Heat-shock proteins in monitoring aging and heat-induced tolerance in germinating wheat and barley embryos

Wheat and barley seeds were subjected to accelerated aging conditions at 12% moisture content and 35 degrees C temperature over 28 days of storage, and to heat-shock treatment carried out by 4 h of incubation at 40 degrees C following 16 h of imbibition at 20 degrees C. Heat-treated, aged seeds showed altered germination behaviour and increasing leakage electroconductivity as well as a reduced incorporation of [S-35]-methionine into embryo proteins, in comparison with the corresponding untreated seeds. Two-dimensional electrophoresis of labelled proteins from embryos gave evidence of further quantitative and qualitative changes: (a) 'normal' germination protein synthesis in wheat and barley was slightly modified by age, but following heat-shock treatment a general reduction of most of the control polypeptides occurred; (b) heat-shock response resulted in the production of several HSPs with different MW and pl, but a uniform general decline in their synthesis was not observed. Highly labelled HSPs (e.g., those with MW 66.7 or 89.3-66.7 kDa in wheat or barley, respectively) did not change over the entire period of aging, white some smaller HSPs with MW >29 kDa either decreased in intensity or disappeared. Conversely, specific low molecular weight HSPs (MW 17-14.2 kDa) were synthesized more in extremely aged embryos of both species. The hypothesis that these polypeptides may be used as biochemical markers in monitoring both vigour loss and heat-shock induced tolerance in aged seeds is discussed.