Nitric oxide application improves photosynthetic light-response through enhancing photosystem II efficiency of bean plants (Phaseolus vulgaris L.) submitted to manganese stress

Toxicity of manganese (Mn) affects plant metabolism, leading to tissue dysfunction and reduced yields. Excessive Mn levels interfere with photosynthesis and cause oxidative stress, damaging cellular structures and impairing plant development. This study examines the role of nitric oxide (NO), a molecule enhancing cellular antioxidant defenses, in mitigating Mn stress in bean (Phaseolus vulgaris L.) plants. Manganese at 500 µM impaired plant biomass and led to Mn accumulation in roots and shoots, reducing carbon assimilation (A) and decreasing stomatal conductance (gs) and transpiration (E) rates. Despite Mn stress, chlorophyll fluorescence and photosystem II function, remained stable, while non-photochemical quenching (NPQ) increased. Application of sodium nitroprusside (SNP, as NO donor) to Mn-stressed plants ameliorated biomass yield through enhancing A, gs, and E rates, thus improving light energy use. This was accompanied by reduced glutathione-ascorbate cycle enzyme activities in leaves. These findings underscore the dual role of SNP in enhancing Mn stress tolerance in bean plants possibly by facilitating Mn compartmentalization within roots, protecting shoots from toxicity, thereby the photosynthetic machinery and promoting plant growth. This study highlights SNP's potential in managing metal stress in plants, with implications for improving agricultural productivity under adverse environmental conditions.