Sudderth Erika A, Muhaidat Riyadh M, McKown Athena D, Kocacinar Ferit, Sage Rowan F
Department of Organismic and Evolutionary Biology, Harvard University, Biological Laboratories, 16 Divinity Ave., Cambridge, MA 02138 11, USA.
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S1A1, Canada.
Funct Plant Biol. 2007 Mar;34(2):118-129. doi: 10.1071/FP06263.
Flaveria (Asteraceae) is one of the few genera known to contain both C and C species, in addition to numerous biochemically-intermediate species. C-C and C-like intermediate photosynthesis have arisen more than once in different phylogenetic clades of Flaveria. Here, we characterise for the first time the photosynthetic pathway of the recently described species Flaveria kochiana B.L. Turner. We examined leaf anatomy, activity and localisation of key photosynthetic enzymes, and gas exchange characteristics and compared these trait values with those from related C and C-like Flaveria species. F. kochiana has Kranz anatomy that is typical of other C Flaveria species. As in the other C lineages within the Flaveria genus, the primary decarboxylating enzyme is NADP-malic enzyme. Immunolocalisation of the major C cycle enzymes, PEP carboxylase and pyruvate, orthophosphate dikinase, were restricted to the mesophyll, while Rubisco was largely localised to the bundle sheath. Gas exchange analysis demonstrated that F. kochiana operates a fully functional C pathway with little sensitivity to ambient oxygen levels. The CO compensation point (2.2 µbar) was typical for C species, and the O-response of the CO compensation point was the same as the C species F. trinervia. Notably, F. vaginata (B.L. Robinson & Greenman), a putative C-like species that is the nearest relative of F. kochiana, had an identical response of the CO compensation point to O. Furthermore, F. vaginata, exhibited a carbon isotope ratio (-15.4‰) similar to C species including F. australasica Hooker, F. trinervia Spreng. C. Mohr and the newly characterised F. kochiana. F. vaginata could be considered a C species, but additional studies are necessary to confirm this hypothesis. In addition, our results show that F. kochiana uses an efficient C cycle, with the highest initial slope of the A/C curve of any C Flaveria species.
黄缨菊属（菊科）是少数已知既包含C₄和C₃物种，又有众多生化中间类型物种的属之一。C₄ - C₃和类似C₄的中间型光合作用在黄缨菊属的不同系统发育分支中不止一次出现。在此，我们首次对最近描述的物种科氏黄缨菊（Flaveria kochiana B.L. Turner）的光合途径进行了表征。我们研究了叶片解剖结构、关键光合酶的活性和定位以及气体交换特征，并将这些性状值与相关的C₄和类似C₄的黄缨菊属物种进行了比较。科氏黄缨菊具有典型的其他C₄黄缨菊属物种的花环结构。与黄缨菊属内的其他C₄谱系一样，主要的脱羧酶是NADP - 苹果酸酶。主要C₄循环酶磷酸烯醇式丙酮酸羧化酶和丙酮酸，磷酸双激酶的免疫定位仅限于叶肉，而核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）主要定位于维管束鞘。气体交换分析表明，科氏黄缨菊运行着一个功能完全正常的C₄途径，对环境氧气水平几乎不敏感。二氧化碳补偿点（2.2微巴）是C₄物种的典型值，并且二氧化碳补偿点对氧气的响应与C₄物种三脉黄缨菊（F. trinervia）相同。值得注意的是，与科氏黄缨菊亲缘关系最近的假定类似C₄的物种阴道黄缨菊（F. vaginata (B.L. Robinson & Greenman)）对氧气的二氧化碳补偿点响应相同。此外，阴道黄缨菊的碳同位素比值（-15.4‰）与包括澳大拉西亚黄缨菊（F. australasica Hooker）、三脉黄缨菊（F. trinervia Spreng. C. Mohr）和新表征的科氏黄缨菊在内的C₄物种相似。阴道黄缨菊可被视为C₄物种，但需要进一步研究来证实这一假设。此外，我们的结果表明，科氏黄缨菊利用了一个高效的C₄循环，其A/C曲线的初始斜率是所有C₄黄缨菊属物种中最高的。
