MORPHOLOGICAL AND HISTO-ANATOMICAL ASPECTS AT SOME DICOTILEDONATE SEEDLINGS RELATED TO THE VASCULAR TRANSITION

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1 Analele ştiinţifice ale Universităţii Al. I. Cuza Iaşi Tomul LII, s. II a. Biologie vegetală, 2006 MORPHOLOGICAL AND HISTO-ANATOMICAL ASPECTS AT SOME DICOTILEDONATE SEEDLINGS RELATED TO THE VASCULAR TRANSITION RODICA RUGINĂ, C.TOMA, LĂCRĂMIOARA IVĂNESCU Abstract: The authors investigate the morphology and structure of seedlings from 4 different species of herbal dicotyledonate: Mirabilis jalapa L., Pisum sativum L., Ricinus communis L. and Tropaeolum majus L., some with epigeal and some with hipogeal germination. Studying the structure of the vascular system during 21 days from the germination, we distinguished the transformation from the primary structure of the root to the primary structure of the stem, underlining the level where the histological changes take place along the axis of the seedlings, the order in which the xylem vessels appear, extinguish and other appear in different positions. The gathered data support the theory of torsion as well as the theory of desmogenesis. The type of germination does not influence the level where the vascular transition takes place. Key words: blastogeny, vascular transition. Introduction The metamorphosis of the alternative structure of the vascular apparatus of the root into the overlapped structure of the stem has been a very interesting topic since the beginning of the 20th century, especially for the French school of Botanic. During the last decades, very many theories and hypothesis were stated, among which the desmogenesis developed by G. Chauveaud, revolutionary as thinking manner through its data about the hystogenesis. Although numerous pieces of information accumulated conclude in this direction, it seams that the theory of rotation and torsion is assimilated by the majority of the botanists in their studies regarding the hystogenesis of the vascular system.in this paper we wish to show based on the analyzed material that the theory of rotation actually provides data in favor of the Chauveaud theory. The lack of information regarding the hystogenesis of the vascular apparatus in the Romanian literature of specialty encouraged us in this work, even if it will only become a starting point for future research in the field of vegetal histology. Botanical Garden of Iassy University Al.I.Cuza Iassy, Faculty of Biology 123

2 Historical references As we have already mentioned, at the beginning of the 20 th century and during its course the French botanists have approached many aspects regarding the structure of the vascular apparatus at seedlings and its transformations in ontogenesis. Thus, Lenoir M. [3], as follower of torsion and deduplication, supports this theory with the modifications of the vascular system at seedlings from Veronica and Cucumis species, also given the histological data and the physiological argumenţs. Chauveaud G. [1] rejects vehemently the previous theories regarding the vascular transition, elaborating a new one related to the evolution of the vascular system and to desmogensis, distinguishing the, alternative position of the vascular bundles (characteristic to the root), the intermediary one (characteristic to hypocotyl) and overlapped (characteristic to the stem). The author also claims that the first elements conductor of phloem and then of xylem appear from the direct differentiations of the fundamental parenchyma and the next ones from the differentiation of a meristem (procambium). The same G. Chauveaud first defines the notion of contingent, taken over later by A. Tronchet [5, 6] and used to describe the structure modifications of the vascular system at Brassicaceae. H. Hayward [1967] in his monographic work named "The structure of economic plants", studying the morphology and anatomy of some culture plants, also refers to a few particularities of the germination of seeds, to the structure of seedlings and to the hystogenesis of their vascular system. The school of vegetal morphology and anatomy from Iaşi, considering some aspects of blastogenie at different species of Fabaceae [4] underlined the fact that the most important characters with taxonomic value are offered by the shape and size of the cotyledons, of the folios and tendrils. Material and methods The morphology of germination and seedlings (starting with its cotiledonar phase and lasting until the appearance of the first 2-3 leaves) was studied on material obtained from sowing in Petri boxes or flower pots. We analyzed seedlings from 3 to 21 days old belonging to the following species: Mirabilis jalapa L., Pisum sativum L., Ricinus communis L. and Tropaeolum majus L. To observe the changes of the vascular tissues, the hysto-anatomical analyze was done on transversal sections at three levels trough the root, the hypocotyls and epicotyls. The sections were done using the hand microtome but also using the one with paraffin and then they were colored with Heidenhaim hematoxyline and/or with green iodine and alaunat carmine. 124

3 The purpose being to research the evolution of the vascular system, our attention was focused on the central cylinder and less on the other anatomical zones of the investigated organs in which the modifications were not very significant during the first 21 days from germination. Results Mirabilis jalapa L. (Nyctaginaceae) The morphology of the seedlings. The germination is epigeous and takes place after 14 days from the sowing, when at the surface of the soil the two asymmetrical cotyledons appear. After another 2-3 days, the root measures 6-7 cm and. the hypocotyl 2 cm. At seedlings of 21 days the growth is obvious the growth in length of the root and of cotyledons and less at the hypocotyl that forms tubers (just cm). The cotyledons, big and foliaceous have the limb of times wider than its length, with a long and emarginated tip. The slightly heterocotily and the forming of tubers are characteristic also to other species from the same family (for example Abronia umbellata). The structure of the seedling. The structure of the central cylinder of the root from a 14-day old seedling (at the upper and middle level) is diarch. The ligneous fascicles are next to the centre trough the metaxylem vessels relatively large and the phloem forms two blades tangential at the pericycle. In the upper third of the root new metaxylem vessels appear, lateral to the ones already mentioned above, along the axis of the organ forming a compact xylem corp. After 2 (3) days, in the same area but especially at the lower third of the hypocotyls, the central cylinder becomes very thick; in its axis we can find a parenchyma mass with very big cells. Meanwhile, other new ligneous vessels have formed in the shape of tangential blades that alternate with the two fascicules of primary xylem still persistent; almost simultaneously new groups of phloem elements are formed. During this phase of siphonostele, the vascular system is represented by 4 fascicles with overlapped xylem and phloem, typical structure for the stem. The hypocotyl prepare a stem structure with 4 fascicles at the lower and 8 at the upper part. The conductor tissue of the epicotyl (the epicotyledonary internode) has a ring shaped type, with procambium in two layers, which has produced in the exterior groups of phloem elements overlapped on some vessels of xylem. In the medullar parenchyma we can distinguish more libero ligneous fascicles (12-13). Pisum sativum L. (Fabaceae) The morphology of the seedling. The germination is hypogeous and takes place 12 (14) days after the sowing. It is visible when trough the micropyl the axis root125

4 hypocotyls appear at 1-2 (3) mm in length at the beginning. In 5-6 days it reaches cm; in this stage the first layer of epicotyl internode is also visible of 2-3 mm in length. It is curved at the beginning but in 14 days it becomes straight and measures cm; on the surface of the root we observe 3 orthostichies of lateral roots as nipples shaped. The first two leaves look like some bractei and it seems that they have formed previous to the germination; only the third leaf is a typical nomophyll. The structure of the seedling. Inside the central cylinder of a root belonging to a 14-day old seedling (in the lower and middle third) and then to a 21-day old (in the lower third) we can observe 3 fascicles of xylem and 3 of phloem. Each fascicule of xylem present 7-8 narrow vessels of protoxylem (of 10-20μm) and 4-6 wide vessels of metaxylem (of μm). The phloem fascicules contain 4-5 (6) vessels next to the pericycle. In the small length (3-4 mm) of the hypocotyl the axis becomes parenchymatic. The xylem vessels group in 3 tangential blades neighbors to 2 groups of phloem vessels fascicles. Under the cotyledons, 2 of the phloem fascicles together with the new formed will penetrate toward their inside. In the epicotyl internode (in the lower and middle third) we find a typical structure for the root, with the xylem occupies the center at this day with 4 xylemic poles; next to them, at side, we distinguish 4 groups of phloem elements. The next internodes of the epicotyls (2 and 3) have a intermediary structure between root and stem: 4 blades of tangential xylem and 4 of phloem opposed to the fîrst; next to them, in the centre, the initial protoxylem and metaxylem persist. In the upper third of the internode number 3 and all along internode number 4 the typical caulinar structure ofthe conductor tissue consists of 6 libero ligneous fascicles, among which 2 belong to [Hayward H., 1967] the 3 and 4 nomopylls; these are vîsible since the fîrst epicotilar internode, as the 2 cortical fascicles probably belonging to l and 2 bracteant leaves. Ricinus communis L. (Euphorbiaceae) The morphology of the seedling. At 14 days from the sowing, the epigean germination takes place. The growth of the root's length happens simultaneously with the hypocotyl s. At the beginning, the hypocotyl is curved and then becomes straight reaching the extraction of the cotyledons from the albumen. Until the first leaves appear (after 21 days) the cotyledons grow and become foliaceous so able of photosynthesis with a 5-6 cm petiole and a slightly oval limb of 6-7 cm in length and 5-6 cm wide. The structure of the seedling. The central cylinder of the root is tetrarch. At a 14-day, the xylem from the lower third of the organ is represented by 4 fascicles with 9-10 tight vessels each, with polygonal contour in transversal section, alternating with the same number of phloem fascicles. After a week, at the same level at the root, between the mentioned fascicles 8-9 long metaxylem vessels appear. At the same age (21 days) at the upper part of the root, the axis of the central cylinder becomes parenchymatic trough the 126

5 resorbtion of the metaxylem. We can still see protoxylem vessels (alternative) and the phloem vessels opposed to them; the new vessels of xylem are wide, with thin and still nonlignified walls. Discussions and conclusions A long time scientists considered that the transition from the root's structure to the stem's one was done in the collet area. But, as we have already seen, the transition from the alternative structure of the root to the overlapped structure of the stem takes place at different levels in the root, hypocotyl and epicotyl. According to G. Chauveaud [1] the three organs represent different stadiums of evolution of the vascular system. During the ontogenetic evolution different phenomena took place: appearance of xylem and phloem vessels, their resorbtion, re-settlement of the new vascular elements, passing from the altern stage to the intermediary (tangential) one and overlapped. The start of the overlapping phase is given by the appearance of a meristematic tissue which will produce xylem and phloem in centrifugal direction and respectively centripetal. These structures are not different types but are different phases of the general evolution type of the conductor system. The alternative structure we observed at the 4 species studied is found only at the lower third of the root; at the middle and superior level (basal),the tangential phase is obvious at Ricinus communis L. and even overlapped at Mirabilis jalapa L. and Tropaeolum majus L. At Pisum sativum L. the modifîcation of the conductor system take place in the l, 2, 3 and 4 internodes of the epicotyl. In the basal internode of the epicotyl (1) on a small area of its base, we find a xylemic central core characteristic to the root. The vascular evolution in the hypocotyl, even if only conserving the tangential phase, makes us believe that this formation belongs to the hypocotyl root axis. The type of germination epigeal and hipogeal does not influence the level of vascular transformations along the axis; it can be produced in the epicotyl (Pisum sativum L.) or in the root (Tropaeolum majus L.). BIBLIOGRAPHY 1. CHAVEAUD G., 1911 L appareil conducteur des plantes vasculaires et les phases principales de son évolution. Ann. Des Sci. Nat., Bot., sér. 9, 13: HAYWARD H., 1967 The structure of economic plants. Ed. Cramer J., New York 3. LENOIR M., 1920 Evolution du tissus vasculaire chez quelques plantules de Dicotylédones. Ann. Des Sci. Nat., Bot., sér. 10, 2: TOMA C., GEORGETA TEODORESCU, ANGELA TONIUC, 1975 Donées morphologiques concernant les plantules de quelques Légumineuses. An. st. Univ. Al. I. Cuza Iasi, s. II a (biol.),

6 5. TRONCHET A., 1930 Recherches sur les types d organisation les plus répandus de la plantule des Dicotylédones. Leurs principales modifications, leur rapports. Extr. d Arch. De Bot., 4, 1: TRONCHET A., 1952 La valeur de notion de convergent chez Phanérogames et la réalité des phénomènes d acceleration basifuge. L Année biol., 56e ann., sér. 3, 28, 7 8 : Explanation of plates Plate I Mirabilis jalapa L. Transections at various level of root and hypocotyl Plate II Ricinus communis L. Transections at various level of root and hypocotyl Plate III Pisum sativum L. Transections at various level of root and epicotyl 12, 14, 16, 21 d day of the seedlings Abreviations A, B, C root, at lower (A), middle (B) and upper (C) level D, E hypocotyls, at lower (D) and upper (E) level F, G - epicotyl, 2 (F) and 3 (G) internode 1 cortical parenchyma; 2 endodermis; 3 pericycle; 4, 5 alternative xylem: proto- (4) and metaxylem (5); 6 tangential xylemic vessels; 7 superposed xylemic vessels; 8 alternative phloem; 9 tangential phloem; 10 superposed phloem; 11 cambium; 12 pith ray; 13 pith. 128

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HISTO-ANATOMICAL LESS KNOW ASPECTS UPON SOME LAMIACEAE TAXA CAMELIA IFRIM *, IRINA TOMA ** Introduction. Material and method

Analele ştiinţifice ale Universităţii Al. I. Cuza Iaşi Tomul L, s. II a. Biologie vegetală, 2004 HISTO-ANATOMICAL LESS KNOW ASPECTS UPON SOME LAMIACEAE TAXA CAMELIA IFRIM *, IRINA TOMA ** Abstract: The