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Year: 2005  |  Volume: 4  |  Issue: 1  |  Page No.: 39 - 48

Accumulation of Osmolytes and Stress Proteins, Alteration of Levels of Gene Expressions and DNA Profiles in Two Wheat Cultivars as a Response to Amelioration of pH Stress by IAA

Maher M. Shehata    

Abstract: Grains of two wheat (Triticum vulgare L.) cultivars (Gemmiza 7 and Giza 164) previously presoaked in phosphate buffer at different pHs, as well as an optimum concentration of IAA, were sown and grown at the green house to the M2 grains in order to study the possible adaptive mechanisms to ameliorate the pH stress on osmolytes (proline and betaine as chemical chaperones), stress proteins (molecular chaperones), alteration of levels of gene expression (mRNA and proteins) and DNA profiles. The results revealed that plants under acidic pH have an obvious effect on total proteins, RNA and DNA macromolecules. Cultivar Giza 164 plants accumulated higher levels of proline than Gemmiza 7 under pH stress. In both cultivars betaine and the level of mRNA increased with pH stress and the expression was coincided with the observed betaine accumulation. The yields of poly(A)+ RNA were in the range of 0.5-1.5%±1 in Cv. Giza 164 as compared to that of Gemmiza 7 (0.3-1.1%±0.7). Exogenous application of IAA can stimulate resistance against the unfavourable environmental pH value and improve plant under stress by developing various mechanisms, which include increase in both the soluble protein, betaine and proline that acts as a free radical scavenger and limits the cytoplasmic acidification, quantitative and qualitative increase in mRNA and low molecular weight proteins (9-29 kDa) that play an important role in the readjustment of plant cell`s osmotic potential and protecting cytoplasmic enzymes. RAPD analysis was effective in detecting informative qualitative and quantitative changes in both wheat cultivars as a response to pH stress and hormonal application. The thirty used different primers have different performances in detection of genetic changes. The number of amplified fragments generated ranges between 10 and 22 with molecular size ranges between 50 and 2130 bp. Quantitative changes by one common band were shown in stressed Giza 164 samples using thirteen primers as compared to nine primers in Gemmiza 7 stressed samples. Qualitative changes were recorded using all primers (thirty) in Gemmiza 7 and in Giza 164 using sixteen primers only. These changes were found to be reproducible when repeated at different times under the same amplification conditions. The expression of many proteins is known to be regulated by biotic and abiotic stresses, suggesting the occurrence of complex mechanisms that control gene expression in response to environmental stresses. The disappearance of some protein bands may be attributed to the alteration of their structural genes and RNA transcripts. The results of this study suggest that an adaptive mechanism has been developed by Triticum vulgare L. cultivars (Gemmiza 7 and Giza 164) in response to exogenous hormonal application under acidic pH stress. Also, the biochemical and molecular criteria which may affect on crop yield productivity and quality were improved. The synthesis of chemical and molecular chaperones to maintain osmotic adjustment is the main strategy that has evolved to maintain growth. The difference in the ability to maintain osmotic potential under pH conditions between the two cultivars reflects the differences in their genetic background.

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