Photosynthesis inhibitor-mediated biochemical and physiological changes in wheat plants challenged with Pyricularia oryzae

Blast, caused by Pyricularia oryzae, has negatively impacted wheat yield. This study investigated whether the level of resistance of wheat plants from a moderately resistant cultivar (BRS 220) could be lowered by an inhibitor of photosynthesis following further inoculation with P. oryzae. A 2 × 2 factorial experiment, consisting of non-inoculated (NI) and inoculated (I) plants sprayed with 3-(3,4-dichlorophenyl)-1,1-dimethylurea) (DCMU; 10 μM solution) (+DCMU plants) or water (−DCMU plants), was arranged in a completely randomized design. Photosynthetic performance, histochemical detection of superoxide anion radical and hydrogen peroxide in leaf tissues, activities of antioxidant enzymes, and concentrations of carbohydrates, amino acids, and protein were determined in plants from −DCMU NI, −DCMU I, +DCMU NI, and +DCMU I treatments. The +DCMU I plants increased their susceptibility (high severity values) to blast and showed great photosynthetic changes (lower net CO2 assimilation rate (A), stomatal conductance to water vapor, and transpiration rate values and higher internal CO2 concentration values) than −DCMU I plants. Highest superoxide anion radical deposition indicated oxidative damage in the leaves of +DCMU NI and +DCMU I plants. Many necrotic lesions and high malondialdehyde concentration were noticed for +DCMU I plants. There was great hydrogen peroxide deposition in the leaves of +DCMU I plants from 48 to 72 h after inoculation. Ascorbate peroxidase, catalase, peroxidase, and superoxide dismutase activities were great for −DCMU I plants than for +DCMU I plants. Lower A values for +DCMU I plants limited carbohydrates synthesis and resulted in lower starch concentration. Lower sucrose concentration and great fructose and glucose concentrations were noticed for +DCMU I plants compared to +DCMU NI plants. The results of this study indicate that a proper photosynthetic apparatus, great carbohydrate metabolism, and a more robust antioxidative system are all needed for wheat resistance against blast and can be collectively altered by a photosynthesis inhibitor.