumbaginaceae and sometimes these glands secrete mucilage in addition to calcium carbonate (Fahn, 1988; Grigore and
Toma, 2016). Salt glands of P. auriculata are found on the epidermal axials of the leaves and are exo-recreto (excrete salt
that form crystals on leaf surfaces) (Ceccoli et al., 2015).
a
b
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c
Figure 3: Structure of salt glands in various species: a) Salt glands (g) in the leaf of Plumbago europaea (After Grigore and
Toma, 2016); b) ) Cross section of a generalized salt gland (After Hasanuzzaman et al., 2014); c) Electron micrograph
showing the ultrastructure of an almost median longitudinal section from a secreting Plumbago auriculata salt gland (After
Faraday and Thomson, 1986a); TZ-Transfusion zone; SB- subbasal cell; Scale bar 80 µm.
Trichomes
Trichomes are often referred to as epidermal appendages that can either be singular or multicellular, developing
outwards on the surface of plant organs (Payne, 1978; Fahn, 1988). Their morphology varies greatly among tissue and
species and according to botanical literature there are over 300 descriptions to characterize various morphological types,
outlining a few in (Figure 4) (Payne, 1978; Wagner, 1991). Trichomes occur in all major groups of terrestrial plants and
are needed to carry out the following functions: light reflectance; reduction of waterloss through transpiration;
thermoregulation; herbivory; defence against radiation, pathogen attack. However, the role of trichomes can be considered
species specific (Wagner, 1991; Bauer et al., 2015). As outlined by Payne (1978), trichomes can be either glandular or nonglandular and are often found occurring on different parts of the plant. Glandular trichomes are the primary secretory
structures in most flowering plants and distributed over the vegetative aerial part of plants (Kaya et al., 2006). They vary in
their structure, function and location as well as chemical compostion in the substances they secrete (Payne, 1978; Rusydi et
al., 2013). Morphologically, glandular trichomes are classified as either peltate or capitate and generally consist of a foot, a
stalk that is usually unicellular or bicellular and a secretory head (Payne, 1978; Ascensao et al., 1997; Salmaki et al., 2009).
Capitate trichomes vary widely in stalk length, head shape and secretion type but a general rule is that the stalk length
measures more than half the height of the head whereas peltate trichomes are usually made up of a short wide stalk, several
head cells and one basal epidermal cell ( Ascensao and Pais, 1998; Kaya et al., 2006). Capitate trichomes secrete a small
amount of essential oils and some polysaccharides and these exudates are mostly excreted to the surrounding environment
via pores in the cuticle of the head cell (Kamatou et al., 2007). The peltate trichomes are most important for essential oil
production because most of the secretory cells are in the head and the exudates are stored in the subcuticular spaces
between the head cell walls and the cuticle. They function as storage structures for the secreted exudates (Salmaki et al.,
2009).
Non-glandular trichomes are also found occurring on the aerial vegetative parts of the plant as well as within plant
tissue and can be described as follows (Fahn, 1988; Maclachlan and Carlquist, 1992): a) simple unicellular or multicellular,
non flattened hairs; b) squamiform hairs which are conspicuously flattened, multicellular hairs. These trichomes are termed
‘scales’ if they are sessile or peltate hairs if they are stalked; c) branched, multicellular hairs which may be stellate; d)
shaggy hairs which consist of a base and two or more contiguous rows of cells. The function and location of non-glandular
trichomes are species-specific. Non- glandular trichomes of some Kalanchoe spp demonstrated how diverse these type of
trichomes are in terms of length, number of cells in the stalk, shape of the upper part, density of occurrence , occurence of
wax on their surface and cuticle ornamentation (Weryszko-Chmielewska and Chernetskyy, 2005). Trichome viability also
acts as a determinant for the function of the trichome i.e. dead non-glandular trchomes found on the surface of Kalanchoe
leaves provide a protective structure to the leaves enabling surface moisture. The function of trichomes is dependent on the
species as well as the environment.
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1. Abietiform; candelabra; orthocladous.
2. Acerate; acicular.
3. Acinaciform.
4. Acuminate terminal cell; belemonoid.
5. Anchor hairs, uncinate and with terminal fluke cells;
barbed.
6. Ancistrous; anchor; barbed; glochids.
7. Aduncate; anfractuose; curly; ribbon-hair; serpentine.
8. Angler; hamate; hooked; uncinate.
9. Antler; pedate (sometimes termed stellate).
10. Anvil; malpighiaceous.
11. Apicircinatus; circinate.
12. Arrect.
13. Arthrodactylous.
14. Asciiform; hatchet-shaped.
15. Attenuate.
16. Bifid; dichotomous; forked; furcate.
17. Biseriate; colleter; gland.
18. Bootjack.
19. Bosselated; nodose; postulate.
20. Brevicollate.
21. Brevifurcate.
22. Clavate.
23. Cruciate; stellate.
24. Cup-shaped.
25. Cushion hair.
26. Cystolith hair (with cystolith in basal cell)
27. Dolabrate.
28. Doliform head of colleter.
29. Falcate.
30. Flagelliform; whip-like.
31. Fusiform.
32. Geniculate.
33. Heliciform; snail-shaped.
34. Lageniform; pulvinate.
35. Lunate; solenoid.
36. Limaciform.
37. Ornithorhynchous.
38. Osteolate cells of uniseriate hair.
39. Peltate.
40. Penicillate.
41. Plumose.
42. Spiral.
43. Stellate.
44. Subulate.
45. Surculate.
46. Sympodial.
47. Torulose
48. Trochlear; trochleariform.
Figure 4: Trichome types (After Payne, 1978)
The calyx of P. auriculata bear large mucilage secreting trichomes (Figure 5a), which resemble those of the genus
Drosera (Droseraceae) and Drosophyllum (Droserophyllaceae) that also occur in the order Caryophyllales (Stoltzfus et al.,
2002; Panicker and Haridasan, 2016). The trichomes on the calyx can also be termed “colleters” meaning it secretes a
sticky substance and usually consist of a multicellular stalk and head. However due to its close resemblance to Drosera the
trichomes can also be considered as digestive glands due to their function in insect entrapment (Figure 5b) (Fahn, 1952).
Naidoo and Heneidak (2013), studied the glandular hairs of Drosera capensis L. and reported that the leaves are
characterized by eight types of glandular hairs with a red-coloured stalk and stalk head making it more attractive to insects
These trichomes function to capture and entrap insects, absorb nutrients, produce mucilage and digestive enzymes, as well
as secrete proteases in response to stimulation by certain salts (Stoltzfus et al., 2002; Naidoo and Heneidak, 2013; Bauer et
al., 2015). Trichomes of Droseraceae were also found to exhibit phosphatase activity in the external glands (Plachno et al.,
2006). Studies by Rashmilevitz and Joel (1976), mentioned in Stoltzfus et al. (2002), that trichomes of Plumbago have a
resinous secretion and showed a positive response when stained with Sudan IV, therefore proving it has a substantial
hydrophobic constituent. It was reported that trichomes of the genus Plumbago exclude crawling insects from the flowers,
therefore favouring flying insects for cross pollination (Jose et al., 2014) Trichomes of P. auriculata produce a sticky
transparent exudate which traps winged insects which resembles a cobweb. The exudate is known to turn brown upon
maturity of the plant in Plumbago species, however nothing has been reported with regards to P. auriculata. (Panicker and
Haridasan, 2016). Non-glandular trichomes are also found on the calyx of P. auriculata (Figure 5c), but the function of the
206
trichomes is unknown in this species. However, it has been reported in other species that these trichome types provide
shade to the plant and serve as a mechanical barrier to prevent insects from piercing the leaf (Gonzales et al., 2008).
a
Glandular
b
Non-glandular
Figure 5: Types of trichomes on the calyx of Plumbago auriculata: a) Scanning electron microscopy (SEM) micrograph of
glandular trichomes and non-glandular trichomes; b) SEM micrograph of an ant captured on calyx. Scale bar 100µm.
Chemical Composition
Plants are of great importance to humans for use as ornaments, food preparations and medicines.. The use of
herbal medicines has always been in great demand (Balunas and Kinghorn, 2005). There is an intense interest in medicinal
plants in which phytochemical constituents can have long-term health promoting properties (Kennedy and Wigthman,
2011). Plants naturally produce secondary metabolites, commonly referred to as phytochemicals or biologically active
compounds that exhibit a holistic healing approach (Kennedy and Wigthman, 2011). These include alkaloids, saponins,
tannins, glycosides, flavonoids, terpenoids, naphthaquinones, carbohydrates, proteins, phenolic compounds, fixed oils and
fats (Katsoulis et al., 2000; Pourmorad et al., 2006). Alkaloids and phenolic compounds are often the two major
phytochemical compounds that are of medicinal importance. A wide range of medicinal properties of P. auriculata are
attributed to plumbagin and other secondary metabolites.
Phytochemical Screening
Methanolic leaf extract of P. auriculata revealed the presence of the following phytochemicals- tannins,
flavonoids, phenols, alkaloids, saponins, proteins, and carbohydrates with phenols being the most abundant compound
(Lakshmanan et al., 2016). Aerial parts of P. auriculata extracted in the following solvents: acetone, chloroform, petroleum
ether, ethanol and ethyl acetate showed positive results when tested for steroids, carbohydrates, phenolics, tannins,
saponins, flavonoids and terpenoids, however the aqueous extract only showed positive for the presence of tannins
(Tharmaraj and Antonysamy, 2013). It can be concluded that aqueous extractions are not as effective as other solvents for
phytochemical screening. Systematic fractionation and phtochemical examination of the methanolic root extract of
Bioactive Compounds
P. auriculata revealed the presence of the following compounds: α-amyrin, capensisone, α-amyrin acetate,
isoshinanolene, β-sitosterol, diomuscinone, plumbagin and β-sitosterol-3β-glucoside (Table 2)(Padhye et al., 2010;
Ariyanathan et al., 2011; Saeidnia et al., 2014; Khan and Hossain, 2015). Capensisone is a novel quinone that was first to
be characterized from the roots of P. capensis and, in their study, isoshinanolone and diomuscinone were reported for the
first time for the genus Plumbago (Ariyanathan et al., 2011).
Table 2: Bioactive compounds reported in plant extracts of Plumbago auriculata
Compounds
Medicinal/ pharmacological uses
Plumbagin
Anticancer, antifungal, anti-inflammatory, antibacterial,
antifertility, antimalarial, antidiabetic and antioxidant
properties.
α-amyrin and α-amyrin acetate
capensisone
isoshinanolene
Antibacterial and antifungal properties.
β-sitosterol (Beta-sitosterol)
Heart disease and high cholesterol, gallstones, common
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cold and flu, rheumatoid arthritis, asthma, migraine
headaches, menopause symptoms, enlarged prostrate,
chronic fatigue syndrome, cervical cancer. It also boosts
the immune system and prevents colon cancer as well as
enhances sexual activity.
Antioxidant, hypertension and antidiabetic properties
(used to control menstrual bleeding.
Wound healing, antimicrobial and anti-inflammatory
properties.
β-sitosterol-glucoside
diomuscinone
Plumbagin
In the genus Plumbago, a highly potent and broad spectrum biological compound known as plumbagin is
commonly found (Tyagi and Menghani, 2014). Plumbagin is a 5-hydroxy-2-methyl-1,4-naphthoquinone-(C11H8O3) (Figure
7) present in the roots, stems and leaves of various Plumbago species; with the roots predominantly having the highest
concentration of plumbagin (Padhye et al., 2010). Plumbagin is naturally a yellow pigment that was first isolated in 1829
via solvent extraction of powdered plant material and has since been of interest for research due to its high medicinal value
(Tyagi and Menghani, 2014). Plumbagin is soluble in a variety of solvents such as acetone, benzene, alcohol, methanol,
acetic acid and chloroform. Plumbagin exhibits anticancer, antifungal, anti-inflammatory, antibacterial, antifertility,
antimalarial, antidiabetic and antioxidant properties (Mallavadhani et al., 2002; Checker et al., 2009; Padhye et al., 2010;
Jose et al., 2014). It is also reported to have other therapeutic properties such as stimulant action on the intestine, nervous
system and heart as well as rheumatic pain relief (Galal et al., 2012). All parts of P. auriculata contain plumbagin with the
highest amount of plumbagin accumulating in the leaves and stems of the plant in comparison to P. zeylanica and P. rosea
(Jose et al., 2014). This shows that different species accumulate plumbagin in different parts of the plant.
Figure 6: Structure of Plumbagin (After Padhye et al., 2010).
Mode of Action of Plumbagin
Anticancer activities
Plumbagin displays anticancer activities over a wide range of tumors such as breast cancer, ovarian cancer,
prostrate cancer, pancreatic cancer, lung cancer, skin cancer, leukemia, liver cancer, renal cancer, cervical cancer. Studies
have revealed that plumbagin is an effective inhihibitor of cell growth and when administered in combination with
radiotherapy plumbagin has the ability to augment cell growth inhibition very effectively in comparison to a higher dose of
radiation alone. (Padhye et al., 2010). Extensive publications exist on the anticancer effect of plumabin outlined in Padhye
et al (2010).
Antifungal activities
The findings of the antifungal activity of plumbin by Dzoyem et al. (2007) suggested that the naphthoquinone
delayed germination of the fungus and was capable of inhibiting growth when abministered at higher concentrations.
Anti-inflammatory
Plumbagin has been reported to be a topoisomerase-II inhibitor by displaying inhibitory activities of corresponding
enzymes involved in rheumatoid arthritis (RA) (Jackson et al., 2008). Checker et al (2009) reported that plumbagin
suppresses NF-kB (ubiquitous transcription factor) activation in tumor cells, and hence might have an effect on biological
functions of leukocytes actively participating in various immune responses.
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Antibacterial activity
Extensive publications reported the antibacterial activity of plumbagin as outlined by Padye et al (2010). However
to summarize these findings, plumbagin displays potent antibacterial activity against a range of bacterial strains such as:
Staphylococcus aureus, Myobacterium smegmatis and various Myobacterium tuberculosis strains and Escherichia coli.
However, plumbagin does display cytotoxic activity and needs to be administered at the appropriate concentration.
Antifertility activity
Plumbagin has been reported to be an irritant to the smooth muscle of the uterus when administered orally at high
concentrations. Therefore it needs to be administered with caution. Madhavan et al (2009) reported that antifertility effects
were found to be effective with doses of 1 mg/100 gm of body weight in female rats. Plumbagin also displays a significant
effect on estrogen cycle and hormonal levels of female rats.
Antimalarial activity
Antimalarial activity of plumbagin was reported by Sumsakul et al (2014) by investigating In vitro antimalarial
activity of plumbagin against K1 and 3D7 Plasmodium falciparum and In vivo antimalarial activity in Plasmodium bergheiinfected mouse model (a 4-day suppressive test). Their study concluded that plumbagin exhibited efficient antimalarial
activity in both In vivo and In vitro experiments and displayed a fairly low toxicity at the dose levels up to 100 (single oral
dose) and 25 (daily doses for 14 days) mg/kg body weight for acute and subacute toxicity.
Antidiabetic
It was reported that orally administered plumbagin significantly reduced the blood glucose levels and altered all
other biochemical parameters to near normal. Further, it increased the activity of hexokinase and decreased the activities of
glucose-6-phosphatase and fructose-1,6-bisphosphatase in diabetic rats. Plumbagin also enhanced GLUT4 mRNA and
protein expression. It also contributed to glucose homeostasis. (Sunil et al., 2012).
Antioxidant
Plumbagin contributes to EGFR activation in ROS-related mechanisms (Padhye ett al., 2010). It was also found to
significantly reduce the catechol-induced DNA damage, and inhibit ascorbate and NADPH-dependent lipid peroxidation
against mouse lymphoma cells (Demma et al., 2009).
Medicinal Uses and Pharmacology of Plumbago auriculata Extracts
Plumbago auriculata has a strong medicinal value and for many years has been used in the traditional medicinal
market as an alternate remedy for the prevention and control of certain human ailments. All parts of the plant are reported
to have therapeutic properties for example, the leaves and roots have cardiotoxic, neuroprotective, anti-atherogenic and
hepatoprotective properties (Deshpande et al., 2014). Roots and leaves are also reported to be used for warts, as emetics,
fractures, oedema, headaches, skin lesions, piles, rheumatism, diarrhoea and malaria (Elgorashi et al., 2003; Chen and Gao,
2013). In Mozambique where malaria is endemic, aerial parts of P. auriculata are used for the treatment of symptoms
associated with malaria such as vomiting and fever (Ramalhete et al., 2008). In Manchale, a rural village in India, it was
reported that herbal healers use the root of the plant for the treatment of piles by forming a paste with water and applying
directly (Poornima et al., 2012). Certain indian tribes also make use of the root extract by preparing fresh roots in rainwater
and drinking for a week to combat acidity (Jain et al., 2010). Plants are not only used for the treatment and control of
human ailments but it has been reported that plant extracts can also be used in ethnoveterinary as low-cost treatments for
diseases of livestock and other animals (McGaw and Eloff, 2008). Root extracts of P. auriculata are used in as a treatment
for diarrhaea in cows (Dold and Cocks, 2001). A fair amount of studies have been conducted to isolate and evaluate the
pharmacological activities of the extracts of P. auriculata.
Antiulcer Activity
Different species of Plumbago plants were collected from different regions of Kerala, India. Roots of plants were
dried and coarsely powdered, soaked in limewater and then extracted using ethanol as a solvent (Ittiyavirah and Paul,
2016). Goat intestines were used to test for antiulcer activity of the ethanolic root extracts by treating small pieces of the
intestines (1.5-2 cm long) with 1ml P.auriculata extract. The results of this study reported that P. auriculata showed
209
significant acid neutralizing capacities as well as excellent antioxidant properties observed from the DPPH assay. The use
of goat intestine can be used as a standard test for in vitro antiulcer activities of plant extracts.
Antifungal Activity
Fresh plant material of P. auriculata such as roots, leaves, stems and flowers were extracted using distilled water
as a solvent (Rajasekaran et al., 2015). Each extract was then mixed with a 1mM silver nitrate solution in a 1:10 ratio to
form a silver nanoparticle. Only the root, flower and stem extracts were effective in the synthesis of silver nanoparticles and
were further used in the application of the newly synthesized nanoparticles for antifungal activity. Antifungal activity was
tested by spore germination assay on the following fungi: Aspergillus fumigatus, Fusarium oxysporium, Aspergillus flavus,
Curvularia lunata and Trichoderma sp. Results of this study reported that the efficacy of the particle reflects on its size i.e.
bigger paritcles were effective on larger spore such as Curvularia lunata and ineffective against smaller spore bearing fungi
(Rajasekaran et al., 2015)
Antibacterial Activity
Roots of P. auriculata were dried and ground to a fine powder and, active components were extracted using the
following solvents water, chloroform, methanol and ethanol (Muringani and Makwikwi, 2017). Antibacterial activity was
tested using the kerbybaur disc diffusion method. Bacterial strains used were about 150 E.coli isolated from water and
patient stool samples from the Mthata Region, Eastern Cape, South Africa. The results of this study reported that the
ethanolic root extract showed the highest rate of activity against all the examined strains of the E. coli samples.
Antibacterial activity of aerial parts of Plumbago species have also been reported. Aerial parts of the plants were dried and
extracted using various solvents and antibacterial assay was determined using the agar-well diffusion method (Tharmaraj
and Antonysamy, 2015). The following bacterial strains used were Streptococcus pyrogenes, Pseudomonas aeruginosa,
Staphylococcus aureus, Bacillus subtilis, Morganella morganii and Bacillus subtilis and antibiotic amikacin (30 µg/ disc)
was used as a standard to compare its effect on the bacterial strains with the plant extracts. The results of the study for
P.auriculata reported that the ethanolic extract showed the highest activity (70%) and the highest zone of inhibition (23 ±
0.3 mm), followed by petroleum ether and chloroform extracts. The ethanolic extract of P. auriculata showed above 50%
activity against Gram positive bacteria and 26% against Gram negative bacteria. The overall results of the study showed
that P. zeylanica and P. rosea had the highest activity against Gram positive bacteria whilst P. auriculata had the least
activity and the antibacterial potentials of Plumbago species is probably due to the presence of alkaloids and phenolic
compounds (Tharmaraj and Antonysamy, 2015).
Plasmid-mediated multiple drug resistance is a serious and emerging problem in the treatment of infectious
diseases because bacteria have become resistant to most of the drugs available. Scientists have developed a way to combat
this problem by combining herbal extracts with antibiotics to inhibit the development and spread of R-plasmids
(Patwardhan et al., 2015). P. auriculata root extracts were used to cure plastid-mediated antibiotic resistance, The plasmids
curing activity of the root extract was determined by growing Escherichia coli, Proteus vulgaris and Klebsiella
pneumonia, in the root extract. Ethanol root extract demonstrated the highest antibacterial activity as well as the maximum
plastid curing activity (13-32%) compared to chloroform, acetone or petroleum ether root extracts. P. auriculata root
extracts can be used as plasmid curing agents in the treatment of nosocomial infections.
Cytotoxic activity
Gastric ulcer is one of the most common gastrointestinal disorders in recent times (Paul et al., 2013). AntiHelicobacter and cytotoxic activity of detoxified ethanol root extracts of P. auriculata were assessed by preparing the roots
in lime water and extracting them using ethanol as a solvent (Paul et al., 2013). Cell viability was assessed by Microculture
tetrazolium (MTT) Assay in the presence and absence of different plant extracts. The study reported that the ethanol root
extract has possible activity against H.pylori, cytotoxicity with MTT assay HGE-17 cell lines and the zone of inhibition test
of P. auriculata ethanol root extracts showed significant activity. Paul et al. (2013), also revealed in their study that
Plumbago species show cytotoxic activity, even in the absence of bioactive plumbagin.
Methanolic leaf extracts also showed significant cytotoxic activity when assayed against human lung cancer
(A549) and ovarian cancer (PAI) cell lines using MTT assay (Lakshmanan et al., 2016). For A549, it showed a minimum
cytotoxic activity at 45µg/ml and 10µg/ml cell line and for PAI 10µg/ml and 60µg/ml cell line at 24 hours and 48 hours,
respectively.
Anticancer Activity
Cancer is a common, most dreadful life threatening disease reported worldwide and is often difficult to control and
cure (Balunas and Kinghorn, 2005). Bioactive compounds extracted from plants are being extensively researched and
utilized as a possible anticancer agent. In vitro P. auriculata leaves were dried and extracted using methanol as a solvent
210
(Lakshmanan et al. 2016). The leaf extract was tested against ovarian (PAI), lung (A549) and malignancy cell lines for
apoptotic and anti-proliferative activities. The GC-MC analysis of the methanolic extract revealed the presence of the
compound sitosterol, hence showing good anticancer activity at minimal concentration 10-40µg. The study was successful
in reporting that P. auriculata constitutes novel anticancer compounds.
Toxicity
Bioactive compounds found in plants often have many therapeutic uses and are of high medicinal value.
Hoiwever, these compounds can exhibit toxic effects which can result in detrimental side-effects . Plumbagin, often
referred to as the marker compound in the genus Plumbago is also toxic, as it generates superoxide anion reactive oxygen
species that can damage various biomolecules (Jose et al., 2014). It is a powerful irritant in low doses that inhibits cell
mitosis and, in higher than recommended doses, it can cause death from respiratory failure, paralysis as well as nucleotoxic
and cytotoxic effects. Other commonly known side effects of plumbagin include skin rashes, diarrhoea, increase in
neutrophil counts and white blood cells, hepatic toxicity and increase in acid phosphatase and serum phosphatase levels
(Padhye et al., 2010). P. auriculata is assigned to toxicity class 4 meaning the juice sap or thorns of the plant can have
adverse effects on the skin, resulting in dermatitis (Stone and King, 1997). It has been reported that traditional tribes in
India that make use of roasted P. auriculata roots for wound healing use very small quantitites and for a limited time period
because prolonged exposure and large quanties can lead to death by irritation (Jain et al., 2010).
Propagation Techniques
Plumbago auriculata makes a good ornamental plant that can be planted indoor or outdoors. Plant management is
quite simple because of tolerance to high humidity, high temperatures and diseases and even though the plant secretes salt it
is not limited to saline conditions (Joy et al., 1998; Aubrey, 2001). The common propagation method of this species is seed
sowing. However, seed germination rate is very low and seed prices are often too expensive (Batten, 1986; Chen and Gao,
2013). Due to its high medicinal value, the conventional method of propagating P. auriculata is often difficult and cannot
meet the growing demand for the plant in the traditional medicine and pharmaceutical markets due to poor germination and
death of young seedlings under natural conditions. Therefore, researchers have developed plant tissue-culture as a method
to produce seedlings which have certain advantages over conventional propagation methods. Chen and Gao (2013.),
micropropagated 1 year old plants of P.auriculata using the nodals and leaves. They concluded that young nodals are best
to use as explants because leaves have a high differentiation grade and the ability of regeneration is weak. Deshpande et al.
(2014), reported that P.auriculata increased callus in vitro mass production by using various growth hormones such as
indoleacetic acid (IAA), 1-Naphthaleneacetic acid (NAA) and Indole-3-butyric acid (IBA). IAA is a simple compound
(auxin) that assists in plant growth and development (Davies, 2004). IBA is most commonly used commercially for plant
propagation due to its efficacy to stimulate adventitious root growth and is often more stable than IAA against in vivo
catabolism (Davies, 2004). NAA is a synthetic plant hormone widely used in agriculture, horticulture and plant tissue
culture to increase cellulose fiber formation (Davies, 2004). However, it is toxic to the plant in high concentrations. Growth
hormone NAA exhibited higher production of callus formation in all the explants; combination of hormones IBA and NAA
showed best callusing from leaf explants. Combinations of BAP and NAA showed best callusing from stem and shoot apex
explants. BAP are synthetic cytokinins used in tissue culture to promote cell division, bud formation and stem branching
(Zhang et al., 2005; Madhavam et al., 2009). It has been reported that this species can also be propagated vegetatively by
placing 15cm long stem cuttings in polybags and applying IAA and IBA treatments to improve rooting (Joy et al., 1998;
Lakshmanan et al., 2016).
In related studies plumabin production was enhanced using root cultures of Plumbago indica L. through precursor
feeding using l-alanine followed by in situ adsorption of plumbagin on the nonpolar copolymer adsorbent, styrene–
divinylbenzene resin (Diaion® HP-20) (Jaisi and Panichayupakaranant, 2017) Roots were fed with L-alanine
(concentration 5 mM) for 14 days followed by the sequential addition of Diaion® HP-20 (10 g L−1) after 36 hours of Lalanine-feeding. Plumbagin production was significantly increased. Productivity levels obtainted were higher than that
achieved using untreated root cultures or L-alanine feeding alone. Jaisi and Panichayupakaranant (2017) concluded that
their study suggests the use of precursor feeding in combination with in situ adsorption as an easy and cost effective tool for
the commercial production of medicinally important bioactive compounds like plumbagin. Overall tissue culture is a
beneficial propagation technique for increasing plumbagin production in Plumbago spp as well as the production of other
medicinal plant compounds.
Conclusion
The genus Plumbago yields many medicinally important species throughout the world. There is a lack in
knowledge on some species within the genus thus providing an opportunity for future research. This review clearly shows
the importance of Plumbago auriculata as a useful medicinal plant and also its level of toxicity. This species is used
throughout the world, however limited research exists in South Africa where it is native. While the morphology of
211
trichomes has been studied, the detailed trapping mechanisms of insects are still unknown. The structure and function of
secretory structures occurring in this species are not well documented. Although much pharmacological studies have been
conducted, studies on the secretory structures are limited to only a small number of publications dealing with secretory
structures, especially the types of trichomes present and ultrastructure of the leaf glands. However, the nature of the
secretions from these structures are unknown. Micropropagation results viewed in this study are aimed at encouraging and
attracting researchers to promote rapid regeneration of P. auriculata to ensure easy availability of the plant for horticulture,
medicinal and pharmacological uses. The use of plant hormones in tissue culture techniques proved to be effective in
optimizing the production of medicinal plants, thus increasing the availability of bioactive compounds. Other techniques
such as genetic engineering has not yet been explored for the genus and could prove useful in commercializing this
medicinally important genus.
Acknowledgements: The authors wish to thank the University of KwaZulu Natal, Westville Campus for providing the
resources needed to conduct the research. The National Research Foundation (NRF) for funding this research.
Conflict of interest: The authors declare that there is no conflict of interest.
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