M. M. Chaves1,3,*
M. M. Oliveira2,3
1Departamento Botânica e Engenharia Biológica, Instituto
Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda,
1349-017 Lisboa, Portugal
2Faculdade de Ciência, Universidade de Lisboa, Lisboa, Portugal
3Instituto de Tecnologia Química e Biológica, Oeiras, Portugal
Journal of Experimental Botany 2004 55(407):2365-2384.
Drought is one of the greatest limitations to crop expansionoutside the present-day agricultural areas. It will become increasinglyimportant in regions of the globe where, in the past, the problemwas negligible, due to the recognized changes in global climate.Today the concern is with improving cultural practices and cropgenotypes for drought-prone areas; therefore, understandingthe mechanisms behind drought resistance and the efficient useof water by the plants is fundamental for the achievement ofthose goals. In this paper, the major constraints to carbonassimilation and the metabolic regulations that play a rolein plant responses to water deficits, acting in isolation orin conjunction with other stresses, is reviewed. The effectson carbon assimilation include increased resistance to diffusionby stomata and the mesophyll, as well as biochemical and photochemicaladjustments. Oxidative stress is critical for crops that experiencedrought episodes. The role of detoxifying systems in preventingirreversible damage to photosynthetic machinery and of redoxmolecules as local or systemic signals is revised. Plant capacityto avoid or repair membrane damage during dehydration and rehydrationprocesses is pivotal for the maintenance of membrane integrity,especially for those that embed functional proteins. Among suchproteins are water transporters, whose role in the regulationof plant water status and transport of other metabolites isthe subject of intense investigation. Long-distance chemicalsignalling, as an early response to drought, started to be unravelledmore than a decade ago. The effects of those signals on carbonassimilation and partitioning of assimilates between reproductiveand non-reproductive structures are revised and discussed inthe context of novel management techniques. These applicationsare designed to combine increased crop water-use efficiencywith sustained yield and improved quality of the products. Throughan understanding of the mechanisms leading to successful adaptationto dehydration and rehydration, it has already been possibleto identify key genes able to alter metabolism and increaseplant tolerance to drought. An overview of the most importantdata on this topic, including engineering for osmotic adjustmentor protection, water transporters, and C4 traits is presentedin this paper. Emphasis is given to the most successful or promisingcases of genetic engineering in crops, using functional or regulatorygenes. as well as to promising technologies, such as the transferof transcription factors.
Diffusional and metabolic limitations, genetic engineering, photosynthesis, water deficits, water-saving irrigation