Effect of High Temperature During Grain-filling on the Structure of Developing and Malted Barley Grains

High temperatures (up to 35 °C) were applied to plants of malting barley, Hordeum vulgare L. (‘Schooner’) for a period of 5 d during grain-filling. Heat treatment had a profound effect on the structure of the mature barley grain. There was evidence of degradation of endosperm storage products in heat-treated grain. Starch granule development was reduced in sub-aleurone cells following heat treatment and alterations to starch granule distribution and growth were observed in the endosperms of these grains. Endosperm cell wall and crushed cell layer (CCL) development were sensitive to high temperatures, with the reduced thickness of the CCL and generally patchy Calcofluor fluorescence of endosperm cell walls indicative of partial hydrolysis of β-glucans. Increased growth of the embryo took place in heat-treated grains compared with control grains. Endosperm texture was generally more friable in heat-treated grains than in control grains, and these grains overmodified during malting, with considerable degradation of starch in the form of extensive pitting of A-type starch granules. Evidence is presented for developmental and germination events occurring simultaneously within the developing grain.