Germination-related cell death in the aleurone layer of malting barley

Abstract

Malting of barley grain represents the most economically favourable application of this cereal. Most studies of barley grain germination have stemmed from the need to optimise the malting process, thus saving resources and obtaining a superior product. The need to optimise the malting process remains important and represents the background for the research reported in this thesis. One of the most functionally important tissues of the barley grain during germination is the aleurone layer, since it secretes most of the hydrolytic enzymes necessary for the degradation of the products stored in the endosperm. The extent of the degradation of complex carbohydrates and proteins of the endosperm is a crucial parameter evaluated during the malting process. The aleurone layer cells use their own reserves for the production and secretion of the hydrolytic enzymes, and once these have been depleted the cells die under a programmed cell death response. This thesis describes the development of two techniques to study programmed cell death of aleurone layer cells of malting barley varieties under conditions that replicate germination. The first technique developed was a protocol for the isolation of aleurone-layer protoplasts from mature dry grains. The isolated protoplasts were shown to be viable and were successfully characterised to evaluate their death response via incubation with gibberellic acid (GA). The second technique developed was the use of activity-based protein profiling (ABPP) for the characterisation of enzyme activities in aleurone layer cells. Through the use of ABPP, changes in activity of various groups of enzymes were evaluated for isolated aleurone layers and aleurone-layer protoplasts upon incubation with GA in the presence of abscisic acid (ABA). The techniques developed in this thesis will improve the understanding of the behaviour of the aleurone layer during germination. This knowledge is likely to contribute to the optimisation of the barley malting process.