Analysis of variability in the amaranthus betacyanin assay for cytokinins: effects of "aging" excised cotyledons.

"Aging" of excised cotyledons plus the top part of the hypocotyl of Amaranthus tricolor seedlings was carried out by washing in distilled H(2)O for varying periods. This led to increased betacyanin accumulation during the subsequent 24-hour induction period in the presence of tyrosine and Na(+) + K(+) phosphate. Endogenous accumulation as well as that dependent on added benzyladenine and on added fusicoccin was stimulated. This stimulation could not be due to a carryover of a wound-induced burst of ethylene since 2-chloroethylphosphonic acid (Ethrel) was shown to be extremely inhibitory to betacyanin synthesis if present during the induction process. It is possible that a wound-induced burst of ethylene could give rise to increased betacyanin synthesis as an after effect. The procedure for obtaining good induction with the most reproducible results is described.