This study elucidates the involvement of auxin with Zn-efficiency (ZE) in Zn-efficient rice var. Pokkali. Pokkali showed no significant decrease in morpho-physiological features, electrolyte leakage and total soluble proteins due to Zn deficiency as compared with Zn-sufficient seedlings. However, auxin inhibitor under Zn deficiency severely affected these characteristics, suggesting that ZE is associated with auxin signaling in rice. Results further revealed significant decreases in the expression of Zn transporter genes (OsIRT1, OsZIP4 and OsZIP1), OsDMAS1 (deoxymugeneic acid synthase) and phytochelatin in roots due to auxin inhibitor. It implies that auxin signaling may trigger Zn uptake, transport and chelation in rice seedlings to withstand Zn-deficiency. Further, significant reduction of major S-metabolites (cysteine, methionine, glutathione) and antioxidant enzymes (superoxide dismutase and glutathione reductase) along with increased H 2 O 2 content, due to auxin inhibitor under Zn deficiency compared with controls. Taken together, these findings reveal that mechanisms associated with ZE in Pokkali are dependent on auxin signaling. ARTICLE HISTORY

Heavy metal chromium (Cr) is considered to be a serious environmental contaminant due to its toxic effect on living organisms. To mitigate and reduce the negative impacts of Cr in rice plant, the effect of exogenous supplementary calcium was evaluated as it functions as a signaling molecule at cellular level. In this study, growth parameters, protein content, and membrane stability were found to be restored due to calcium under Cr stress. Further, Atomic absorption spectrophotometric analysis revealed that calcium inhibits Cr translocation from root to shoot in rice seedlings. This event was addressed by the enhanced accumulation of phytochelatin that leads to vacuolar sequestration of Cr in roots. Furthermore, increased activity of Catalase, Peroxidase, and Glutathione reductase along with elevated glutathione also assures that calcium enhances antioxidant defense mechanism to cope with Cr toxicity.

High chromium (Cr) in rice causes reduced yield and health hazards. This work investigates how Si alleviates Cr toxicity in rice. Addition of Si under Cr stress restored the growth parameters, total protein content, and membrane stability along with reduced Cr content in shoots, confirming that Si plays critical roles in Cr detoxification in rice. However, Si supplementation under Cr stress caused no significant changes in root Cr content but decreased shoot Cr concentrations compared with Cr-stressed plants, indicating that alleviation of Cr toxicity might be associated with Cr sequestration in roots. Further, concentration of Fe and expression of Fe transporter (OsIRT1) showed no significant changes due to Si supplementation under Cr stress, implying that Fe regulation is not involved with Si-mediated mitigation of Cr toxicity in rice. Further, phytochelatin accumulation and OsPCS1 (phytochelatin synthase) transcripts strongly induced due to the dual treatment of Si and Cr compared with Cr-stressed plants, suggesting that phytochelatin might bind to Cr, which leads to vacuolar sequestration in roots. Furthermore, increased glutathione reductase activity in roots implies that active involvement of ROS scavenging partially ameliorates Cr toxicity in rice plants. The study illustrates first evidences on the effect of Si alleviating Cr toxicity in rice plants.

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The growth of meristem was observed on semisolid MS medium supplemented with 0.05 mg/l Kn + 0.1 mg/l GA 3 . After three weeks, meristems were transferred to MS supplemented with BA, Kn, IBA, NAA and IAA singly or in combination for shoot elongation and root initiation. Among different treatments for shoot initiation with elongation were obtained in MS supplemented with 1.0 mg/l BA + 0.1 mg/l IBA + 0.3 mg/l GA 3 . On the other hand good rooting was observed when 0.5 mg/l IBA and 0.1 mg/l NAA were used to fortify MS semisolid medium. Ten weeks old in vitro plantlets were successfully planted in soil through gradual acclimation.