Protoplasma
DOI 10.1007/s00709-017-1097-9
ORIGINAL ARTICLE
Flower palate structure of the aquatic bladderworts Utricularia
bremii Heer and U. minor L. from section Utricularia
(Lentibulariaceae)
Bartosz J. Płachno 1 & Małgorzata Stpiczyńska 2 & Łukasz Krajewski 3 & Piotr Świątek 4 &
Lubomír Adamec 5 & Vitor Fernandes Oliveira Miranda 6
Received: 20 January 2017 / Accepted: 1 March 2017
# The Author(s) 2017. This article is published with open access at Springerlink.com
Abstract There is an enormous diversity in the structure of
the flower palate of the carnivorous rootless genus
Utricularia. This study aims to examine the structure of the
palates in Utricularia bremii Heer and U. minor L of the
Utricularia sect. Utricularia, which have a glandular palate
type. In both species, the palate has only one type of glandular
trichomes. Because of the occurrence of cell wall ingrowths in
its glandular cells, any exudation may be transported via
eccrinous secretion. It was proposed that the palate trichomes
of the examined species act as scent glands and that the palate
may play a role as an unguentarium. Both U. bremii and
U. minor are of an open flower type. Thus, U. bremii and
U. minor flowers can be penetrated by small, weak insects,
which then easily have access to their generative structure.
Small Hymenoptera (member of families Mymaridae and
Handling Editor: Hanns H. Kassemeyer
* Bartosz J. Płachno
bartosz.plachno@uj.edu.pl
1
Department of Plant Cytology and Embryology, Jagiellonian
University in Kraków, 9 Gronostajowa St., 30-387 Kraków, Poland
2
Faculty of Biology, Botanic Garden, University of Warsaw, Al.
Ujazdowskie 4, 00-478 Warsaw, Poland
3
Wetland Conservation Center, ul. Cieszkowskiego 1-3/31,
01-636 Warszawa, Poland
4
Department of Animal Histology and Embryology, University of
Silesia in Katowice, 9 Bankowa St., 40-007 Katowice, Poland
5
Institute of Botany of the Czech Academy of Sciences, Section of
Plant Ecology, Dukelská 135, CZ-37982 Třeboň, Czech Republic
6
Faculdade de Ciências Agrárias e Veterinárias, Jaboticabal,
Departamento de Biologia Aplicada à Agropecuária, Universidade
Estadual Paulista (Unesp), São Paulo, Brazil
Braconidae) were observed as flower visitors of the malesterile species Utricularia bremii.
Keywords Bladderwort . Carnivorous plant . Floral
micro-morphology . Lentibulariaceae . Osmophore .
Pollination . Sect. Utricularia . Ultrastructure
Introduction
A member of the genus Utricularia, subg. Utricularia, sect.
Utricularia sensu Taylor (1989) is composed of the 34 species. However, two other species from this section have now
been accepted as recognised species—U. stygia Thor and
U. tenuicaulis Miki (Fleischmann 2012), and another new
species was recently described—Utricularia corneliana
R.W. Jobson (2012). In the case of their morphology, Taylor
(1989) thought that the section Utricularia was derived compared to the other sections. Species from this section are
suspended or affixed aquatic plants and that have a worldwide
distribution. Utricularia species from section Utricularia, like
other species from this genus, have a bilabiate corolla that
extends posteriorly to form a floral spur. Most Utricularia
have a palate that is the inflated base of the lower lip of the
corolla and that differ both morphologically and sometimes
also in terms of colour, from the remaining part of the perianth
(Taylor, 1989; Płachno et al. 2016, 2017). Palates in the species from section Utricularia are very diverse morphologically, and five main types can be distinguished: a pubescent palate (e.g. U. aurea, U. inflexa, U. stellaris, U. muelleri,
U. geminiscapa, U. striata, U. floridana, U. poconensis,
U. gibba), a densely hairy palate (U. reflexa, U. warmingii),
a glabrous palate (U. raynalii, U. inflata, U. australis,
U. intermedia, U. ochroleuca), a glandular palate (U. minor,
U. bremii) and an ill-defined palate (U. biovularioides,
B.J. Plachno et al.
U. cymbantha, U. naviculata) (Taylor 1989). However, ultrastructural and histochemical data about the palates of the species from section Utricularia are sorely lacking. Recently, it
has been shown that the prominent floral palate of
U. cornigera and U. nelumbifolia (both from section Iperua)
may function as an unguentarium—a structure that bears
osmophores. However, palate could be also treated as a zone
or area of osmophores in the flower when we choose nomenclature used by Endress (1994). In both of these species, the
palate has a diverse micro-morphology that comprises unicellular, conical to villiform papillae and various types of multicellular, uniseriate, glandular trichomes (Płachno et al. 2017).
Transmission electron microscopy further demonstrated that
the palate papillae in these species may play a key role in
providing the olfactory stimulus to attract insect pollinators
due to the presence of relatively large, polymorphic plastids
(chromoplasts) that contain many plastoglobuli. Moreover,
the palate of some Utricularia members of sect. Pleiochasia
may also function as an unguentarium, especially since it is
papillose in these species. It also bears glandular trichomes in
U. uniflora and U. paulinae (Płachno et al. 2016).
This study aims to examine the structure of the palate in
two Utricularia species from the section Utricularia, which
are the glandular palate type. In particular, it aims to ascertain
whether these palates function as an unguentarium or they
produce nectar to attract flower visitors. Another question is
whether sterile male U. bremii invest in the glands to attract
insects, because this species does not produce seeds. Thus, we
chose the very closely related species fertile U. minor and
sterile U. bremii.
Material and methods
The species used in this study include Utricularia bremii
Heer—collected from a shallow sand-pit Cep I in Suchdol
nad Lužnicí, S Bohemia (Czech Republic), the Kuźnica
Warężyńska sand-pit in Dąbrowa Górnicza (Poland)
(Krajewski and Płachno, 2015); U. minor L.—collected from
a fen bog in Nowa Wieś, Myszków (Poland). Plants with
flowers were observed in natural condition in order to record
flower visitors or pollinators. The insects were observed in the
afternoon and photographed using a Canon PowerShot A480.
Some additional material of U. minor from Herbarium KRA
(voucher number 0401113) was also analysed.
Floral structure and histochemistry
The distribution of the secretory glandular trichomes was determined by examining whole flowers using a Nikon SZ100
stereoscopic microscope.
Floral parts that bore glandular trichomes, namely the palate, were examined using light microscopy (LM), scanning
electron microscopy (SEM) and transmission electron microscopy (TEM) as follows: Firstly, the epidermis of the floral
palate was examined during anthesis, and pieces of the floral
tissues were excised and fixed in 2.5% (v/v) glutaraldehyde/
4% (v/v) formaldehyde in a 0.1 M sodium cacodylate buffer
(pH 7.0) for several days, washed three times in a 0.1 M sodium cacodylate buffer pH 7 and post-fixed in a 1.5% (w/v)
osmium tetroxide solution for 1.5 h at 0 °C. Dehydration using
a graded ethanol series and infiltration and embedding using
an epoxy embedding medium kit (Fluka) followed. Following
polymerisation at 60 °C, sections were cut at 70 nm for transmission electron microscopy (TEM) using a Leica ultracut
UCT ultramicrotome, stained with uranyl acetate and lead
citrate (Reynolds 1963) and were examined using a Hitachi
H500 transmission electron microscope at an accelerating
voltage of 75 kV.
Semi-thin sections (0.9–1.0 μm thick) were prepared for
light microscopy (LM) and stained for general histology using
aqueous methylene blue/azure II (MB/AII) for 1–2 min
(Humphrey and Pittman 1974) and were examined with an
Olympus BX60 light microscope. The periodic acid-Schiff
(PAS) reaction was also used to reveal the presence of insoluble polysaccharides, and Sudan Black B was used to detect
the presence of lipids (Jensen 1962). Staining for total proteins
was performed using Coomassie brilliant blue R250 or
Ponceau 2R (Fisher 1968; Ruzin 1999).
Nikon Eclipse Ni-U and Olympus BX60 microscopes were
used for the general photography and micrometry/photomicrography, respectively.
For SEM, the representative floral parts were fixed (as
above or in 70% ethanol) and later dehydrated and subjected
to critical-point drying using liquid CO2. They were then
sputter-coated with gold and examined at an accelerating voltage of 20 kV using a Hitachi S-4700 scanning electron microscope (Hitachi, Tokyo, Japan), which is housed in the
Scanning Microscopy Laboratory of the Department of
Biological and Geological Sciences, Jagiellonian University
in Kraków).
Results
Utricularia bremii
The corolla of Utricularia bremii was yellow in colour with
red nectar marks on the palate. The lower corolla lip formed a
wide platform. Its basal part formed palate (Fig.1a–c). The
corolla palate was elongated and formed a rim of tissue, and
its distal surface was covered with glandular trichomes
(Figs. 1c and 2a–c). Glandular trichomes also occurred in
the throat and the spur (Fig. 2a). No droplets of secretion were
seen on the palate in the live material (Fig. 1a).
Flower palate structure of the aquatic bladderworts
Fig. 1 Floral morphology of
Utricularia bremii. a–b Floral
morphology of Utricularia bremii
from the sand-pit Cep I in
Suchdol nad Lužnicí–palate
(arrows) with distinct nectar
guides. c Morphology of the
lower corolla lip–palate (arrow).
bar = 1 mm
Palate glandular trichomes were composed of a single basal
cell, a unicellular stalk (pedestal cell) and a multi-celled head
(Fig. 3a, b). All cell types were different in the case of
vacuolisation and the degree of cytoplasm density (Fig. 3b).
The basal cell was highly vacuolated, while the nucleus and
most of the cytoplasm with the usual organelles were located
in the upper part of the cell near the pedestal cell (Fig. 3a, c).
The lateral wall of the basal cell lay partly embedded in the
epidermis. Its outer part had a well-developed cuticle that was
continuous with the cuticle of the epidermal cells and the
cuticular deposits of the pedestal cell (Fig. 3 c, d). The basal
cell also bordered the parenchyma cells, which contained
starch grains (Fig. 3a).
The pedestal cell had a thick radial wall, which was impregnated with cutin (Fig. 3d). Cutin deposits also occurred in
the transverse walls between the basal cell and the pedestal
cell (Figs. 3d and 4a) and the pedestal cell and the terminal
cells (Fig. 3d). Branched plasmodesmata occurred in the transverse walls between the basal cell and the pedestal cell
(Fig. 4a). The plasmalemma in the region of the pedestal cell
lateral wall displayed a wavy profile. In the pedestal cell,
mitochondria had well-developed cristae (Fig. 4b), and they
were associated with the cell wall ingrowths. A wall labyrinth
(reticulate cell wall ingrowths) occurred on the transverse wall
and partially on the lateral wall (Figs. 3d and 4c). Some
myelin-like figures were also observed (Fig. 4b).
The protoplasts of the head cells were electron-dense and
had a prominent, nucleus that contained a paracrystalline protein inclusion (Figs. 4c and 5a). Cell wall ingrowths not only
occurred on the inner surface of the outer wall but also on the
inner walls between the terminal cells (Figs. 4c and 5a–d).
Intravacuolar myelin-like figures and flocculent electrondense material were present (Figs. 4c and 5a, c–d).
Mitochondria with well-developed cristae, profiles of rough
endoplasmic reticulum (RER) and dictyosomes were common
in the cytoplasm (Figs. 4c and 5a, c, d). Plastids were common
and contained an electron-dense stroma; sometimes they were
cube-shaped and were associated with the smooth endoplasmic reticulum (SER) (Fig. 5c). Part of the plastid contained
small lipid globules (not shown). The thick cuticle frequently
B.J. Plachno et al.
Fig. 2 Micro-morphology of the
lower corolla lip of a Utricularia
bremii flower. a General
morphology of the lower corolla
lip–palate (P), throat (Th), spur
(S); bar = 500 μm. b Palate with
numerous glandular trichomes.
bar = 200 μm. c Part of the
section through the palate with
glandular trichomes and
subepidermal parenchyma
showing large intercellular
spaces; note that in one trichome,
the head cells were degenerated
(arrow), vascular bundle (Vb);
bar = 20 μm
became distended and separated from the cell walls of the
head cells, especially in the apical part of the cells (Fig. 5a,
b). Some lipid or cutin material was observed between the
cuticle and the cell wall (Fig. 5b). Although the protoplasts
of the terminal cells collapsed in some trichomes (Fig. 2c), the
protoplasts of the terminal cells were active in the
neighbouring trichomes.
The cytoplasm of the head cells of the glandular trichomes
stained deeply with methylene blue/azure II (Fig. 2c). Small
lipid droplets were visible in the cytoplasm of the head cells in
LM, but they were not frequent (not shown). SBB stained the
cuticle of the terminal cells.
On the surface of the flowers of Utricularia bremii, visitors
(small Hymenoptera: member of family Mymaridae, probably
genus Polynema and members of family Braconidae) were
observed (Fig. 6a, b). They penetrated the palate and the throat
of the flowers. The flowers were of the open type (Fig. 6a, b).
Utricularia minor
The flowers were of the open type (Fig. 7a). The corolla palate
was elongated and formed a rim of tissue, and its distal surface
was covered with glandular trichomes (Fig. 7b, c). The structure (Fig. 7d) and histochemistry of these trichomes resembled
the glandular trichomes from the U. bremii palate. The palate
parenchyma cells were rich in starch grains.
Discussion
The described glandular trichomes of the palates of U. bremii
and U. minor have an architecture that is similar to the glands
of the unguentarium of U. dunlopii and the palates of
U. uniflora and U. paulinae (Płachno et al. 2016) but are
different from the long-stalked glandular trichomes of the palates of U. cornigera and U. nelumbifolia (Płachno et al. 2017).
U. bremii and U. minor palates do not have the long papillae
that are characters of the palates of U. dichotoma, U. uniflora,
U. paulinae (Płachno et al. 2016), U. cornigera and
U. nelumbifolia (Płachno et al. 2017). The characters of the
ultrastructure glandular trichomes of the U. bremii palate are
very similar to the trichomes of the unguentarium of
U. dunlopii, and this might suggest that they have a similar
function. Moreover, no nectar was observed on these trichomes in either of the species. Nonetheless, using TEM,
we found lipid globules in the plastids of the terminal cells
of U. bremii, similar to those that were found in U. dunlopii.
The close association of the plastids with SER, which we
observed in U. bremii, is a common character of the cells that
Flower palate structure of the aquatic bladderworts
Fig. 3 Structure of the palate trichomes of Utricularia bremii. a General
structure of the glandular trichome; note that the head cells of the
trichomes stain intensely with MB/AII–terminal = head cells (Tc),
pedestal cell (Pc), basal cell (Bc), parenchyma cell (Pc) with starch
grains; bar = 20 μm. b Longitudinal section showing terminal = head
cells (Tc), pedestal cell (Pc), basal cell (Bc); bar = 2.80 μm. c
Ultrastructure of a basal cell (Bc) and a pedestal cell (Pc)–nucleus of a
basal cell (N), thickened impregnated anticlinal wall of a pedestal cell
(star), epidermal cell (Ep); bar = 2.05 μm. d Section through a terminal
cell (Tc) and a pedestal cell (Pc) showing wall ingrowths forming the
labyrinth wall in a pedestal cell (Lw), thickened impregnated anticlinal
wall of a pedestal cell (star), plasmodesmata between a pedestal and a
basal cell (circle), cuticular deposits in the wall between a pedestal cell
and a terminal cell (arrow), nucleus of a terminal cell (N); bar = 1.35 μm
produce terpenoids (Lange and Turner 2013). The tissue of the
U. dunlopii unguentarium was rich in starch grains, similar to
the starch that was recorded in the parenchyma cells of
U. bremii palate. It is well known that starch is exploited as
a source of energy in scent production (Vogel 1990; Nepi
2007) and that plastids that have starch grains are a common
character of osmophore cells (e.g. Stern et al. 1987; Curry
et al. 1991; Pansarin et al. 2009; Melo et al. 2010; Płachno
et al. 2010; Antoń et al. 2012; Stpiczyńska and Davies 2016).
The occurrence of cell wall ingrowths in the head
cells may be evidenced that the secreted material is
transported via an eccrinous mode of secretion (Lüttge
1971), especially since we did not find neither the active
dictyosomes nor the secretory vesicles. The occurrence
of well-developed cell wall ingrowths in the pedestal cell
indicates that there is intensive short-distance transport
between the pedestal cell and the head cells (Gunning
and Pate 1969).
B.J. Plachno et al.
Fig. 4 Ultrastructure of a
glandular trichome from the
palate of Utricularia bremii. a
Branched plasmodesma (star) in
the transverse walls between a
basal cell and a pedestal cell, note
the cuticular deposits (arrows);
bar = 0.25 μm. b Ultrastructure of
pedestal and terminal cells; note
the well-developed labyrinth wall
(Lw) in the pedestal cell,
paracrystalline protein inclusion
(In) in the nucleus of a terminal
cell; bar = 1.35 μm. c
Ultrastructure of a pedestal cell;
note the numerous mitochondria
(m), myelin-like figures (My) and
dictyosomes (arrow);
bar = 0.8 μm
Fig. 5 Ultrastructure of the
glandular trichomes from the
palate of Utricularia bremii. a–d
Ultrastructure of terminal cells;
note the paracrystalline protein
inclusion (In) in the nucleus,
dense cytoplasm with numerous
plastids (P), mitochondria (m),
dictyosomes (black arrows). In
the vacuoles (V), there are myelinlike figures (My) and flocculent
electron-dense material. Cell wall
ingrowths (white arrows) on the
inner surface of the outer wall but
also on the inner walls between
the terminal cells–smooth endoplasmic reticulum (SER), Rough
endoplasmic reticulum (RER),
cuticle (c), material in
subcuticular space (star); a
bar = 1.3 μm, b bar = 0.95 μm, c
bar =0.55 μm, d bar = 0.80 μm
Flower palate structure of the aquatic bladderworts
Fig. 6 Visitors on the surface of
the palate of Utricularia bremii. a
Female, member of family
Mymaridae, probably genus
Polynema visiting U. bremii
flower. b Members of family
Braconidae visiting U. bremii
flower
Although the cell wall ingrowths are a ubiquitous feature of
the nectary cells (e.g. Schnepf and Pross 1976; Kronestedt and
Robards 1987; Stpiczyńska et al. 2012), these structures are
rarely recorded in the osmophore cells possibly because a
granulocrine mode of secretion is most often suspected in
the osmophores (Caissard et al. 2004 and literature therein).
However, recently Kowalkowska et al. (2016) found cell wall
ingrowths in cells in the petals of Bulbophyllum weberi Ames,
which may function as osmophores.
In Utricularia cell wall ingrowths, a terminal cell and a
pedestal cell with various types of secretory trichomes that
are connected with carnivory (on the external and internal trap
surface) and also sessile trichomes on the stolon and phylloclade surface, which play role in nutrients absorption from
water, were recorded (e.g. Fineran and Lee, 1975, 1980;
Fineran 1980, 1985; Płachno and Jankun, 2004). Thus, cell
wall ingrowths are common character of secretory or absorptive trichomes in the Utricularia.
In both trichomes on the unguentaria of the U. dunlopii and
U. bremii palates, TEM observations revealed that the cuticle
Fig. 7 Floral morphology and
structure of Utricularia minor. a
General floral morphology of
Utricularia minor–palate
(arrows). b General morphology
of the lower corolla lip–palate
(arrow), spur (S); bar = 1 mm. c
Palate with numerous glandular
trichomes; bar = 500 μm. d Part
of a section through the palate
with glandular trichomes–
terminal = head cells (Tc),
pedestal cell (arrow), basal cell
(Bc); bar = 50 μm
frequently became distended and separated from the cell walls
of the head cells. Thus, a subcuticular space is formed, which
suggests a subcuticular accumulation of secretions.
Intravacuolar myelin-like figures were recorded in variety
of plant tissues (Davies et al. 1992, and references therein),
also is secretory cells e.g. in orchid elaiophore cells (Davies
and Stpiczyńska 2009). These structures are probably related
to tissue differentiation and senescence (Davies et al. 1992).
However, other authors suggested that myelin-like figures
might be an artefact caused by tissue fixation for TEM (e.g.
Hwang and Chen 1997).
In contrast to the large flowered species that were analysed,
U. reniformis (Clivati et al. 2014), U. cornigera and
U. nelumbifolia (Płachno et al. 2017), which need large,
strong pollinators, both U. bremii and U. minor are of an open
flower type. Thus, U. bremii and U. minor flowers can be
penetrated by small, weak insects, which then easily have
access to their generative structure. In the case of U. bremii,
the observed insects cannot be called pollinators because this
species is considered to be sterile as a consequence of the
B.J. Plachno et al.
disturbations that occurred during their microsporogenesis
(Casper and Manitz, 1975). Recently, Beretta and co-authors
(2014) showed that over 95% of the pollen grains in U. bremii
are malformed and anomalous. This species reproduces vegetatively via shoot fragmentation and turions (Taylor 1989).
Conclusion
Only one type of glandular trichome occurred on the palates of
U. bremii and U. minor, and this is different than the
U. cornigera and U. nelumbifolia palates, which have various
glandular trichomes and well-developed papillae. Due to the
similarity of the glandular trichomes of the U. bremii and
U. minor palates to the U. dunlopii unguentarium trichomes,
we suggest that the U. bremii and U. minor palates may also
act as unguentaria. Given the enormity of the Uricularia genus (about 240 species on six continents), we realise that a
much greater concerted effort to characterise the anatomical,
histochemical and ultrastructural characteristics of the floral
secretory tissue is required before arriving at any generalisations. Thus, we treat our study as one more step toward developing an understanding of both the palate function and pollination syndrome in the Utricularia genus.
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
interest.
Open Access This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the
Creative Commons license, and indicate if changes were made.
References
Antoń S, Kamińska M, Stpiczyńska M (2012) Comparative structure of
the osmophores in the flowers of Stanhopea graveolens Lindley and
Cycnoches chlorochilon Klotzsch (Orchidaceae). Acta Agrobot 65:
11–22
Beretta M, Rodondi G, Adamec L, Andreis C (2014) Pollen morphology
of European bladderworts (Utricularia L., Lentibulariaceae). Rev
Palaeobot Palynol 205:22–30
Caissard JC, Joly C, Bergougnoux V, Hugueney P, Mauriat M, Baudino S
(2004) Secretion mechanisms of volatile organic compounds in specialized cells of aromatic plants. Recent Res Dev Cell Biol 2:1–15
Casper SJ, Manitz H (1975) Beiträge zur Taxonomie und Chorologie der
mitteleuropäischen Utricularia-Arten. 2. Androsporogenese,
Chromosomenzahlen und Pollenmorphologie. Feddes repert 86(4):
211–232
Clivati D, Cordeiro GD, Płachno BJ, Miranda VFO (2014) Reproductive
biology and pollination of Utricularia reniformis a.St.-Hil.
(Lentibulariaceae). Plant Biol 16(3):677–682
Curry KJ, McDowell LM, Judd WS, Stern WL (1991) Osmophores,
floral features and systematics of Stanhopea (Orchidaceae). Am J
Bot 78:610–623
Davies KL, Davies MS, Francis D (1992) Vacuolar development in the
root meristem of Festuca rubra L. New Phytol 121:581–585
Davies KL, Stpiczyńska M (2009) Comparative histology of floral
elaiophores in the orchids Rudolfiella picta (Schltr.) Hoehne
(Maxillariinae sensu lato) and Oncidium ornithorhynchum H.B.K.
(Oncidiinae sensu lato). Ann Bot 104:221–234
Endress P (1994) Diversity and evolutionary biology of tropical flowers.
Cambridge University Press
Fineran BA (1980) Ontogeny of external glands in the bladderwort
Utricularia monanthos. Protoplasma 105:9–25
Fineran BA (1985) Glandular trichomes in Utricularia: a review of their
structure and function. Isr J Bot 34:295–233
Fineran BA, Lee MSL (1975) Organization of quadrifid and bifid hairs in
the trap of Utricularia monanthos. Protoplasma 84:43–70
Fineran BA, Lee MSL (1980) Organization of mature external glands on
the trap and other organs of the bladderwort Utricularia monanthos.
Protoplasma 103:17–34
Fisher DB (1968) Protein staining of ribboned epon sections for light
microscopy. For Hist 16:92–96
Fleischmann A (2012) The new Utricularia species described since Peter
Taylor’s monograph. Carnivorous Plant Newsl 41:67–76
Gunning BES, Pate JS (1969) BTransfer cells^ plant cells with wall ingrowths, specialized in relation to short distance transport of solutes
their occurrence, structure and development. Protoplasma 68:107–
133
Humphrey C, Pittman G (1974) A simple methylene blue-azure II-basic
fuchsin for epoxy-embedded tissue sections. Stain Technol 49:9–14
Hwang YH, Chen SC (1997) Effect of tonicity and additives to the fixative on ultrastructure of mesophyllous cells in Kandelia candel (L.)
Druce (Rhizophoraceae). Bot Bull Acad Sin 38:21–28
Jensen WA (1962) Botanical histochemistry—principles and practice.
University of California, Berkeley. W. H. Freeman and Company
J o b s o n RW ( 2 0 1 2 ) U t r i c u l a r i a c o r n e l i a n a R . W. J o b s o n ,
(Lentibulariaceae), a new species from the North Kennedy district
of Queensland. Austrobaileya 8(4):601–607
Krajewski Ł, Płachno BJ (2015) Utricularia bremii (Lentibulariaceae) in
Poland. Pol Bot J 60(1):105–109
Kowalkowska AK, Turzyński S, Kozieradzka-Kiszkurno M, Wiśniewska
N (2016) Floral structure of two species of Bulbophyllum section
Cirrhopetalum Lindl.: B. weberi Ames and B. cumingii (Lindl.)
Rchb. f. (Bulbophyllinae Schltr., Orchidaceae). Protoplasma. doi:
10.1007/s00709-016-1034-3
Kronestedt EC, Robards AW (1987) Sugar secretion from the nectary of
Strelitzia. Protoplasma 137:168–182
Lange BM, Turner GW (2013) Terpenoid biosynthesis in trichomes—
current status and future opportunities. Plant Biotech J 11:2–22
Lüttge U (1971) Structure and function of plant glands. Ann Rev Plant
Physiol 22:23–44
Melo MC, Borba EL, Paiva EAS (2010) Morphological and histological
characterization of the osmophores and nectaries of four species of
Acianthera (Orchidaceae: Pleurothallidinae). Plant Syst Evol 286:
141–151
Nepi M (2007) Nectary structure and ultrastructure. In: Nicolson SW,
Nepi M, Pacini E (eds) Nectaries and nectar. Springer, Rotterdam,
pp 129–166
Pansarin LM, Moraes CM, Sazima M (2009) Osmophore and elaiophores
of Grobya amherstiae (Catasetinae, Orchidaceae) and their relation
to pollination. Bot J Linn Soc 159:408–415
Płachno BJ, Jankun A (2004) Transfer cell wall architecture in secretory
hairs of Utricularia intermedia traps. Acta Biol Cracov series Bot
46:193–200
Flower palate structure of the aquatic bladderworts
Płachno BJ, Świątek P, Szymczak G (2010) Can a stench be beautiful?
Osmophores in stem-succulent stapeliads (ApocynaceaeAsclepiadoideae-Ceropegieae-Stapeliinae). Flora 205:101–105
Płachno BJ, Stpiczyńska M, Świątek P, Davies KL (2016) Floral micromorphology of the Australian carnivorous bladderwort Utricularia
dunlopii, a putative pseudocopulatory species. Protoplasma 253(6):
1463–1473. doi:10.1007/s00709-015-0900-8
Płachno BJ, Stpiczyńska M, Davies KL, Miranda VFO (2017) Floral
ultrastructure of two Brazilian aquatic-epiphytic bladderworts:
Utricularia cornigera Studnička and U. nelumbifolia Gardner
(Lentibulariaceae). Protoplasma 254:353–366. doi:10.1007/
s00709-016-0956-0
Reynolds ES (1963) The use of lead citrate at high pH as an electronopaque stain for electron microscopy. J Cell Biol 17:208–212
Ruzin SE (1999) Plant microtechnique and microscopy. Oxford
University Press, New York
Schnepf E, Pross E (1976) Differentiation and redifferentiation of a transfer cell: development of septal nectaries of Aloe and Gasteria.
Protoplasma 89:105–115
Stern WL, Curry KJ, Pridgeon AM (1987) Osmophores of Stanhopea
(Orchidaceae). Amer J Bot 74:1323–1331
Stpiczyńska M, Davies KL (2016) Evidence for the dual role of floral
secretory cells in Bulbophyllum. Acta Biol Cracov Ser Bot 58(2):
57–69
Stpiczyńska M, Nepi M, Zych M (2012) Secretion and composition of
nectar and the structure of perigonal nectaries in Fritillaria
meleagris. Plant Syst Evol 298:997–1013
Taylor P (1989) The genus Utricularia—a taxonomic monograph. Kew
Bull Addit Ser 14:1–724
Vogel S (1990) The role of scent glands in pollination: on the structure
and function of osmophores. Amerind, New Delhi