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The micromorphological typology of seed surfaces was investigated in rapid-cycling Brassica (RCBr) forms, using scanning electron microscopy. Four types of basic ornamentation pattern were recognized: reticulate (B. rapa, B. juncea), reticulate-foveolate (B. nigra), randomly reticulate (B. oleracea, B. napus) and reticulate-rugose (B. carinata). The seed coats showed variation in the shape and size of the testa epidermal cells and the structure of the outer periclinal and anticlinal cell walls. The surface patterns in RCBr seeds were less exposed and were moderately reticulated compared to cultivated Brassica species. The micromorphological characteristics of the seed coats may provide valuable additional diagnostic criteria for delimitation of RCBr forms, and can be used in identification of seeds.
The structural and developmental features of the diploid and tetraploid plants of Arabidopsis thaliana ecotype Wilna were studied by light and scanning electron microscopy (SEM). The diploid and tetraploid plants differ in the following morphological characters: general habit, length of life cycle, and shape and size of leaves, flowers, pollen grains, seeds and fruits. The developmental pattern of generative structures, such as ovule initiation, integument differentiation and seed formation, is similar in the two forms but differs in details. These differences concern the gradual degradation and thickening of integument layers and the deposition of polysaccharides within testa layers. SEM analysis of generative (pollen grains, seeds, fruits) and vegetative organs (stems) shows variation in their surface structure. The siliques and stem surfaces additionally exhibit different tertiary sculpture. Analysis of seeds shows variation in the shape and size of the testa epidermal cells and the curvature of the outer periclinal cell walls. There are significant differences between mature pollen grains in grain size and the number of exine furrows. In the examined plants, micromorphological features of both pollen grains and seeds can be conveniently used as good diagnostic characters for determination of the ploidy level of Arabidopsis thaliana plants.
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