Study On The Role Of Sorbitil/Sucrose In Resisting Drought Stress In Apple Leaves

Carbohydrate is not only the important energy material and structural components in plant, but also plays a crucial role as signaling molecule in vivo and in osmotic adjustment,regulating the expression of thousands of of genes in plants and involved in the stress responses like drought stress. In apple leaves, In besidessucrose, also contains a lot of high permeability light contract carbohydrates sorbitol. To further clarify the fuctions of sorbitol /sucrose in drought, in this thesis, we measured the soluble sugar content in apple leaves, key metabolic enzyme activities and gene expression in short-term, long-term drought conditions,analysed the impacts of sorbitol / sucrose changes on drought resisting of apple, the main results are as follows:1.In‘Greensleeves’ apple, we analyzed the impacts of the short-term drought on sugar metabolism. The results showed that under short-term drought conditions, sorbitol, fructose,glucose and galactose content of Greensleeves’ apple leavesincreased remarkably with the aridity gravating, buta marked recovery after watering 2d, however, the content of sucrose under drought stress decreased significantly and did not show significant recovery even after watering 2d.The activity and genes expression level of A6 PR,the key enzymes in sor Synthesis,was also dramatically increased under drought stress conditions. SPS, which is the key rate-limiting enzyme of Suc synthetic, activity increased, and the expression Md SPS1 of Class A of SPS gene family also increased while the other five Md SPS genes showed a significant suppression during drought conditions. Combinating the research progress of Md SPS, these results gave further support that, SPS of class C may have decisive rolein Suc synthesis. in addition, Md SDH, Md CWINV, Md NINV and Md HK, Md SUT Md FK and transport proteins and Md SOT genes of Suc metabolism also express participation in Sor under drought stress showed a different response, such as Md SDH1 / 2, Md FK1 / 2, Md HK1,Md SUT3 / 5, Md SOT1 / 2, etc. under short-term drought, Md NINV1 / 2, Md FK4, Md HK3 and Md SUT2 are significantly suppressed by drought. These results indicate that, Sor plays a more important role than Suc in the response to short-term drought stress of ’Greensleeves’ apple’s and and the increase of Sor synthesis changed the balance of sugars in apple leaves, caughtthechange of the sugar metabolic patterns so that it could adapt to the change of flow of carbon in apple leaves and the carbon need to survive under drought stress.2. ’Qinguan’ and ’Naganofuji No.2’ apple plants were used to study the responses of metabolism of sugar in apple leaves to prolonged drought conditions. The results showed that under the long-term water shortage conditions, sucrose, sorbitol, glucose, fructose and galactose of ’Qinguan’ and ‘Naganofuji No.2’ leaves contents were significantly decreased.Compared with ‘Naganofuji No.2’, ’Qinguan’ crown leaves decline smaller significantly,especially in the content of Sor. A6PR’s which is Sor biosynthetic enzymes activity and expression in the apple also significantly increased in ’Qinguan’.Md SPS5 / 6 and Md SDH1 / 2which is belong to Class C of SPS gene family have been significantly inhibited, while Md FK1 / 2, Md SUT3 / 4 / 5, Md SOT1 were significantly induced increase in the expression.Md CWINV1 / 2/ 3, Md NINV1, Md HK1 / 3 showed different patterns of change, the expression of Md HK1 / 3 and Md NINV1 / 2 reduced in ‘Qinguan’, and the expression of Md HK1 / 3 and Md NINV1 / 2 were consistent regulation. These results also show that, Sor is related to Apple drought-related, and may be involved in sucrose NINV and HK signal-regulated in drought resistance.3.To further ascertain the role of Sor and Suc in apple drought resistance,we the test materials by transgenic’Greensleeves’apple which is suppressed respectively synthesized of Sor and Suc,researching their changes of drought resistance.The results show耳朵that the reducing of Sor or Suc makes reduction of the blade’s water retention capacity and also affect stomatal conductance.They can increase the transpiration rate,reduce the water use efficiency of the blade,and reduce the resistance of transgenic apples.These results suggest耳朵that the apple not only uses Sor and Suc as an osmotic regulator of leaf water potential and water retention capacity and influces the drought resistance of the apple,but Sor also regulates the opening of the apple leaf’s stomatal guard cells.