Responses of some crops to various abiotic stress factors and its physiological and biochemical basis of resistances: a review.

The present paper reviews the physiological, biophysical and biochemical mechanisms developed by various crops against various abiotic stress factors such as salinity, high temperatures and drought. Special emphasis is givpen to Phaseolus bean. These abiotic stress factors greatly affect the growth and development and physiological functions of the crops. They affect different phenological stages starting from the seedling to the maturity of the crops thereby redUcing yields. Crop cultivars differ in their responses to these stress factors. In general, growth rate and photosynthesis are reduced. The cultivars offer different mechanisms for resistance to these stress factors: phenological manipulation, morphological and ultrstructural characteristics, the accumulation of biochemical components for osmotic adjustment, minor leakage of osmolites may be mentioned. The resistant lines show less disorganisation of thylakoids, more accumulation of starch grains, mitochondria and lipids acting as high energetic materials. Accumulation of HCN, proline, abscisic acids, soluble sugars, total proteins and the de novo synthesis of specific proteins are some mechanisms that resistant plants have to adapt to abiotic stress factors. A concrete knowledge of these mechanisms of resistance will help the breeders and biotechnologists to manipulate their techniques for the genetic improvement of crops for resistance to various stress factors.