Previous studies of Crassulacean acid metabolism (CAM) pathway during stress have been directed at individual drought and salinity stress, here, we studied the effects of a combination of drought and salt on CAM expression, chlorophyll fluorescence and antioxidant parameters in the C3 -CAM facultative Sedum album and C4 -CAM facultative Portulaca oleracea plants. While salinity alone was not able to induce functional CAM expression in P. oleracea leaves, we showed that salinity induced low level of nocturnal acid accumulation in S. album species. After 20 days (d) of exposure to the combination of simultaneous salt and drought stress, P. oleracea plants exhibited more resistance to photoinhibition as compared to S. album plants. The decrease of maximum quantum yield (Fv /Fm ) in S. album leaves under combined stress was in parallel with the largest suppression of CAM expression of > 50%, probably displaying the withdrawal of functional CAM back to C3 pathway. However, under drought treatment alone, S. album plants exhibited higher photosynthetic flexibility, which was associated with the up-regulation of antioxidant enzymes activities and maintenance of glutathione (GSH) pool, and consequently higher photochemical functioning. The levels of nitric oxide (NO) correlated well with CAM expression, which was observed only in S. album, suggesting that NO acts in a different way in C3 and C4 species during CAM induction. Additionally, in both species, over the course of CAM induction, the changes in CAM expression parameters exhibited a similar pattern to that of antioxidant capacity and photochemical functioning parameters. This article is protected by copyright. All rights reserved.

中文翻译：

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复合胁迫下景天和马齿苋CAM表达、光化学和抗氧化反应的比较

先前对胁迫期间景天酸代谢 (CAM) 途径的研究针对个体干旱和盐分胁迫，在这里，我们研究了干旱和盐分组合对 C3-CAM 兼性中 CAM 表达、叶绿素荧光和抗氧化参数的影响景天和 C4 -CAM 兼性马齿苋植物。虽然单独的盐度不能在 P. oleracea 叶子中诱导功能性 CAM 表达，但我们表明盐度在 S. album 物种中诱导了低水平的夜间酸积累。在同时暴露于盐和干旱胁迫的组合下 20 天 (d) 后，与 S.album 植物相比，P.oleracea 植物对光抑制表现出更多的抗性。S 中最大量子产率 (Fv /Fm ) 的降低。组合胁迫下的专辑叶与 CAM 表达的最大抑制 > 50% 平行，可能显示功能性 CAM 撤回 C3 途径。然而，在单独的干旱处理下，S. album 植物表现出更高的光合灵活性，这与抗氧化酶活性的上调和谷胱甘肽 (GSH) 库的维持有关，因此具有更高的光化学功能。一氧化氮 (NO) 的水平与 CAM 表达密切相关，这仅在 S.album 中观察到，表明 NO 在 CAM 诱导期间在 C3 和 C4 物种中以不同的方式起作用。此外，在这两个物种中，在 CAM 诱导过程中，CAM 表达参数的变化表现出与抗氧化能力和光化学功能参数相似的模式。本文受版权保护。版权所有。