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

The effect of inhibition of phenylpropanoid biosynthesis on the growth of M edicago 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 deri vatives in a fem hours after cell inoculation into ALP medium, The treatmen t of alfalfa suspension culture with this inhibitor increased the extractab le PAL activity and elevated ethylene production during the growth cycle. T he addition of AIP (10 mu M) stimulated cell division activity during the g rowth 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 l evel of hydroxycinnamic acid derivatives, which represent the phenolic conj ugation partners of free polyamines (PAs), influenced the rate of PA conjug ation, Consequently, the balance between free and conjugated PAs mas shifte d in favor of the free PA form. ii potential role of the reduction of the p ool of phenolic acids in the enhancement of cell division of alfalfa cell s uspension culture is discussed.