Salt tolerance and salinity effects on plants: a review.

ions and to some extent Cl and SO 4 2 of Mg 2+ and nutrient imbalance caused by excess of Na + and Cl ions. Salinity stress response is multigenic, as a number of processes i n- volved in the tolerance mechanism are affected, such as var ious compatible solutes/osmolytes, polyamines, reactive oxygen species and antioxidant defence mecha- nism, ion transport and compartmentalization of inj u- rious ions. Various genes/cDNAs encoding proteins involved in the above-mentioned processes have been identified and isolated. The role of genes/cDNAs e n- coding proteins involved in regulating other genes/ pro- teins, signal transduction process involving hormones like ABA, JA and polyamines, and strategies to i mprove salinity stress tolerance have also been di scussed. EXCESS amount of salt in the soil adversely affects plant growth and development. Nearly 20% of the world's cul- tivated area and nearly half of the world's i rrigated lands are affected by salinity 1

Physiology and molecular biology of salinity stress tolerance in plants

Effect of exogenous salicylic acid under changing environment: a review

Abscisic acid (ABA) was discovered in the 1950s to be a phytohormone affecting leaf abscision and bud dormancy. It was soon characterized as a sesquiterpene derived from mevalonate although certain steps of its biosynthesis in plants are still unknown (Li and Walton, 1987; Zeevaart and Creelman, 1988). Continuing work on ABA has shown that it mediates various developmental and physiological processes that affect the agronomic performance of crop plants (Austin et al., 1982; Ramagopal, 1987). These proc? esses include embryo maturation and germination as well as the response of vegetative tissues to osmotic stress (Singh et al., 1987; Zeevaart and Creelman, 1988). ABA levels increase in tissues subjected to osmotic stress by desiccation, salt, or cold (Henson, 1984; Mohapatra et al., 1988). Under these conditions, specific genes are ex? pressed that can also be induced in unstressed tissues by the application of exogenous ABA (Singh et al., 1987; Gomez et al., 1988; Mundy and Chua, 1988). Some of these genes are also expressed during the normal embryogenic program when seeds desiccate and embryos be? come dormant (Dure et al., 1981). Although different sets of ABA-responsive genes exhibit different patterns of de? velopmental and tissue-specific expression, some of them appear to be part of a general reaction to osmotic stress. This system is a normal part of the embryogenic program but is inducible in vegetative tissues at other times in the plant life cycle. Several ABA-responsive genes have now been isolated (Baker et al., 1988; Gomez et al., 1988; Marcotte et al., 1988; Mundy and Chua, 1988; Vilardell et al., 1990; Yamaguchi-Shinozaki et al., 1990). A major goal of the research discussed below is to understand the role these genes play in osmotic stress and desiccation tolerance.

Gene expression in response to abscisic acid and osmotic stress.

Changes in the hormonal status of wheat seedlings induced by salicylic acid and salinity

Protein changes induced by salinity stress were investigated in two barley cultivars, California Mariout, a salt-tolerant variety and Prato, a salt-sensitive variety. Rapidly growing young barley seedlings were exposed to NaCl and the newly synthesized proteins were resolved on two dimensional polyacrylamide gels following isoelectric focusing or nonequilibrium pH gradient gel electrophoresis in the first dimension. Salinity induces distinct protein changes in root and shoot tissues. In roots, the salinity effects are identical in both cultivars. First, salinity modulates the synthesis of two different sets of proteins, one of which is elevated, and the other, depressed. Second, six new proteins are induced all of which are low in molecular weight, 24 to 27 kilodaltons, with an isoelectric point range of 6.1 to 7.6. In contrast to roots, salinity induces cultivar-specific shoot proteins. Five new shoot proteins are induced whose molecular weights and isoelectric points fall within the range of 20 to 24 kilodaltons and 6.3 to 7.2, respectively. Three of the newly induced proteins are unique to Prato. In addition, salinity inhibits the synthesis of a majority of shoot proteins. The new proteins produced in roots and shoots are unique to each tissue and their induction is apparently regulated coordinately during salinity stress.

/pdf/salinity-stress-induced-tissue-specific-proteins-in-barley-4x9nw0del4.pdf

Salinity Stress Induced Tissue-Specific Proteins in Barley Seedlings

The molecular and genetic bases of salinity tolerance in plants are not understood. Gene expression at the mRNA level was investigated in a salt-tolerant and a salt-sensitive genotype of barley. Seedlings were exposed to NaCl stress and translatable mRNAs were isolated from root and shoot tissues. A reticulocyte cell-free system was programed with barley mRNAs and the in vitro products were resolved on two-dimensional polyacrylamide gels following isoelectric focusing or nonequilibrium pH gradient gel electrophoresis in the first dimension. The functional mRNAs in unstressed seedlings were qualitatively almost indistinguishable in the two genotypes. However, salinity stress triggered differential transcription of specific mRNAs depending upon genotype and tissue. In roots, 12 new mRNAs were induced that encoded proteins of 21-34 kDa, with a pI range of 6.1-7.7. In shoots, the 9 new mRNAs coded for proteins of 18-50.5 kDa, with a pI range of 5.4-7.8. These new stress mRNAs represented one of two main classes. Class I consisted of mRNAs shared by both genotypes. Class II represented mRNAs specific to each genotype; unique mRNAs of roots accumulated preferentially in the salt-tolerant genotype, whereas those of shoots accumulated in the salt-sensitive genotype. The findings suggest that transcriptional as well as posttranscriptional mechanisms regulate gene expression in barley during salinity stress.

Differential mRNA transcription during salinity stress in barley.

A maize (Zea mays, L) callus was exposed to media containing different levels of NaCl (0 to 3%) and mannitol (0 to 18.2%) for a period of 4 weeks, and the changes in growth and protein synthesis were determined. Cells are able to tolerate and grow in NaCl up to 1% (0.17 M) or mannitol up to 9.1% (0.5 M), but the relative overall growth rates are about 1/6 and 1/8 of the control, respectively. Protein synthesis, as assessed by pulselabeling of the cells with 35S-methionine after exposure to the stress reagents at various times of incubation, suggests that the relative rates of amino acid uptake and its incorporation into proteins are inhibited as early as 4 h after exposure, and the extent of inhibition does not increase appreciably until after 1 week. Severe inhibition of uptake and protein synthesis results from prolonged exposures at growth-inhibitory concentrations of NaCl and mannitol. In general, the overall mean inhibition of cellular uptake and protein synthesis in the first 2-week period are approximately 50% and 35% for the NaCl (1%) and mannitol (7.3 %) treatments, respectively. No detectable differences are apparent in the abundant, steady state protein population as revealed by SDS-PAGE and on staining with Coomassie blue or silver, but random losses of individual proteins occur after 2 weeks at 2% and 3% NaCl and at 18.2% mannitol. Of the newly-synthesized proteins, discernible changes are found in 7 and 4 polypeptides in NaCl and mannitol treatments, respectively. Apparently three new proteins (74 kd, 28.5 kd, and 26.2 kd) are induced de novo under both treatments. Other proteins (39.5 kd, 39.0 kd, 30 kd, and 16.5 kd) show an increased or decreased level of synthesis. NaCl levels above 0.5% or mannitol levels above 3.6% do not after the pattern of newly-synthesized proteins. This altered expression of newly-made proteins in the maize callus occurs only after a week of exposure to salinity or osmotic stress and coincides with the cell growth phase.

Subbanaidu Ramagopal

Papers

Salinity Stress Induced Tissue-Specific Proteins in Barley Seedlings

Differential mRNA transcription during salinity stress in barley.

Protein synthesis in a maize callus exposed to NaCl and mannitol.

Barley Proteins Associated with Tissue Dedifferentiation

Messenger RNA Changes during Drought Stress in Maize Leaves