Correlation between Photoinhibition Sensitivity and the Rates and Relative Extents of Xanthophyll Cycle De-epoxidation in Chlorina Mutants of Barley (Hordeum vulgare L.)

We compared photoinhibition sensitivity to high irradiance (HI) in wild-type barley (wt) and both its chlorina f ₁₀₄-nuclear gene mutant, that restricts chlorophyll (Chl) a and Chl b synthesis, and its f ₂-nuclear gene mutant, that inhibits all Chl b synthesis. Both F_v/F_m and _PS2 decreased more significantly in f ₂ than f ₁₀₄ and wt with duration of HI exposure. Chl degraded more rapidly in the f ₂ than in either f ₁₀₄ or wt. Most sensitivity to photoinhibition was exhibited for f ₂, whereas there was little difference in response to HI between the f ₁₀₄ and wt. The highest de-epoxidation (DES) value at every time point of exposure to HI was measured for f ₂, 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 f ₁₀₄ both displayed larger amplitudes of both de-epoxidation lifetimes than f ₂. The difference between the final de-epoxidation state (DES = [Z + A]/[V + A + Z]) in the light compared to the dark expressed as DES for wt, f ₁₀₄, and f ₂ was 0.630, 0.623, and 0.420, respectively. The slow lifetime component and overall larger DES in the wt and f ₁₀₄ correlated with more photoprotection, as indicated by relatively higher F_v/F_m and _PS2, compared to the f ₂. 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 DES.     

Effects of Low Temperature on Photosynthesis in Flag Leaves of Rice (Oryza sativa L.)

After low temperature (16℃) treatment, the net photosynthetic rate, chlorophyll content and FBPase activity tended to decrease and ratio of chlorophyll a/b, stomatal resistance, sucrose and starch content tended to increase in rice flag leaves at heading stage. However, the Pi content and water potential did not show pronounced change. The flag leaf chloroplasts contained large starch grains after three days at low temperature. The recovery of net photosynthetic rate in the flag leaves which had recieved stress at 16℃ for three days and transferred to normal nature condition was gradually increased. It almost came up to the value of control after five days. However, the decrease in stomatal resistance was rapid. It was almost lowered to the value of control after one day. Under normal nature comdition for five days, the chlorophyll content and FBPase activity reached near to the value of control. Meanwhile, the ratio of chlorophyll a/b, the sucrose and starch content almost declined to the value of control. The large starch grain in flag leaf chloroplast also disappeared. According to the experimental results, we discussed the relationship between the above-mentioned various changes and net photosynthetic rate We suggested that the effect of low temperature on photosynthesis might be one of factors in yield-reduction of rice.     

超级杂交稻两优培九及其亲本低温强光适应特性

以超级杂交稻两优培九(培矮64S/9311)和母本培矮64S(PA64S)以及父本中籼9311为材料,以叶绿素荧光参数和活性氧代谢等指标研究生育后期亲本和后代对低温强光的适应特性。结果显示:低温强光处理后,与父母本相比,两优培九的叶绿素、PSⅡ原初光化学效率(Fv/Fm)和光化学猝灭系数(qP)和实际PSⅡ光能捕获的效率(φPSⅡ)的降低较少,说明在低温强光下,超级杂交稻两优培九吸收的光能较多地转化为化学能;同时两优培九的内源活性氧清除酶系如超氧化物歧化酶和过氧化物酶诱导的活性高,表现耐低温强光的特性,从而能有效清除叶片内的活性氧,因而膜脂过氧化较轻。试验结果表明:在生育后期超级杂交稻两优培九对低温强光适应的特性具有超双亲偏母本的现象。     

光照条件下低温对水稻籼粳亚种幼苗抗氧化物质含量的影响

与对低温不敏感的粳稻台北309和武育粳相比,对低温敏感的籼稻IR64、CA212和Pusa经光照条件下8℃处理后最大光合速率(Pmax)和原初光化学效率(Fv/Fm)下降较多,出现了O2-·、过氧化氢、氧化型谷胱甘肽(GSSG)和氧化型抗坏血酸(DHA)的大量累积,其GSSG和DHA的含量分别与叶绿素含量的下降呈极显著负相关,表明光照条件下低温胁迫下,还原态的谷胱甘肽(GSH)和抗坏血酸的再生受阻,不能有效地清除活性氧,导致其叶绿素含量降低和光合能力受抑,而汕优63的变化位于上述两种类型之间。其中AsA/DHA和GSH/GSSG的变化与叶绿素含量的变化呈极显著正相关。     

Chlorophyll-Deficient Mutant in Oak (Quercus petraea L.) Displays an Accelerated Hypersensitive-Like Cell Death and an Enhanced Resistance to Powdery Mildew Disease

Plants of the discovered chlorophyll-deficient mutant of oak (ML) display enhanced disease resistance to the fungus Erysiphe cichoracearum, causal agent of powdery mildew. Quantitative imaging of chlorophyll (Chl) fluorescence revealed that the net photosynthetic rate (P _N) declined progressively in both untreated and invaded ML leaves as well as in inoculated wild-type (WT) leaves. Images of non-photochemical fluorescence quenching (NPQ) in both untreated and infected mutant leaves suggested that the capacity of Calvin cycle had been reduced and that there was a complex metabolic heterogeneity within the ML leaf. The ML mutant accumulates reactive oxygen species, ROS (H₂O₂) from the oxidative burst followed by spontaneous cell death that mimic the hypersensitive response. Reduction in pathogen sporulation on ML leaves correlated with the accumulation of soluble saccharides and a more rapid induction of defence responses including expression of some defence proteins (-1,3-glucanase and chitinase). Unlike to WT plants, ML- conferred phenotype activates and/or de-represses multiple defence responses, making them more easily induced by pathogens.