Two new yellow rice chlorophyll (Chl) b-less (lack) mutants VG28-1 and VG30-5 differ from the other known Chl b-less mutants with larger amounts of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase small sub-unit and smaller amounts of Chl a. We investigated the altered features of Chl-protein complexes and excitation energy distribution in these two mutants, as compared with wild type (WT) rice cv. Zhonghua 11 by using native mild green gel electrophoresis and SDS-PAGE, and 77 K Chl fluorescence in the presence of Mg2+. WT rice revealed five pigment-protein bands and fourteen polypeptides in thylakoid membranes. Two Chl b-less mutants showed only CPI and CPa pigment bands, and contained no 25 and 26 kDa polypeptides, reduced amounts of the 21 kDa polypeptide, but increased quantities of 32, 33, 56, 66, and 19 kDa polypeptides. The enhanced absorption of CPI and CPa and the higher Chl fluorescence emission ratio of F685/F720 were also observed in these mutants. This suggested that the reduction or loss of the antenna LHC1 and LHC2 was compensated by an increment in core component and the capacity to harvest photon energy of photosystem (PS) 1 and PS2, as well as in the fraction of excitation energy distributed to PS2 in the two mutants. 77 K Chl fluorescence spectra of thylakoid membranes showed that the PS1 fluorescence emission was shifted from 730 nm in WT rice to 720 nm in the mutants. The regulation of Mg2+ to excitation energy distribution between the two photosystems was complicated. 10 mM Mg2+ did not affect noticeably the F685/F730 emission ratio of WT thylakoid membranes, but increased the ratio of F685/F720 in the two mutants due to a reduced emission at 685 nm as compared to that at 720 nm. and Zhu-Fang Lin ... [et al.].
We compared the responses of wild type (WT) and three mutants including npq1 (lutein-replete and violaxanthin deepoxidase-deficient), lut2 (lutein-deficient), and lut2-npq1 (double mutant) to high irradiance (HI, 2 000 μmol m-2 s-1) at both low (LT, 5 °C) and room (25 °C) temperature. Xanthophyll-dependent energy dissipation was highest in the WT, followed by the lut2, npq1, and npq1-lut2. At 25 °C the relative stress tolerance expressed by Fv/Fm was consistent with the energy dissipation capacity for the first 2 h of treatment. After 3-4 h, the Fv/Fm levels in lut2 and npq1 converged. Under combined LT and HI the relative tolerance sequence was in contrast to the energy dissipation capacity being WT > npq1> lut2 > lut2-npq1. There were little or no significant change in the contents of xanthophylls and carotenes or the chlorophyll (Chl) a/b ratio in any of the materials. Thus lutein (L) substitution possibly alters the conformation/organisation of L binding proteins to enhance damage susceptibility under HI at LT. The enhanced vulnerability is not compensated for the energy dissipation capacity in the lut2 background at LT. and Chang-Lian Peng, A. M. Gilmore.
We compared photoinhibition sensitivity to high irradiance (HI) in wild-type barley (wt) and both its chlorina f104-nuclear gene mutant, that restricts chlorophyll (Chl) a and Chl b synthesis, and its f2-nuclear gene mutant, that inhibits all Chl b synthesis. Both Fv/Fm and ΦPS2 decreased more significantly in f2 than f104 and wt with duration of HI exposure. Chl degraded more rapidly in the f2 than in either f104 or wt. Most sensitivity to photoinhibition was exhibited for f2, whereas there was little difference in response to HI between the f104 and wt. The highest de-epoxidation (DES) value at every time point of exposure to HI was measured for f2, whereas the wt had the lowest value among the three strains. There were two lifetime components resolved for the conversion of violaxanthin (V) to zeaxanthin plus antheraxanthin (Z + A). The most rapid lifetime was around 6 min and the slower lifetime was >140 min, in both the mutants and wt. However, the wt and f104 both displayed larger amplitudes of both de-epoxidation lifetimes than f2. The difference between the final de-epoxidation state (DES = [Z + A]/[V + A + Z]) in the light compared to the dark expressed as ΔDES for wt, f104, and f2 was 0.630, 0.623, and 0.420, respectively. The slow lifetime component and overall larger ΔDES in the wt and f104 correlated with more photoprotection, as indicated by relatively higher Fv/Fm and ΦPS2, compared to the f2. Hence the photoprotection against photoinhibition has no relationship with the absolute DES value, but there is a strong relationship with de-epoxidation rate and relative extent or ΔDES. and Chang-Lian Peng ... [et al.].
Two yellow rice mutants VG28-1 and VG30-5 were obtained during the tissue culture process from a rice plant (cv. Zhonghua No.11 japonica) with inserted maize Ds transposon element. Absorption spectra and pigment composition showed that two mutants had no chlorophyll (Chl) b and lower Chl a content in comparison to the wild type (WT). Net photosynthetic rate (PN), total electron transport rate (JF), photochemical quenching (qp), quantum yield of PS2 dependent non-cyclic electron transport (ΦPS2), fraction of Prate, and leaf area were lower but Fv/Fm and apparent quantum yield (AQY) remained at similar levels as in the WT plant. Xanthophyll cycle pool size (V+A+Z) on a Chl basis, and de-epoxidation state were enhanced in the mutants. The mutants had larger amounts of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), especially the small subunit of RuBPCO, than WT. The characteristics of two rice mutants differed somewhat from the other common Chl b-less mutants originating from mutagenic agent treatments. and Zhi-Fang Li ... [et al.].