The plants evolved from simple algae and later colonized the landmass; the first tiny terrestrial plants to complex seed plants endure environmental challenges for survival. Plants being sessile are strongly affected by climatic changes and pathogenic attack. Furthermore, the plants in nature do not face a single stress at a time but are subjected to different stresses simultaneously. These factors cause metabolic toxicity, membrane disorganization, closure of stomata, decreased photosynthetic activity, generation of reactive oxygen species (ROS) and altered nutrient acquisition. Plants respond and adapt to these conditions during their entire lifecycle with an array of biochemical and physiological changes.
A complex network of stress–responsive signal transduction pathways, converge and diverge in co-operation for combating and imparting biotic and abiotic stress tolerance. The molecular and cellular responses to abiotic and biotic stresses include signal perception then signal transduction to cytoplasm and nucleus, gene expression and finally metabolic-biochemical changes leading to stress endurance. Although plants have gradually evolved a remarkable ability to cope with such highly variable environmental onslaughts, the stresses nevertheless represent a primary cause of crop-loss worldwide.