Table_1_Flavonoid Naringenin Alleviates Short-Term Osmotic and Salinity Stresses Through Regulating Photosynthetic Machinery and Chloroplastic Antioxidant Metabolism in Phaseolus vulgaris.doc

The current study was conducted to demonstrate the possible roles of exogenously applied flavonoid naringenin (Nar) on the efficiency of PSII photochemistry and the responses of chloroplastic antioxidant of salt and osmotic-stressed Phaseolus vulgaris (cv. Yunus90). For this aim, plants were grown in a hydroponic culture and were treated with Nar (0.1 mM and 0.4 mM) alone or in a combination with salt (100 mM NaCl) and/or osmotic (10% Polyethylene glycol, −0.54 MPa). Both caused a reduction in water content (RWC), osmotic potential (ΨΠ), chlorophyll fluorescence (Fv/Fm), and potential photochemical efficiency (Fv/Fo). Nar reversed the changes on these parameters. The phenomenological fluxes (TRo/CS and ETo/CS) altered by stress were induced by Nar and Nar led to a notable increase in the performance index (PIABS) and the capacity of light reaction [ΦPo/(1-ΦPo)]. Besides, Nar-applied plants exhibited higher specific fluxes values [ABS/RC, ETo/RC, and ΨEo/(1-ΨEo)] and decreasing controlled dissipation of energy (DIo/CSo and DIo/RC). The transcripts levels of psbA and psbD were lowered in stress-treated bean but upregulated in Nar-treated plants after stress exposure. Nar also alleviated the changes on gas exchange parameters [carbon assimilation rate (A), stomatal conductance (gs), intercellular CO2 concentrations (Ci), transpiration rate (E), and stomatal limitation (Ls)]. By regulating the antioxidant metabolism of the isolated chloroplasts, Nar was able to control the toxic levels of hydrogen peroxide (H2O2) and TBARS (lipid peroxidation) produced by stresses. Chloroplastic superoxide dismutase (SOD) activity reduced by stresses was increased by Nar. In response to NaCl, Nar increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), as well as peroxidase (POX). Nar protected the bean chloroplasts by minimizing disturbances caused by NaCl exposure via the ascorbate (AsA) and glutathione (GSH) redox-based systems. Under Nar plus PEG, Nar maintained the AsA regeneration by the induction of MDHAR and DHAR, but not GSH recycling by virtue of no induction in GR activity and the reduction in GSH/GSSG and GSH redox state. Based on these advances, Nar protected in bean chloroplasts by minimizing disturbances caused by NaCl or PEG exposure via the AsA or GSH redox-based systems and POX activity.

本研究旨在探讨外源施用类黄酮柚皮素（Nar）对盐胁迫与渗透胁迫下菜豆（Phaseolus vulgaris，品种Yunus90）光系统II（PSII）光化学效率以及叶绿体抗氧化响应的潜在调控作用。为达成该研究目标，实验采用水培体系种植菜豆，分别单独施用0.1 mM与0.4 mM的Nar，或将其与100 mM NaCl盐胁迫、10%聚乙二醇（PEG，渗透势-0.54 MPa）渗透胁迫单独或联合处理。盐胁迫与渗透胁迫均可导致菜豆的相对含水量（RWC）、渗透势（ΨΠ）、叶绿素荧光参数Fv/Fm以及潜在光化学效率Fv/Fo显著降低。Nar可逆转上述胁迫诱导的参数变化。

胁迫改变的现象学通量（TRo/CS与ETo/CS）可被Nar恢复，且Nar可显著提升性能指数PI_ABS以及光反应能力[ΦPo/(1-ΦPo)]。此外，施用Nar的植株具有更高的比通量值[ABS/RC、ETo/RC以及ΨEo/(1-ΨEo)]，同时降低了受控能量耗散（DIo/CSo与DIo/RC）。

胁迫处理的菜豆中psbA与psbD基因的转录水平下调，但经Nar处理后，该两类基因在胁迫暴露后的转录水平显著上调。Nar还可缓解气体交换参数的异常变化，包括净光合速率（A）、气孔导度（gs）、胞间CO2浓度（Ci）、蒸腾速率（E）以及气孔限制值（Ls）。

通过调控分离叶绿体的抗氧化代谢，Nar可有效控制胁迫诱导产生的过氧化氢（H2O2）与硫代巴比妥酸反应物（TBARS，反映脂质过氧化水平）的毒性积累量。胁迫诱导降低的叶绿体超氧化物歧化酶（SOD）活性可被Nar显著提升。在NaCl盐胁迫响应中，Nar可提升抗坏血酸过氧化物酶（APX）、谷胱甘肽还原酶（GR）、单脱氢抗坏血酸还原酶（MDHAR）、脱氢抗坏血酸还原酶（DHAR）以及过氧化物酶（POX）的活性。Nar可通过抗坏血酸（AsA）与谷胱甘肽（GSH）氧化还原系统，缓解NaCl胁迫对菜豆叶绿体的损伤。

在PEG渗透胁迫处理组中，Nar可通过诱导MDHAR与DHAR的活性维持AsA的再生，但无法通过调控GR活性实现GSH的循环利用，且会导致GSH/GSSG比值以及谷胱甘肽氧化还原状态下降。基于上述实验结果，Nar可通过AsA或GSH氧化还原系统以及POX活性，缓解NaCl或PEG胁迫对菜豆叶绿体造成的干扰，从而实现对菜豆叶绿体的保护。