Nocardiopsis lucentensis and thiourea co-application mitigates arsenic stress through enhanced antioxidant metabolism and lignin accumulation in rice

Abstract

Arsenic (As) is a group-1 carcinogenic metalloid that threatens global food safety and security, primarily via its phytotoxicity in the staple crop rice. In the present study, ThioAC, the co-application of thiourea (TU, a non-physiological redox regulator) and N. lucentensis (Act, an As-detoxifying actinobacteria), was evaluated as a low-cost approach for alleviating As(III) toxicity in rice. To this end, we phenotyped rice seedlings subjected to 400 mg kg^-1 As(III) with/without TU, Act or ThioAC and analyzed their redox status. Under As-stress conditions, ThioAC treatment stabilized photosynthetic performance, as indicated by 78 % higher total chlorophyll accumulation and 81 % higher leaf biomass, compared with those of As-stressed plants. Further, ThioAC improved root lignin levels (2.08-fold) by activating the key enzymes of lignin biosynthesis under As-stress. The extent of reduction in total As under ThioAC (36 %) was significantly higher than TU (26 %) and Act (12 %), compared to those of As-alone treatment, indicating their synergistic interaction. The supplementation of TU and Act activated enzymatic and non-enzymatic antioxidant systems, respectively, with a preference for young (TU) and old (Act) leaves. Additionally, ThioAC activated enzymatic antioxidants, specifically GR (∼3-fold), in a leaf-age specific manner and suppressed ROS-producing enzymes to near-control levels. This coincided with 2-fold higher induction of polyphenols and metallothionins in ThioAC-supplemented plants, resulting in improved antioxidant defence against As-stress. Thus, our findings highlighted ThioAC application as a robust, cost-effective ameliorative strategy, for achieving As-stress mitigation in a sustainable manner.

Keywords: Actinomycetes; Antioxidant; Heavy metal; Lignin; Metabolism; Metallothionins; Redox-homeostasis.