The effects of simulated SO2 treatment on the photosynthetic apparatus were investigated in five subtropical forest plants, namely Plnus massonlana Lamb., Schlma superba Gardn. et Champ., Castanopsls flssa （Champ. ex Benth.） Rehd. et Wils., Acmena acuminatissima （BI.） Merr et Perry, and Cryptocarya concinna Hance. After leaf sections had been immersed in 0, 20, 50, and 100 mmol/L NaHSO3 for 20 h, total chlorophyll （Chl） content, Chl a/b, maximal photochemical efficiency, and the photochemical quantum yields of photosystem Ⅱ of all five woody plants were reduced to different degrees, whereas lutein content （Chl base） was increased. Two protective mechanisms, namely the xanthophyll cycle （de-epoxidation） and an anti-oxidant system （1,1-diphenyl-2-picrylhydrazyl radical-scavenging capacity）, showed differences in the degree of modulation under simulated SO2 treatment. Compared with control （distilled water treatment）, the revised normalized difference vegetation index, a leaf reflectance index, was lowered with Increasing concentrations of NaHSO3. Cryptocarya conclnna, a dominant species in the late succession stage of subtropical forests in South China, exhibited less sensitivity to NaHSO3. Conversely, Pinus massonlana, the pioneer hellophyte species, was most susceptible to NaHSO3 treatment. It Is suggested that SO2 pollution may accelerate the succession of subtropical forest.
Nan LiuChang-Lian PengZhi-Fang LinGui-Zhu LinLing-Ling ZhangXiao-Ping Pan
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. ecotype Landsberg erecta （Ler） and three mutants deficient in anthocyanins biosynthesis （tt3, tt4, and tt3tt4） were investigated during treatment with temperatures ranging 25-45 ℃. In comparison with the wild type, chlorophyll fluorescence parameters Fv/Fm, φps,, electron transport rate （ETR）, Fv/Fo and qP in three anthocyanin-deficient mutants showed a more rapidly decreasing rate when the temperature was over 35 ℃. Non-photochemical quenching （NPQ） in these mutants was almost completely 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 ℃ at 0.5 ℃/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 mutants had lower activities of superoxide dismutase （SOD） and ascorbate peroxidase （APX） and an inferior scavenging capability to DPPH （1.1-diphenyl-2-picrylhy.drazyl） radical under heat stress, and in particular tt3tt4 had the lowest antioxidative potential. The results of the diaminobenzidine-H2O2 histochemical staining showed that H2O2 was accumulated in the leaf 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 in normal plants might provide protection from high temperature injury, by enhancing its antioxidative capability under high temperature stress.
Ling ShaoZhan ShuShu-Lan SunChang-Lian PengXiao-Jing WangZhi-Fang Lin
The adaptations and responses of photosynthesis to long- and short-term growth light gradient treatments were investigated in five subtropical forest plants, namely Pinus massoniana Lamb., Schima superba Gardn. et Champ., Castanopsis flssa （Champ. ex Benth.） Rehd. et Wils., Acmena acuminatissima （BI.） Merr et Perry, and Cryptocarya concinna Hance. With diurnal changes in sunlight and air temperature, the de-epoxidation state and lutein content in the five woody plants under three light Intensities first increased and then decreased during the day. However, maximal photochemical efficiency （FvFm; where Fm is the maximum fluorescence yield and Fv Is variable fluorescence） and the photochemical quantum yields of photosystem （PS）Ⅱ （φPSⅡ） of the species examined changed in the opposite manner, with those in plants grown under 100% natural light changing the most. After long-term treatment （21 months）, anti-oxidant capacity （1,1-diphenyl-2-picrylhydrazyl radical （DPPH.）-scavenging capacity） and utilization of excitation energy showed differences in modulation by different light intensities. It was shown that A. acuminatissima and C. concinna, as dominant species in the late succession stage of a subtropical forest in Dinghu mountain, South China, were better able to adapt to different light environments. However, P. massonlana, the pioneer species of this forest, exhibited less adaptation to low light intensity and was definitely eliminated by the forest succession process.
Nan LiuChang-Lian PengZhi-Fang LinGui-Zhu LinXiao-Ping Pan
