ABSTRACT
Plants growing under normal natural conditions are often exposed to multiple climatic factors at once, hence growth and production challenged by several abiotic stress factors simultaneously. The importance of plants in the world food supply, the sensitivity of plants to abiotic stresses, and activation of adaptive mechanisms by phytohomones and their transcriptional reprogramming at different levels of organisation have been intensively studied for the last two decades. Phytohormones have proven themselves as the biological switches in controlling the cellular homesostasis under stress conditions by varying the biochemical and physiological profiles of plants. They regulate a wide range of genes by controlling different transcriptional factors against multiple abiotic stresses. However, despite the intensive research, the exact mechanism of action of most phytohormones against specific abiotic stress still needs to be elucidated. The reason for this lag is that most research has so far been limited to mitigating individual stress, while plants are often exposed to multiple stresses at once. Multiple mechanisms work together, known as crosstalk among phytohormones, with the same biological effects in their mechanisms and actions, transcriptional regulation, and biological response to plant stress. In this chapter, the classical and new era phytohormones are reviewed for their biological response to multiple abiotic stresses and transcriptional re-programming. This will provide valuable information about commonalities in plant responses to multiple phytohormones under multiple stress conditions and interactions among phytohomones for common stress factors and transcriptional regulation of phytohormones. This review will emphasise the objective to address the role of phytohormone in response to multiple stresses.
