Effects of Low Temperature and Weak Light Stress on Chlorophyll Fluorescence Characteristics and Energy Allocation in Cotton Seedlings

【Objective】The aim of this study was to investigate the response mechanism of chlorophyll fluorescence characteristics and energy allocation in leaves of cotton seedlings under low temperature and weak light stress,and to provide a theoretical basis to screen suitable indexes for evaluating chilling-tolerance of cotton varieties.【Method】Chlorophyll fluorescence parameters in leaves of cotton seedlings of six different genotypes were determined under 5℃、100 μmol/(m2·s) in 12 hours.【Result】Under low temperature and weak light stress,the initial fluorescence(Fo) and the PFD limitation(L(PFD)) increased significantly,whereas the maximal efficiency of PSII photochemistry(Fv/Fm),photochemical efficiency of open reaction centers of PSII(Fv′/Fm′),quantum yield of PSII electron transport(ΦPSII),electron transport rate(ETR),photochemical quenching(qP) decreased dramatically,and the level of non-photochemical quenching(NPQ) increased at the initial stage and decreased at the later stage.At the same time,PSI distribution index of excitation energy(σ) and antenna heat dissipation rate(Drate) increased significantly,PSII distribution index of excitation energy(β) and Photochemical effieiency(Prate) decreased.【Conclusion】The results indicate that low temperature and weak light stress decreased the activity of PSII reaction center and photochemical electron transfer rate,inhibited pathways of photosynthetic electron transport,and distribution balance of excitation energy between PSI and PSII,which led to the structural damage of photosynthetic apparatus and functional descend in photosynthetic ability.Analysis of these chlorophyll fluorescence parameters of the leaves of all the cotton genotypes showed that these varieties performed cold tolerance in the order: Xinluzhong28 and Zhongmiansuo50Xinluzao42 and Zhongmiansuo43Xinluzao33 and Xinluzao19.