Some Chemical and Morphological Changes Induced by Gibberellic Acid in Embryo-free Wheat Grain

Abstract

Chemical changes which occur in components of the cell walls of wheat endosperm have been followed during gibberellic acid induced modification of embryo-free wheat grain. Water-soluble polysaccharides, which are mainly arabinoxylans, increased approximately threefold in yield during 3 days treatment with gibberellic acid while their molecular weights decreased progressively. The changes in arabinogalactan-peptide were obscured by the large increases in low-molecular-weight arabinoxylan but were probably slight.

Parallel morphological studies using the scanning electron microscope showed that degradative changes occurred initially in the subaleurone endosperm and progressed towards the central endosperm. Between 1 and 2 days modification, cell walls in the subaleurone endosperm were pariially degraded and there was a rapid disappearance of matrix protein. Erosion of starch granules became apparent later.

The results show that under conditions simulating germination, arabinoxylan depolymerizing enzymes are operating in addition to starch and protein hydrolases. Their action is manifest at a very early stage and the pattern of erosion of cell walls is consistent with the progressive liberation of arabinoxylan hydrolases from the aleurone or alternatively to the progressive activation or release from inhibition of a latent form of the enzyme in the endosperm.