ULTRASTRUCTURE OF THE CELL WALLS OF THE TRANSPORT PATHWAY FOR GIBBERELLIC ACID IN BARLEY ALEURONE LAYER

Abstract

Transmission and scanning electron microscopic studies of the scutellum-aleurone junction of barley suggest that, in the absence of plasmodesmata connections, the transport of gibberellic acid from the scutellum to the aleurone layer is effected by apoplastic transport across 3–4 μm thick cell walls. Transport of gibberellic acid along the aleurone could be apoplastic as well as symplastic because large numbers of plasmodesmata are present in the 4 μm thick cell walls, through which the hormone could pass from cell to cell. Structurally, the scutellum is separated from the starchy endosperm by a 30 μm thick layer of compressed cell wall material across which transfer of either gibberellic acid to the aleurone or small quantities of non-specific β-glucanase enzymes (E1) from the scutellum to the starchy endosperm would be restricted. No such barrier is present between the aleurone layer and the starchy endosperm, where cell wall thickness is about 4 μm, and the release of endosperm-degrading enzymes into the starchy endosperm is not restricted.