Ogawa Takako, Sonoike Kintake
Faculty of Education and Integrated Arts and Sciences, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo, 162-8480 Japan Japan Society for the Promotion of Science, Japan.
Faculty of Education and Integrated Arts and Sciences, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo, 162-8480 Japan
Plant Cell Physiol. 2016 Mar;57(3):558-67. doi: 10.1093/pcp/pcw010. Epub 2016 Feb 8.
Estimation of photosynthesis by Chl fluorescence measurement of cyanobacteria is always problematic due to the interference from respiratory electron transfer and from phycocyanin fluorescence. The interference from respiratory electron transfer could be avoided by the use of DCMU or background illumination by blue light, which oxidizes the plastoquinone pool that tends to be reduced by respiration. On the other hand, the precise estimation of photosynthesis in cells with a different phycobilisome content by Chl fluorescence measurement is difficult. By subtracting the basal fluorescence due to the phycobilisome and PSI, it becomes possible to estimate the precise maximum quantum yield of PSII in cyanobacteria. Estimated basal fluorescence accounted for 60% of the minimum fluorescence, resulting in a large difference between the 'apparent' yield and 'true' yield under high phycocyanin conditions. The calculated value of the 'true' maximum quantum yield of PSII was around 0.8, which was similar to the value observed in land plants. The results suggest that the cause of the apparent low yield reported in cyanobacteria is mainly ascribed to the interference from phycocyanin fluorescence. We also found that the 'true' maximum quantum yield of PSII decreased under nitrogen-deficient conditions, suggesting the impairment of the PSII reaction center, while the 'apparent' maximum quantum yield showed a marginal change under the same conditions. Due to the high contribution of phycocyanin fluorescence in cyanobacteria, it is essential to eliminate the influence of the change in phycocyanin content on Chl fluorescence measurement and to evaluate the 'true' photosynthetic condition.
通过叶绿素荧光测量来估算蓝细菌的光合作用一直存在问题，这是由于呼吸电子传递和藻蓝蛋白荧光的干扰。呼吸电子传递的干扰可以通过使用二氯苯基二甲基脲（DCMU）或蓝光背景照明来避免，蓝光可氧化往往因呼吸作用而被还原的质体醌库。另一方面，通过叶绿素荧光测量精确估算不同藻胆体含量细胞中的光合作用是困难的。通过减去藻胆体和光系统I（PSI）产生的基础荧光，就有可能估算蓝细菌中光系统II（PSII）精确的最大量子产率。估算的基础荧光占最小荧光的60%，这导致在高藻蓝蛋白条件下“表观”产率和“真实”产率之间存在很大差异。PSII“真实”最大量子产率的计算值约为0.8，这与陆地植物中观察到的值相似。结果表明，蓝细菌中报道的表观低产率的原因主要归因于藻蓝蛋白荧光的干扰。我们还发现，在缺氮条件下PSII的“真实”最大量子产率降低，这表明PSII反应中心受损，而在相同条件下“表观”最大量子产率仅略有变化。由于藻蓝蛋白荧光在蓝细菌中的贡献很大，消除藻蓝蛋白含量变化对叶绿素荧光测量的影响并评估“真实”光合状况至关重要。
