Plant Responses to Abiotic Stress: Physiological and Molecular Considerations
Arie Altman
The Otto Warburg Center For Agricultural Biotechnology, Faculty of Agriculture, The Hebrew University of JerusalemP.O. Box 12, Rehovot 76100, Israel. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it.
Abiotic stress is expressed in plants by a series of morphological, physiological, biochemical and molecular changes which adversely affect plant growth and productivity. This is true, however, to a different degree and affecting different plant biological processes, for all types of abiotic stress conditions (e.g., drought, salinity, specific ion toxicity, low and high temperature, chemical pollution, anaerobiosis, free radical and irradiation). Water (drought) and salinity stress are especially harmful to food production in all arid and semi-arid regions world-wide, resulting in increased desertification. Previous studies have concentrated on the physiological and biochemical responses of stressed plants. The use of novel molecular probes for elucidating the molecular control mechanisms of water stress tolerance is based on recent findings on the expression of specific stress-related genes, resulting in 'activation' of specific proteins (structural and enzymatic) and/or osmolytes, and/or other effectors. The role of a number of mechanisms that might be associated with stress tolerance, will be reviewed. The possible use of physiological, biochemical and molecular 'stress markers' in breeding plants for stress tolerance will be critically examined:
1. Availability of markers for marker-assisted selection - Developmental (fresh and dry weight accumulation, elongation, cambial activity and thickening, bud sprouting, leaf drop, root branching, survival). Physiological and biochemical (water potential, transpiration, stomata resistance, photosynthesis, specific metabolite accumulation, senescence). Molecular (presence and expression of specific DNA markers, mRNAs and proteins).
2. Can we use molecular markers - basic science aspects? Yes, if the marker is: drought stress-specific (i.e., induced), expressed rapidly (with a typical kinetics), its expression is related to the magnitude of stress, its expression is modified once the stress is removed (i.e., rehydration), its expression is causally correlated with at least some developmental and/or physiological responses to drought, it shows some correlation with related known types of stress and/or mechanisms (i.e., salinity, ABA, proline accumulation), it is differentially expressed in genotypes differing in their drought stress response and/or tolerance, and if a tolerance function can be attributed to the expressed marker.
3. Can we use molecular markers - practical aspects? Yes, if the marker is: easy and cheap to use, a large number of assays can be handled, it is reliable and reproducible, it yields clear-cut answers, it is independent of tissue age and similar variables, and if it can be used (with the required modifications) in other genotypes.