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Incorporation of Oxygen into Abscisic Acid and Phaseic Acid from Molecular Oxygen

Robert A. Creelman and Jan A. D. Zeevaart
Plant Physiology
Vol. 75, No. 1 (May, 1984), pp. 166-169
Stable URL: http://www.jstor.org/stable/4268634
Page Count: 4
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Incorporation of Oxygen into Abscisic Acid and Phaseic Acid from Molecular Oxygen
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Abstract

Abscisic acid accumulates in detached, wilted leaves of Xanthium strumarium. When these leaves are subsequently rehydrated, phaseic acid, a catabolite of abscisic acid, accumulates. Analysis by gas chromatography-mass spectrometry of phaseic acid isolated from stressed and subsequently rehydrated leaves placed in an atmosphere containing 20% ${}^{18}\text{O}{}_{2}$ and 80% N2 indicates that one atom of 18O is incorporated in the 6′-hydroxymethyl group of phaseic acid. This suggests that the enzyme that converts abscisic acid to phaseic acid is an oxygenase. Analysis by gas chromatography-mass spectrometry of abscisic acid isolated from stressed leaves kept in an atmosphere containing ${}^{18}\text{O}{}_{2}$ indicates that one atom of 18O is present in the carboxyl group of abscisic acid. Thus, when abscisic acid accumulates in water-stressed leaves, only one of the four oxygens present in the abscisic acid molecule is derived from molecular oxygen. This suggests that either (a) the oxygen present in the 1′-, 4′-, and one of the two oxygens at the 1-position of abscisic acid arise from water, or (b) there exists a stored precursor with oxygen atoms already present in the 1′- and 4′-positions of abscisic acid which is converted to abscisic acid under conditions of water stress.

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