Wu Pei, Ma Yadong, Ahammed Golam Jalal, Hao Baoyu, Chen Jingyi, Wan Wenliang, Zhao Yanhui, Cui Huimei, Xu Wei, Cui Jinxia, Liu Huiying
Department of Horticulture, Agricultural College, Shihezi University, Shihezi, China.
The Key Laboratory of Special Fruits and Vegetables Cultivation Physiology and Germplasm Resources Utilization in Xinjiang Production and Construction Group, Shihezi University, Shihezi, China.
Front Plant Sci. 2022 Nov 3;13:1029854. doi: 10.3389/fpls.2022.1029854. eCollection 2022.
In this study, the differences in chlorophyll fluorescence transient (OJIP) and modulated 820 nm reflection (MR) of cucumber leaves were probed to demonstrate an insight into the precise influence of melatonin (MT) on cucumber photosystems under low temperature stress. We pre-treated cucumber seedlings with different levels of MT (0, 25, 50, 100, 200, and 400 μmol · L) before imposing low temperature stress (10 °C/6 °C). The results indicated that moderate concentrations of MT had a positive effect on the growth of low temperature-stressed cucumber seedlings. Under low temperature stress conditions, 100 μmol · L (MT 100) improved the performance of the active photosystem II (PSII) reaction centers (PIabs), the oxygen evolving complex activity (OEC centers) and electron transport between PSII and PSI, mainly by decreasing the L-band, K-band, and G-band, but showed differences with different duration of low temperature stress. In addition, these indicators related to quantum yield and energy flux of PSII regulated by MT indicated that MT (MT 100) effectively protected the electron transport and energy distribution in the photosystem. According to the results of ≥ 1 and MR signals, MT also affected PSI activity. MT 100 decreased the minimal value of MR/MR and the oxidation rate of plastocyanin (PC) and PSI reaction center (P700) ( ), while increased △MR/MR and deoxidation rates of PC and P ( ). The loss of the slow phase of MT 200 and MT 400-treated plants in the MR kinetics was due to the complete prevention of electron movement from PSII to re-reduce the PC and P700 . These results suggest that appropriate MT concentration (100 μmol · L) can improve the photosynthetic performance of PS II and electron transport from primary quinone electron acceptor (Q) to secondary quinone electron acceptor (Q), promote the balance of energy distribution, strengthen the connectivity of PSI and PSII, improve the electron flow of PSII Q to PC and P from reaching PSI by regulating multiple sites of electron transport chain in photosynthesis, and increase the pool size and reduction rates of PSI in low temperature-stressed cucumber plants, All these modifications by MT 100 treatment promoted the photosynthetic electron transfer smoothly, and further restored the cucumber plant growth under low temperature stress. Therefore, we conclude that spraying MT at an appropriate concentration is beneficial for protecting the photosynthetic electron transport chain, while spraying high concentrations of MT has a negative effect on regulating the low temperature tolerance in cucumber.
在本研究中，探究了黄瓜叶片叶绿素荧光瞬变（OJIP）和调制820 nm反射（MR）的差异，以深入了解褪黑素（MT）在低温胁迫下对黄瓜光系统的精确影响。在施加低温胁迫（10℃/6℃）之前，我们用不同浓度的MT（0、25、50、100、200和400 μmol·L）预处理黄瓜幼苗。结果表明，中等浓度的MT对低温胁迫下黄瓜幼苗的生长有积极影响。在低温胁迫条件下，100 μmol·L（MT 100）主要通过降低L波段、K波段和G波段，改善了活性光系统II（PSII）反应中心（PIabs）的性能、放氧复合体活性（OEC中心）以及PSII与PSI之间的电子传递，但在不同低温胁迫持续时间下表现出差异。此外，这些与MT调节的PSII量子产率和能量通量相关的指标表明，MT（MT 100）有效地保护了光系统中的电子传递和能量分布。根据≥1和MR信号的结果，MT也影响PSI活性。MT 100降低了MR/MR的最小值以及质体蓝素（PC）和PSI反应中心（P700）的氧化速率（），同时增加了△MR/MR以及PC和P的脱氧速率（）。MT 200和MT 400处理的植株在MR动力学中慢相的丧失是由于完全阻止了电子从PSII移动以重新还原PC和P700。这些结果表明，适当的MT浓度（100 μmol·L）可以提高PS II的光合性能以及从初级醌电子受体（Q）到次级醌电子受体（Q）的电子传递，促进能量分布平衡，加强PSI和PSII的连接性，通过调节光合作用电子传递链的多个位点，改善PSII从Q到PC和P到PSI的电子流，增加低温胁迫下黄瓜植株中PSI的库大小和还原速率，MT 100处理的所有这些改变促进了光合电子传递的顺利进行，并进一步恢复了低温胁迫下黄瓜植株的生长。因此，我们得出结论，喷洒适当浓度的MT有利于保护光合电子传递链，而喷洒高浓度的MT对调节黄瓜的低温耐受性有负面影响。
