Hydrogen peroxide-induced proline and metabolic pathway of its accumulation in maize seedlings.

Exogenous H(2)O(2) treatment led to a significant accumulation of proline in coleoptiles and radicles of maize seedlings. It also induced an almost immediate and rapid increase of activity of the key enzymes Delta(1)-pyrroline-5-carboxylate synthetase and glutamate dehydrogenase of the glutamate pathway of proline biosynthesis and an up-regulation of Delta(1)-pyrroline-5-carboxylate synthetase gene expression. Activities of the key enzymes arginase and ornithine aminotransferase of the ornithine pathway of proline biosynthesis increased only after 12h of H(2)O(2) treatment. Furthermore, the H(2)O(2) treatment caused an early decrease of the activity of proline dehydrogenase, a key enzyme of proline degradation. These results indicate that H(2)O(2) might be involved in signal transduction events, leading to proline accumulation in maize seedlings, and that the H(2)O(2)-induced proline accumulation is a combined result of the sequential activation of the glutamate and ornithine pathways of proline biosynthesis and the simultaneous inhibition of proline degradation by H(2)O(2).