Improved oxidative tolerance in suspension‐cultured cells of C_4-pepctransgenic rice by H_2O_2 and Ca^(2+)under PEG-6000

To understand the molecular responses of PC （Overexpressing the maize C4‐pepc gene, which encodes phosphoenolpyruvate carboxylase （PEPC））, to drought stress at cel level, we analyzed changes in the levels of signaling molecules （hydrogen peroxide （H2O2）, calcium ion （Ca2t）, and nitric oxide （NO）） in suspension‐cultured PC and wild‐type （WT） rice （Oryza sativa L.） cel under drought stress induced by 20%polyethylene glycol 6000 （PEG‐6000）. Results demonstrated that PC improved drought tolerance by enhancing antioxidant defense, retaining higher relative water content, survival percentages, and dry weight of cel s. In addition, PEPC activity in PC under PEG treatment was strengthened by addition of H2O2 inhibitor, dimethylthiourea （DMTU） and NO synthesis inhibitor, 2‐（4‐carboxyphenyl‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide （cPTIO）, respectively, while that in PC was weakened by addition of free calcium chelator, ethylene glycol‐bis（b‐aminoethylether）‐N,N,N0 ,N0‐tetraacetic acid （EGTA） t calcium channel outflow inhibitor, ruthenium red （RR） t plasma membrane channel blocker La（NO3）3, but EGTA t RR did not. Results also showed that NO and Ca2t was lying downstream of H2O2 in drought‐induced signaling. Calcium ion was also involved in the expression of C4‐pepc in PC. These results suggested that PC could improve oxidative tolerance in suspension‐cultured cel s and the acquisition of this tolerance required downregulation of H2O2 and the entry of extracel ular Ca2t into cel s across the plasma membrane for regulation of PEPC activity and C4‐pepc expression.