Effects of different nitrogen rate on the functions of flue-cured tobacco seedlings photosystemII under drought stress

Taking the polyphasic rise of the chlorophyll a fluorescence transients(OJIP)as probe,this study was conducted to determine the effects of different nitrogen rate(0,0.36,0.72 g·kg-1)on photosystemⅡ(PSⅡ)functions in leaves of flue-cured tobacco seedlings during the transplantation stage under drought stress.A flue-cured tobacco variety'Longjiang 911'was used as experimental material.The results showed that the maximum photochemical efficiency(Fv/Fm),potential activities of PSⅡ(Fv/F0)and the apparent electron transport rate(ETR)in leaves of flue-cured tobacco seedlings decreased under drought stress,the proportion of energy which was used for photochemical reaction also reduced,and the photoinhibition of photosynthesis occurred evidently under drought conditions,and the PSⅡ reaction centre was hurt.The appropriate amount of nitrogen fertilizer application(0.36 g·kg-1,pure nitrogen in soil)could increase the opening degree in surplus activity center and maintain the stability of electron-transport chain,and it also could improve the amount of light energy by capturing(φPo),the quantum yield for electron transport(φEo)and the electron transport efficiency of per reaction center(ETo/RC)by reducing the degradation of protein that was related to light energy capturing and electron transport in leaves of flue-cured tobacco seedlings.At the same time,the appropriate amount of nitrogen fertilizer application protected the flue-cured tobacco from injury during drought stress by increasing the heat dissipation,and observably improved the drought resistance of flue-cured tobacco seedlings.But the over-fertilization of nitrogen always caused the reduction of the drought resistance of flue-cured tobacco seedlings.