Some Effects of Buthidazole on Corn (Zea mays) Photosynthesis, Respiration, Anthocyanin Formation, and Leaf Ultrastructure

Abstract

The effect of the herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on photosynthesis, respiration, anthocyanin formation and leaf ultrastructure of corn (Zea mays L. ‘Pioneer 3780’) was studied following pre- or postemergence applications. Total photosynthesis and dark respiration were measured with an infrared CO2 analyzer in an open air flow system 12, 18, and 24 days after preemergence treatment with 0, 0.56, 1.12, and 2.24 kg/ha of buthidazole. The 0.56 and 1.12 kg/ha preemergence treatments had no effect on total corn photosynthesis even 24 days after treatment, whereas buthidazole at 2.24 kg/ha inhibited photosynthesis as early as 12 days. Total photosynthesis and dark respiration were also measured in whole plants, 30 cm tall, before herbicide application and 4, 24, 48, and 96 h after postemergence treatment with buthidazole at 0, 0.28, 0.56, 0.84, and 1.12 kg/ha. Following postemergence treatment, buthidazole inhibited total corn photosynthesis at any rate examined as early as 4 h after treatment. Neither pre- or postemergence buthidazole applications influenced respiration with the exception of a transitory increase caused by 0.56 kg/ha 12 days after preemergence treatment and by 0.84 and 1.12 kg/ha 4 h after postemergence treatment. Transmission electron micrographs revealed that buthidazole applied postemergence at 0.28 and 1.12 kg/ha reduced or prevented the accumulation of starch in bundle sheath chloroplasts as early as 24 h after treatment. Ultrastructural disruptions in some mesophyll chloroplasts of treated corn plants were also evident. Preemergence application of buthidazole at rates of 0.28, 0.42, 0.56, and 1.12 kg/ha inhibited anthocyanin formation indicating an alteration in corn metabolism.