Effect of inhibition of phenylalanine ammonia‐lyase activity on growth of alfalfa cell suspension culture: Alterations in mitotic index, ethylene production, and contents of phenolics, cytokinins and polyamines

Abstract

The effect of inhibition of phenylpropanoid biosynthesis on the growth of Medicago sativa L. suspension culture was studied. 2‐Aminoindan‐2‐phosphonic acid (AIP), a potent inhibitor of phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5), caused a marked reduction in the amount of hydroxycinnamic acid derivatives in a few hours after cell inoculation into AIP medium. The treatment of alfalfa suspension culture with this inhibitor increased the extractable PAL activity and elevated ethylene production during the growth cycle. The addition of AIP (10 μM) stimulated cell division activity during the growth cycle, although the onset of cell division was slightly delayed. The maxima of cytokinin content as well as of the mitotic index were postponed in AIP‐treated cells, however, the unchanged content of cytokinins did not correlate with increased mitotic activity of treated cells. The decreased level of hydroxycinnamic acid derivatives, which represent the phenolic conjugation partners of free polyamines (PAs), influenced the rate of PA conjugation. Consequently, the balance between free and conjugated PAs was shifted in favor of the free PA form. A potential role of the reduction of the pool of phenolic acids in the enhancement of cell division of alfalfa cell suspension culture is discussed.