Abstract: In order to determine the influence of temperature and light intensity on the photosynthesis of tobacco during transplanting stage in Northern China,in the present study,the impacts of weak light (200 μmol/(m²·s) and strong light (1 000 μmol/(m²·s)) on photochemical activity,PS Ⅱ electron transfer and polymerization of thylakoid membranes of tobacco seedling leaves that had been treated for 2 hours under low temperature ((8±2)℃) were examined according to fast-phase chlorophyll fluorescence kinetics.The results suggested that the weak-light treatment at low temperature didn't apparently change the shape of OJIP curve of tobacco seedling leaves,whereas remarkable changes occurred to the curve shape when the leaves were treated by strong light after low-temperature treatment,as the tobacco seedling leaves were treated by strong light after low-temperature treatment,both F_v/F_m and the PI_ABS declined significantly,in other words,PSⅡ photochemical activity of the leaves was weakened,while it wasn't obviously decreased when the leaves were treated with weak light after low-temperature treatment,this indicated that strong light was an important cause of light inhibition for tobacco seedling leaves.After low-temperature treatment,the V_J,M_o and S_m of tobacco seedling leaves weren't changed when treated by weak light,nevertheless,there presented a significant increase in V_J and M_o when tobacco seedling leaves were treated with strong light after low-temperature treatment,but no prominent changes to S_m,this reflected that the electron transfer ability of tobacco seedling leaves at the receptor side of PSⅡ wasn't inhibited under the situation that they were treated by weak light after low-temperature treatment,however,the electron transfer ability was apparently weakened within the distance from Q_A to Q_B at the receptor side of PSⅡ when tobacco seedling leaves were treated by strong light after low-temperature treatment,which was directly associated with the declined ability of Q_B to receive electrons rather than the indirect consequence of the decrease in PQ capacity.After low-temperature treatment,both the weak and the strong light didn't obviously changed V_L and V_K of tobacco seedling leaves,namely,the strong and the weak light neither decreased OEC activity of tobacco seedling leaves nor dissociated chloroplast thylakoids after the leaves had been treated under low temperature ((8±2)℃) for two hours.Strong light is a crucial factor that induces light inhibition of tobacco seedling leaves after low temperature stress is enhanced,in northern areas,it is advisable to consider transplanting in cloudy days or moderate shadowing at noon in the period of transplanting tobacco in spring,so as to protect the tobacco from strong light.

Key words: Low temperature, High light, Flue-cured tobacco, PSⅡ

CLC Number: 

• Q945.1