The Photosynthetic Physiology Of Tobacco Seedlings Resistant To Drought Induced By Exogenous Substances During Transplanting Stage

The researth aimed to improve survival rates of flue-cured tobacco seedlings in the process of transplanting and shorten recovering stage after transplanting. Using flue-cured tobacco of the major conomic crops of China as test material, this paper studied the effects of spraying different exogenous substances on drought resistance of tobacco seedlings under different degree of drought resistance. In order to studing on some mechanism that different exogenous substances enhanced the drought resistance of flue-cured tobacco seedlings, determinted on the changes of photosynthetic gas exchange parameters, chlorophyll fluorescence parameters, membrane permeability, osmotic adjustment substance, water use efficiency and antioxidant enzymes activities were done as main referential indexes. The main resu Its were as follows:1. Drought stress inhibited the photosynthesis of tobacco seedlings as indicated by a partial inactivation of photosynthetic electronic transfer center and the downregulation of photochemical efficiency. Tobacco could improve itself resistance by the stomatal closure, which is beneficial to the water use efficiency and the maintenance of relatively high water content. drought stress could induce obvious photoinhibition in the leaves of flue-cured tobacco seedlings with low conversion efficiency (Fv/Fm) of PSII and electron transport rate (ETR). Under drought stress VJ and Mo increased significantly in tobacco seedling leaves, Sm declined, active response center opening degree is reduced, QB site changed and PQ database is lower, PS II electronic receptors side be remarkably damage, PSⅡresponse center inactivation or degradation, cpPo is reduced, and cpDo increase, so the used usually QA- later electronic transfer energy ratio reduce, DIo/RC, large increased and TRo/RC, ETo/RC reduce, Explain flue-cured tobacco leaves the PSⅡunder drought stress response center hurt, But leaves of tobacco seedlings can stimulate consumption by heat dissipation, this excess to relieve pressure PSⅡ, played an important role.2. The effects of exogenous CaCl2 on photosystemⅡ(PSII) functions in leaves of tobacco seedlings were studied under drought stress. The fast OJIP chlorophylla (chl a) fluorescence transients were utilized as probe.,The results showed that the treatment with spraying 10.0 mmol·L-of CaCl2 solution on leaves, the quantum yield for electron transport (cpEo) decreased by 20.37% on 10th day of the drought treatment compared with 1st day, whereas the control(CK) decreased by 25.14%. However, the electron transport flux per RC(ETo/RC) increased by 3.69%compared with CK on 10th day of drought stress. Foliar spraying 10 mmol·L-lCaCl2 solution could increase the amount of electron transport by capturing light energy for photosynthesis, and increase efficiency of the electron-transport chain energy transport rate in surplus activity center. And then PSII could produce more NADPH and ATP for energy required to increase drought resistance. PSII would remain relatively higher activity on leaves of flue-cured tobacco seedlings with spraying CaCl2 solution without damaged and inhibited under drought stress. It could be one of the main reasons to improve drought resistance.3. The spraying of 0.2 and 0.5 mmol·L-1 MeJA had a obviously positive influence on the photosynthetic and physiological characteristics such as net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr),and SS content and SOD, POD activity under drought stress. However, the Ci and MDA were lower than CK. But,1.0 mmol·L-1 of MeJA showed no obvious protection.After rehydration, all the index had been recovered,the MeJA treatment was more closed to the standard level before drought stress than CK. This indicated that MeJA can protect cell wall stability from leaves of flue-curing tobacco spire during drought stress, it also had positive influence on the osmoregulation substance and antioxidant enzyme activity. Photosynthesis functions of flue-curing tobacco spire was protected from injury, and the decreases of photosynthesis during drought stress were released.At the same time, it ensured the rapid undo of photosynthetic and physiological characteristics after rehydration. MeJA had a concentration effect in the harm caused by alleviating drought, but had not shown significant dose effect in the recovery after rehydration.4. The spraying of 0.2 and 0.5 mmol·L-1 MeJA had a obviously positive influence on the chlorophyll content and chlorophyll fluorescence characteristics such as maximum fluorescence (Fm), potential activities of PSII (Fv/Fo), PS II photochemical efficiency (Fv/Fm), actual photochemical efficiency(ΦPSⅡ), electron transport rate (ETR) and photochemical quenching (qP) under drought stress. But,1.0 mmol·L-1 of MeJA did not have a significant effect.After rehydration, all the index had been recovered, the MeJA treatment was more closed to the standard level before drought stress than CK. This indicated that MeJA can reduce the degradation of chlorophyll, and make the PSII remain relatively high activity under drought stress, enhance the drought resistance of the tobacco seedlings. At the same time, the MeJA guaranteed the rapid recovery of chlorophyll fluorescence parameters after rehydration. which ensure the regrew of flue-cured tobacco seedings. 5. Spraying 0.5mmol·L-1 and 1.0mmol·L-1 SA on leaves of flue-curing tobacco could reduce content of MDA to protecte effectively the membrane system in leaves of flue-cured tobacco. Meanwhile,0.5mmol·L-1and 1.0 mmol·L-1SA could alleviate the decomposition of chlorophyll release the damage of thylakoid membranes and PSⅡreaction center under drought stress, and improve greatly the drought-resistance.0.5～1.0 mmol·L-1 SA were the optimal concentrations to spray on leaves of tobacco, but 2.0 mmol·L-1SA would be toxic to tobacco seedlings.6. Spraying 1.0 mmol-L"1 ASA and 10 mmol·L-1 CaCl2 improved the photosynthetic capacity of flue-cured tobacco seedlings and alleviated photoinhibition under drought stress and the mixed-ues of ASA and CaCl2 show a certain synergistic effect. After rewatering, these photosynthetic parameters of tobacco seedlings spraying different exogenous substances quickly recovered and recovery characteristics spraying of 1.0 mmol·L-1 ASA and10 mmol·L-1 CaCl2 were also better than the controls, in particular, spraying both CaCl2 and ASA in the recovery effect were more abvious. Flue-cured tobacco seedlings spraying exogenous substances can rapidly recovery growth after drough stress when rain arriving or artificial irrigation under the conditions.