Drought stress in plants: A review on water relations

The term stress is used, most often subjectively, with various meanings, the physiological definition, and appropriate term as responses in different situations. The flexibility of normal metabolism allows the development of responses to environmental changes which fluctuate regularly and predictable over daily and seasonal cycles. Thus every deviation of a factor form its optimum does not necessarily result in stress. Stress being with a constraint or with highly unpredictable fluctuations imposed on regular metabolic patterns that cause injury, disease, or aberrant physiology. Among the environmental stresses, drought stress is one of the most adverse factors of plant growth and productivity. The biochemical and molecular responses to drought is essential for a holistic perception of plant resistance mechanism to water limited condition in higher plants. In this review, we tried to describe some aspects of drought induced changes in water relations in higher plants.