Salinity stresses, plant responses

Cells exposed to saline stress encounter reduced water availability, ion toxicity and reduced availability of essential nutrients. These cellular level responses are also reflected at the whole-plant level. An understanding of these cellular responses will undoubtedly contribute to an understanding of the response of a plant growing in a saline environment. 

A frequently observed response of plant cells exposed to saline stress is the accumulation of proline. Two cell lines of tobacco, one resistant and the other sensitive to growth inhibition by NaCl, accumulated proline when exposed to 1.5% w/v NaCl in the growth media (Dix Pearce, 1981). The NaCl sensitive line accumulated proline more rapidly than did the resistant line, though the levels accumulated were not adequate to provide osmotic protection against salt stress. The authors suggested that proline accumulation may have a protective role other than osmoregulation and may be symptomatic of stress injury, the nature of which was not discussed. 

Figure 5. The growth response to salinity stress. The solid green line represents the change in the growth rate after the addition of NaCl. (a) The broken green line represents the hypothetical response of a plant with an increased tolerance to the osmotic component of stress, (b) The broken red line represents the response of a plant with an increased tolerance to the ionic component of stress, (c) The green-and-red line represents the response of a plant with increased tolerance to the osmotic and ionic components of stress [83].

Wang W., Vinocur B., Altman A. Plant responses to drought, salinity and extreme temperatures towards genetic engineering for stress tolerance. Planta 2003 218(1) 1-... 

Fig. 10.1 Overview of plant responses to salinity and drought stresses. Stress signals activate several molecular responses to re-establish cellular homeostasis. The stress-responsive mechanisms include, selective ion transport across membranes of different cellular compartments, gene activation by specific transcription factors, synthesis of com-...

Plant cells selected for tolerance to stress show varied responses to the imposed osmotic gradients. In adapted cells, tolerance to salinity or to water stress was not found to increase proportionately with increases in turgor (Handa et al., 1983 Binzel et al., 1985). It was suggested from these observations and from studies by Heyser Nabors (1981) that no relationship existed between turgor and growth and that stress adaptation may alter the relationship between turgor and cell expansion (see also Chapter 6). 

Drbak, B.K., and Watkins, P.A., 2000, Inositol(l,4,5)trisphosphate production in plant cells an early response to salinity and hyperosmotic stress. FEBS Lett. 481 240-244. 

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