Proton pump activation and growth promotion by cinchomeronic acid in radish

Cinchomeronic acid (CA, 3,4-dicarboxypyridine or 4-carboxynicotinic acid) promoted hypocotyl elongation of radish seedlings when added to the medium or applied to the hypocotyls. On microscopic observation of epidermal cells of the plant, the length of each cell was elongated several times when compared to those of the controls. The mechanism of the plant-growth promotion by CA was investigated with plasma membrane vesicle prepared from radish seedlings. CA elevated the Vmax of vanadate-sensitive H--ATPase in plasma membrane vesicle by 1.8 times. It was found that CA and quinolinic acid were activators, and isocinchomeronic acid and 2,4-lutidinic acid were inhibitors for the H+-ATPase. These results reflected the effects of these compounds on plant growth. It is suggested that CA activates ATP-dependent proton transport and leads to plant-growth promotion by acid.