Drought and heat stability of the photosynthetic apparatus in bread wheat and in aegilops species

The responses of CO2 gas exchange, and heat stability were examined in two wheat (Triticum aestivum L.) cultivars and in Aegilops genotypes originating from habitats with different annual rainfalls and daily temperatures. Desiccation in soil pots resulted in moderate water loss in Ae. biunciais MvGB 377, 382 and Ae. bicornis MvGB 585, parallel with a high degree of stomatal closure and significant decrease in the net CO2 fixation (A), while in Ae. tauschii MvGB 605, 589 stomatal conductance (gs) and A remained relatively high in the desiccation period, and parallel with this gs and A were more tolerant to decrease in RWC than in wheat cultivars and in the above-detailed Aegilops genotypes. In spite of this, the decrease of RWC was fast and considerable in Ae. biuncialis MvGB 642, Ae. speltoides MvGB 1042, 624, and in Ae. tauschii MvGB 426 with a low degree of stomatal closure but A was more tolerant to water loss, especially in Ae. speltoides MvGB 1042. On the other hand, higher water deficit (RWC ~75%, 10-14 days drought treatment) resulted in a significant increase in the thermal stability of PS II for wheat and for some Aegilops genotypes. The results indicate that some Aegilops genotypes originating from arid habitats have better drought and desiccation induced heat tolerance than wheat, making them appropriate for improving the heat tolerance of wheat to survive dry and hot periods in the field. Keywords: drought stress, thermal tolerance, photosynthesis, wheat, Aegilops sp