Promotion of root elongation by pyridinecarboxylic acids known as novel cut flower care agents

Pyridinedicarboxylic acid (PDCA) analogs, including 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-PDCA, accelerate flower opening and retard senescence of spray-type carnation flowers. In addition the present study revealed that 2,3-PDCA promoted root elongation in lettuce, carrot and rice seedlings, whereas 2,4-PDCA inhibited it. Then, the action of PDCA and pyridinecarboxylic acid (PCA) analogs on root elongation was further examined using rice seedlings. 2,3-, 3,4- and 3,5-PDCA promoted rice root elongation, whereas 2,4 and 2,6-PDCA inhibited, and 2,5-PDCA had little effect. 3-PCA (nicotinic acid) promoted rice root elongation, but 2-and 4-PCA did not. Moreover, 3-PCA amide (nicotinamide) did not promote root elongation. These findings indicated that a carboxyl group substituted on position 3 of the pyridine ring is necessary to promote root elongation, and that the promoting effect of 3-PCA was not from its action as vitamin B 3, but from its intrinsic activity as a 3-COOH substituted pyridine. On the other hand, all the PCA and PDCA analogs tested in this study, except 2,6-PDCA and 4-PCA, promoted shoot elongation of rice seedlings.