Phonolic components of the primary cell wall and their possible rôle in the hormonal regulation of growth.

The insoluble cell wall polymers of cultured spinach cells contained esterified ferulic acid at 2-5 mg g(-1) dry weight. Gibberellic acid (GA3, 10(-11)-10(-6) M) promoted the expansion of these cells and simultaneoulsy suppressed peroxidase secretion, reduced the activity of cellular phenylanine ammonia-lyase and favoured the accumulation of wall-esterified ferulate and of extracellular soluble phenolic aglycones. When growth was prevented with 0·7 M sorbitol, GA3 still evoked the phenolic and peroxidase effects. It is suggested that peroxidase restricts growth by rigidifying the cell wall in two ways: (a) covalently by catalysing the conversion of feruloyl side-chains into diferuloyl cross-links and (b) non-covalently by catalysing the conversion of soluble phenolics into hydrophobic quinones (or polymers). GA3 is hypothesised to prevent this rigidification by inhibiting peroxidase secretion.