Plant Responses to Drought and Stress Tolerance

In the natural environment plants are well adapted to minimize damages which only occurs under extreme conditions. In the frame of “physiological window” mild drought induces in plants regulation of water loss and uptake allowing maintenance of their leaf relative water content within the limits where the photosynthetic capacity shows no or little changes. But severe drought induces in plants unfavourable changes leading to inhibition of photosynthesis and growth. The most severe drought stress is desiccation. On the basis of presence or absence of bulk water, the mechanisms of protection are different. While the mechanisms conferring drought tolerance are mainly based on structural stabilization by preferential hydration, desiccation tolerance mechanisms are based on the replacement of water by molecules that form hydrogen bonds. The roles of stomatal and non-stomatal limitation, the behaviour of PS2, specific proteins and Rubisco, lipids and sugars, as well as mechanisms of acclimation and stress tolerance in droughted plants are discussed.