Thermostability of photosynthesis in two new chlorophyll b-less rice mutants

Abstract

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 degrees C in the dark for 30 min or gradually elevated temperature from 30 degrees C to 80 degrees C at 0.5 degrees C/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 F(o)-temperature curves between the Chl b-less mutants and the wild type plant, and the temperature of F(o) rising threshold was shifted 3 degrees C lower in the Chl b-less mutants (48 degrees C) than in the wild type (51 degrees C). At temperature up to about 45 degrees C, 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 ultrastructure in the wild type showed no obvious alteration. After 55 degrees C 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 certain 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 internal oxidative stress produced at severely high temperature.

Enhancement of susceptivity to photoinhibition and photooxidation in rice chlorophyll b-less mutants

“…5) indicated that chloroplast ultrastructure of rice Chl b-less mutants was not altered as much in our planting conditions as it was in the barley Chl b-less mutant. The normal chloroplast ultrastructure, with intact envelope and grana stacking in rice Chl b-less mutants, was also seen when the leaves were given a 35 ºC treatment for 30 min in the dark (Lin et al 2005). Therefore, our results in this context differ from the reports of Staehelin (1986) or Rozak et al (2002).…”

“…The LHC apoproteins need Chl b for stable integration (Preiss and Thornber 1995). An evidenced modulation of Chl-protein complexes and the ratio of excited energy distribution between two photosystems have been observed in two Chl b-less mutants in our previous work (Lin et al 2003b). Hence, the sensitivity of chloroplast ultrastructure to photooxidation stress in these mutants in particular grown under HI is reasonably ascribed to the instability of chloroplast structure and function in the absence of Chl b.…”

“…6). The typical symptom of oxidative destruction in chloroplasts was also shown in rice leaves with heat shock (Lin et al 2005). The destruction of chloroplast ultrastructure by the action of MV in the light was seen in accordance with the inactivation of PS2 function and a decrease in membrane leakage rate in the purple rice leaves (Peng et al 2006).…”

“…Fixation and preparation of ultra-thin sections were performed routinely as described by Lin et al (2005). The ultrastructure of chloroplasts was observed and photographed with a transmission electron microscope (JEM-1010, JEOL, Tokyo, Japan).…”

Midday photoinhibition of two newly developed super-rice hybrids

“…2E). This agrees with the results obtained for other high-yielding rice mutants (Dai et al 2003, Lin et al 2003a.…”