ABSTRACT Rice ( Oryza sativa L.) is an essential food crop, usually grown in flooded soils. However, these environments, especially with low pH, favor iron (Fe) toxicity due to the low redox potential, which increases the Fe 2+ availability. Excessive Fe concentrations are highly detrimental, compromising the growth, physiology, and productivity of rice plants. In this context, dopamine has emerged as a bioactive molecule with the potential to mitigate stresses in plants. Therefore, the objective of this study was to evaluate whether the exogenous application of dopamine attenuates oxidative damage in the photosynthetic apparatus of rice leaves subjected to excess Fe, as well as to analyze anatomical changes, production of reactive oxygen species (ROS), activity of antioxidant enzymes, and the nutritional status of plants. Fe excess caused the accumulation of this element in roots and leaves, reducing the uptake of other essential nutrients. However, the application of dopamine significantly increased the nutritional status while reducing the accumulation of Fe in plants. In the anatomy, dopamine promoted improvements in root structures, primarily in the thickness of the root epidermis (21%), as well as enhancements in leaves, including an increase in chlorophyll parenchyma (11%). Exogenous dopamine also minimized damage to the photosynthetic apparatus, increasing the levels of photosynthetic pigments and significantly increasing the effective quantum yield of PSII photochemistry (13%) and electron transport rate (13%). In gas exchange, the dopamine application in plants under Fe excess promoted increases in the net photosynthetic rate and water use efficiency with increases of 14% and 25%, respectively. The antioxidant defense was intensified by dopamine, with increases in the activities of superoxide dismutase (33%), catalase (29%), ascorbate peroxidase (75%) and peroxidase (17%). In parallel, there was a reduction in the ROS accumulation, including superoxide (14%) and hydrogen peroxide (8%), as well as malondialdehyde (37%) and electrolyte leakage (4%). Finally, the biomass was negatively impacted by excess Fe; however, dopamine promoted increases in stem and root growth, proving its effectiveness in mitigating the toxic effects of Fe in rice.
Silva et al. (Thu,) studied this question.