Analele ştiinţifice ale Universităţii Al. I. Cuza Iaşi Tomul LIV, fasc. 1, s. II a. Biologie vegetală, 2008 THE LEAF STRUCTURE OF SOME NEPENTHES DANSER SPECIES IRINA STĂNESCU, C. TOMA Abstract: The authors analyze a few aspects referring to the modified leaf of four Nepenthes species, at different levels, stress being laid on the structure of the vascular bundles, digestive and nectariferous glands. Key words: Nepenthes, digestive glands, nectariferous glands, hydathodes. Introduction The Nepenthes genus consists of more than 80 tropical species [8], spread around S- E Africa, Sri-Lanka and Madagascar. Etienne de Flancourt described it in 1658 for the first time [3] and in 1753 Linné called it Nepenthes. The plant is a climbing, weakly branched liana. It presents a basal rosette of leaves with short internodes when young; on sexual maturity, the internodes become elongated and the plant starts being climbing or prostrate, according to the species. The plant creates a special impression by its bizarre leaves, consisting of a basal assimilatory part, a tendril which rolls up around different supports and a trap [2]. This trap is like a pitcher with a lid, which covers the trap, avoiding the dilution of the liquid from inside the trap by the rainwater. Some authors believe that the assimilatory part, the tendril and the pitcher belong to the petiole of an archaic leaf, while the lid represents the limb. Others consider that the pitcher and the lid form the limb, and the assimilatory part and the tendril form the petiole. Darwin stated that a carnivorous plant attracts, captures and digests the prey; the supplementary nutritive elements brought by the prey are necessary in developing and blooming. The capturing system in Nepenthes is passive; the plant does not need to move to capture the prey, unlike those which have active traps, such as Dionaea muscipula. The plants bear flowers with shiny colours and abundant nectar to attract the pollinating insects; on the other hand, the plants use different traps with different attraction elements: shiny colours or the reflection of the UV radiation, attracting odours or nectar secreted by the nectariferous extrafloral glands; all these characteristics belong to the leaf. Some authors [5, 7] evidenced the structure of the digestive glands; others [1, 6] considered that the digestive glands are closely associated with the vascular bundles. Some histoanatomical aspects were evidenced in a previous work [9] devoted to Nepenthes maxima. Botanical Gardens of Iasi, Dumbrava Roşie Street, no. 7-9, Romania Al. I. Cuza University, Faculty of Biology, Carol I. Bd., no. 20A, 700506, Iaşi, Romania 5
Materials and methods The material under study, coming from the collection of the Alexandru Borza Botanical Gardens of Cluj-Napoca, belongs to four taxa: N. x coccinea Mast, N. distillatoria L., N. maxima Reinw. ex Nees and N. northiana Hook f. The material subjected to analysis (the modified leaves of the plants) has been fixed and preserved in 70% ethylic alcohol. The sections (from the assimilatory part, tendril and pitcher) were cut with a microtome, then coloured with iodine green and alaun-carmine, mounted in gel and analyzed on a Novex (Holland) light microscope. The light micrographs were performed by means of Novex (Holland) microscope, using a Canon A95 camera. Results and discussions As already mentioned, the leaf of Nepenthes consists of three parts: a basal, assimilatory one, a tendril and a pitcher which represents the trap of the plant. In front side view, the upper epidermis of the assimilatory part appears as formed of polygonal cells (Fig. 1); here and there, a few hydathodes are present. The lower epidermis consists of small cells, bearing weakly waved walls (Fig. 2). Here and there, stomata of the anomocytic type and hydathodes are present. A hydathode bears a short pedicel formed of a few cells and a stellate part, formed of 4-10 cells. Another author [4] suggests that the hydathodes do not only secrete water, but even absorb it from time to time. In cross section, the upper epidermis evidences small cells covered by a thick cuticle. Just beneath the epidermis, a few isodiametric-celled layers are present, forming an acviferous tissue (Fig. 3); some authors [5] call it an acviferous hypodermis. Then, a 2-3 layered palisade tissue, with short cells, in which chloroplasts can be observed, is present. The lacunary tissue is multi-layered, with small aeriferous spaces between the component cells. A lot of isolated mechanical cells (idioblasts) with spiral thickenings can be observed in the mesophyll; these were evidenced by other authors [5], too. The lower epidermis consists of small, isodiametric cells, covered by a cuticle thinner than the one covering the upper epidermis. Numerous stomata are present, as well as numerous calcium oxalate crystals in the mesophyll. The midvein is very prominent at the lower side of the assimilatory part (Fig. 4). A large number of vascular bundles is present (8 big bundles, one of its being situated in the centre or 6 bundles and a central one at N. northiana); most of them are implanted in a thick sclerenchyma ring, formed of sclerenchymatic fibres with thickened and lignified walls (or unlignified at N. coccinea). The vascular bundles have different orientation in the sclerenchymatic ring. A vascular bundle (Fig. 5) consists of a phloem (sieved tubes and companion cells) and a xylem (xylem vessels separated by celulosic parenchyma). Sometimes, the sclerenchyma sheath bears very small vascular bundles, consisting of a few phloem elements or of phloem and 1-2 xylem vessels. In the fundamental, external parenchyma, idioblasts and small, isolated vascular bundles are present, often consisting of a few phloem elements, surrounded by a thin sclerenchymatic sheath. 6
The tendril In cross section, the tendril shows a circular shape, with 7-8 ribs at N. maxima (Fig. 6). Small cells, covered by a thick cuticle, form the epidermis. Here an there, hydathodes, short, sometimes branched tector hairs and stomata prominig above the epidermis are present. The cortical parenchyma is formed of 5-6 layers of large cells. Most of the vascular bundles are implanted in a strong sclerenchyma ring. There is a high variability regarding the number of bundles and on their position (N. coccinea and N. maxima present a lot of vascular bundles of different size in the sclerenchyma ring and a central one in the fundamental parenchyma; N. distillatoria presents 2 big vascular bundles in the center of the parenchyma and a smaller one, close to them, while N. northiana shows the largest number of vascular bundles, implanted in the sclerenchyma ring, and also two smaller ones in the fundamental parenchyma, but close to the sclerenchyma. The tendril has an homogenous parenchyma, formed of big, turgescent cells and a few idioblasts. Near the pitcher, the cross section of the tendril is quite circular. The vascular bundles form 2-3 rings (the internal bundles are bigger than the external ones, in the fundamental parenchyma). A sclerenchymatic sheath surrounds each vascular bundle. Numerous calcium oxalates are present in the fundamental parenchyma. At the inferior level of the pitcher, a typical limb structure is present. In front side view, the internal epidermis presents polygonal elongated cells, with thick walls. Here and there, a lot of multicellular digestive glands are present (Fig. 7); a small epidermal prolongation can be observed near each gland, yet without touching it. The external epidermis (Fig. 8) consists of small polygonal cells with thin walls, anomocytic stomata, hydathodes and nectariferous glands, which appear like multicellular, massive structures, communicating with the exterior through a short channel. In cross section, the wall of the pitcher is quite thick. The internal epidermis shows elongated cells, covered by a thick cuticle. Numerous big digestive glands are present in small epidermal cavities (Fig. 9); the epidermal cells form a small fold, without touching the gland. A digestive gland shows 2-3 layers of oblate cells, 1-2 layers of isodiametrical cells and an external layer of columnar-shaped cells. Each digestive gland is associated with small vascular bundles (tracheids with ringed and spiral thickenings). In longitudinal section, the small fold can be better observed (Fig. 10). The external epidermis consists of small cells, covered by a thin cuticle. The nectariferous glands are formed of three layers of cells delimiting a cavity which opens towards the exterior through a short channel (Fig. 11). The nectariferous glands attract the insects (the prey) to the trap and make them climb the wall of the pitcher to reach the slippery peristome. The assimilatory parenchyma is thick, homogenous, formed of small cells outside and bigger inside. A lot of calcium oxalates are present all over the parenchyma. The vascular bundles have different sizes, the biggest ones occupying the external part of the parenchyma, while the smallest ones occupy the centre of it. Each vascular bundle consists in phloem facing the exterior part of the pitcher and a xylem facing the internal one, so that the internal epidermis represents the old upper epidermis of an archaic leaf and the external epidermis represents the old lower epidermis. All the studied species show mechanical sheaths surrounding the vascular bundles, consisting of fibres with 7
moderately thickened and lignified walls. The assimilatory parenchyma also presents a few idioblasts. The middle level of the pitcher presents a quite similar structure to that of the anterior level. In front side view, the internal epidermis consists of polygonal cells with thick walls and secretory glands, smaller than those occurring at the inferior level; the integumentary fold do not touch the gland (Fig. 12). The external epidermis is formed of polygonal cells, anomocytic stomata, multicellular tector hairs, nectariferous glands and hydathodes (Fig. 13). In cross section, the pitcher shows a thinner wall. The internal epidermis presents digestive glands which communicate with the tracheids (Fig. 14). In longitudinal section, the fold can be better observed (Fig. 15). The external epidermis consists of small cells covered by a thin cuticle. Anomocytic stomata, hydathodes, nectariferous glands (Fig. 16) and multicellular tector hairs, often branched, are present. In the assimilatory parenchyma, numerous calcium oxalates can be observed. Each vascular is bounded by a sclerenchymatic sheath (Fig. 17). There are vascular bundles consisting only of a few phloem elements. The assimilatory parenchyma presents idioblasts, too. The superior level of the pitcher shows the same structure as the other levels. In front side view, the internal epidermis presents large polygonal cells and digestive glands (Fig. 18) smaller than those occurring at the other levels. The epidermal fold covers more than half of the digestive glands. The external epidermis (Fig. 19) consists of small polygonal cells, with waved lateral walls, tector hairs, hydathodes, nectariferous glands and anomocytic stomata. Cross section through the superior level of the pitcher shows the digestive glands in their incipient stage of development (Fig. 20), consisting of a small number of cells. Almost half of the gland is covered by the integumentary fold (Fig. 21); the developing stages of the glands during ontogenesis were previously presented [9]. The external epidermis shows similar structures to those of the anterior levels (Figs. 22 and 23). The assimilatory parenchyma is thinner; the vascular bundles are bounded by a very thin mechanical sheath, consisting of fibres with thickened walls, but weakly lignified; some of the bundles present only a few phloem elements; calcium oxalates are not present. The lid In front side view, both the upper and the lower epidermis present polygonal cells, with waved lateral walls, anomocytic stomata, secretory glands surrounded by an integumentary fold (Fig. 24) and hydathodes (Fig. 25); tector hairs, sometimes branched, are present only in the lower epidermis. The cross section of the lid is similar to that occurring in the pitcher s wall. Numerous digestive glands (Fig. 26) are present in both epidermis. The fundamental parenchyma presents vascular bundles of different sizes (Fig. 27), the largest occupying the centre of the parenchyma. All vascular bundles are surrounded by a thin sclerenchyma sheath formed of thin-walled and weakly lignified fibres. The peristome (Fig. 28) is a common characteristic of the pitcher plants. All four investigated Nepenthes species have a ridged peristome. The epidermal cells are small, covered by a very thick cuticle. Stomata and hydathodes are present in the lower epidermis. 8
The peristome has an homogenous parenchyma, with large cells, a few idioblasts and small vascular bundles, most of them consisting of phloem elements surrounded by sclerenchyma fibres, with cellulosed unthickened walls. Conclusions In spite of the high variability of the pitcher size recorded from one species to another, their histo-anatomy is quite similar. There have been observed mostly quantitative differences (number of the vascular bundles, size of the digestive glands at different levels, thickness of the sclerenchymatic sheath, length of the integumentary fold which covers each digestive gland) and not qualitative differences. REFERENCES 1. ANDERSON A. N., 1994 - Secretion and absorbtion in glands of the carnivorous plant Nepenthes alata. B. A. honors thesis, Connecticut College, New London, C. T. 2. DALTON M. JOS., 1859 - Note sur l origin et le développement des urnes dans les plantes du genre Nepenthes. Ann. des Sci. Nat.; sér.bot., 12: 125-129 3. LLOYD F. E., 1942 - The Carnivorous Plants. Chronica Botanica, 9. Ronald Press, New York 4. MACFARLANE J. M., 1889 - Observations on pitchered insectivorous plants. Part I. Ann. of Bot., 3: 253-265 5. METCALFE C. R., CHALK L., 1972 - Nepenthaceae in Anatomy of the Dicotyledons. 1: 1105-1111, Clarendon Press, Oxford 6. STERN K., 1917 - Contribution to the knowledge of Nepenthes. Flora, 109: 213 283 7. PARKES D. M., 1980 - Adaptive mechanisms of surfaces and glands in some carnivorous plants. MSc Thesis, Monash University, Clayton, Victoria, Australia 8. STAROSTA P., LABAT J.-J., 1993. - L univers des plantes carnivores. Éd. Du May, Paris 9. TOMA I., TOMA C., STĂNESCU I., 2002 - Histo-anatomical aspects of the Nepenthes maxima Reinw. ex Nees metamorphosed leaf. Rev. Roum. Biol., sér. Biol. végét., 47, 1-2: 3-7 Acknowledgments The authors gratefully thank to Felician Micle PhD, Ex-Director of the Botanical Garden of Cluj-Napoca and to Elena Rânba for supplying the material for the present investigation. 9
Explanation of plates: Plate I 1. The upper epidermis of the assimilatory part of N. maxima, in front side view 2. The lower epidermis of the assimilatory part of N. distillatoria, in front side view 3. The mesophyll of the assimilatory part of N. distillatoria 4. Cross section through the midvein of the assimilatory part of N. maxima 5. The biggest vascular bundle of the midvein belonging to the assimilatory part of N. maxima 6. Cross section through the tendril of N. maxima Plate II 7. The internal epidermis of the inferior level of N. distillatoria pitcher, in front side view 8. The external epidermis of the inferior level of N. distillatoria pitcher, in front side view 9. Cross section through the inferior level of N. distillatoria pitcher 10. Longitudinal section of the inferior level of N. maxima pitcher 11. Cross section through the inferior level of N. distillatoria pitcher 12. The internal epidermis of the middle level of N. northiana pitcher, in front side view Plate III 13. The internal epidermis of the middle level of N. maxima pitcher, in front side view 14. Cross section through the middle level of N. northiana pitcher 15. Longitudinal section through the middle level of N. maxima pitcher 16. Cross section through the middle level of N. distillatoria pitcher 17. Cross section through the middle level of N. maxima pitcher 18. The internal epidermis of the superior level of N. coccinea pitcher, in front side view Plate IV 19. The internal epidermis of the superior level of N. distillatoria pitcher, in front side view 20. Cross section through the superior level of N. distillatoria pitcher 21. Longitudinal section through the superior level of N. maxima pitcher 22. Cross section through the superior level of N. distillatoria pitcher 23. Cross section through the superior level of N. northiana pitcher 24. The upper epidermis of the lid belonging to N. northiana pitcher, in front side view Plate V 25. The lower epidermis of the lid belonging to N. northiana pitcher, in front side view 26. Cross section through the lid of N. coccinea pitcher 27. Cross section through the lid of N. northiana pitcher 28. Cross section through the peristome of N. northiana pitcher 10
IRINA STĂNESCU, C.TOMA PLATE I 1 2 3 4 5 6 11
IRINA STĂNESCU, C.TOMA PLATE II 7 8 9 10 11 12 12
IRINA STĂNESCU, C.TOMA PLATE III 13 14 15 16 17 18 13
IRINA STĂNESCU, C.TOMA PLATE IV 19 20 21 22 23 24 14
IRINA STĂNESCU, C.TOMA PLATE V 25 26 27 28 15