ABSTRACT

Plant hormones play central roles in the ability of plants to adapt to changing environments, by mediating growth, development, nutrient allocation, and source/sink transitions. Although ABA is the most studied stress-responsive hormone, the role of cytokinins, brassinosteroids, and auxins during environmental stress is emerging. Recent evidence indicated that plant hormones are involved in multiple processes. Crosstalk between the different plant hormones results in synergetic or antagonic interactions that play crucial roles in response of plants to abiotic stress. The characterization of the molecular mechanisms regulating hormone synthesis, signaling, and action are facilitating the modification of hormone biosynthetic pathways for the generation of transgenic crop plants with enhanced abiotic stress tolerance.

INTRODUCTION

As sessile organisms, plants must regulate their growth and development in order to respond to numerous external stimuli and an ever-changing environment [1__]. These adaptations include the responses to temperature fluctuations, water and nutrients imbalance, and pathogens, etc. These responses are mediated by plant growth regulators (phytohormones), compounds derived from plant biosynthetic pathways that can act either at the site of synthesis or following their transport, elsewhere in the plant. Collectively, plant hormones regulate every aspect of plant growth and development and the responses of plants to biotic and abiotic stresses. Plant growth regulators include the five classical phytohormones: abscisic acid (ABA), ethylene, cytokinin (CK), auxin (IAA), gibberellin (GA), jasmonate (JA), as well as brassinosteroids (BR), salicylic acid (SA), nitric oxide (NO), and strigolactone (SL), and it is likely that additional growth regulators are yet to be discovered.

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