Leaves of the two new chlorophyll b-less rice mutants VG28-1, VG30-5 and the wild type rice cv. Zhonghua 11 were subjected to temperatures 28, 36, 40, 44 and 48℃ in the dark for 30 min or gradually elevated temperature from 30℃ to 80℃ at 0.5℃/min. The thermostability of photosynthetic apparatus was estimated by the changes in chlorophyll fluorescence parameters, photosynthetic rate and pigment content, chloroplast ultrastructure and tissue location of H2O2 accumulation. There were different patterns of Fo-temperature curves between the Chl b-less mutants and the wild type plant, and the temperature of Fo rising threshold was shifted 3℃ lower in the Chl b-less mutants (48℃) than in the wild type (51℃). At temperature up to about 45℃, chloroplasts were swollen and thylakoid grana became misty accompanied with the complete loss of photosynthetic oxygen evolution in the two Chl b-less mutants, but chloroplast ultrastruc- ture in the wild type showed no obvious alteration. After 55℃ exposure, the disordered thylakoid and significant H2O2 accumulation in leaves were found in the two Chl b-less mutants, whereas in the wild type plant, less H2O2 was accumulated and the swollen thylakoid still maintained a cer- tain extent of stacking. A large extent of the changes in qP, NPQ and Fv/Fm was consistent with the Pn decreasing rate in the Chl b-less mutants during high temperature treatment as compared with the wild type. The results indicated that the Chl b-less mutants showed a tendency for higher thermosensitivity, and loss of Chl b in LHC II could lead to less thermostability of PSII structure and function. Heat damage to photosynthetic apparatus might be partially attributed to the in- ternal oxidative stress produced at severely high temperature.
LIN Zhifang1,PENG Changlian1,Xu Xinlan1,LIN Guizhu 1 & ZHANG Jingliu2 1.South China Institute of Botany,Chinese Academy of Sciences,Guangdong Key Laboratory of Digital Botanical Garden,Guangzhou 510650,China
Chlorophyll fluorescence and antioxidative capability in detached leaves of the wild type Arabidopsis thaliana L.ecotypeLandsberg erecta(Ler)and three mutants deficient in anthocyanins biosynthesis(tt3,tt4,and tt3tt4)were investigatedduring treatment with temperatures ranging 25-45℃.In comparison with the wild type,chlorophyll fluorescence parametersFv/Fm,Φ_(PSII),electron transport rate(ETR),Fv/Fo and qP in three anthocyanin-deficient mutants showed a more rapidlydecreasing rate when the temperature was over 35℃.Non-photochemical quenching(NPQ)in these mutants was almostcompletely lost at 44℃,whereas the content of heat stable protein dropped and the rate of the membrane leakage increased.Fo-temperature curves were obtained by monitoring Fo levels with gradually elevated temperatures from 22℃ to 72℃ at0.5℃/min.The inflexion temperatures of Fo were 45.8℃ in Ler,45.1℃ in tt3,44.1℃ in tt4 and 42.3℃ in tt3tt4,respectively.The temperatures of maximal Fo in three mutants were 1.9-3.8℃ lower than the wild type plants.Meanwhile,three mutantshad lower activities of superoxide dismutase(SOD)and ascorbate peroxidase(APX)and an inferior scavenging capabilityto DPPH(1.1-diphenyl-2-picrylhy.drazyl)radical under heat stress,and in particular tt3tt4 had the lowest antioxidativepotential.The results of the diaminobenzidine-H_2O_2 histochemical staining showed that H_2O_2 was accumulated in theleaf vein and mesophyll cells of mutants under treatment at 40℃,and it was significantly presented in leaf cells of tt3tt4.The sensitivity of Arabidopsis anthocyanins-deficient mutants to high temperatures has revealed that anthocyanins innormal plants might provide protection from high temperature injury,by enhancing its antioxidative capability under hightemperature stress.
Ling ShaoZhan ShuShu-Lan SunChang-Lian PengXiao-Jing WangZhi-Fang Lin
