Cell wall peroxidase against ferulic acid, lignin, and NaCl-reduced root growth of rice seedlings

The changes in cell wall peroxidase activity against ferulic acid (FPOD) and lignin level in roots of NaCl-stressed rice seedlings and their correlation with root growth were investigated. Increasing concentrations of NaCl from 50 to 150 mmol L-1 progressively decreases root growth. The reduction of root growth by NaCl is closely correlated with the increase in FPOD activity extracted from the cell wail. In contrast, lignin level was reduced by NaCl. Since proline and ammonium accumulations are associated with root growth inhibition caused by NaCl, we determined the effect of proline or NH4Cl on root growth and FPOD in roots. Exogenous application of NH4Cl or proline markedly inhibited root growth and increased FPOD activity in rice seedlings in the absence of NaCl. An increase in FPOD activity in roots preceded inhibition of root growth caused either by NaCl, NH4Cl, or proline. Our results suggest that cell-wall stiffening catalyzed by FPOD may participate in the regulation of root growth reduction of rice seedlings caused by NaCl.