Bekki Sae, Suetsugu Kenji, Kobayashi Koichi
Department of Biology, Graduate School of Science, Osaka Metropolitan University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531, Japan.
Department of Biology, Graduate School of Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, Hyogo, 657-8501, Japan.
J Plant Res. 2025 Mar;138(2):323-336. doi: 10.1007/s10265-024-01608-2. Epub 2024 Dec 24.
Crassulacean acid metabolism (CAM), a specialized mode of photosynthetic carbon assimilation characterized by nocturnal fixation of atmospheric CO and vacuolar malic acid storage, is found in a wide variety of vascular plant species, mainly those inhabiting water-limited environments. Identifying and characterizing diverse CAM species enhances our understanding of the physiological, ecological, and evolutionary significance of CAM photosynthesis. In this study, we examined the effect of CO elimination on chlorophyll fluorescence-based photosynthetic parameters in two constitutive CAM Kalanchoe species and six orchids. In CAM-performing Kalanchoe species, the effective quantum yield of photosystem II showed no change in response to CO elimination during the daytime but decreased with CO elimination at dusk. We applied this method to reveal the photosynthetic mode of epiphytic orchids and found that Gastrochilus japonicus, Oberonia japonica, and Bulbophyllum inconspicuum, but not B. drymoglossum, are constitutive CAM plants, which were also confirmed by malate determination. Our data propose a novel approach to identify and characterize CAM plants without labor-intensive experimental procedures. Although B. drymoglossum leaves had relatively high malate content, they did not depend on it to perform photosynthesis even under water-deficient or increased light conditions. Anatomical comparisons revealed a notable difference in leaf structure between B. drymoglossum and B. inconspicuum; B. drymoglossum leaves possess large water storage tissue internally, unlike B. inconspicuum leaves, which develop pseudobulbs. Our findings suggest different evolutionary adaptations to water deficit between closely related B. drymoglossum and B. inconspicuum.
景天酸代谢（CAM）是一种特殊的光合碳同化模式，其特征为夜间固定大气中的二氧化碳并在液泡中储存苹果酸，在多种维管植物物种中都有发现，主要是那些生活在水分有限环境中的植物。识别和表征不同的景天酸代谢物种有助于我们理解景天酸代谢光合作用的生理、生态和进化意义。在本研究中，我们研究了去除二氧化碳对两种组成型景天酸代谢的长寿花属植物和六种兰花基于叶绿素荧光的光合参数的影响。在进行景天酸代谢的长寿花属植物中，光系统II的有效量子产量在白天对去除二氧化碳没有反应，但在黄昏时随着二氧化碳的去除而降低。我们应用这种方法来揭示附生兰花的光合模式，发现日本盆距兰、日本鸢尾兰和微小石豆兰是组成型景天酸代谢植物，而毛唇石豆兰不是，这也通过苹果酸测定得到了证实。我们的数据提出了一种无需繁琐实验程序即可识别和表征景天酸代谢植物的新方法。尽管毛唇石豆兰的叶子苹果酸含量相对较高，但即使在缺水或光照增加的条件下，它们也不依赖苹果酸进行光合作用。解剖学比较显示毛唇石豆兰和微小石豆兰的叶片结构存在显著差异；毛唇石豆兰的叶子内部有大量储水组织，而微小石豆兰的叶子则不同，它会形成假鳞茎。我们的研究结果表明，亲缘关系密切的毛唇石豆兰和微小石豆兰对水分亏缺有不同的进化适应。
