Study On Hydraulics Characteristic And Aquaporin Expression Of Different Malus Rootstocks Under Drought Stress And Salt Stress

In present thesis, The plant materials used were the apple dwarfing self-rooted rootstocks M9, M26, MM106, GM256, SH6. In our study, Leaf water potential(ψ), photosynthetic indexes, hydraulic characteristics and the expression of PIPs(MpPIP1:1, MpPIP2:1), TIPs(MpTIP1:1, MpTIP2:1, MpTIP2:2)were measured. The relative expressions of mRNA encoding five putative aquaporins were determined by Q-RT-PCR. Meanwhile, two different salt tolerance varieties, Malus zumi Rehd. and Malus baccata Borkh. were used as plant materials. The experiment used a NaCl concentration gradient of 0(CK), 0.1%(S1), 0.2%(S2) and 0.3%(S3). The impact on hydraulic conductance and aquaporin expression of different salinity treatments between the salt-tolerant Malus zumi Rehd. and salt-sensitive Malus baccata Borkh. was studied, to understand their mechanisms for salinity tolerance at physiological and molecular levels. The following results were obtained in this study:1. Leaf water potential(ψ) in five apple dwarf rootstocks decreased when subjected to drought stress. Under water deficit(WD) conditions, net photosynthetic rate, transpiration, stomatal conductance and intercellular CO2 concentration of aerial parts also decreased. Drought stress reduced root hydraulic conductance of five apple dwarf self-rooted rootstocks, but there was no significant difference between suitable soil moisture treatment and drought stress treatment. Compared to other rootstocks, MM106 had the minimum root hydraulics conductance difference between moisture treatments. It may be associated with a higher amount of PIPs(MpPIP1:1, MpPIP2:1) and MpTIP2:1 expression in MM106 rootstock roots under water stress conditions.2. MpPIP1:1, MpPIP2:1, MpTIP1:1, MpTIP2:1, MpTIP2:2 showed tissue-organspecific expression in five apple dwarf rootstocks, MpTIP1:1 had higher expression level in the MM106 rootstock leaf than in the root, MpPIP1:1, MpPIP2:1, MpTIP2:1, MpTIP2:2 had higher expression level in all rootstocks root than in the leaf. Expression of mRNA aquaporins in response to water deficit(WD) differed greatly in the five rootstocks studied. After drought stress, PIPs and TIPs genes had different expression patterns, some genes increased expression level in rootstocks, whereas others decreased expression level;3. After induced by drought stress, AQPs had different expression patterns in different varieties of apple dwarf rootstocks. Aquaporins play a positive role in plant-water transport, water maintenance in the cells and adequate levels of leaf water potential and photosynthesis in plants under water stress, which facilitates tolerance to water stress in apple dwarf rootstocks.4. Leaf water potential(ψ) in two different salt tolerance apple rootstock varieties decreased when subjected to low salinity stress, but increased in high NaCl concentration.With the increase of NaCl concentration, net photosynthetic rate, stomatal conductance and transpiration of aerial parts decreased, but there was difference between varieties. Salt stress also reduced root hydraulic conductance of two apple rootstocks, but there was no significant difference.5. Salinity affects water channel expression,which depending on the extent of the stress. In addition, we observed that expression of mRNA aquaporins in response to salinity differed greatly in the two rootstocks studied, this could be closely related to the different salt tolerance between two genotypes. Malus zumi Rehd. had better tolerance to salinity stress. When saline levels are high, an optimum water balance is important for maintaining homeostasis, and aquaporins may be one of the mechanisms that operate under such stress conditions.