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Annals of RSCB Vol. XVI, Issue 1 HISTOLOGY OF THE FOLIAR TRICHOMES IN SOME PELARGONIUM L'HERIT SPECIES Rodica Bercu, Livia Broască DEPARTMENT OF BOTANY, FACULTY OF NATURAL AND AGRICULTURAL SCIENCES “OVIDIUS” UNIVERSITY, CONSTANTZA Summary This paper is a part of a complex study concerning ornamental plants histoanatomy and proposes a histological analysis of the leaf trichomes (hairs) of three Pelargonium species, popular ornamental plants known as geraniums: Pelargonium grandiflorum (Andr.) Willd., Pelargonium peltatum (L.) Aiton ex L'Herit, Pelargonium zonale (L.) L'Herit. Anatomically, is clear that the main criterion for the foliar trichomes differentiation both epidermal and glandular trichomes, are the length, structure (differences in shape and dimensions of the foot cells) and their density both on the upper and lower epidermis and among the species blades. The protective trichomes of all three species are simple unicellular with a sharp apex. Rare 4celled protective trichomes occur. The glandular trichomes are all many-celled composed of five cells for P. zonale and P. grandiflorum and two for P. peltatum, the last cell being the one-celled gland (more voluminous for P. peltatum) with secretive product inside. The protective and secretive trichomes of the petiole are almost the same as regard their structure with those of the blade. Key words: blade, histology, secretive trichomes, protective trichomes, Pelargonium. [email protected]; [email protected] Pelargonium grandiflorum is a shrubby, glabrous and glaucous, in mature stage. Introduction Genus Pelargonium L'Herit is originally from South Africa and includes over 175 species according to some authors or, even more than 300 species after another. The plants, known improper as "geranium" have entered Europe in the eighteenth century and have spread rapidly in all its areas. They are herbaceous plants, perennial, pubescent, rarely high, stems soft, succulent and rich foliage (Charrier, 2000, Mc Hoy, 1996). The species of this genus are very diverse, general appearance, color of flowers, but especially after leaf morphology. Geraniums are classified in the family Geraniaceae ornamental plants, most species being bred for their decorative flowers and, some, liked the smell of the leaves. Fragrant leaves of these species contain geraniina a rate higher or lower. This substance is used to obtain oils with therapeutic properties (Viljoen et al., 1995). Pelargonium grandiflorum (Andr.) Willd. The plant leaves have long petioles, palmately 5–7-nerved, deeply 5–7-lobed with the lobes coarsely toothed. The stipules are ovate and mucronate. The leaves are not zoned and the flowers are larger often in different combinations of colors (from white to red) and shades (Raimondo et al. 2009; Van der Walt, 1977; Nichols, 2005). 394 Annals of RSCB Vol. XVI, Issue 1 Pelargonium peltatum is a climbing, semi-succulent perennial, trailing through other trees and shrubs in its habitat. The climber has long, straggling shoots, which can reach a height of 2m. This plant is characterized by its ivyshaped leaves. Some of the leaves have distinctive zonal markings, but this is not a common characteristic. It produces clusters of flowers varying from mauve or pinkish mauve to pale pink or white. It flowers mainly in September to December (Van der Walt, 1977). The flower color ranges from rosepink to all shades of red as well as pure white. The distinctly irregular flowers are borne in a typically umbel-like inflorescence. P. zonale flowers throughout the year with a peak in spring (September-November) (Della Beffa, 1999, Turner, 1998). The literature references are focused mostly on the leaf cytology, morphology and petiole anatomy, in particular for P. zonale species, lack a histological trichomes study especially concerning those of P. grandiflorum and P. peltatum. On the other hand trichomes are the criteria for identification of species. Material and methods The plants were collected from S.C. IRIS International S.R.L. greenhouse. Paradermal sections of mature and juvenile leaves were performed by the usually metods used in vegetal histology (Bercu & Jianu, 2003). The samples were stained with saphranin 1% (Dilcher, 1974). Histological observations and micrographs were performed with a BIOROM –T bright field microscope, equipped with a TOPICA 6001A video camera. Pelargonium peltatum (L.) Aiton ex L'Herit This erect or scrambling softly woody shrub Pelargonium zonale usually grows up to 1m but it can reach heights of 3m. The branches are almost succulent and are usually covered with hairs, while the older stems harden with age. The large palmately-nerved leaves are often smooth and a characteristic dark horseshoe-shaped mark is often present. Results and discussions Pelargonium grandiflorum leaves present, mostly in juvenile stages, trichomes while the mature leaves are almost glabrous. Upper and lower epidermis possesses protective and glandular trichomes (Peterson et al., 2008). The protective trichomes of the upper epidermis are longer or shorter (probably the latter in training) with a sharp apex and widened at the base. They are composed of 3 cells with peripheral cytoplasm and nucleus inside, covered by cuticle on the outside. They are short, straight, very few are inclined (Fig. 1, A, B). The glandular trichomes consist of five cells with a widened basal cell, a long narrow cell, followed by a slightly wider cell than those of the second and the last cell which is the one-celled more or less spherical gland with the product of secretion inside (Fig. 1, C, D). Pelargonium zonale (L.) 'Herit 395 Annals of RSCB Vol. XVI, Issue 1 In the lower epidermis as well are long and short protective trichomes (probably in training) (Batanouny, 1992). They may be straight, tilt the middle or may be sickle-shaped. They consists of three, rarely four cells (Fig. 2, A, B). The lower epidermis possesses glandular trichomes similar in structure to those on the upper epidermis, but they are more rare (Fig. 2, C, D). Fig. 1. Trichomes of the upper epidermis of Pelargonium grandiflorum: protective trichomes (A, B, x, 60; x 200); glandular trichomes (C, D, x 185, x 400): G- the gland, TF- trichome foot. The petiole protective trichomes equate the appearance and structure of the lower epidermis trichomes, but rare The petiole glandular trichomes, even if are 3celled, are shorter than those of the blade. Like the previous species, Pelargonium peltatum presents trichomes on the entire surface of the leaf in juvenile stage. At maturity the leaves are almost glabrous. Paradermal sections disclose that the upper epidermis is provided with protective and glandular trichomes. The many-celled protective trichomes are uniseriate, consisting of three, rare four, cells, arrising from an epidermal socle (Bavaru & Bercu 2002). The basal and second cells are shorter and slightly widened comparatively to the latter sharpened cell. The trichomes are covered by a thick cuticle (Fig. 3, A). 396 Annals of RSCB Vol. XVI, Issue 1 Fig. 2. Trichomes of the lower epidermis of Pelargonium grandiflorum: protective trichomes (A, B, x 75, x 80); protective and glandular trichomes - amsamble(C, x 50), glandular tricnome (D, x 200): E- epidermis, S- socle. The glandular trichomes are dense comparativelly with the protectives, simple, many-celled too with a short feet, composed of two cells, a long widened basal cell. In the foot cells may be observed the usually cytological elements such as in the protective trichomes cells. The second cell is shorter and more or less rectangular in shape. The last cell is the one-celled and voluminous gland, containing the secretive product (Fig. 3, B). Resemble the lower epidermis is provided with protective and glandular trichomes too. Protective trichomes are smaller and rarer than those of P. zonale. They may be tilt from the middle or entirely curved form the base (Fig. 4, A). The small glandular trichomes are formed by two cells, as well, the latter being the one-celled spherical secretive one (Fig. 4, B). The petiole possesses rarest protective and glandular trichomes than those of the blade. Both types of trichomes (secretive and glandular) are similar to those of the lower epidermis. Pelargonium zonale (L.) L'Herit exhibits in epidermal paradermal sections, as Marais (2005), reported for other Pelargonium species (P. moniliformis) protective trichomes, interspersed with soft patent hairs, both on the upper and lower epidermis. 397 Annals of RSCB Vol. XVI, Issue 1 Fig. 3. Trichomes of the upper epidermis of Pelargonium peltatum: protective trichome (A, x 145); glandular trichome (B, x 400). Fig. 4. Trichomes of the lower epidermis of Pelargonium peltatum: protective trichomes (A, x 60); glandular trichome (B, x 300). The protective trichomes of the upper epidermis are uniseriate manycelled, provided with three or four cells, externally covered by a thick cuticle. Inside is one nucleus, cytoplasm and a large vacuole. The protective trichomes are pointed at the top arrising on an epidermal socle. Some are slightly inclined to the right or left on the epidermis surface. However most of them are stiff (Fig. 5, A, B). The glandular trichomes are in a small number comparatively to the protective trichomes. The glandular trichomes, as Bavaru & Bercu (2002) and Esau (1963) reported, are longer composed of four or five cells, covered by a thick cuticle. 398 Annals of RSCB Vol. XVI, Issue 1 Fig. 5. Trichomes of the upper epidermis of Pelargomium zonale: protective trichomes- ansamble (A, x 70), protective trichome - detail (B, x 140); glandular trichome– detail (C, x 120). Fig. 6. Trichomes of the lower epidermis of Pelargonium zonale: protective trichomes (A, x 160); protective and glandular trichomes (B, x 145). 399 Annals of RSCB Vol. XVI, Issue 1 density, both for those on the upper and lower epidermis and among the three species blade. Generally, the protective and glandular trichomes of the petiole are the same as regards their structure and lenght with those of the blade but rare (mostly the secretive trichomes) for P. peltatum and P. grandiflorum. P zonale trichomes are dense on the blade lower epidermis comparatively those of the upper epidermis. Cells are becoming narrower towards the top, and the last is the onecelled gland, spherical in shape possessing the product of secretion (Fig. 5, C). The protective trichomes of the lower epidermis even more dense, they are longer than those of the upper epidermis, although there are small hairs too. Most of them are likely, very few, straight, formed by three or four cells (Fig. 6, A, B). The glandular hairs are also larger and more numerous than those of the upper epidermis surface. They consist of four or five cells, ending with the spherical gland cell (Andrei, 1978) (Fig. 6, B). The petiole protective trichomes are patent soft, many-celled, like those of the lower epidermis and the glandular can be equated with those of the upper epidermis being short and extremelly rare (1-2 on the petiole surface). References Andrei, M.: Anatomia plantelor, 1978. Edited by Didactică şi Pedagogică, Bucureşti. Batanouny, K.H.: Anatomy of Plants, 1992. Edited by Univ. Press, Cairo. Bavaru A., Bercu R.: Morfologia şi anatomia plantelor 2002. Edited by Ex Ponto, Constanţa. Bercu R., Jianu, D.L.: Practicum de Morfologia şi anatomia plantelor. 2003. Edited by “Ovidius” University Press, Constanţa. Charrier, M. (réalisation): Jardins Ręvés et Réussis. Catalogue Végétal Sélection 2001. Jardilland S. A., (Paris), 8: 111-112, 2000. Della Beffa, M.: Plante de apartament, 1999. Edited by All, Bucureşti. Dilcher, D.: Aproaches to the identification of the angiosperm leaf remains. The Botanical Review (Bot. Garden, New York), 40: 24-103, 1974. Esau, K.: Plant anatomy. 1963. Edited by Wiley & Sons, New York. Marais E. M.: Differences between Pelargonium moniliforme (Geraniaceae) and the closely. South African Journal of Botany, 71(2): 221–227, 2005. Mc Hoy, P.: Les plantes d’appartament, 1996. Edited by Celiv, Paris. Nichols, G.: In the ivy league: the indigenous garden. Farmer's Weekly, 28 Jan.: 78, 79, 2005. Peterson, R.I., Peterson, C.A., Melville, L. H.: Teaching plant anatomy through laboratory exercises, 2008. Edited by NRC Press, Ottawa, Ontario. Raimondo, D., Von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A., Manyama, P.A. (eds): Red List of South African plants, 2009. Edited by South African National Biodiversity Institute, Pretoria. Turner, R.G.: Botanica - the most complete garden encyclopedia ever published, 1998. Edited by Barnes and Noble Books, New York. Van der Walt, J.J.: Pelargoniums of southern Africa, 1977. Edited by Purnell, Cape Town. Viljoen, A. M., Demarne, F. E., Van der Walt, J.J. A, Swart J. P. J.,: A study of variation in the essential oil and morphology of P. capitatum (L.) L’ Herit (Geraniaceae), S. Afr. J. Bot., 61(3): 105-113, 1995. Conclusions Without exception, two types of trichomes are present, protective and glandular, on the blade and petiole of the studied leaves, even if they are numerous in the juvenile stage in P. grandiflorum or almost absent in mature blade of P. peltatum. The blade protective trichomes are mostly three-celled and uniseriate, possessing a basal socle, a more or less long foot, the latter with a sharp apex (all species). Rare 4-celled trichomes occur. Differences arise in particular as regards the trichomes lenght (long for P. zonale and P. grandiflorum and smaller for P. peltatum), density and shape (stright for all species, rare curved, less for P. zonale trichomes). The trichomes density differs on both upper and lower blade surfaces too, being rare in the latter for P. grandiflorum and P. peltatum. Comparativelly, the blade trichomes of P. zonale density is inversed. The glandular trichomes are uniseriate for all species, differences arrising as regards the number of the feet cells and the size of the last cell – the gland cell. Other diferences arise as regards the 400