Cell wall storage polysaccharides in cotyledons ofLupinus angustifolius L. I. Deposition during seed development

Summary Cotyledons of developing seeds ofLupinus angustifolius cv. Unicrop were examined by light and electron microscopy from 14 days after anthesis until maturity. Cell wall storage polysaccharides are deposited as secondary wall in the mesophyll cells from about 30 days after anthesis. Wall thickness increases from 0.2 to 20 m except in the pit areas around the plasmodesmata. Concentric layers within the secondary wall were revealed following staining with periodic acid-Schiff's reagent and with calcofluor white. Layers are seen as alternating bands of closely- and loosely-packed fibrils in the electron microscope. During maturation, these layers become compressed and radial striations appeared. During wall thickening, dictyosome vesicles contain fibrils of carbohydrate material which is apparently discharged into the periplasm. Evidence strongly suggests that the Golgi apparatus is active in wall deposition. Protein and lipid reserves fill the mesophyll cells at maturity. Starch which was abundant during development is present only in trace amounts in the cotyledons of mature seeds.This work was carried out at the former ARC Unit of Developmental Botany, Cambridge.