Structure of the Developing Pea Seed Coat and the Post‐phloem Transport Pathway of Nutrients

• Published in: Annals of botany Vol. 91; no. 6; pp. 729 - 737
• Main Authors: VAN DONGEN, JOOST T., AMMERLAAN, ANKIE M. H., WOUTERLOOD, MADELEINE, VAN AELST, ADRIAAN C., BORSTLAP, ADRIANUS C.
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.05.2003; Oxford Publishing Limited (England)
• Subjects: amino-acids; anatomy; apoplast; Arylsulfonates; Biological Transport; Cell Membrane - metabolism; Cell walls; cellular pathway; Chlorenchyma; Cotyledons; cryo‐SEM; development; Epidermal cells; Fluorescence; HPTS; Key words:Pisumsativum L; legume; Nutrient transport; Original; Parenchyma; parenchyma cells; pea; Peas; phaseolus-vulgaris l; phloem unloading; photosynthate transfer; Pisum sativum - cytology; Pisum sativum - metabolism; pisum-sativum; plasma-membrane; pyranine; seed coat; Seeds; Seeds - cytology; Seeds - metabolism; Seeds - ultrastructure; sieve element transport; Solutes; sucrose; Testa; transport; vicia-faba l
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mcg066

An important function of the seed coat is to deliver nutrients to the embryo. To relate this function to anatomical characteristics, the developing seed coat of pea (Pisum sativum L.) was examined by light‐ and cryo‐scanning electron microscopy (cryo‐SEM) from the late pre‐storage phase until the end of seed filling. During this time the apparently undifferentiated seed coat tissues evolve into the epidermal macrosclereids, the hypodermal hourglass cells, chlorenchyma, ground parenchyma and branched parenchyma. Using the fluorescent symplast tracer 8‐hydroxypyrene‐1,3,6‐trisulfonic acid, it could be demonstrated that solutes imported by the phloem move into the chlorenchyma and ground parenchyma, but not into the branched parenchyma. From a comparison with literature data of common bean (Phaseolus vulgaris L.) and broad bean (Vicia faba L.), it is concluded that in the three species different parenchyma layers, but not the branched parenchyma, may be involved in the post‐phloem symplasmic transport of nutrients in the seed coat. In pea, the branched parenchyma dies during the storage phase, and its cell wall remnants then form the boundary layer between the living seed coat parenchyma cells and the cotyledons. Using cryo‐SEM, clear images were obtained of this boundary layer which showed that many intracellular spaces in the seed coat parenchyma are filled with an aqueous solution. This is suggested to facilitate the diffusion of nutrients from the site of unloading towards the cotyledons.