ABA is a plant growth regulator that has been identified as a messenger in stress-perception-response pathways (Jia and Lu, 2003) such as drought, high temperature, low temperature, and salinity stress (Zhang et al., 2001). ABA is also involved in many physiological processes such as photosynthesis. It has been demonstrated that ABA plays important roles in stomatal movements, the regulation of photosynthetic enzyme activities, stabilityof photosynthetic apparatus, and expressions involved in chloroplasts (Jia and Lu, 2003).