Drought Stress Tolerance in Relation to Polyamine Metabolism in Plants

Abstract

Polyamines (PAs) are small protonated molecules with amine groups that are found in most living organisms. In plants, most abundant polyamines are putrescine, spermidine, spermine, and its isomer thermospermine. These compounds can be found in free or conjugated forms to hydroxycinnamic acids. Their homeostasis is tightly regulated through modulation of PA biosynthesis, conjugation, and transport. Genetic approaches in the recent years have unraveled key functions of PAs on stress protection. Indeed, the levels of different PAs increase in response to diverse abiotic and biotic stresses. During drought, the PA pathway is activated which leads to a putrescine to spermine canalization that is ABA- dependent. Differences between drought tolerant and sensitive cultivars seem to be associated with the capacity of plants to accumulate different PAs over a minimum threshold. This way, genetic engineering of the PA pathway has been successful in obtaining drought-resistant plants that exhibit reduced transpiration rate, accumulation of compatible solutes, or activation of ROS detoxification activities. Therefore, molecular mechanisms of PA protection against stress seem to be diverse and additive. We summarize in this chapter the recent advances on PA metabolism in relation to drought stress tolerance and its implications in generating drought-tolerant crops.