Abstract

Melatonin plays an important role in the enhancement of plant tolerance to drought stress. The underlying mechanisms of this melatonin-induced protection of the photosynthetic apparatus against drought stress are still not fully understood in maize (Zea mays L.). This study investigated the effects of 100 and 200 μM exogenous melatonin additions on the photosynthetic electron transport process in maize seedlings under drought stress. The chlorophyll a fluorescence transient (OJIP) and modulated 820 nm reflection (MR) analysis showed that drought stress damaged the donor and acceptor side of photosystem II (PSII). Furthermore, the function of PSII reaction centers and the quantum yields of PSI and PSII were significant reduced. These fluorescence parameters were restored in melatonin-treated plants. Energy conversion analysis indicated that melatonin-treated plants maintained a stronger ability to ensure high photosynthetic capacity, as evidenced by higher PSI photochemical quantum yield Y(I) and PSII photochemical quantum yield Y(II). Melatonin treatment decreased the regulated energy dissipation Y(NPQ) and non-regulated energy dissipation Y(NO) in PSII. Moreover, melatonin treatment mitigated the limitations of both the acceptor-side and donor-side of PSI under drought stress, as indicated by lower PSI acceptor side limitation Y(NA) and PSI donor side limitation Y(ND). In addition, 100 μM melatonin was the more effective concentration to alleviate the damage to the photosynthetic apparatus. Thus, exogenous melatonin alleviated the drought stress-induced damage of the photosynthetic apparatus in maize by improving the photosynthetic electron transport efficiency between both photosystems and by enhancing the quantum yields of PSI and PSII photochemistry.

中文翻译：

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褪黑素减轻了干旱对玉米幼苗光合装置的伤害

摘要

褪黑素在增强植物对干旱胁迫的耐受性中起重要作用。在玉米中（玉米（Zea mays L.）），褪黑素诱导的光合装置抗干旱胁迫的潜在机制仍未被完全理解。这项研究调查了100和200μM外源褪黑素添加对干旱胁迫下玉米幼苗光合电子传递过程的影响。叶绿素a荧光瞬态（OJIP）和820 nm反射调制（MR）分析表明，干旱胁迫损坏了光系统II（PSII）的供体和受体。此外，显着降低了PSII反应中心的功能以及PSI和PSII的量子产率。这些荧光参数在褪黑素处理的植物中得以恢复。能量转化分析表明，褪黑素处理过的植物保持较强的能力以确保较高的光合能力，较高的PSI光化学量子产率Y（I）和PSII光化学量子产率Y（II）证明了这一点。褪黑素处理降低了PSII中的调节能量耗散Y（NPQ）和非调节能量耗散Y（NO）。此外，褪黑素处理减轻了干旱胁迫下PSI受体侧和供体侧的限制，如下PSI受体侧限Y（NA）和PSI供体侧限Y（ND）所示。此外，100μM褪黑素是减轻光合作用设备损害的更有效浓度。因此，外源褪黑激素通过提高两个光系统之间的光合作用电子传输效率以及提高PSI和PSII光化学的量子产率，减轻了干旱胁迫对玉米光合装置的损害。