Influence of calcium and calcium and calmodulin antagonists on the cytokinin-induced amaranthin accumulation in Amaranthus tricolor

Abstract

The concentration of kinetin and kinetinriboside plays an essential role in the induction of amaranthin accumulation in cotyledons of Amaranthus tricolor during germination. The dose/effect ratio shows that kinetin induced 3- to 3.5-fold more amaranthin than kinetinriboside at the same molecular concentration. Various concentrations of exogenous Ca2+ did not influence the effects of kinetin on the betacyanin synthesis. However, when Ca2+ was applied together with kinetinriboside, the amaranthin production was stimulated. Time-course experiments show a lag phase of 16 h starting from the incubation with kinetin and a distinct increase of amaranthin thereafter. If the seedlings were treated simultaneously with kinetin and Ca2+, the increase of amaranthin started after 12 h. At 16 h of incubation in kinetin/Ca2+, the amount of amaranthin increased significantly compared to controls incubated with kinetin alone. If Ca2+ ions (16 h kinetin/Ca2+ incubation) were removed from the medium after 2 h, 4 h, and up to 14 h, the amaranthin content was enhanced compared to controls without Ca2+. The stimulating effect was highest in the presence of Ca2+ for 8 h. These data show that exogenous Ca2+ stimulated the amaranthin synthesis mainly during the first 12 h of incubation. The Ca2+ antagonists EGTA, chlorotetracycline, and CoCl2 reduced the amaranthin content up to 80%. The calmodulin antagonists chloropromazine and trifluoperazine inhibited the betacyanin accumulation up to 97% when applied at the beginning of the incubation. Neither Co2+ nor trifluoperazine after 12 h of preincubation in kinetin had inhibiting effects on the amaranthin production. Therefore, we presume that a specific period of competence is required for calmodulin-mediated Ca2+ effects on the accumulation of amaranthin induced by cytokinins in the seedlings of Amaranthus tricolor.