Phytohormonal signaling under abiotic stress

Abstract Abiotic stresses prompt a wide range of signals in plant cells, which are coordinated and united into various growth and development–related processes. Plants are able to respond to stress trough phytohormones (plant growth regulators), which are signal molecules and respond to environmental stimuli. Adaptive responses of plants to abiotic stresses are fine-tuned by a network of phytohormones’ signaling and their cross talk, which play a vital role in the molecular mechanisms that optimize the response of plants under such stresses. In recent years, recognizing mechanisms of phytohormonal signaling by plants to cope with hostile growth conditions and to ensure sustainable crop production under stress conditions is an important area of plant research. The significant contribution of abscisic acid as “stress hormone” and other classical phytohormones including auxins, brassinosteroids, ethylene, gibberellins, cytokinins during the wide range of abiotic stresses is well characterized. Recently, the role of other phytohormones, such as jasmonic acid, salicylic acid, and nitric oxide (NO), during responses to abiotic stress(es) has also been demonstrated, and the role of other new class of phytohormones, such as strigolactones and karrikins, has also been investigated, which has been covered in this chapter. These phytohormones provide adaptation to abiotic stresses, and simultaneously regulate various physiological processes, such as stomatal closing, thereby leading to reducing water loss, and thus enhancing osmotic stress tolerance. Generally, during abiotic stress the phosphorylation cascades as cross talk points in phytohormonal signaling prompt changes in gene expression, which can affect the biosynthesis, signaling, and action of other phytohormones.