Integrative Biochar and Melatonin Application Mitigates Lead Toxicity in Rice by Modulating Antioxidant Activities, Iron Plaque Formation and Downregulating the Expression of Metal Uptake Genes

Tahir Abbas Khan¹Qitao Su^2*Huang Guoqin¹Du Zhixuan²Mehmood Ali Noor¹Tahani A.Y. Asseri³Dr. Muhammad Umair Hassan¹

• ¹Jiangxi Agricultural University, Nanchang, Jiangxi, China
• ²Jinggangshan University, Ji'an, China
• ³King Khalid University, Abha, Saudi Arabia

Lead (Pb) is a common toxic metal that causes severe health and environmental problems.However, the defensive role and underlying mechanism of combined biochar (BC) and melatonin (MT) against Pb stress are still unclear. Therefore, to fill this gap, the following study investigated the impacts of BC and MT on rice growing in Pb-polluted soil. The study included different treatments; control, Pb stress (300 mg kg -1 ), Pb stress (300 mg kg -1 ) + BC (2%), Pb stress (300 mg kg -1 ) +MT (30 µM) and Pb stress (300 mg kg -1 ) + BC (2%) + MT (30 µM). Lead Pb reduced rice growth and yield by hindering photosynthetic pigments, relative water contents (RWC), osmolyte synthesis, nutrient uptake, and increasing oxidative markers and Pb accumulation. Biochar and MT increased rice productivity by increasing chlorophyll synthesis, osmolytes, nutrient uptake, and decreasing Pb accumulation. Co-applied BC and MT decreased Pb accumulation in the roots (30.40%) and shoots (72.79%), the translocation factor (30.01%), the biological accumulation coefficient (20.17%), and the soil Pb concentration (59.02%). Co-applied BC and MT = enhanced proline (39.65%), soluble protein (47.09%), ascorbate peroxidase (APX: 26.47%), catalase (CAT: 65.51%), peroxidase (POD: 89.56%) and superoxide dismutase (SOD: 65.53%) activities which ensured the better productivity. Additionally, BC + MT application increased the expression of antioxidant defense genes (OsAPX, OsCAT, OsPOX, and OsSOD) and decreased the expression of metal transporter genes (OsHMA9 and OsNRAMP5), which protected the rice plantsfrom 2 damage caused by Pb toxicity. These results suggested that BC+MT could be a promising strategy to mitigate Pb toxicity and maintain sustainable and safer food production.