The Metabolism and Transport of Abscisic Acid During Grain Fill in Wheat

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Abstract
The metabolism and transport of (±)-l2-14Clabscisic acid and its metabolites was investigated during the period of grain development in wheat. Forty-five hours after feeding the hormone into the flag leaf blade, or after injection into the grains, nine metabolites could be extracted with acetone. Four of these compounds have been identified. They are phaseic acid, dihydrophaseic acid, abscisyl-β-D-glucopyranoside and the polar metabolite. As well as the acetone-soluble metabolites a number of others have been found which are insoluble in acetone. These appear to be conjugated to lipids, ‘gluten-like’ proteins, and carbohydrates. ABA and its metabolites were transported to all parts of the plant above the flag leaf node when the radioactive hormone was introduced into the blade. However, when it was injected into the grain the radioactivity remained there until the point when dry matter accumulation ceased, after which it was found only in the peduncle. The results suggest that the increasing level of ABA during the period of dry matter accumulation is due to biosynthesis within the grain and that the decrease after dry matter accumulation ceases is due to both metabolism and redistribution within the plant.