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

Evren Yildiztugay,Mustafa Kucukoduk,Ismail Turkan,Ceyda Ozfidan-Konakci

doi:10.3389/fpls.2020.00682

Abstract

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.

Highlights

Plants are simultaneously subjected to the combination of salinity and osmotic stresses rather than the effects of an individual stress
After chloroplast isolation of sampling groups in bean (Phaseolus vulgaris L.) leaves, we have focused on explanation the effects of exogenously applied Nar in five steps: (i) the effects of Nar on water content and osmotic potential under salt and/or osmotic stresses; (ii) the effects of Nar on gas exchange parameters such as carbon assimilation rate, transpiration rate, stomatal conductance and stomatal limitation; (iii) the determination the effects of Nar on the photochemical reactions and fluorescence transients and, on the expression levels of genes encoding the major extrinsic proteins of photosystem II (PSII) such as psbA and psbD; (iv) the effects of Nar on the responses of antioxidant in chloroplasts of stress-treated plants; and (v) the effects of Nar on reactive oxygen species (ROS) content and lipid peroxidation in chloroplasts
Our study confirms that Nar applications prevented inhibition on relative water content (RWC), osmotic potential and photosynthetic efficiency (Fv/Fm, Fv/Fo, and Fo/Fm) effected by NaCl and/or PEG in bean chloroplasts

Summary

Introduction

Plants are simultaneously subjected to the combination of salinity and osmotic stresses rather than the effects of an individual stress. Due to the highly energetic reactions of photosynthesis, the reduction of molecular oxygen generates toxic reactive oxygen species (ROS), which interacts with essential and important molecules such as DNA, photosynthetic pigments, and proteins (Miller et al, 2010; Flowers et al, 2015). The responses of photosynthetic apparatus with these parameters are evaluated through OJIP fluorescence transients (called a JIP test). The OJIP test was developed by Strasser et al (1995), and the parameters are calculated using the generated chlorophyll fluorescence induction curve according to the JIP-test method (Zeliou et al, 2009). The JIP test shows the measurement of several phenological and biophysical expressions of PSII including the fluxes of absorption, trapping, and electron transport (Strasser et al, 2000)

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