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Abscisic Acid metabolism by source and sink tissues of sugar beet
1United States Department of Agriculture, Agriculture Research Service, Crops Research Laboratory, Utah State University, UMC 63, Logan, Utah 84322.
Abstract:
The fate of exogenously applied, labeled abscisic acid (+/-)-(ABA) was followed in source leaves and taproot sink tissues of sugar beet (Beta vulgaris cv AH-11). The objective was to determine if differential pathways for ABA metabolism exist in source and sink tissues. Tissue discs were incubated for up to 13 hours in a medium containing 1 micromolar labeled ABA. At various time intervals, samples were taken for metabolite determination by reverse-phase high performance liquid chromatography. The labeled metabolites were identified by retention times using an online scintillation counter.Dihydrophaseic acid (DPA) aldopyranoside, DPA, phaseic acid (PA), ABA glucose ester (ABA-GE), and two unidentified compounds were recovered from both tissues. An additional unidentified metabolite was also present in root tissue. Leaf tissue discs exhibited a higher capacity for ABA conjugation, and root discs showed a greater preference for ABA catabolism to PA and DPA. After 4 to 5 hours, ABA incorporation into the various metabolites was proportional to the external ABA concentration in both tissues. But the internal ABA pool size was independent of external concentrations below 10(-6) molar. These results suggested that rates of ABA metabolism was proportional to the rates of uptake in both tissues.
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