Inhibition by isonicotinyl hydrazide of pigment formation in higher plants

The inhibition of greening of illuminated etiolated maize seedlings by isonicotinyl hydrazide can be alleviated by serine or pyruvate. The similar inhibition in barley can be reversed only by pyruvate. In both plants earlier intermediates in the glycollate pathway and other related compounds were ineffective in overcoming the inhibition of greening produced by isonicotinyl hydrazide. In maize seedlings radioactivity from l-serine-[3-¹⁴C] is poorly incorporated into β-carotene, a typical chloroplast terpenoid, unless glycine and formate or, more effectively, glycine together with isonicotinyl hydrazide are supplied. These supplementations may minimize interconversion of serine and glycine, and hence dilution of radioactivity at C-3 of l-serine by unlabelled C-1 units, before incorporation into terpenoids. The results support the view that in young greening tissue the C2-3 fragment of l-serine can give rise to acetyl-CoA, an obligatory precursor of chloroplast terpenoids.