Sensitivity of two wheat species's seeds (Triticum durum, variety Karim and Triticum aestivum, variety Salambô) to heat constraint during germination.

The aim of this study is determine the effect of different temperature regimes on germination of wheat seeds and early germination events. Germination is very sensitive to environment conditions, particularly the temperature. Physiological and biochemical responses of wheat seed germination during time at various temperatures (5, 15, 25, 35 and 45 degrees C) have shown that optimal temperature (25 degrees C) favorites a good aptitude to germinate, whereas low (5 degrees C) and high temperature (45 degrees C) were extend the delay of germination. Residuary dry matter's mass of germinating, both Karim and Salambô wheat species, Seeds at 5 and 45 degrees C decreased lightly. This show a less mobilization of reserves to embryo. The activity of totals solubles peroxidases changes with temperature of wheat seed germination. At low (5 degrees C) and high (45 degrees C) temperatures, for both two cultivars, peroxidase activity decreases during germination. With exception, during imbibition (2 h), only 45 degrees C involves a high stimulation of this activity for Karim cultivar. This increase is considered as a biochemical response to high temperature. In control temperature (25 degrees C), we have obtained a light increase in peroxidase activity in comparison with that of dry seeds for both these two wheat species. At the end of this study, we have studied the effect of heat stress on totals proteins content. Nevertheless, both for these two wheat cultivars, at 5 degrees C there is no a markedly change in proteins amount during germination. In control condition (25 degrees C) of germination, there is a slight decrease in this content. Germination under high temperature, for Karim variety, induces a rapid synthesis of Heat Shock Proteins (HSPs) and concomitantly a weak degradation of normal proteins. The opposite phenomenon was observed for Salambô variety (weak synthesis of HSPs and important degradation of normal proteins).