Effects of drought on photosynthetic parameters and heat stability of PSII in wheat and in Aegilops species originating from dry habitats

Abstract

The effects of water deficit induced by withholding water in soil pots were examined on processes related to photosynthesis and heat stability of PSII in wheat cultivars and in Aegilops species. Decrease in relative water content (RWC) of leaves resulted in fast and considerable stomatal closure and decrease in net photosynthetic CO2 fixation (A) in Ae. bicornis and in wheat cultivars, while in Ae. tauschii and Ae. speltoides stomatal conductance (gs) and A remained relatively high between 90 and 70% RWC. Parallel with this, A was limited by the CO2 diffusion to the intercellular spaces (stomatal limitation, Ls) even at a lower RWC in Ae. taushii and in Ae. speltoides, while a significant mesophyll limitation (Lm) was observed for Ae. bicornis and for wheat. On the other hand, drought stress resulted in a significant increase in the thermal stability of PSII in wheat and Aegilops genotypes. The results indicate that some genotypes of Ae. taushii and Ae. speltoides have better drought tolerance with satisfactory heat stability than wheat, making them appropriate for improving the heat tolerance of wheat to survive dry and hot periods in the field.