Components of the photosynthetic electron transport chain in pea (Pisum sativum L.) leaves under in vivo conditions showed the following sensitivity to the inhibitory action of chromium(VI): intersystem electron transport > photosystem I > photosystem II. Inhibitory effects of chromium (VI) (K2Cr2O7, Cr) on the light reactions of photosynthesis were studied in vivo in Pisum sativum L. by using Multi-function Plant Efficiency Analyser (M-PEA-2). Photosynthetic parameters related to photosystem (PS) II, PSI and intersystem electron carriers were calculated from the light-induced kinetics of prompt chlorophyll a fluorescence (OJIP transient), delayed chlorophyll a fluorescence (DF), and 820 nm modulated reflection (MR). We showed that the I2 step of DF induction is sensitive to inhibition of the Q0 site of the cytochrome b6f complex. Such parameters as δRo of the JIP test related to the functional state of photosynthetic reactions beyond the PQ pool, Vred of the MR induction assigned to the overall rate of P700+ and plastocyanin reduction, and I2 step of the DF induction were significantly altered in the presence of low-dose Cr(VI). Moderate doses of Cr affected mainly PSI-related parameters including Vox and ΔMR parameters of the MR induction, whereas high-dose treatment influenced JIP test parameters φPo(= FV/FM) and ψEo related to PSII. The obtained results showed that the earliest Cr(VI) effect on the photosynthetic electron transport chain manifests itself by inhibition of the intersystem electron transport, rather, at the level of the cytochrome b6f complex. Inhibitory effects of Cr on PSI were more pronounced than those on PSII. Sensitivity of the used kinetic parameters toward the functional state of photosynthetic reactions makes this approach suitable for early diagnostics of toxic action of pollutants on plants.

中文翻译：

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铬对豌豆 (Pisum sativum L.) 光合电子传递的影响

体内条件下豌豆(Pisum sativum L.)叶片的光合电子传递链组分对铬(VI)的抑制作用表现出以下敏感性：系统间电子传递>光系统I>光系统II。使用多功能植物效率分析仪（M-PEA-2）在体内研究了铬（VI）（K2Cr2O7，Cr）对豌豆光合作用光反应的抑制作用。与光系统​​ (PS) II、PSI 和系统间电子载体相关的光合参数是根据瞬发叶绿素 a 荧光 (OJIP 瞬态)、延迟叶绿素 a 荧光 (DF) 和 820 nm 调制反射 (MR) 的光诱导动力学计算的。我们发现 DF 诱导的 I2 步骤对抑制细胞色素 b6f 复合物的 Q0 位点敏感。JIP 测试的 δRo 等参数与 PQ 池以外的光合反应的功能状态有关，MR 诱导的 Vred 分配给 P700+ 和质体蓝素还原的总体速率，以及 DF 诱导的 I2 步骤在存在的情况下显着改变低剂量 Cr(VI)。中等剂量的 Cr 主要影响 PSI 相关参数，包括 MR 诱导的 Vox 和 ΔMR 参数，而高剂量处理影响与 PSII 相关的 JIP 测试参数 φPo(= FV/FM) 和 ψEo。所得结果表明，Cr(VI) 对光合电子传递链的最早影响表现为抑制系统间电子传递，而不是在细胞色素 b6f 复合物的水平上。Cr对PSI的抑制作用比对PSII的抑制作用更明显。