Regulation of protein synthesis in root, shoot and embryonic tissues of germinating barley during salinity stress
Abstract Protein synthesis during seed germination, a stage vulnerable to salinity stress, was investigated. The responses of barley genotypes, CM72 (California Mariout 72) and Prato, toward salinity were different during seed germination. Germination of CM72 was unaffected up to 0.34 kmol m−3 (2%) NaCl, but that of Prato was reduced 30% by 0.17 kmol m 3 NaCl and 75% by 0.34 kmol m−3 NaCl. Therefore, the former genotype is relatively more salt-tolerant than the latter. Protein synthesis in roots, shoots, and embryos was investigated in these two genotypes before and after salinity stress. The uptake of S-methionine and its incorporation into protein were significantly reduced by salinity in both genotypes. The inhibition of global protein synthesis was significant in roots and shoots. Proteins from different tissues were resolved by single and two dimensional gels. The steady-state protein levels were maintained remarkably well during salinity stress in roots and shoots. Likewise, proteins in germinating embryos were stable except for a 42-kilodalton protein unique to the salt tolerant genotype which was apparently degraded during salinity stress. Salinity, around 0.34 kmol m−3 NaCl, induced both quantitative and qualitative changes in the expression of some proteins labelled in vivo. The quantitative changes included repression or enhancement of synthesis of selected groups of proteins. Around 8% of the nearly 400 resolved proteins in a tissue was affected this way. Some of the proteins in this category were specific to each genotype. About 1 % of the total showed qualitative changes; these proteins were expressed only during salinity stress. In roots, two proteins (28, 41.7 kilodaltons) were detected in CM72 and five (28, 45, 60.5, 76.5, 82.5 kilodaltons) in Prato; only the 28-kilodalton protein was common to both genotypes. In shoots, four proteins (45, 60.5, 76.5, 82.5 kilodaltons) were found only in Prato and these were similar to those induced in roots. The four new proteins (32, 37.5, 89, 92 kilodaltons) in germinating embryos were apparently induced only in CM72; these were distinctly different from those detected in developed roots and shoots. The unique protein changes induced by salinity stress during germination (this study) and seedling growth studies reported earlier (Ramagopal, 1987b) are apparently different. The findings demonstrate that ontogeny plays an important role in the expression of tissue-specific proteins during salinity stress in the salt tolerant and sensitive barley genotypes.