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Crassulacean acid metabolism-cycling in Euphorbia milii

机译：大戟小循环中的十字绣花酸代谢

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Crassulacean acid metabolism (CAM) occurs in many Euphorbiaceae, particularly Euphorbia, a genus with C3 and C4 species as well. With the aim of contributing to our knowledge of the evolution of CAM in this genus, this study examined the possible occurrence of CAM in Euphorbia milii, a species with leaf succulence and drought tolerance suggestive of this carbon fixation pathway. Leaf anatomy consisted of a palisade parenchyma, a spongy parenchyma and a bundle sheath with chloroplasts, which indicates the possible functioning of C2 photosynthesis. No evidence of nocturnal CO2 fixation was found in plants of E. milii either watered or under drought; watered plants had a low nocturnal respiration rate (R). After 12 days without watering, the photosynthetic rate (PN) decreased 85 % and nocturnal R was nearly zero. Nocturnal H+ accumulation (ΔH+) in watered plants was 18 ± 2 (corresponding to malate) and 18 ± 4 (citrate) μmol H+ (g fresh mass)?1. Respiratory CO2 recycling through acid synthesis contributed to a night-time water saving of 2 and 86 % in watered plants and plants under drought, respectively. Carbon isotopic composition (δ13C) was ?25.2 ± 0.7 ‰ in leaves and ?24.7 ± 0.1 ‰ in stems. Evidence was found for the operation of weak CAM in E. milii, with statistically significant ΔH+, no nocturnal CO2 uptake and values of δ13C intermediate between C3 and constitutive CAM plants; ΔH+ was apparently attributable to both malate and citrate. The results suggest that daily malate accumulation results from recycling of part of the nocturnal respiratory CO2, which helps explain the occurrence of an intermediate value of leaf δ13C. Euphorbia milii can be considered as a CAM-cycling species. The significance of the operation of CAM-cycling in E. milii lies in water conservation, rather than carbon acquisition. The possible occurrence of C2 photosynthesis merits research.
机译：大戟科，特别是大戟属，也具有C 3 和C 4 属的大戟科植物发生了新陈代谢。为了有助于我们了解该属中CAM的进化，本研究研究了在大戟属中的CAM可能发生，该种植物具有叶片多汁和耐旱性，提示该碳固定途径。叶片解剖结构由栅栏薄壁组织，海绵薄壁组织和具有叶绿体的束鞘组成，表明C 2 光合作用的可能功能。在水和干旱条件下，E.milii.E.milii植物均未发现夜间固定CO 2 的证据。浇水的植物夜间呼吸率（R）低。在不浇水的12天后，光合速率（P N ）下降了85％，夜间R几乎为零。浇灌植物的夜间H + 累积量（ΔH + ）为18±2（对应苹果酸）和18±4（柠檬酸）μmolH + （每克新鲜质量）？1 。通过酸合成进行的呼吸CO 2 循环利用，在浇水植物和干旱植物中夜间节水分别达到2％和86％。叶片中碳同位素组成（δ 13 C）为？25.2±0.7‰，茎中为？24.7±0.1‰。有证据表明，在弱肠埃希菌中存在弱CAM的操作，具有统计学上显着的ΔH + ，无夜间CO 2 摄取和δ 13 3 和组成型CAM植物之间的> C中间体; ΔH + 显然归因于苹果酸和柠檬酸。结果表明，夜间呼吸中CO 2 的循环利用导致苹果酸的每日积累，这有助于解释叶片δ 13 C中间值的发生。大戟一品红可以被认为是一种CAM循环物种。大肠杆菌中的CAM循环操作的意义在于节水，而不是碳的获取。 C 2 光合作用的可能发生值得研究。

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    《AoB PLANTS》 |2013年第v1期|共页
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    Ana Herrera;

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  • 中图分类 植物学;
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  • 入库时间 2022-08-18 07:58:58

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