DISTURBED NITROGEN-METABOLISM ASSOCIATED WITH THE HYPERHYDRIC STATUS OF FULLY HABITUATED CALLUS OF SUGAR-BEET

The content of polyamines and proline was much lower in a normal (N) c allus of Beta vulgaris L. than in a fully habituated hyperhydric (H) c allus. The H callus also contained more glutamate and had a higher glu tamate dehydrogenase activity. The excess of glutamate, in this chloro phyll-deficient callus, was linked to accumulation of proline and poly amines. Experiments with alpha-difluoromethylornithine (DFMO) and alph a-difluoromethylarginine (DFMA) showed that both ornithine decarboxyla se and arginine decarboxylase participated in the synthesis of polyami nes (especially spermidine and putrescine) and removal of ammonia. It is hypothesized that the H callus was subjected to ammonia stress from the start of the culture. Experiments with gabaculine, an inhibitor o f ornithine aminotransferase, showed that this enzyme linked proline d egradation to polyamine synthesis through the production of ornithine. This disturbed nitrogen metabolism appeared to be characteristic of t he fully habituated callus and might explain the low growth of this hy perhydric tissue.