Dimethipin (2,3-Dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide) Effects on Soybean Seedling Growth and Metabolism

摘要

Three-day-old dark-grown soybean Glycine max(L.) Merr. seedlings were transferred to 2 mmCaSO4or 10−5mdimethipin in 2 nmCaSO4and root-fed via liquid culture. Plants were placed in continuous darkness or in continuous white light (200μE.m−2·s−11, PAR) at 25°C. Dimethipin inhibited root and shoot elongation in dark-grown plants after 24 h and 48 h, respectively. In the light, root elongation was inhibited also after 24 h, but hypocotyl elongation was not significantly affected. Extractable phenylalanine ammonia-lyase (PAL) activity per axis in dimethipin-treated dark-grown axes was not generally affected but, in the light dimethipin caused a significant decrease in PAL activity (24 to 96 h). Total soluble hydroxyphenolics in axes were not affected by dimethipin in light- or dark-grown plants. Anthocyanin and chlorophyll levels were lowered in hypocotyls of dimethipin-treated plants after 48 to 96 h. Soluble protein in hypocotyls of light- or dark-grown seedlings was not substantially affected by dimethipin. Nitrate reductase (NR) activity (per organ) was generally not affected by dimethipin in light-grown cotyledons, but in the roots of these seedlings, NR activity was significantly decreased. Proteolytic enzyme activity using three substrates (leucine-p-nitroanilide, LPNA; proline-p-nitroanilide, PPNA; and benzoylarginine-p-nitroanilide, BAPA) indicated little effect on enzyme activities per organ in roots and hypocotyls. These data suggest that dimethipin at low concentrations can cause significant growth inhibition in soybean seedlings grown in either light or darkness and that furthermore, extractable activities of some enzymes associated with nitrogen metabolism and secondary metabolism are altered by this chemical. Light also plays a role in the activity of this