STRATEGIES FOR ENGINEERING WATER-STRESS TOLERANCE IN PLANTS

Water deficit is the commonest environmental stress factor limiting pl ant productivity. The ability of plants to tolerate water deficit is d etermined by multiple biochemical pathways that facilitate retention a nd/or acquisition of water, protect chloroplast functions, and maintai n ion homeostasis. Essential pathways include those that lead to synth esis of osmotically active metabolites and specific proteins that cont rol ion and water flux, support scavenging of oxygen radicals, or may act as chaperones. The ability of plants to detoxify radicals under co nditions of water deficit is probably the most critical requirement. M any stress-tolerant species accumulate methylated metabolites, which p lay a crucial dual role as osmoprotectants, and as radical scavengers. Their synthesis is correlated with stress-induced enhancement of phot orespiration. However, transfer of individual genes from tolerant plan ts only confers marginally increased water-stress tolerance to stress- sensitive species: tolerance engineering will probably require the tra nsfer of multiple genes.