ABSTRACT
Plants are often exposed to biotic or abiotic stresses. Stress may be defi ned as the external situation which causes adverse effects on plant growth, development and productivity. Abiotic stresses are caused by the defi ciency or excess of a factor required for plant growth. Among these are fl ooding, drought, high or low temperature, soil salinity, defi ciency of soil mineral nutrients and excessive or insuffi cient light. In general, abiotic stresses can be addressed to some extent by changes in agronomy, soil and water management and choice of variety. However, current and future challenges imposed by the weather and the environment on fi eld crops will need to be faced with continued innovation by breeders, molecular biologists, biotechnologists and farmers, with collaboration across a range of disciplines (Ober and Rajabi 2010; Rajabi and Ober 2012). Tolerance or susceptibility to various types of stresses depends on species, genotype, the growth stage of the plant during the stress period, and the severity and duration of the stress (Buchanan et al. 2002). In this chapter, drought and salinity will be emphasized from the molecular response point of view, as these are the most important environmental stresses limiting crop growth and productivity (Munns 2011).
