Chilling-induced Photoinhibition of Photosynthesis in Myrica rubra Leaves

Abstract:

Gas exchange and chlorophyll fluorescence were investigated in young Chinese strawberry tree （Myrica rubra var. astropurea Tsen.） leaves treated with different chilling temperatures （12℃. 6℃ and 2℃） under differentirradiance levels （0, 70 and 350 μmol m^-2s^-1） for 12 hours by a portable photosynthesis system HCM-1000 and a portable modulation fluorometer PAM-2000. The results showed that exposure of strawberry tree leaves to various low temperature and light resulted in the increases in Ci/Ca （internal/external CO₂ concentration）, Fo （initial fluorescence）, qN （non-photochemical quenching） and （Fi-Fo）/（Fp-Fo） （amount of inactive PS Ⅱ centers）, butdecreases in Pn （net photosynthesis rate）, Gs （stomata conductance）, Fv/Fm （maximal photochemical efficiency of PSⅡ）, qP （photochemical quenching） and ФPSⅡ （quantum yield of PS Ⅱ ）. At the same levels of low temperature, moderate irradiance （350 μmol m^-2s^-1） enhanced the inactivation or damage of PSⅡ reaction centers which needed longer time for recovery. It was shown that the inhibition of photosynthesis in treated plants induced by low temperature under light condition can be attributed to the loss of activity in photosynthetic apparatus. It is suggested that the accumulation of QQ_A^- and non-reducing Q_B is a possible cause for the inactivation or damage of PSⅡ reaction centers, and non-radiative energy dissipation probably plays an important protective role against the photoinhibition induced by chilling.