Mitigating cadmium stress in rice (Oryza sativa L.) using succinic and oxalic acids with focus on cellular integrity and antioxidant responses.

Soil contamination with toxic heavy metals [such as cadmium (Cd)] is becoming a serious global problem due to the rapid development of the social economy. Organic chelating agents such as succinic acid (SA) and oxalic acid (OA) are more efficient, environmentally friendly, and biodegradable compared to inorganic chelating agents and they enhance the solubility, absorption, and stability of metals. To investigate this, we conducted a pot experiment to assess the impact of SA (0.25 and 0.5 mM) and OA (0.25 and 0.5 mM) on enhancing the phytoremediation of Cd under its toxic concentration of 0.1 mM, using rice (Oryza sativa L.) plants. The research outcomes indicated that elevated levels of Cd stress in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, and gas exchange attributes. However, Cd stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA) and hydrogen peroxide (HO), which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant (P < 0.05) increase in proline metabolism, the AsA-GSH cycle, and the pigmentation of cellular components was observed. In addition, scanning electron microscopy (SEM) revealed that Cd toxicity significantly affected double membranous organelles. Although, the application of SA and OA showed a significant (P < 0.05) increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress. In addition, the application of SA and OA enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in O. sativa plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.