Structural Aspects of the Pathways of Nutrient Flow to the Developing Embryo and Cotyledons of Pisum sativum L

Abstract

The pea seed requires large quantities of nutrient during its growth and development. In the early stages a large proportion of this nutrient is obtained from the endosperm surrounding the embryo in the embryo sac. A number of structural specializations, such as increased surface areas of the embryo sac boundary wall and the extra-embryonic wall and breakdown of the inner ovular cells, may aid in the passage of nutrient to the developing embryo. This study has shown that the amount of vascular tissue in the funicle and ovule increases markedly between the time of cotyledon initiation and the commencement of storage protein synthesis and deposition. Large numbers of transfer cells are associated with the sieve elements in the pod and funicle, but not in the ovule. Also, the numbers of xylem and sieve elements in the funicle decrease as the strand passes from the pod to the ovule. Two strands of phloem tissue were found to branch from the main vascular bundle in the ovule and to sweep across the base of the seed and around either side of the narrow tubular arm of the embryo sac which contains the radicle.