Analele ştiinţifice ale Universităţii Al. I. Cuza Iaşi Tomul LV, fasc. 1, s.ii a. Biologie vegetală, 2009 DROSERA CAPENSIS L.: HISTO-ANATOMY OF THE VEGETATIVE ORGANS IRINA STĂNESCU *, C. TOMA ** Abstract. The investigated species (Drosera capensis L. and three forms: D. capensis L. Alba, D. capensis L. Narrow Leaf and D. capensis L. Rubra ) show common characters, regarding the structure of the vascular bundles, the type of stomata, the presence of the secretory trichomes, the homogenous mesophyll. The species present different quantities of a red pigment in the head of the tentacles which makes them attractive for the insects. Key words: vegetative organs, stalked trichomes Introduction Drosera, known as sundews, represents one of the largest genera of carnivorous plants. They grow in a poor mineral soil, but they show a great variety of physical characteristics and adaptations [1 and 2]. The structure of the leaves, their shape and unique elements pay for out attention. The sundews use insects or other small animals to supplement their nutrition, helped by the stalked mucilaginous glands (tentacles) which cover their leaf surface. Drosera species are spread all over the world, except Antarctica. The paper is focused on the anatomy of Drosera capensis L. known as the Cape sundew, which belongs to the cape area of South Africa and its forms D. capensis L. Alba, D. capensis L. Narrow Leaf and D. capensis L. Rubra. In D. capensis, the head of the mature tentacles contains a red pigment which makes them attractive for the insects; the young (immature) tentacles contain the same pigment, but in a smaller quantity. The same aspect is present in D. capensis L. Narrow Leaf and D. capensis L. Rubra. In D. capensis L. both petiole and head of the tentacles are green (do not present the red pigment). Material and methods The material subjected to the histological analysis (the vegetative organs of Drosera capensis L. (Fig. 1) and three forms: D. capensis Alba (Fig. 2), D. capensis Narrow Leaf (Fig. 3) and D. capensis Rubra (Fig. 4), coming from the collections of the Botanical Gardens Alexandru Borza of Cluj-Napoca, has been fixed and preserved in 70% ethylic alcohol. The sections were cut by microtome, coloured with iodine green and alauncarmine, 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. Results and discussions The root (Fig. 5-7) * Anastasie Fătu Botanical Garden, Al. I. Cuza University, irinastanescu2005@yahoo.com ** Faculty of Biology, Al. I. Cuza University, ctoma@uaic.ro 11
The root in all analyzed species presents a primary structure. In Drosera capensis and D. capensis L. Narrow Leaf, the rhizodermis, the exodermis and most of the cortical parenchyma are exfoliated. In the other analyzed species, the rhizodermis present root hairs, the exodermis is not organized and the cortical parenchyma is quite thin (3-7 rows of amiliferous cells). All species have a secondary type endodermis, with uniform, but moderately-thickened and suberized walls, excepting the cells which check the diffusion of water from xylem to cortex and show only thin, cellulosed walls.. The central cylinder shows a poliarchic type structure, with numerous dispersed phloemic bundles; the xylem vessels, solitary or grouped, present thickened and weak lignified walls; they are also dispersed in the central cylinder and separated by the cells of the cellulosed parenchyma, rich in starch grains. The rhizome (Figs. 8-12) The epidermis of the rhizome consists of cells with thick external wall and sessile secretory trichomes. The rhizome evidences a thick amiliferous cortex, a secondary type endodermis, consisting of cells with thickened and suberized walls. The central cylinder is very thick and exhibits numerous vascular bundles disorderly dispersed in the fundamental parenchyma, most of them presenting a leptocentric structure. The xylem vessels have thick but weak lignified walls, while the phloem consists of sieved tubes and guard cells. Foliar vascular bundles are present in D. capensis Rubra (Fig. 12). The aerial stem (Fig. 13-20) In front side view, the epidermis presents cells with straight lateral walls. Stomata, sessile secretory trichomes, stalked secretory trichomes (except D. capensis Narrow Leaf ) are present. Only D. capensis Alba shows long protective hairs consisting of elongated cells disposed on two parallel rows. In all analyzed species, the cross section reveals a primary structure. The epidermis consists of isodiametric cells of various dimensions. Stomata are prominent above the surroundings cells; sessile (Fig. 15) and stalked (Fig. 16) secretory trichomes are also present. The cortex is chlorenchymatic, formed of three layers of cells with thin, cellulosed walls. The central cylinder shows a sclerenchymatic sheath consisting of 7-8 layers of cells with thickened and lignified walls. The fundamental parenchyma evidences 5 (6 in D. capensis Rubra, 7 in D. capensis Alba ) vascular bundles (Figs. 17-19). The xylem vessels, with thin, but lignified walls, form an arc which surrounds the phloem and come into contact completely (D. capensis Alba ) or not (D. capensis Rubra, D. capensis Narrow Leaf ) with the sclerenchymatic sheath. The phloem consists of sieved tubes and guard cells. The pith is parenchymatic-cellulosed, of meatic type (Fig. 20), bearing big polygonal cells with very thin walls. The leaf The leaf shows long petiole and long lamina. The mature tentacles contain a red pigment, while in the young ones the pigment is not present or it is in a smaller quantity, only in the glandular head, making them very attractive for the insects, together with the shiny droplet. In D. capensis Alba neither the mature tentacles nor the immature ones present the red pigment in the glandular head that is why the form is called Alba. The petiole (Figs. 21-27) In all analyzed species, the cross section has a semicircular shape, with two adaxial crests (Fig. 21), except D. capensis Rubra. The epidermis displays a great variety of 12
elements: isodiametric cells; with the external wall of the cells covered by a thin cuticle, anomocytic stomata, prominent above the surrounding cells, sessile (Fig. 24) and stalked secretory trichomes. In D. capensis, only the sessile secretory trichomes are present. The fundamental parenchyma consists of big, round cells, three adaxial vascular bundles (Fig. 25-27) and other two in the adaxial crests. The petiole of D. capensis Rubra does not present adaxial bundles. All of them consist of phloem (sieved tubes and guard cells) and xylem (vessels with thickened, but weak lignified walls and xylemic parenchyma). The foliar limb (Figs. 28-34) In front side view, the epidermis shows polygonal cells, bearing waved lateral walls. Stomata are present in both epidermis, so the limb is amfistimatic. The tentacles are present in the adaxial face of the limb and on its edges, together with the sessile secretory trichomes. The tentacles present on the center of the leaf are shorter than the others present on the edges. If pray comes to the leaf, the longer tentacles curl towards the center of the leaf, to cover the insect. At the same time, the entire leaf curls towards the prey. All investigated species, except D. capensis Rubra, show stalked secretory trichomes; the limb of D. capensis Alba bears protective hairs, too. The tentacles (Figs. 31-34) consist of stalked glands of complex structure; the gland is egg-shaped and contains a red pigment which attracts the prey. The stalk bears tracheids surrounded by parenchymatic cells. The glandular part bears numerous cells with twisted thickenings, which communicate with the tracheids; the outer part of the tentacles head is composed of 2-3 layers of glandular radial elongated cells (especially those from the external layer) [3-5]. First of all, the gland secretes mucilage which catches the prey and enzymes which degrade the small animal. Then, the resulted compounds of the digestion have to be absorbed and used in the plant. This process is done by the tentacles, on one hand, and by the sessile and stalked secretory trichomes, on the other hand. The latter trichomes help the tentacles absorbing all resulted compounds and maintaining a clean leaf superficies. The sessile secretory trichomes consist of a small number of cells. They show two basal cells, two stalked cells and 2 (4) glandular cells. The stalked ones present multicellular gland and a stalk of two layers of cells. The protective hairs consist of two rows of elongated cells. The cross section of the limb appears quite thin, just a little bit thicker toward the middle vein. The mesophyll has a uniform structure, bearing round cells and 7 (7-9 in D. capensis Narrow Leaf, D. capensis Rubra ) vascular bundles (Fig. 30), with the same structure as those of the petiole. The smaller bundles bear only a few phloemic elements. Conclusions In all investigated species, the root has a primary structure. The rhizodermis persists or is exfoliated; the exodermis is not organized; the endodermis has secondary structure; the central cylinder consists of xylemic and phloemic vascular bundles. The rhizome has sessile secretory trichomes. All investigated species have thick, amyliferous cortex, with secondary endodermis and several vascular bundles, collateraly closed or leptocentric and a meatic parenchyma, the later consisting of large isodiametric cells with slightly wavy walls. 13
The aerial floriferous stem has a primary structure. The epidermis presents sessile and stalked secretory trichomes. D. capensis Alba shows, also, protective trichomes. The central cylinder is surrounded by a peripheral sclerenchymatic sheath. The central cylinder contains many vascular bundles. The petiole is elliptic at all the studied species, rarely half-round in cross section. The lamina is amphistomatic with anomocytic stomata. All the studied species have sessile and stalked secretory trichomes or protective trichomes, as well as tentacles. All secretory elements have various positions in the epidermis, various length, number of cells. REFERENCES 1. Juniper, B. E., Robins, R. J., Joel, D. M., 1989- The Carnivorous Plants. Academic Press, San Diego 2. Metcalfe C. R., Chalk L., 1972, Anatomy of the Dicotyledons. 1: 581-585, Clarendon Press, Oxford 3. Stănescu Irina, Toma C., 2008- Secretory structures of the carnivorous plants belonging to the Droseraceae family. Proceedings of the 1 st International Conference: Environment- Natural Science- food industry in European Context, Baia Mare, 1: 323-326 4. Stănescu Irina, Gostin Irina, Toma C., 2008- Leaf structure considerations of some Drosera L. species. Acta Horti Botanici Bucurestiensis, 33: 77-82 5. Irina Stănescu, Irina Toma, C. Toma, 2005- Considerations of the stem structure of some Drosera L. species. Contribuţii Botanice, Cluj-Napoca, 40: 215-220 Explanation of plates Fig. 1: Drosera capensis Fig. 2: Drosera capensis Alba Fig. 3: Drosera capensis Narrow Leaf Fig. 4: Drosera capensis Rubra Cross section of the root. Fig. 5: Drosera capensis Fig. 6: Drosera capensis Alba, Fig. 7: Drosera capensis Rubra Cross section of the rhizome. Fig. 8: Drosera capensis Fig. 9: Drosera capensis Alba Fig. 10: Drosera capensis Narrow Leaf Fig. 11-12: Drosera capensis Rubra Cross section of the aerial stem. Fig. 13, 15, 16, 17, 20: Drosera capensis Fig. 14, 19: Drosera capensis Narrow Leaf Fig. 18: Drosera capensis Alba Cross section of the petiole. Fig.: 21, 25: Drosera capensis Alba Fig. 22, 23, 24: Drosera capensis Fig. 26: Drosera capensis Narrow Leaf Fig. 27: Drosera capensis Rubra. Cross section of the foliar limb. Fig. 28, 31 (tentacle): Drosera capensis L. Fig. 29, 33 (tentacle): Drosera capensis Narrow Leaf. Fig. 30, 32 (tentacle): Drosera capensis Alba. Fig. 34 (tentacle): Drosera capensis Rubra 14
PLATE I Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 15
PLATE II Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 16
PLATE III Fig. 13 Fig. 14 Fig. 15 Fig. 16 Fig. 17 Fig. 18 17
PLATE IV Fig. 19 Fig. 20 Fig. 21 Fig. 22 Fig. 23 Fig. 24 18
PLATE V Fig. 25 Fig.26 Fig. 27 Fig. 28 Fig. 29 Fig. 30 19
PLATE VI Fig. 31 Fig. 32 Fig. 33 Fig. 34 20