Pathway of Photosynthate Transfer in the Developing Seed of Vicia faba L. Transfer in Relation to Seed Anatomy

The seed coat vascular system of the developing seed of Viciafaba consists of a chalazal and two lateral veins. The veinsare embedded in parenchymatous tissue which lies beneath thehypodermis and is divided into chlorenchyma, ground parenchymaand thin-walled parenchyma. The thin-walled parenchyma cellsand, in old seed coats, the vascular parenchyma of the veinsundergo additional secondary wall development to form transfercells. Thus, transfer cells line the entire inner surface ofthe seed coat. Initial distribution of ¹⁴C-photosynthates andsodium fluorescein within the seed coat was in the vascularsystem. Subsequent transfer towards the embryo was either radiallythrough vascular parenchyma and thin-walled parenchyma to thin-walledparenchyma/transfer cells, or by lateral spread within the groundand thin-walled parenchyma/transfer cells of the non-vascularregion of the seed coat prior to radial transfer. One-thirdof the ¹⁴C-photosynthate delivered to the enclosed embryo wasestimated to be transferred via the non-vascular region of theseed coat. The cotyledons consist of a single-layered epidermisenclosing storage parenchyma in which a differentiating reticulatevascular system is embedded. Epidermal cells juxtaposed to theseed coat develop wall ingrowths characteristic of transfercells. Initial distribution of ¹⁴C-photosynthate within thecotyledons reflected the unequal delivery to the seed apoplastfrom the vascular and non-vascular regions of the seed coat.Subsequent even distribution of photosynthate within the cotyledonspossibly occurred by transfer within their vascular system. Key words: Cellular pathway, photosynthate transfer, seed anatomy, transfer cell