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 stages based on morphological and histochemical characteristics: the globular stage, the early and late heart stage and four stages covering early to late cotyledon development. Specific criteria of these stages allow their easy identification independent of growth conditions and thus provide necessary reference points for any developmental studies. The distribution of mitotic activity followed by cell elongation and endopolyploidisation during seed development suggests a developmental gradient expressed in a specific spatial and temporal pattern at two levels between individual seed organs and within single organs. The accumulation pattern of storage proteins legumin and vicilin and their mRNAs, analysed by immunohistostaining and in situ hybridisation and the pattern of starch accumulation are directly correlated with these gradients, i.e., storage function is related inversely to mitotic activity and directly to cell elongation and endopolyploidisation. All seed organs synthesize storage proteins. Thus the expression of vicilin and legumin genes is not embryo specific but seed specific. Mobilisation of transiently stored storage proteins in suspensor, seed coat and endosperm occurs together with the degradation of the respective cell layers during development in a temporally regulated manner.