Evaluation of the Thermostability of English Oak and Rock Oak and Their Degree of Adaptation to the Effects of Heat Shock

Abstract

The leaves of sessile oak (Quercuspetraea Liebl.) and pedunculate oak (Quercusrobur L.) were subjected to heat shock at various high temperatures. The damage caused by the heat shock to the cellular structures of the leaves was determined using the electrolyte leakage technique. In the investigated species, a sigmoidal increase of electrolyte leakage from leaf tissues, depending of the applied temperatures, was observed. Pedunculate oak leaves, as compared with sessile oak ones, have shown increased resistance to high temperatures, suggesting that heat tolerance in pedunculate oak is higher than in sessile oak. Experiments with fractionation of heat shock doses allowed the estimation of the influence of the first dose value on induction of the lives adaptive capacity of the sessile oak leaves during different periods of time after their application. If the first fraction of dose was moderate, the thermotolerance of leaves grew rapidly. So, the functional status of leaves depended on three components that characterized the fractionation of dose: the value of the first part of dose (1), the value of the second part of dose two (2), the duration of the period that has passed between two fractions of dose (3). Summary effect of fractionated dose of heat shock is the result of balance between processes of degradation, recovery of damages, and adaptation. After application of moderate fractions of heat shock dose. the processes of the induction of adaptation dominated. Because of this the thermotolerance of leaves after application of the first dose of heat shock increased. After the application of higher fractions of dose, the processes of degradation prevailed under those of the recovery and adaptation. In combination they lead to the reduction leaves thermotolerance. The obtained results suggest that the method of fractional heat shock doses make possible determination of the initial thermotolerance and the adaptive capacity of leaves. Pooling of the processes that determine the initial leaves thermotolerance and their adaptive potential under variation of seasonal temperatures is important for plants survival in arid conditions.