Ayyaz Ahsan, Amir Misbah, Umer Sarah, Iqbal Muhammad, Bano Hussan, Gul Hafiza Saima, Noor Yamna, Kanwal Aneela, Khalid Ayesha, Javed Muhammad, Athar Habib R, Zafar Zafar Ullah, Farooq Muhammad Ahsan
Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan, 60000, Pakistan.
Department of Botany, University of Okara, 56300, Pakistan.
Heliyon. 2020 Jul 14;6(7):e04364. doi: 10.1016/j.heliyon.2020.e04364. eCollection 2020 Jul.
Chromium toxicity is considered as a major problem for agricultural soil that reduced crop productivity by affecting photosynthetic tissues. Exogenous application of melatonin can alleviate the adverse effects of chromium toxicity on plant growth. However, little is known about its effect on thylakoidal protein complexes responsible for conversion of solar energy to biochemical energy. Chlorophyll fluorescence transients considered one of the best non-invasive and rapid method for the evaluation of photosynthetic (Photosystem II) efficiency of plants and plant health under environmental stress conditions. In the present study, three-week old plants of two canola cultivars AC-Excel and DGL were applied to melatonin (0, 1, 5, 10 μM) when grown under chromium stress (0, 50 and 100 μM) for further two weeks. Chromium stress reduced the growth (fresh and dry weights of shoots and roots) of both canola cultivars and exogenous application of 5 and 10 μM melatonin improved the growth of canola at 50 or 100 μM chromium stress. This improvement was greater in cv DGL than in AC-Excel. Increasing chromium decreased the photosynthetic pigments (chlorophyll and chlorophyll ). However, 5 and 10 μM melatonin application improved chlorophyll a at 50 μM chromium stress. Structural stability and efficiency of photosystem II (PSII) measured as performance index (PI) and ratios of fluorescence (Fv/Fm, Fv/Fo) Fv decreased due to chromium stress. JIP-test parameters showed that chromium stress increased the absorption and trapping fluxes with decrease in electron transport fluxes which caused the damage to reaction centers (RC), detachment of oxygen evolving complex (OEC) from RC or inefficiency of electron transfer from OEC to RC. Such adverse effects were greater in cv AC-Excel. However exogenous application of melatonin improved PI, electron transport per reaction center (ET/RC), reduced variable fluorescence at J step (V) reflecting melatonin protected PSII from chromium stress induced damage by protecting OEC. Thus, OJIP fluorescence transients are quite helpful for understanding the intersystem electron transport beyond photosystem II in canola cultivars due to melatonin application under chromium stress.
Exogenous application of melatonin alleviated toxic effects of chromium on plant growth of canola by modulating photosynthesis, enhanced photosystem II efficiency and regulation of electron transport flux to protect photo-inhibition of PSII from oxidative damage.
铬毒性被认为是农业土壤的一个主要问题，它通过影响光合组织降低了作物生产力。外源施用褪黑素可以减轻铬毒性对植物生长的不利影响。然而，关于其对负责将太阳能转化为生化能量的类囊体蛋白复合物的影响知之甚少。叶绿素荧光瞬变被认为是在环境胁迫条件下评估植物光合（光系统II）效率和植物健康状况的最佳非侵入性快速方法之一。在本研究中，两个油菜品种AC-Excel和DGL的三周龄植株在铬胁迫（0、50和100μM）下生长两周时施用褪黑素（0、1、5、10μM）。铬胁迫降低了两个油菜品种的生长（地上部和根部的鲜重和干重），外源施用5和10μM褪黑素改善了50或100μM铬胁迫下油菜的生长。这种改善在cv DGL中比在AC-Excel中更大。铬含量增加会降低光合色素（叶绿素a和叶绿素b）。然而，施用5和10μM褪黑素在50μM铬胁迫下提高了叶绿素a含量。作为性能指标（PI）以及荧光比率（Fv/Fm、Fv/Fo）测量的光系统II（PSII）的结构稳定性和效率由于铬胁迫而降低。JIP测试参数表明，铬胁迫增加了吸收和捕获通量，同时电子传递通量减少，这导致反应中心（RC）受损、氧气释放复合物（OEC）与RC分离或OEC向RC的电子传递效率低下。这种不利影响在cv AC-Excel中更大。然而，外源施用褪黑素提高了PI、每个反应中心的电子传递（ET/RC），降低了J步骤的可变荧光（V），这表明褪黑素通过保护OEC保护PSII免受铬胁迫诱导的损伤。因此，OJIP荧光瞬变对于理解铬胁迫下由于施用褪黑素而在油菜品种中光系统II之外的系统间电子传递非常有帮助。
外源施用褪黑素通过调节光合作用、提高光系统II效率和调节电子传递通量来减轻铬对油菜植物生长的毒性作用，从而保护PSII的光抑制免受氧化损伤。
