Study On Physiological Responses And Quaporin Expression Of Two Malus Rootstocks Under Drought Stress And The Function Of MpPIP1;1

Drought is one of the most serious problems for sustainable agriculture, which influenceplant growth and crop yield in agricultural production in many regions of the world. However,the mechanism research on drought influence of fruit trees is behind other crops. Apple is oneof the world's major fruit trees of cultivated species and the mostly cultivated deciduous fruittree in northern China. Apple propagation rely on grafting and its stress resistance abilitymainly depends on rootstocks, so further study the drought-resistance ability and adaption tothe damage in terms of both physiological and molecular mechanism has importantsignificance for improving their ability of fruit production and development of droughttolerant through genetic improvement.In present thesis, two apple rootstocks with significant differences in drought tolerancewere used as plant materials. One-year old potted plants were subjected to drought bywithholding water. Leaf water content (LWC), photosynthetic indexes, changes ofendogenous hormones contents, and expression of aquaporins were studied. Six Malusaquaporin genes were cloned. The subcellular location and procaryotic expression ofMpPIP1;1were also examined. The main results are as follows:1. Throughout the experimental period, M. prunifolia had higher readings for all fourphotosynthetic indexes as well as LWC. Values for LWC were rapidly reduced under stress,especially for M. hupehensis. ABA, as a signal material, which can inhibit growth,increased significantly in M. prunifolia compared with that of M. hupehensis under droughtcondition, especially on day7and day14. However, IAA, which can promote growth,decreased significantly in drought-tolerant rootstock M. prunifolia. Moreover, at most timepoints, drought-tolerant rootstock M. prunifolia had higher values than that ofdrought-sensitive rootstock M. hupehensis in terms of GAs and ZR contents. Differentendogenous hormones contents and variation tendencies under drought stress probably playcertain roles in influencing drought-tolerance in Malus.2. Comparisons between the predicted amino acid sequences from six cloned appleaquaporins and those from other members of the aquaporin super-family revealed several keyfeatures, including six trans-membrane domains, five alternating extracellular/intracellular loop regions, and two NPA motifs. Our phylogenetic analysis demonstrated that these sixaquaporin genes belong to five subfamilies based on their structural characteristics.3. Real-time analysis revealed that, except for TIP2;1, the transcript abundance ofmost aquaporin genes was elevated after drought stress, reaching a peak at Day14beforedeclining in the leaves and roots of both species. For TIP2;1, however, the transcriptlevel was continuously reduced in M. prunifolia leaves throughout the entire course oftreatment. Expression of aquaporin genes varied according to the gene, water status, andplant organ being examined. We conclude that Malus aquaporins are responsive to waterstress at the transcriptional level, probably playing several roles in conferring droughttolerance.4. MpPIP1;1locates on plasma membrane and nuclear. Over-expression MpPIP1;1in E. coli enhanced its drought and salt tolerance but not low temperature. Under thecultivation environment of150mM mannitol and300mM NaCl, the colony counts of E.coli over-expressed MpPIP1;1were much more than the control, but this did not go withlow temperature cultivation.