Acclimation to cold stress reduces injury from low temperature and bispyribac-sodium on rice.

Background: In subtropical areas, early planting exposes rice seedlings to cold stress, impairing seedling growth and making them more vulnerable to other stresses including herbicide injury. The objectives of this work were: to evaluate the effect of cold stress on bispyribac-sodium selectivity in rice; to determine the mechanisms of cold tolerance in sensitive ('Epagri 109') and tolerant ('IRGA 424') rice cultivars; and to ascertain that cold acclimatization influences bispyribac-sodium selectivity in rice.

Results: Prolonged cold stress caused high lipid peroxidation, increased rice injury, and stunted growth. Short-term acclimation with cold stress reduced rice injury with bispyribac-sodium. Total phenols were upregulated in rice exposed to cold stress. Prolonged cold stress increased the superoxide dismutase and catalase activity in IRGA 424. Antioxidant activity was higher in the cold-tolerant than in the cold-sensitive cultivar. Only catalase activity was responsive to bispyribac-sodium. OsRAN2, OsGSTL2, and CYP72A21 were upregulated by cold and herbicide stress in both cultivars. OsGSTL2 was upregulated more in IRGA 424 than in Epagri 109. OsFAD8 was upregulated in cold-sensitive rice exposed to short-duration cold stress but was not responsive to bispyribac-sodium.

Conclusion: Cold stress reduces bispyribac-sodium selectivity in rice. Short-term acclimation to cold stress reduces the effect of cold stress and enhances bispyribac-sodium selectivity. The tolerance of rice (IRGA 424) to cold stress is due to differential induction of protection genes CYP72A21 and OsGSTL2 associated with herbicide metabolism, together with the accumulation of total phenols and higher activity of antioxidant enzymes.