EMBRYOGENESIS OF VICIA-FABA L - HISTODIFFERENTIATION IN RELATION TO STARCH AND STORAGE PROTEIN-SYNTHESIS

Seed development of Vicia faba is described and divided into seven sta ges based on morphological and histochemical characteristics: the glob ular stage, the early and late heart stage and four stages covering ea rly to late cotyledon development. Specific criteria of these stages a llow their easy identification independent of growth conditions and th us provide necessary reference points for any developmental studies. T he distribution of mitotic activity followed by cell elongation and en dopolyploidisation during seed development suggests a developmental gr adient expressed in a specific spatial and temporal pattern at two lev els between individual seed organs and within single organs. The accum ulation pattern of storage proteins legumin and vicilin and their mRNA s, analysed by immunohistostaining and in situ hybridisation and the p attern of starch accumulation are directly correlated with these gradi ents, i.e., storage function is related inversely to mitotic activity and directly to cell elongation and endopolyploidisation. All seed org ans synthesize storage proteins. Thus the expression of vicilin and le gumin genes is not embryo specific but seed specific. Mobilisation of transiently stored storage proteins in suspensor, seed coat and endosp erm occurs together with the degradation of the respective cell layers during development in a temporally regulated manner.