Anther-derived plants of Melandrium album were analysed by flow-cytometric, phenotypic, cytological, and genetic means: more than 90% were classified as females, while no male plants were observed. Instead, one hermaphrodite and several atypical female parental plants were identified. One highly androgenic plant (M5045) turned out to possess two extra autosomes (2n = 26,XY) instead of the ordinary male formula, 2n = 24 (24,XY). The results are discussed in light of possible developmental interactions among the three classes of chromosomes in this dioecious species: male (Y), female (X), and autosomes.Key words: Melandrium album, dioecious, haploids, sex chromosomes, embryogenic development, hormones.
Overexpression of the budding yeast RAS2 gene in Nicotiana plumbaginifolia cells revealed that RAS2 acted as 'suicide' gene in freshly isolated protoplasts from leaves and blocked cell proliferation in cell suspension-derived protoplasts. Among a series of genes tested (such as npt II, CDC35, PDE2), RAS2 was the only one to block the expression of the cat gene, as measured in a transient gene expression assay. Another ras gene, v-Ha-ras, had similar effects. Furthermore, the RAS2 effect was species-specific and depended on the modulation of hormonal metabolism in the transfected cells, while no differences were noticed between the normal and the activated val19 gene. Transfected plant cells are shown to synthesize a RAS2 protein of the same electrophoretic mobility as the yeast RAS2 product. The results are discussed in the broader context of the evolutionarily conserved ras genes involved in vital cellular functions.
Conditions for protoplast isolation and culture in the dioecious species Melandrium album (Silene alba) are described and differences between female and male plants subjected to in vitro culture identified. Plant regeneration was achieved in the case of female plants only. Selection for high regeneration capacity lines was initiated aiming at creating responsive experimental material for further studies. The regeneration behaviour in this dioecious plant is discussed in the context of hormonal models on sex determination.
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