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|Anatomical, morphological and cytological comparative study of leaves and cotyledons from forestry species II. Comparison between the the morpho-anatomical and cytological structures of cotyledons and leaves of black locust (Robinia pseudoacacia l)
|Burescu L., Cachiţă D., Crăciun C.
|1University of Oradea, Faculty of Sciences; 2„V. Goldiş” University from Arad, Faculty of Sciences, Engeniering and Informatics; 3„Babeş-Bolyai” University from Cluj-Napoca, Electron Microscopy Center;
|The role of cotyledons in seed physiology depends on the species it is experimented with. The black locust (Robinia pseudoacacia L) has an embryo with two epigeal cotyledons that, after the plant rises, turn green and their metabolism switches from a heterotrophic regime to an autotrophic photosynthetic process. The cotyledons supply the embryo with water, nutrients and energy that helps the plant to break the seed coat and the hypocotyl together with the cotyledons to raise above the ground. The life span of the cotyledons is approximately 40 days depending on the environmental conditions. After the black locust plantlets emerge, the epycotyl rises between the two cotyledons and produce odd pinnate leaves. They have elliptical-shaped folioles about 2.5 cm in lenght. The folioles are thinner than the cotyledons. At about 14 days after the onset of germination, the cotyledons have an average lenght of 1 cm and a thickness of about 3 – 4 mm. The foliar lamina is crossed by a main visible midvein that is well defined on their lower side. This morpho-anatomical formation is missing in cotyledons. The secondary veins are rare and thin. The folioles epidermis has stomata and the inferior one has live unicellular hairs. Between the two epidermises the foliole laminas have an assimilation mesophyll made of 5 – 7 layers of parenchyma cells. Here is also located the hypoderm whose cells contain secondary metabolites that are stained in blue with „Epoxy tissue stain”. The cotyledons have an elongated shape. The outline of the transversal sections is plano convex, the upper epidermis being planar and the lower epidermis is slightly convex. The cotyledon veins are scarce and are very fine. The cotyledons have a very well ordered tissue structure. The upper and lower epidermis has rectangle shaped cells and both have only pre-stomata. Between the two epidermises there are 16 -20 assimilating parenchyma layers, the one right below the epidermis is of palisade type. From a cytological point of view, the assimilating mesophyll of the cotyledons is poor in chloroplasts but both the foliary and cotyledonary mesophyll have in their vacuolar content secondary metabolites which toghether with the staining reagents, aggregate leading to corpuscular formations or electron-dense vacuolar structures.
|Robinia pseudoacacia L; leaf, cotyledons; morpho-anatomical structure.
|Constantin Craciun, Ph. D., Babes-Bolyai University Cluj-Napoca, Electron Microscopy Center, 5-7 Clinicilor Street, Cluj-Napoca 400006, Romania, Phone: +40(0)262722, e-mail: email@example.com