Effect of Silver Ion, Carbon Dioxide, and Oxygen on Ethylene Action and Metabolism

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Abstract
The relationship between ethylene action and metabolism was investigated in the etiolated pea seedling (Pisum sativum L. cv. Alaska) by inhibiting ethylene action with Ag(+), high CO(2), and low O(2) and then determining if ethylene metabolism was inhibited in a similar manner. Ag(+) (100 milligrams per liter) was clearly the most potent antiethylene treatment. Ag(+) pretreatment inhibited the growth retarding action of 0.2 microliters per liter ethylene by 48% and it also inhibited the incorporation of 0.2 microliters per liter (14)C(2)H(4) into pea tips by the same amount. As the ethylene concentration was increased from 0.2 to 30 microliters per liter, the effectiveness of Ag(+) in reducing ethylene action and metabolism declined in a similar fashion. Although Ag(+) significantly inhibited the incorporation of (14)C(2)H(4) into tissue metabolites, the oxidation of (14)C(2)H(4) to (14)CO(2) was unaffected in the same tissue.CO(2) (7%) inhibited ethylene-induced growth retardation but its effectiveness diminished at a greater rate than that of Ag(+) with increasing ethylene concentration. High CO(2) had just the opposite effect of Ag(+) since it inhibited (14)C(2)H(4) oxidation to (14)CO(2) without affecting tissue incorporation. In contrast to Ag(+), CO(2) did not inhibit ethylene action and metabolism to exactly the same extent, and the inhibition of metabolism did not rapidly decline with increasing (14)C(2)H(4) concentration. However, high CO(2) did alter the ratio of (14)C(2)H(4) tissue incorporation to (14)CO(2) production in a manner consistent with changes in ethylene effectiveness.Lowering the O(2) concentration to 5% reduced ethylene-induced growth retardation from 70 to 58% at 0.22 microliters per liter and inhibited (14)C(2)H(4) (0.25 microliters per liter) tissue incorporation and oxidation to (14)CO(2) by 26 and 45%, respectively. However, in contrast to Ag(+) and high CO(2) which slightly promoted growth in ethylene-free air, low O(2) reduced pea seedling growth under these conditions thereby severely limiting its usefulness as a specific antiethylene treatment.Collectively these data suggest that the metabolism of ethylene may be related to its action.

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