Plant polyamines in abiotic stress responses

Significance of naturally occurring intracellular polyamines (PAs), such as spermine, spermidine, and putrescine, in relation to the mechanism and adaptation to combat abiotic stress has been well established in plants. Because of their polycationic nature at physiological pH, PAs bind strongly to negative charges in cellular components such as nucleic acids, proteins, and phospholipids. Accumulation of the three main PAs occurs under many types of abiotic stress, and modulation of their biosynthetic pathway confers tolerance to drought or salt stress. Maintaining crop yield under adverse environmental conditions is probably the major challenge faced by modern agriculture, where PAs can play important role. Over the last two decades, genetic, transcriptomic, proteomic, metabolomic, and phenomic approaches have unraveled many significant functions of different PAs in the regulation of plant abiotic stress tolerance. In recent years, much attention has also been devoted to the involvement of PAs in ameliorating different environmental stresses such as osmotic stress, drought, heat, chilling, high light intensity, heavy metals, mineral nutrient deficiency, pH variation, and UV irradiation. The present review discusses the various reports on the role of PAs in the abiotic stress of plants with a note on current research tendencies and future perspectives. Co-relating all these data into a signal network model will be an uphill task, and solving this will give a clearer picture of the intricate abiotic stress signalling network in the plant kingdom.