The Action of Benzimidazole on Lemna Minor

Abstract

Benzimidazole (BZ) supplied to the medium of aseptically cultured Lemna at about 3.4 x 10-3 [image] induces a modification characterized by a complete inhibition of root-elongation and a 65-75% increase in frond area due to cell-enlargement. High auxin concentrations induce a similar modification in Lemna but plants so produced soon die, in contrast with the continued viability of the BZ-modified plants. BZ-modified plants exhibit a higher sensitivity to auxins and a lower sensitivity to the antiauxin 2,4,6-T than do normal plants. Attempts to prevent the BZ-modification with adenine and related compounds proved unsuccessful. Oxygen consumption of modified plants is unaffected, or increased, by concentrations of cyanide, azide, carbon monoxide and phenylthiourea which inhibit that of normal plants. Homogenates of modified plants have 0-4% of the polyphenol oxidase and ascorbic acid oxidation activity 20-33% of the cytochrome oxidase activity, and 45% or more of the catalase and glycolic acid oxidase activity of normal homogenates, on a fresh weight basis. BZ is a weak direct inhibitor of polyphenol oxidase activity, but not of cytochrome oxidase, in normal homogenates. It forms an insoluble complex with copper. Modified plants contain no less copper than the normal. It is concluded that at least some of the effects of BZ are due to its sequestration of copper within the plant and to the resultant disturbance in copper metabolism.