Biochemical and molecular mechanisms associated with Zn deficiency tolerance and signaling in rice (Oryza sativa L.)

In this study, zinc (Zn) deficiency caused a significant reduction in growth parameters and tissue Zn concentrations in BRRI 33 (sensitive) but not in Pokkali (tolerant). The increase of proton extrusion in both genotypes under high pH suggests that it gets triggered as a common consequence of reducing pH and solubilization of Zn. Real-time PCR showed pronounced upregulation of OsZIP4, OsDMAS1, OsNAS2 and OsPCS1 in Zn-deficient roots of Pokkali, and to a lesser extent in BRRI 33 only for OsZIP4 and OsPCS1. This suggests that OsDMAS1, OsNAS2 and OsPCS1 functions as secondary consequences leading to higher chelation and uptake of Zn under Zn deficiency in Pokkali. Further, a major increase in CAT, POD, SOD, GR and key metabolites suggests that high antioxidant defense plays a critical role in Zn deficiency tolerance in Pokkali. Further, Pokkali self-grafts and plants having Pokkali rootstock combined with BRRI 33 scion showed no significant decline in plant height, root dry matter and Zn concentration along with upregulation of Zn transporters (OsZIP4 and OsIRT1) under Zn deficiency, suggesting that signal driving mechanisms for Zn deficiency tolerance mechanisms are generated in the root and Zn-inefficient BRRI 33 is not capable of producing signals or sensing them.