ANALELE UAIC, Biol. Veg. - Facultatea de Biologie

Analele ştiinţifice ale Universităţii “Al. I. Cuza” Iaşi
Tomul LIII, s. II a. Biologie vegetală, 2007
HISTO-ANATOMICAL ASPECTS OF
PINGUICULA ALPINA L. AND PINGUICULA MORANENSIS H. B. K. SPECIES
IRINA STĂNESCU 1 , C. TOMA 1
Abstract. In the present paper, the authors evidence the most important histo-anatomical aspects of the vegetative
organs of two carnivorous plant species belonging to the Lentibulariaceae family: Pinguicula alpina and P.
moranensis. The leaf represents the trap which uses sessile and stalked glands to attract, retain and digest small
insects which represent the prey.
Key words: epidermis, sessile and stalked glands, Pinguicula.
Introduction
The genus is represented by herbaceous perennial plants. The leaves form a basal
rosette, from the center of which raises the aerial stem, bearing solitary hermaphrodite,
zygomorphic flowers with bilabiate calyx and corolla. The Pinguicula species are called
butterworts, because of the greasy butter-like feel of their leaves. All butterworts grow in
acid bogs. Insects walk or fly onto the leaves, which roll at their edges to prevent escape;
butterworts possess the strongest natural known glues . After digestion the dry insect husk
blows away. Butterworts overwinter as rootless resting buds.
The literature dealing with the anatomy of the especially carnivorous plants is quite
rich, as it results from the synthesis papers referring to the dicotyledons’ anatomy [5, 7] or
to the angiosperms’ [6]. Various histo-anatomical aspects of the Lentibulariaceae species
were mentioned, too [3, 13, 15]; in these synthesis papers the carnivorous plants
accommodation to surroundings were underlined. Some authors evidenced the structure of
the glands which are present on the surface of the blade [1, 4].
As a sequel of our investigation regarding the anatomy of the carnivorous plants [8,
9, 10, 11, 12, 16], in the present paper we evidenced a few structure characters of the
vegetative organs of two Pinguicula species.
Material and Methods
The material subjected to the histological analysis, the vegetative organs of
Pinguicula alpina (collected from the Ceahlău Mountain) and P. moranensis (from the
collection of the Botanical Gardens “Anastasie Fătu” of Iasi) has been fixed and preserved
in 70% ethylic alcohol. The sections were cut by microtome, subsequently coloured with
iodine green and alaun-carmine, then mounted in gel and analyzed in a Novex (Holland)
light microscope. The light micrographs were performed by means of the same light
microscope, using Canon A95 camera.
1 “Al. I. Cuza” University, Faculty of Biology, 20A Carol Bd., Iaşi.
irinastanescu2005@yahoo.com, ctoma@uaic.ro
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Results and Discussion
The root
The root has a primary structure, with the typical anatomical zones: rhizodermis,
cortical parenchyma and central cylinder. The rhizodermis consists of small cells, with
thick walls; rarely ,can we see root hairs. The cortical parenchyma is thick, homogenous
and meatus type (7-8 layers in P. alpina, 5-6 in P. moranensis), having large cells; its most
internal layer, a primary type endodermis, shows Casparian thickenings in the radially walls
of the cells. The central cylinder is thin, with a one-layered pericycle, 4 in P. alpina (Fig.
1), 6 in P. moranensis xylem bundles which alternate with the same number of phloem
bundles. The xylem bundles have few (1-2) vessels with little thickened and little lignified
walls. The phloem bundles form small isles with sieved tubes and companion cells. In the
central part of the root there is parenchymatous, meatus type pith.
The rhizome
The epidermis is exfoliated in P. alpina, while in P. moranensis it persists and
consists of tangentially-elongated cells. The rhizome has a thick cortical parenchyma,
without a typical endodermis, while in P. alpina the cortical parenchyma is thin,
amiliferous type and the endodermis is of secondary type, consisting of cells with thickened
and suberified walls. The central cylinder is thick, having 5-6 collateral vascular bundles
(Fig. 7). The xylem vessels present thickened, but little lignified walls; the phloem consists
of sieved tubes and companion cells. The pericycle forms few rows of adventitious roots.
The aerial stem
The epidermis consists of izodiametric cells, having the external wall thicker than
the others. Here and there sessile glands are present (Fig. 2). in P. moranensis there are
stomata and stalked glands (Fig. 8), too. The stalked glands consist in a long stalk, a
“connector” cell and a glandular part which presents 6-8 radially cells; the sessile ones have
a basal cell among the epidermic cells, a short “connector” cell and a glandular part formed
of few radialy cells.
The cortex is quite thick, formed of 6-9 layers of large, parenchymatic cells, which
form meatus or aeriferous cavities.
The central cylinder (Fig. 3 and 9) is quite thin and consists in a large number of
vascular bundles separated by medullar strikes, larger in the phloem than in the xylem. An
attentive analysis evidences a few polygonal xylem vessels, having little thickened and little
lignified walls, irregular disposed, and a lot of phloem isles which form a circle at the
exterior part of the xylem, consisting in sieved tubes and companion cells. In the central
part there is large parenchymatic, meatus type pith; in P. alpina the cells of the central part
of the stem degrade themselves, resulting an aeriferous cavity (Fig. 3).
The leaf
Front side epidermis view: The upper epidermis presents polygonal elongated cells,
with waved lateral walls (Fig. 4 and 10). Here and there a lot of stalked glands (similar to
those occurring in the stem of P. moranensis) are present. A lot of sessile glands are
present, too, similar to the stalked ones, but they don’t have a stalk. Only P. alpina presents
stomata of diacytic type (Fig. ) and massive multicellular secretory trichomes, having onelayered
stalk and multicellular gland, in the upper epidermis. The stalked glands retain the
preys using the sticky liquid they are secreting, while the sessile ones, called digestive
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glands, secrete a digestive liquid, full of proteolytic enzymes [13]. This latter group is
formed of three compartments: a basal cell, among the epidermic ones, a short stalk cell,
like an endodermis [2] and a group of secretory cells which form the glandular head. The
basal cell is known as “reservoir cell” because of its role in providing the main water source
during the phase of gland discharge.
The lower epidermis presents cells of irregular shape, with waved lateral walls (Fig.
5 and 11). The stomata, of paracytic type in P. alpina and of dialelocytic type [14] in P.
moranensis are numerous in the unit area. Here and there, sessile glands are present, similar
to those occurring in the upper epidermis.
In cross section, the blade has an elliptic shape, modified of two latero-adaxial
wings, which become more and more narrowed to the borders of the blade. Both epidermis
present small cells with thin walls. Here and there stomata, promining above the epidermis,
are present (only in the lower epidermis, in P. moranensis). In the upper epidermis, sessile
and stalked glands are present, too, both categories consisting in a glandular part of 6-8
radially cells; long secretory trichomes with large cells and multicellular gland are present
only in the upper epidermis of P. alpina.
In both species, the aerial stem has an homogenous mesophyll, formed of large,
round cells, which describe meatus or aeriferous cavities between them. In P. alpina, the
vascular tissue forms a lot of collateral vascular bundles (Fig. 6); the median one is bigger
than the others and has an elliptic shape. It presents a lot of phloem isles at the abaxial face
and xylem vessels having little thickened and little lignified walls, at the adaxial face.In P.
moranensis, the vascular tissue forms a lot of phloem isles (having sieved tubes and
companion cells) at the abaxial face and a few xylem vessels with little thickened and little
lignified walls at the adaxial face, grouped in small bundles (Fig. 12).
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Fig. 1 Fig. 2
Fig. 3 Fig. 4
Fig. 5 Fig. 6
Pinguicula alpina. Fig. 1: Cross section through the root (Fig. 1) and through the aerial
stem (Fig. 2 and 3). Front side epidermis view: the upper epidermis (Fig. 4) and the lower
epidermis (Fig. 5). Cross section through the foliar blade (Fig. 6)
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Fig. 7 Fig. 8
Fig. 9 Fig. 10
Fig. 11 Fig. 12
Pinguicula moranensis. Cross section through the rhizome (Fig. 7) and through the aerial
stem (Fig. 8 and 9). Front side epidermis view: the upper epidermis (Fig. 10) and the lower
epidermis (Fig. 11). Cross section through the foliar blade (Fig. 12)
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Conclusions
In both studied species, the root, the rhizome and the aerial stem are quite similar
regarding their anatomy. All the peculiarities evidence quantity differences (different
number of cell layers in the cortical parenchyma of the root, different number of the xylem
and phloem bundles, different location of the collateral vascular bundles in the foliar blade)
and less quality differences (stalked secretory trichomes in the epidermis of the aerial stem
of P. moranensis, amfistomatic type blade in P. alpina and hipostomatic type blade in P.
moranensis).
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