Fructan Metabolism in Expanded Primary Leaves of Barley ( Hordeum vulgare L. cv. Gerbel): Change upon Ageing and Spatial Organization along the Leaf Blade

Abstract

Summary Fructan metabolism in fully expanded primary leaf blades of Hordeum vulgare was found to depend onleaf age and tissue differentiation along the blade. The activities of the key enzyme of fructan synthesis, sucrose sucrose fructosyltransferase (SST), and of acid invertase were high in young leaves but decreased early after expansion. However, the leaves retained the capability to rapidly form SST activity upon excision and illumination for a prolonged period of time. In leaves treated with benzyladenine SST and invertase activities decreased more slowly, SST inducibility was maintained longer, and more sucrose and much more fructan accumulated than in untreated leaves. When young leaves were excised and illuminated or fed with sucrose, the basal part accumulated more fructan and had a higher SST activity than the tip. When seedlings were exposed to low temperatures fructan was accumulated in the basal part of the leaves although the activity of SST remained low. Fructan exohydrolase (FEH) and acid invertase gradually decreased in activity from the base to the tip of the blade. Both activities decreased after excision followed by sucrose feeding of the leaves and after the cold treatment whereas after excision followed by illumination only FEH activity decreased. The results show that the tissue of the fully expanded primary leaf blade of barley is remarkably heterogeneous along its longitudinal axis and changes rapidly with blade age.