Role of Growth Regulators and Phytohormones in Overcoming Environmental Stress

Phytohormones, also termed as plant growth regulators, are chemical molecules that are produced elsewhere and translocated to various parts, which may function either locally or in distant tissues differing the actual site of synthesis. They act as a chemical messenger often controlling every aspect of plant life, majorly growth and development. In addition, these plant hormones have also been identified in regulating stress responses in plants. Such stress may be attributed as abiotic stress caused by salt, low moisture, and excessive heat and cold, or may be as biotic stress caused by pathogens and other parasites. Plants being sessile in nature hold a high degree of plasticity, which helps them to persist under extreme environmental conditions. Multiple reports elaborate the role of plant growth hormones such as auxins, cytokinins, gibberellins, ethylene, abscisic acid, strigolactones, jasmonates, and brassinosteroids in imparting stress tolerance. A stringent regulation in the endogenous levels of hormones is required to confer varying degrees of stress tolerance. Further, these hormones interact in a synergetic or antagonistic manner playing a vital role in generating a response to overcome stress. This is achieved via a complex interplay of various molecular and hormonal signaling pathways at various transcriptional and post-transcriptional levels, which consequently helps them to counter the stressful regimes. The present chapter deals in understanding the overall role of these small chemical messengers and the specific role of abscisic acid, brassinosteroids, salicylic acid, and jasmonic acid in abiotic and biotic stresses, respectively, with major emphasis on role of hormone-associated genes and transcription factors in imparting stress acclimation.