The Influence of Recovery Treatment on the Effects of a Brief Heat Shock on Wheat. II. Fractional Protein Accumulation During Grain Growth

Abstract

In this study, we have sought to identify the nature of the response to both moderately high (25-32°C) and very high (>32"C) temperatures by examining their interactive effects on the accumulation of functionally important proteins during grain-filling. In particular, we wished to determine if the deleterious effects of very high temperature could be alleviated by subsequently cool conditions. To this end, wheat cv. Oxley was exposed to either 21/16 or 40116°C (daylnight) from 15 to 19 days after anthesis and subsequently grown under one of three temperature regimes until maturity: 21/16 (control), 27/22 or 30125°C. Grain samples were taken throughout grain growth and analysed for protein content and composition. Wheat proteins were separated and quantified as albumin,globulin, monomer, SDS-soluble polymer and SDS-insoluble polymer using size-exclusion high-performance liquid chromatography.The various protein fractions responded differentially and usually additively to moderately high and very high temperatures during grain-filling. Cool post-shock conditions did not alleviate the effects of very high temperature on grain protein composition. Heat treatments reduced po1ymer:monomer ratio because the accumulation of monomer was reduced less than that of polymer. 6). Interpretation of grain quality results from wheat variety trials with reference to high temperature stress. . Possible role for the Glu-Dl locus with respect to tolerance to dough-quality change after heat stress. . The relationship between grain-protein content of wheat and barley and temperatures during grain filling. Australian Journal of Plant Physiology 21, 869-873. Doekes, G.J., and Wennekes, L.M.J. (1982). Effect of nitrogen fertilization on quantity and composition of wheat flour proteins. Cereal Chemistry 59, 276-278.

Comparison of sudden heat stress with gradual exposure to high temperature during grain filling in two wheat varieties differing in heat tolerance. II. Fractional protein accumulation

“…As we have found previously, the accumulation of monomer was less sensitive to high temperature treatment than the accumulation of polymer (Stone and Nicolas 1996a;Stone et al 1996). For both varieties, this resulted in a significant response to heat shock, compared with the control, but only in Oxley did the gradual heat treatment differ significantly from the control.…”

“…The heat shock proteins that putatively provide protection from stress may therefore damage wheat quality. In contrast with the apparent enhancement of gliadin synthesis, the down-regulation of protein synthesis in heat-shocked wheat grains does not appear to have been studied extensively (Stone and Nicolas 1996a;Stone et al 1996), but it is unlikely that, if down-regulation of 'normal' protein synthesis occurs during heat shock, it would occur uniformly for all protein fractions. This may be another mechanism whereby heat shock alters protein composition compared with gradual heat stress.…”

“…Flour protein composition was determined by SE-HPLC, using the two-step method of Gupta et al (1993). These methods are described in more detail in Stone et al (1996).…”