Habibi Ghader, Ajory Neda
Department of Biology, Payame Noor University, PO BOX 19395-3697, Tehran, Iran.
J Plant Res. 2015 Nov;128(6):987-94. doi: 10.1007/s10265-015-0748-1. Epub 2015 Aug 28.
Photosynthesis is a biological process most affected by water deficit. Plants have various photosynthetic mechanisms that are matched to specific climatic zones. We studied the photosynthetic plasticity of C3 plants at water deficit using ecotypes of Marrubium vulgare L. from high (2,200 m) and low (1,100 m) elevation sites in the Mishou-Dagh Mountains of Iran. Under experimental drought, high-altitude plants showed more tolerance to water stress based on most of the parameters studied as compared to the low-altitude plants. Increased tolerance in high-altitude plants was achieved by lower levels of daytime stomatal conductance (g s) and reduced damaging effect on maximal quantum yield of photosystem II (PSII) (F v /F m ) coupled with higher levels of carotenoids and non-photochemical quenching (NPQ). High-altitude plants exhibited higher water use efficiency (WUE) than that in low-altitude plants depending on the presence of thick leaves and the reduced daytime stomatal conductance. Additionally, we have studied the oscillation in H(+) content and diel gas exchange patterns to determine the occurrence of C3 or weak CAM (Crassulacean acid metabolism) in M. vulgare through 15 days drought stress. Under water-stressed conditions, low-altitude plants exhibited stomatal conductance and acid fluctuations characteristic of C3 photosynthesis, though high-altitude plants exhibited more pronounced increases in nocturnal acidity and phosphoenolpyruvate carboxylase (PEPC) activity, suggesting photosynthetic flexibility. These results indicated that the regulation of carotenoids, NPQ, stomatal conductance and diel patterns of CO2 exchange presented the larger differences among studied plants at different altitudes and seem to be the protecting mechanisms controlling the photosynthetic performance of M. vulgare plants under drought conditions.
光合作用是受水分亏缺影响最大的生物过程。植物具有多种与特定气候带相匹配的光合机制。我们利用来自伊朗米舒 - 达格山脉高海拔（2200米）和低海拔（1100米）地区的夏至草生态型，研究了水分亏缺条件下C3植物的光合可塑性。在实验干旱条件下，与低海拔植物相比，基于所研究的大多数参数，高海拔植物对水分胁迫表现出更强的耐受性。高海拔植物通过较低的白天气孔导度（gs）以及对光系统II（PSII）最大量子产率（Fv/Fm）的损害作用降低，同时结合较高水平的类胡萝卜素和非光化学猝灭（NPQ），实现了耐受性增强。由于叶片较厚且白天气孔导度降低，高海拔植物表现出比低海拔植物更高的水分利用效率（WUE）。此外，我们研究了H(+)含量的振荡和昼夜气体交换模式，以确定在15天干旱胁迫下夏至草中C3或弱景天酸代谢（CAM）的发生情况。在水分胁迫条件下，低海拔植物表现出C3光合作用特有的气孔导度和酸度波动，而高海拔植物夜间酸度和磷酸烯醇式丙酮酸羧化酶（PEPC）活性的增加更为明显，表明其光合灵活性。这些结果表明，类胡萝卜素、NPQ、气孔导度和CO2交换的昼夜模式的调节在不同海拔的研究植物之间存在较大差异，似乎是干旱条件下控制夏至草植物光合性能的保护机制。
