ABSTRACT
Drought or water deficit stress is the most common and most severe limitation to crop plant productivity (Boyer 1982, Kramer and Boyer 1995). Just under half of the earth’s land surface is considered dryland, and these regions are found on all the continents (Middleton and Thomas 1997). Increasing drought resistance in crop plants grown in semi-arid regions, as well as developing drought resistance in mesophytic crop plants, are common goals in agricultural research programs around the world. Unfortunately, drought is not a simple homogeneous environmental condition. Some semi-arid regions have seasonal summer rains, while in other semi-arid regions the rains come in winter months. Relative humidity and temperature can also be markedly different in regions with similar precipitation rates. All of these climatic factors influence the severity of the drought stress on the plant. Thus, different physiological, anatomical and biochemical mechanisms of drought resistance are likely to be more successful in these different water stressed climates.
