L‐α‐Aminooxy‐β‐phenylpropionic acid inhibits lignification but not the differentiation to tracheary elements of isolated mesophyll cells of Zinnia elegans

Abstract

The influence of L‐α‐aminooxy‐β‐phenylpropionic acid (AOPP), an inhibitor of L‐phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5), and thus of lignin formation, on the differentiation of tracheary elements from isolated mesophyll cells of Zinnia elegans L. cv. Canary Bird was investigated. At low concentrations of AOPP (5–25 μ,M) lignification of differentiating cells was almost completely prevented whereas number of differentiating cells, viability of the cells, fresh and dry weights, and the packed cell volume were higher than corresponding parameters in control cultures. At higher concentrations of AOPP (50–75 μM) the formation of tracheary elements was inhibited but division, elongation and expansion of cells were still observed. Cells cultured for 96 h in the presence of 100 μM AOPP were morphologically similar to cells at 12 h of culture, the time at which AOPP was added. At concentrations of AOPP that did not inhibit differentiation, AOPP caused an increase in the amounts of uronic acid and total carbohydrate (per unit volume of cell suspension) in the extracellular polysaccharide fraction and in the total cell wall fraction, although these parameters were not significantly different from control values when expressed on a dry weight basis. AOPP caused the release of polysaccharides which contained xylose into the medium when added before the onset of visible differentiation and the release of polysaccharides which contained glucose when added at the time when the formation of the secondary cell wall thickenings took place. The results indicate that AOPP at low concentrations specifically inhibits the formation of lignin without adversely affecting the synthesis of cell wall polysaccharides, although the proper integration of these compounds into the wall may be disturbed. O‐Benzylhydroxyla‐mine, on the other hand, did not prove to be a useful agent to affect lignin synthesis in differentiating Zinnia cells.