Involvement of calcium and calmodulin in protein and amino acid metabolism in rice roots under anoxia

The prctreatment of rice roots for 1 h in aerobic conditions with the Ca-channel blockers ruthenium red (RR) and verapamil and the calmodulin (CaM) antagonists N-(6-aminohexyl)-5chloro-1-naphtylenesulfonamide (W-7) and trifluoperazine, induced during 3 h of anoxia: (i) inhibition of amino acid and y-aminobutyric acid (Gaba) accumulation; (ii) a decline in the protein content; (iii) a release of amino acids and K into the growth media. The calcium ionophore A23187 reversed these effects in RR-treated roots. Moreover, the aerobic pretreatment of rice roots with A23187 alone or CaCl2 increased the accumulation of amino acids and Gaba. These data indicate that the Ca/CaM complex is involved in the transduction of an anaerobic signal by inhibiting proteolysis and solute release, and activating the Ca/CaM-dependent glutamate decarboxylase.