Department of Botany, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.
Institute of Plant Breeding and Genetic Resources, Hellenic Agricultural Organisation-Demeter (ELGO-Demeter), 57001 Thessaloniki, Greece.
Int J Mol Sci. 2022 Jun 24;23(13):7038. doi: 10.3390/ijms23137038.
Salicylic acid (SA), an essential plant hormone, has received much attention due to its role in modulating the adverse effects of biotic and abiotic stresses, acting as an antioxidant and plant growth regulator. However, its role in photosynthesis under non stress conditions is controversial. By chlorophyll fluorescence imaging analysis, we evaluated the consequences of foliar applied 1 mM SA on photosystem II (PSII) efficiency of tomato ( L.) plants and estimated the reactive oxygen species (ROS) generation. Tomato leaves sprayed with 1 mM SA displayed lower chlorophyll content, but the absorbed light energy was preferentially converted into photochemical energy rather than dissipated as thermal energy by non-photochemical quenching (NPQ), indicating photoprotective effects provided by the foliar applied SA. This decreased NPQ, after 72 h treatment by 1 mM SA, resulted in an increased electron transport rate (ETR). The molecular mechanism by which the absorbed light energy was more efficiently directed to photochemistry in the SA treated leaves was the increased fraction of the open PSII reaction centers (q), and the increased efficiency of open reaction centers (F'/F'). SA induced a decrease in chlorophyll content, resulting in a decrease in non-regulated energy dissipated in PSII (Φ) under high light (HL) treatment, suggesting a lower amount of triplet excited state chlorophyll (Chl*) molecules available to produce singlet oxygen (O). Yet, the increased efficiency, compared to the control, of the oxygen evolving complex (OEC) on the donor side of PSII, associated with lower formation of hydrogen peroxide (HO), also contributed to less creation of ROS. We conclude that under non stress conditions, foliar applied SA decreased chlorophyll content and suppressed phototoxicity, offering PSII photoprotection; thus, it can be regarded as a mechanism that reduces photoinhibition and photodamage, improving PSII efficiency in crop plants.
水杨酸（SA）是一种重要的植物激素，由于其在调节生物和非生物胁迫的不利影响、作为抗氧化剂和植物生长调节剂方面的作用而受到广泛关注。然而，它在非胁迫条件下对光合作用的作用仍存在争议。通过叶绿素荧光成像分析，我们评估了叶面喷施 1mM SA 对番茄（ L.）植株 PSII 效率的影响，并估计了活性氧（ROS）的产生。叶面喷施 1mM SA 的番茄叶片叶绿素含量较低，但吸收的光能优先转化为光化学能，而不是通过非光化学猝灭（NPQ）耗散为热能，表明叶面喷施 SA 提供了光保护作用。72 小时后，1mM SA 处理导致 NPQ 降低，电子传递速率（ETR）增加。在 SA 处理叶片中，吸收的光能更有效地定向到光化学的分子机制是开放 PSII 反应中心（q）的分数增加，以及开放反应中心（F'/F'）的效率增加。SA 诱导叶绿素含量降低，导致高光（HL）处理下 PSII 中非调节能量耗散（Φ）降低，表明产生单线态氧（O）的三重激发态叶绿素（Chl*）分子数量减少。然而，与对照相比，PSII 供体侧氧释放复合物（OEC）的效率提高，与过氧化氢（HO）形成减少，也有助于减少 ROS 的产生。我们得出结论，在非胁迫条件下，叶面喷施 SA 降低了叶绿素含量并抑制了光毒性，为 PSII 提供了光保护；因此，它可以被视为一种减少光抑制和光损伤、提高作物 PSII 效率的机制。
