ABSTRACT
Plants are often subjected to both abiotic and biotic stresses. Abiotic stresses play a major role in determining productivity of crop yields and distribution of plant species across different types of environment. Drought, salinity, and other abiotic stresses lead to metabolic toxicity, membrane disorganization, generation of ROS, inhibition of photosynthesis, reduced nutrient acquisition, and altered hormonal levels. In response, plants accumulate a variety of osmotically active compounds such as amino acids, polyols, alkaloids, sugars, and inorganic ions resulting in a lowering of the osmotic potential. Under moisture stress, plants slow down the vegetative growth and induce flowering as a defensive mechanism. Stress triggers a range of responses such as changes in gene expression, synthesis of abscisic acid, jasmonic acid, ethylene, and calcium. Soil microbes augment plant productivity and immunity through an increase in antioxidative state. A number of metabolites such as proline, mannitol, trehalose and glycine-betaine are synthesized to protect cellular components from damage following abiotic stresses. The complexity of the drought syndrome can be tackled with a holistic approach integrating cultural, physiological, and molecular techniques. Transgenic approaches are being pursued actively to improve tolerance to biotic and abiotic stresses in a number of crops.
