Influence of high light stress on the photosynthesis of flag leaves of indica subspecies (cv. “Shanyou 63', sensitive to photoinhibition) and japonica subspecies (cv. “Wuyujing', resistant to photoinhibition) of rice ( Oryza sativa L.) was comparatively investigated. In both cultivars of rice, the excitation energy distribution between two photosystems was altered and the excitation energy transfer from light harvesting chlorophyll protein complexes to PSⅡ was inhibited by high light stress. These decreases were more pronounced in indica rice cultivar as compared to japonica one. The analysis of mild SDS_PAGE showed that in indica rice, high light stress almost disaggregated the trimer of light harvesting chlorophyll protein complexes of PSⅡ (LHC Ⅱ 1). The stress reduced the contents of internal antennae chlorophyll protein complexes of PSⅡ (CPa), light harvesting chlorophyll protein of PSⅠ (CPⅠa) and Chl a protein complex of PSⅠ reaction center (CPⅠ) as well as dimer of LHCⅡ (LHCⅡ 2) in indica rice. In japonica subspecies, however, high light stress depressed the contents of LHCⅡ 1, CPa and CPⅠa, but slightly impacted on CPⅠ content. Moreover, the increase in the contents of monomer of LHCⅡ by high light stress was found in both subspecies. In consistent with above results, analysis of polypeptide indicated that the amounts of 27 kD and 25 kD polypeptide of LHCⅡ in particular, as well as that of 21 kD polypeptide of CPⅠa were reduced by high light stress in both subspecies. It was found that, comparing with japonica rice, the stress pronouncedly diminished 43 kD and 47 kD proteins of CPa and 23 kD extrisic protein in indica rice.
Thylakoid membrane preparations of super high-yield hybrid rice (Oryza sativa L.), Liangyoupeijiu (P9) and Shanyou 63 (SH 63) were used for investigating its spectral and time properties by using picosecond time-resolved fluorescence spectrum measuring system. The thylakoid membrane preparations of P9 and SH 63 were excited by an Ar+ laser with a pulse width of 120 ps, repetition rate of 4 MHz and wavelength of 514 nm. The time constants of the excited energy transfer in these two varieties at flowering stage and grain filling stage were calculated from the experimental data. Based on the comparative studies of the time and spectral properties of the excited fluorescence in these ultrafast dynamic experiments the following was found: at both the flowering stage and grain filling stage, the speed of the excitation energy transfer, in photosystem was faster than that in photosystem II in P9 variety; and the speed of the excitation energy transfer at grain filling stage was faster than those at flowering stage for both rice varieties; the experiments also implied that the components and assembly of pigments in SH 63, but not in P9, changed during the process from flowering stage to grain filling stage for in these two rice varieties.
Cytochrome b_559 in photosystem Ⅱ reaction center was purified from spinach ( Spinacia oleracea L.) and rice ( Oryza sativa L.) by a rapid and simple procedure. Their low temperature fluorescence emission and excitation spectra, ultraviolet fluorescence spectra and absolute absorption spectra were presented. The author's purification methods, which enhanced the yield of pure protein and shorted the time for isolation, have several advantages: 1. use of oxygen_evolving PSⅡ core complexes as the starting material in order to avoid disturbing from other cytochromes; 2. isocratic elution of cytochrome b_559 from a DEAE_Sephacel column for eliminating the impurity and yielding the protein in pure state; 3. a simple column procedure for removal of excess Triton X_100. Purified cytochromes b_559 from these species have similar optical spectra and mobility during gel electrophoresis under native conditions. From the results of novel electrophoresis (Tricine_SDS_PAGE), cytochrome b_559 from both spinach and rice reveal two polypeptide bands (apparent molecular weight 9 kD and 4 kD, respectively). By measuring of 77 K fluorescence spectra, it was shown that for the purified cytochrome b_559 there were two excitation peaks at 439 nm and 413 nm, and two emission peaks at 563 nm and 668 nm. This is the first indication that Cyt b_559 is able to emit fluorescence and also transfer excited electrons to chlorophyll. By the use of ultraviolet fluorescence spectra, it was demonstrated for the first time that the location of Trp residue could be in the hydrophobic transmembrane region of cytochrome b_559.
