Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 430074, China.
Hubei Key Laboratory of Wetland Evolution & Ecological Restoration, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 430074, China.
Photosynth Res. 2018 Nov;138(2):219-232. doi: 10.1007/s11120-018-0568-y. Epub 2018 Aug 4.
The freshwater macrophyte, Ottelia alismoides, is a bicarbonate user performing C4 photosynthesis in the light, and crassulacean acid metabolism (CAM) when acclimated to low CO. The regulation of the three mechanisms by CO concentration was studied in juvenile and mature leaves. For mature leaves, the ratios of phosphoenolpyruvate carboxylase (PEPC) to ribulose-bisphosphate carboxylase/oxygenase (Rubisco) are in the range of that of C4 plants regardless of CO concentration (1.5-2.5 at low CO, 1.8-3.4 at high CO). In contrast, results for juvenile leaves suggest that C4 is facultative and only present under low CO. pH-drift experiments showed that both juvenile and mature leaves can use bicarbonate irrespective of CO concentration, but mature leaves have a significantly greater carbon-extracting ability than juvenile leaves at low CO. At high CO, neither juvenile nor mature leaves perform CAM as indicated by lack of diurnal acid fluctuation. However, CAM was present at low CO, though the fluctuation of titratable acidity in juvenile leaves (15-17 µequiv g FW) was slightly but significantly lower than in mature leaves (19-25 µequiv g FW), implying that the capacity to perform CAM increases as leaves mature. The increased CAM activity is associated with elevated PEPC activity and large diel changes in starch content. These results show that in O. alismoides, carbon-dioxide concentrating mechanisms are more effective in mature compared to juvenile leaves, and C4 is facultative in juvenile leaves but constitutive in mature leaves.
淡水大型植物眼子菜是一种碳酸氢盐利用者，在光照下进行 C4 光合作用，在适应低 CO2 时进行景天酸代谢（CAM）。在幼叶和成熟叶中研究了 CO 浓度对这三种机制的调节。对于成熟叶，磷酸烯醇丙酮酸羧化酶（PEPC）与核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的比例无论 CO 浓度如何（低 CO 时为 1.5-2.5，高 CO 时为 1.8-3.4）都在 C4 植物的范围内。相比之下，幼叶的结果表明 C4 是兼性的，仅在低 CO 下存在。pH 漂移实验表明，幼叶和成熟叶都可以利用碳酸氢盐，而与 CO 浓度无关，但成熟叶在低 CO 下的碳提取能力明显大于幼叶。在高 CO 下，幼叶和成熟叶都没有表现出 CAM，表明没有昼夜酸波动。然而，在低 CO 下存在 CAM，尽管幼叶（15-17 μequiv g FW）可滴定酸度的波动略低于成熟叶（19-25 μequiv g FW），这表明随着叶片成熟，CAM 的能力增加。CAM 活性的增加与 PEPC 活性的升高和淀粉含量的昼夜巨大变化有关。这些结果表明，在眼子菜中，与幼叶相比，二氧化碳浓缩机制在成熟叶中更有效，并且 C4 在幼叶中是兼性的，但在成熟叶中是组成型的。
