Rock C D, Bowlby N R, Hoffmann-Benning S, Zeevaart J A
Michigan State University-Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824-1312.
Plant Physiol. 1992 Dec;100(4):1796-801. doi: 10.1104/pp.100.4.1796.
It has been shown that the aba mutant of Arabidopsis thaliana (L.) Heynh. is impaired in epoxy-carotenoid biosynthesis and accumulates the epoxy-carotenoid precursor, zeaxanthin (C.D. Rock, J.A.D. Zeevaart [1991] Proc Natl Acad Sci USA 88: 7496-7499). In addition to providing conclusive evidence for the indirect pathway of abscisic acid biosynthesis from epoxy-carotenoids, the aba mutation offers a powerful means to study the function of xanthophylls (oxygenated carotenoids) in photosynthesis. We measured in vivo the chlorophyll (Chl) fluorescence parameters F(o) (initial), F(m) (maximum), F(v) (variable = F(m) - F(o)), and t((1/2)) (half-rise time of fluorescence induction) of wild-type (WT) and three allelic aba mutants. The mutant genotypes had significantly lower F(o) and F(m) values relative to those of WT. The F(v)/F(m) ratio and t((1/2)), which are parameters affected by photochemical efficiency, photosystem II (PSII), and plastoquinone pool sizes, were similar in the aba alleles and WT. Because the aba genotypes accumulate high levels of zeaxanthin, which is involved in nonphotochemical quenching of Chl fluorescence, we propose that the reduced fluorescence yields in the aba genotypes are a consequence of the accumulated zeaxanthin. Measurement of PSII oxygen evolution rates in isolated thylakoid membranes of WT and aba-4 confirmed that quantum efficiency was not altered in aba-4 but indicated that the mutant had reduced PSII activity in vitro. Electron microscopy revealed an abnormal chloroplast ultrastructure in the aba plants: the mutants had significantly fewer thylakoid lamellae per granum stack but significantly more grana per chloroplast, as well as more chloroplasts per cell than WT. Immunoblot analysis established that aba-4 had normal levels of the Chl a/b-binding core polypeptide of PSII (CP29) and the PSII light-harvesting Chl a/b-binding complex. These results provide evidence for the role of zeaxanthin in nonphotochemical fluorescence quenching and suggest involvement of epoxy-carotenoids and/or zeaxanthin in thylakoid stacking and PSII activity.
研究表明，拟南芥（Arabidopsis thaliana (L.) Heynh.）的aba突变体在环氧类胡萝卜素生物合成方面存在缺陷，并积累了环氧类胡萝卜素前体玉米黄质（C.D. Rock, J.A.D. Zeevaart [1991] Proc Natl Acad Sci USA 88: 7496 - 7499）。除了为脱落酸从环氧类胡萝卜素生物合成的间接途径提供确凿证据外，aba突变还为研究叶黄素（氧化类胡萝卜素）在光合作用中的功能提供了有力手段。我们在体内测量了野生型（WT）和三个等位基因aba突变体的叶绿素（Chl）荧光参数F(o)（初始值）、F(m)（最大值）、F(v)（可变值 = F(m) - F(o)）和t((1/2))（荧光诱导的半上升时间）。相对于野生型，突变体基因型的F(o)和F(m)值显著更低。F(v)/F(m)比值和t((1/2))，这两个受光化学效率、光系统II（PSII）和质体醌库大小影响的参数，在aba等位基因和野生型中相似。由于aba基因型积累了高水平的参与叶绿素荧光非光化学猝灭的玉米黄质，我们推测aba基因型中荧光产量降低是积累的玉米黄质的结果。对野生型和aba - 4分离类囊体膜中PSII放氧速率的测量证实，aba - 4中的量子效率没有改变，但表明该突变体在体外PSII活性降低。电子显微镜显示aba植株中叶绿体超微结构异常：突变体每个基粒堆叠中的类囊体片层显著减少，但每个叶绿体中的基粒显著增多，并且每个细胞中的叶绿体比野生型更多。免疫印迹分析表明aba - 4中PSII的叶绿素a/b结合核心多肽（CP29）和PSII捕光叶绿素a/b结合复合体水平正常。这些结果为玉米黄质在非光化学荧光猝灭中的作用提供了证据，并表明环氧类胡萝卜素和/或玉米黄质参与类囊体堆叠和PSII活性。
