Three apple materials: Malus hupehensis, drought-sensitive, M. sieversii, a drought-tolerance type, and M. micromalus, a middle type, were used in this experiment. The expression characteristics of MaMAPK gene in the three materials were analyzed by Northern blotting. Results showed that MaMAPK gene was expressed in roots and leaves (except for control) of the three species seedlings treated with 20% PEG for different time, and its expression gradually increased with the time, whose peak emerged when the seedlings were treated for 1.5hr, then its expression decreased gradually. Liquid kinase assays indicated that the dynamic changing trend of MAPK kinase activity was very similar to that of the mRNA relative expression amount of MaMAPK. The differences between were that the peak of kinase activity emerged later than the latter's. Although the increase amount of kinase activity decreased after the peak, it was still higher than that of the control until the end of treatment. These results suggested that MaMAPK gene was regulated not only by water stress on transcription level, but also by phosphorylation and dephosphorylation on protein level. In the three researched apple species, the dynamic change of kinase activity was similar to that of the mRNA relative expression amount of MaMAPK. However, there were the highest MAPK activity and the highest mRNA relative expression amount of MaMAPK in M. sieversii, followed by M micromalus and M. hupehensis. The results indicated that the mRNA relative expression amount of MaMAPK and the activity of MAPK both correlated with the ability of drought-tolerance in the three species. Therefore, the differences between the mRNA relative expression amount of MaMAPK and the activity of MAPK were one molecular mechanisms of the different drought-tolerance in the three species of Malus L..

Volatile esters are major aroma components of apple, and an alcohol acyltransferase (AAT) catalyzes the final step in ester biosynthesis. The gene MdAAT2, which encodes a predicted 51.2kDa protein containing features of other acyl transferases, was isolated from Malus domestica Borkh. (cv. Golden Delicious). In contrast to other apple varieties, the MdAAT2 gene of Golden Delicious is exclusively expressed in the fruit. The MdAAT2 protein is about 47.9kDa and mainly localized in the fruit peel, as indicated by immunoblot and immunolocalization analysis. Northern blot and immunoblot analysis showed that the transcription and translation of MdAA T2 have a positive correlation with apple AAT enzyme activity and ester production, except in the later ripening stage, suggesting that MdAAT2 is involved in the regulation of ester biosysthesis and that a post-translation modification may be involved in regulation of AAT enzyme activity. Tissue disk assays of fruit peel revealed that using extraneous alcohols can recover the corresponding ester formation. Transcription and translation of MdAAT2 were both depressed by 1-methylcyclopropene (1-MCP) treatment and subsequent ester production was also prevented. These results suggest that: (1) ester production is mainly regulated by MdAAT2; (2) ethylene is also involved in this regulatory progress and (3) ester compounds rely principally on the availability of substrates.

Volatile esters, primarily synthesized in peel tissues, are major aromatic components of apple fruits [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. The use of cold storage combined with 1-methylcyclopropene (1-MCP) treatment prolongs the life of apples but represses the regeneration of esters during poststorage ripening. In this study, the regeneration of total esters was significantly increased in apple fruits treated with salicylic acid (SA) and Ethephon (ETH) that had been treated once or twice with 1-MCP. However, methyl jasmonate (MeJA) treatment resulted in regeneration of total esters after a single 1-MCP treatment. To determine the mechanism by which SA, ETH, and MeJA regulate ester regeneration, the apple alcohol acyltransferase gene (MdAAT2) was investigated at the mRNA, protein, and enzyme activity levels. Genes associated with ethylene perception were also investigated by RT-PCR. The results suggest that MdAAT2 controls ester regeneration and that MdETR1 plays a key role in ethylene perception and regulation of downstream MdAAT2 gene expression during poststorage. Ester compounds and concentrations differed in peels treated with different signal molecules, indicating that regulation of the pathway upstream of straight-chain ester biosynthesis depended on the regulation of lipoxygenase (LOX) and alcohol dehydrogenase (ADH) activity by SA, ETH, and MeJA during poststorage ripening.

Effects of foltar application of 100 mmol/L glycinebetaine (GB) on PS II photochemistry in wheat (Triticum aestivum) flag leaves under drought stress combined with high irradiantce were investingated. The results show that GB-treated plants maintained a higher net photosynthetic rate during drought stress than non-GB treated plants. Exogenous GB can preserve the photochemical activity of PSII, for GB-treated plants maintain higher maximal photochemistry efficiency of PSII (Fv/Fm)and recover more rapidly from photoinhibition. In addition, GB-treated plants can maintain higher anti, oxidative enzyme activities and suffer less oxidative stress. Our data suggest that GB may protect the PSII complex from damage through accelerating D1 protein turnover and maintaining anti-oxidative enzyme activities at higher level to alleviate photodamage. Dieviyldithocarbamale as well as streptomycin treatment can impair the protective effect of GB on PSII. In summary, GB can enhance the photoinhibition tolerance of PSII.

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), 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 combined measurement of gas exchange and chlorophyll fluorescence. 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 andΦPS2. 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 highΦPS2, and helps PN to be rapidly recovered after re-watering.