Stress tolerance mechanisms

Bohnert, H.J., Q. Gong, P. Li, and S. Ma. 2006. Unraveling abiotic stress tolerance mechanisms—getting genomics going. Curr. Opin. Plant Biol. 9 180-188. 

The techniques of molecular biology have particular potential for rapidly introducing small numbers of single genes. Unfortunately there is strong evidence that the complex compensation mechanisms that exist in plants, and the interactions between different whole-plant and biochemical responses to stress, will make the direct improvement of environmental stress tolerance in crop plants by genetic engineering rather more difficult... 

A more general role of ABA in stress tolerance has been found in carrot cells. When a suspension culture of carrot cells was exposed to ABA and then selected for tolerance to freezing, the ABA-treated cells were found to be more tolerant to the stress (Reaney Gusta, 1987). These results provide further evidence for the presence of common mechanisms conveying tolerance to many of the environmental stresses. 

Vaadia, Y. (1987). Salt and drought tolerance in plants regulation of water use efficiency in sensitive and tolerant species. In NATO Conference on Biochemical and Physiological Mechanisms Associated with Environmental Stress Tolerance in Plants, University of East Anglia, Norwich, 2-7 August 1987. 

Flowers, T.J. Yeo, A.R. (1989). Effects of salinity on plant growth and crop yields. In Biochemical and Physiological Mechanisms Associated with Environmental Stress Tolerance in Plants, ed. J. Cherry. Berlin Springer-Verlag, (in press). 

The phyllosphere (or aerial) parts of plants represent a challenge for the survival of microbes. The exposure to high doses of UV, fluctuations in temperature, and relative humidity all compromise viability (Heaton and Jones, 2008 Whipps et ah, 2008). Bacteria (epiphytes) that exist within the phyllosphere have evolved specialized mechanisms to improve stress tolerance and nutrient acquisition. Pseudomonas spp. form the predominant bacterial population recovered on the leaves of plants (Brandi and Amundson, 2008 Lindow and Brandi, 2003). Epiphytic pseudomonad s produce fluorescent or pigmented compounds that afford protection to UV. 

Plant use of iron depends on the plant s ability to respond chemically to iron stress. This response causes the roots to release H+ and deduct ants, to reduce Fe3+, and to accumulate citrate, making iron available to the plant. Reduction sites are principally in the young lateral roots. Azide, arsenate, zinc, copper, and chelating agents may interfere with use of iron. Chemical reactions induced by iron stress affect nitrate reductase activity, use of iron from Fe3+ phosphate and Fe3+ chelate, and tolerance of plants to heavy metals. The iron stress-response mechanism is adaptive and genetically controlled, making it possible to tailor plants to grow under conditions of iron stress. 

Tolerance to Heavy Metals. In many plants, heavy metals induce iron stress. These metals seem to interfere with the iron stress-response mechanism (13) and in this way cause iron chlorosis to develop. Plants under these conditions will die unless they can respond to iron stress and make more iron available (35). Additional iron counteracts the effect of the heavy metals. 

During our research on BABA-induced resistance we noticed that the priming effect of this chemical was not restricted to the plant s reaction to biotic stresses. BABA-treated plants were also sensitized to react faster and more effectively to abiotic stresses. BABA-treated Arabidopsis, for example showed a 75% survival rate following a treatment of two days at -5 °C, whereas control plants were all killed [83]. We also observed faster reactions at the molecular and phenotypical level to high salt, heat and drought treatment [8,69]. All these observations point to an important involvement of BABA in the expression of general priming mechanisms of stress tolerance. 

The fundamental premise of PICT is that under toxicant stress natural selection occurs for organisms that are more tolerant to the pollutant. This increase in tolerance can occur at the level of the population by the induction of tolerance mechanisms by individuals or by selection for tolerant individuals. The biological community increases its tolerance to change imposed by the pollutant by the elimination of sensitivity individuals, populations, or species and the addition of tolerant organisms. 

Lindquist, S., and E. C. Schirmer (1999). The role of Hspl04 in stress tolerance and prion maintenance. In Molecular Chaperones and Folding Catalysts. Regulation, Cellular Function and Mechanisms (B. Bukau, ed.),pp. 347-380. Harwood Academic Publishers, Amsterdam. 

However, efforts to improve crop performance under environmental stresses have not yet been very fruitful, mainly because the fundamental mechanisms of stress tolerance in plants remain to be completely understood. A genetic approach to the development of specific stress-tolerant crop varieties requires as a pre-requisite the identification of key genetic determinants of stress tolerance-related genes or quantitative trait loci (QTL). The existence of salt-tolerant plants (halophytes) and differences in salt tolerance between genotypes within salt-sensitive plant (gly-cophytes) species clearly indicates that there is a genetic basis to salt response. 

Bohnert, H.J. Thomas, J.C. DeRocher, E.J. Michalowski, C.B. Breiteneder, H. Vernon, D.M. Deng, W. Yamada, S. Jensen, R.G. in Proceedings of a NATO Advanced Research Workshop on Biochemical and Cellular Mechanisms of Stress Tolerance in Plants," J.H. Cherry, Ed., Springer-Verlag, Berlin, New York, 1994, p. 415. 

The movement onto land and the subsequent evolutionary divergence involved a number of innovations including the development of mechanisms to enable plants to withstand atmospheric drought including cuticle, xylem, stomata, and intercellular spaces. All of these innovations occurred during the late Silurian and early Devonian around 400 million years ago (Raven, 1977). Evidently coinciding with these structural innovations came the evolution of compounds that aided both protection from UV-B and water-stress tolerance. 

Screenivasulu, N., S.K. Sopory, and P.B. Kavi Kishor. 2007. Deciphering the regulatory mechanisms of abiotic stress tolerance in plants by genomic approaches. Gene 388 1-13. 

Navari-Izzo F, Quartacci MF. (2001). Phytoremediation of metals. Tolerance mechanisms against oxidative stress. Minerva Biotecnologica 13 73-83. 

It must be emphasized, however, that stress resistance or susceptibility is unlikely to reside in a single factor. Studies of the responses of plants to environmental stresses suggest rather that resistance results from the possession of a number of characteristics. Attempts to explain susceptibility or resistance of plants to environmental stresses in terms of single factors are therefore unlikely to result in plausible theories of environmental adaptation. Changes in nitrogenous compounds can only be regarded as components of the resistance or tolerance mechanisms. 

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