Abstract:

Photosynthesis is an important physiological process related to yield production and biomass accumulation in plants. With the research, development and application of genetically modified (GM) crops in the world, their risk assessment has been paid an increasing attention. In order to find out effects of exogenous genes on photosynthesis in transgenic plants, photosynthetic characteristics of transgenic Bt (Z30) and CpTI-Bt (CCRI41 and SGK321) cotton at seedling stage were studied by pot experiment. The results showed that the changes of stomatal conductance, transpiration rate and intercellular CO2 concentration in the leaves of Bt and CpTI-Bt transgenic cotton were not obvious in comparison with non-transgenic cotton (Z16, CCRI23 and SY321, respectively) and differed among different cotton cultivars. The difference of net photosynthetic rate between Bt transgenic cotton Z30 and non-Bt cotton Z16 was significant. The RuBPcase activity was decreased significantly and the GO activity increased significantly in the leaves of all tested transgenic cotton in comparison with non-transgenic cotton. But there were not significant differences in the content of Chlorophyll a, Chlorophyll b, Chlorophyll a/b, and the total Chlorophyll content between transgenic and non-transgenic cotton. The responses of photosynthetic rate to light intensities in mature cotton leaves were also measured under different light intensity conditions (the light intensities were 0, 10, 20, 40, 60, 80, 100, 200, 400, 600, 800, 1 000, and 1 200 μmol m^-2 s^–1). The parameters of apparent quantum yield, maximum net photosynthetic rate, apparent dark respiration rate, 1ight compensation point and 1ight saturation point were calculated by model fitting. The possible changes of these parameters were observed at a certain extent. But the results still need to be validated through farther test. From these results, the processes of photosynthesis and respiration regulated by RuBPcase and GO are changed possibly. The analysis by combination of dry biomass and photosynthetic characteristics studied in this experiment indicated that the response of biomass accumulation to genetical modification by exogenous genes of Bt and CpTI in transgenic cotton was related to both photosynthesis and other processes which were not studied in this experiment. The unanticipated effects of transgenic crops would be more uncertain and complex along with diversification of transgenic genes.

Key words: Cotton, Bt, CpTI, Photosynthetic characteristics