Nutrient access pathways in the developing embryo of two species of Stylosanthes Sw. (Fabaceae-Aeschinomeneae)

Abstract

In order to contribute to the knowledge of embry nutrition in legumes, different stages in the ovule of Stylosanthes montevidensis Vogel and S. leicarpa Vogel are studied in this paper. as an hypothesis, several definite regions are discussed as responsible for the routes of nutrient uptake processes: 1) a barrier tissue or hypostase connecting the vascular external supply with the inner endosperm at the chalazal region which has a nuclear haustorium and never adopts a cellular structure; 2) a tracheid bar formed by tacheoids with large pits located at seed maturity at the counter integument level in front of the funiculus; 3) the contacting zone of young embryo cotyledons with the starchy layer of outer integument dorsally located in the ovule-seed; 4) protrusive suspensor cells, being the basal cell oversized and in active transference. For the first time, the presence of an endothelium in Aeschynomeneae is reported. Embryo sac and adjacent tissues formation and seed structure and its relation to ecological adaptations of both are also discussed.