Four grapevine cultivars, i.e. Cabernet Sauvignon (a member of the Western Europe cultivar group), Rizamat (a member of the East cultivar group), Red Double Taste (a hybridized cultivar from Vitis vinifera L. and V. labrusca L.), and 1103Paulsen (a hybridized rootstock), were treated by three severity orders of drought stress for 25 d. Then net photosynthetic rate (PN), maximal photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPS2) of photosystem 2, total electron transport rate (JT), and electron transport flows used in carboxylation (JC) and in oxygenation (JO) reactions catalysed by ribulose-1,5-bisphosphate carboxylase/oxygenase were determined. PN was determined again after re-watering for 2 d by gas exchange measurement. Along with the increase in severity of drought stress, PN, Fv/Fm, ΦPS2, JT, and JC in all four cultivars decreased. The range of decrease differed among cultivars. JO expressed various trends from cultivar to cultivar. In Rizamat that received slight and moderate drought stress, PN evidently decreased, but JO markedly increased, thus maintaining high values of JT and ΦPS2. Prior to the moderate drought stress, the Fv/Fm was high in Rizamat, indicating that the photodamage had not happened ahead of the moderate drought stress given. Under the severe drought stress, the photorespiration rate in Rizamat decreased by 70 %, and JT, ΦPS2, and Fv/Fm also dropped to very low values, i.e. the photodamage of photosynthetic apparatus has taken place. This suggested that the photorespiration has consumed the excessive assimilatory power and the photo-protective function of photorespiration is very important for Rizamat. When Cabernet Sauvignon grew under drought stress, its JO decreased in a small range, thus maintaining higher values of JC, JT, ΦPS2, and Fv/Fm; hence no serious photodamage occurred. Despite of the fact that PN of cv. Red Double Taste decreased markedly under the slight drought stress, JO still increased under the severe drought stress. This suggests that photorespiration is important in photoprotection under drought stress. JO in cv. 1103Paulsen markedly decreased under slight stress. Accordingly, PN, Fv/Fm, ΦPS2, JT, and JC decreased to extremely low values. Thus photorespiration effectively protects the photosynthetic apparatus from photo-damage under drought, assists in maintaining a relatively high ΦPS2, and helps PN to be rapidly recovered after re-watering. and X. Q. Guan ... [et al.].
Overexpression of chloroplastic glycerol-3-phosphate acyltransferase gene (LeGPAT) in tomato increased
cis-unsaturated fatty acid content in phosphatidylglycerol (PG) of thylakoid membrane. By contrast, suppressing the expression of LeGPAT decreased the content of cis-unsaturated fatty acid in PG. Under salt stress, sense transgenic plants exhibited higher activities of chloroplastic antioxidant enzymes, lower content of reactive oxygen species (ROS) and less ion leakage compared with the wild type (WT) plants. The net photosynthetic rate (PN) and the maximal photochemical efficiency (Fv/Fm) of photosystem II (PSII) decreased more slightly in sense lines but more markedly in the antisense ones, compared to WT. D1 protein, located in the reactive center of the PSII, is the primary target of photodamage and has the highest turnover rate in the chloroplast. Under salt stress, compared with WT, the content of D1 protein decreased slightly in sense lines and significantly in the antisense ones. In the presence of streptomycin (SM), the net degradation of the damaged D1 protein was faster in sense lines than in other plants. These results suggested that, under salt-stress conditions, increasing
cis-unsaturated fatty acids in PG by overexpression of LeGPAT can alleviate PSII photoinhibition by accelerating the repair of D1 protein and improving the activity of antioxidant enzymes in chloroplasts. and Y. L. Sun ... [et al.].