In vitro cultured cocklebur (Xanthium strumarium L.) responses to dimercaptopropanesulfonic acid and monosodium methanearsonate

Abstract

Monosodium methanearsonate (MSMA) is an effective herbicide used for the control of Xanthium strumarium (cocklebur), a serious weed problem in cotton production. Recently, MSMA-resistant cocklebur was reported, which reduced MSMA effectiveness in the cocklebur control strategy. The mode of action of MSMA may involve the reduction of the pentavalent arsenic in MSMA to a trivalent form, which may then form a complex with sulfhydryl-containing enzymes. Dimercaptopro-panesulfonic acid (DMPS) chelates trivalent arsenic, resulting in a nontoxic complex. The objective of this study was to determine the effect of DMPS and MSMA on the growth of in vitro grown cocklebur shoot and callus tissues. Lateral and terminal shoots were grown on basal Murashige and Skoog medium containing 6.25 mg L−1 (0.0428 mm) MSMA alone and with various concentrations of DMPS. Callus was cultured on basal callus medium also containing 6.25 mg L−1 MSMA alone and an equimolar concentration of DMPS. Shoot injury symptoms, dry root weight, and fresh weight of callus were recorded. Susceptible cocklebur shoots showed severe discoloration and death when treated with MSMA. Resistant shoots and cultured shoot tips were not adversely affected. DMPS alone did not inhibit growth of these tissues. Callus induced from susceptible tissue was inhibited by MSMA and DMPS alone. In all combinations of DMPS and MSMA tested, DMPS did not counteract the MSMA response. Thus, the pentavalent form of arsenic in MSMA apparently is not reduced to the trivalent form by the plant and hence is not involved in the mechanism of action