Metabolism and translocation of 3-amino-1,2,4-triazole in Pinus pinea

Abstract

Metabolism of 3-amino-1,2,4-triazole was studied in 28-day-old seedlings of Pinus pinea injected with 5-14C-labelled 3-amino-1,2,4-triazole into the hypocotyl or tip of one of the 13 cotyledons. The seedlings were allowed to metabolize the labelled triazole for a period of 4, 14, or 21 days and were harvested and separated into cotyledons, apex, hypocotyl, and roots. The label upon extraction from the various parts was partially purified through a Dowex 50 W-8 resin exchange column and eluted with NH4OH and water for thin-layer chromatography. The radioautographs showed several metabolites including unmetabolized amitrole in all parts after 4 days of metabolism. Two of the slower running metabolites correspond to 'unknown I' orX1 and X3 previously reported in Pinus ponderosa and Abies concolor and the two faster running metabolites have not been reported before. The metabolism of amitrole seems to occur in both hypocotyl and cotyledons (sites of injection) and the metabolites, as well as unmetabolized, free amitrole, are transported to all other parts of the plant, concentrating in the apex and cotyledons. Injection of labelled amitrole into the xylem of hypocotyl and root respectively results in upward translocation through the apoplast. Application to the exposed phloem resulted in lateral movement from symplast to apoplast and transport to the upper regions of the seedlings. Injection into one cotyledon resulted in symplastic movement to the apex and hypocotyl, followed by transfer in the hypocotyl to the apoplast and subsequent redistribution to other cotyledons. These patterns of translocation support the proposals put forth by Crafts.