Genetic analysis of osmotic adjustment in crop plants

Plant water deficit is a component of several different stresses, including drought, salinity and low temperature, which severely limit plant growth and crop productivity. Genetic modification of plants to allow growth and yield under unfavourable conditions is an important component of the solution to problems of environmental stress. While disagreement and even confusion may characterize some of the discussions on what constitutes a significant and an effective mechanism of drought resistance in crop plants, osmotic adjustment (OA) is receiving increasing recognition as a major mechanism. This paper starts with the review of OA functions, genetic variation and inheritance, and theories and principles involved in commonly used protocols for quantifying OA, Emphasis Is placed on a summary of current molecular strategies and advances in the improvement of plant stress resistance through manipulating OA. They include a genetic engineering approach and a QTL mapping approach. Future promising strategies for improving drought resistance lie in molecular technology that allows genes or QTLs controlling OA to be tagged and isolated, these genes to be expressed in transgenic plants, and efficiency of breeding via marker-assisted selection to be improved. Aspects of QTL utilization in plant genetics, breeding and physiology and future research directions are discussed.