EFFECT OF HIGH-TEMPERATURE DURING GRAIN-FILLING ON THE STRUCTURE OF DEVELOPING AND MALTED BARLEY GRAINS

High temperatures (up to 35 degrees C) were applied to plants of malti ng barley, Hordeum vulgare L. ('Schooner') for a period of 5 d during grain-filling. Heat treatment had a profound effect on the structure o f the mature barley grain. There was evidence of degradation of endosp erm storage products in hear-treated grain. Starch granule development was reduced in sub-aleurone cells following heat treatment and altera tions to starch granule distribution and growth were observed in the e ndosperms of these grains. Endosperm cell wall and crushed cell layer (CCL) development were sensitive to high temperatures, with the reduce d thickness of the CCL and generally patchy Calcofluor fluorescence of endosperm cell walls indicative of partial hydrolysis of beta-glucans . Increased growth of the embryo took place in heat-treated grains com pared with control grains. Endosperm texture was generally more friabl e in heat-treated grains than in control grains, and these grains over modified during malting, with considerable degradation of starch in th e form of extensive pitting of A-type starch granules. Evidence is pre sented for developmental and germination events occurring simultaneous ly within the developing grain. (C) 1998 Annals of Botany Company.