Effects of a dicamba/MCPA/mecoprop herbicide mixture on the leaves of a barley variety

Abstract

Abstract. Plants of a barley cultivar Porno were sprayed at 2-node stage with a herbicide mixture, 'Mepro Special', containing dicamba, MCPA and mecoprop, and the plants were grown at two different temperatures. 15°C and 23°C. The effects of the herbicide on the morphology and anatomy were studied by light and electron microscopes and the effects on the chlorophyll content of leaves were studied at various intervals after the spraying.First sign of damage in the morphology of plants grown both at 23°0 and 15°C were observable 10 12 days after the spraying but those in the ultrastructure as soon as 1 day after the treatment. The cells of the vascular bundle sheath Were most sensitive while the mesophyll cells were unchanged during the total observation period of 12 days at 15°C. At a higher temperature injuries of various stages were observable also in the mesophyll 6 days after the treatment.The clearest alterations became visible in the chloroplasts. They swelled to spherical in shape, the intergrana and later also grana lamellae formed vesicles by dilating, later they broke down, and ultimately the plastid envelope disintegrated. The amount of starch and chlorophyll decreased, whereas the number and size of osmiophilic plastoglobuli increased significantly.The mitochondria swelled, the cristae frequently disappeared and the outer membrane of the envelope distended largely. The nucleus was best capable of resisting the toxic effects of the herbicide. The tonoplast and plasmalemma were broken down a short time before the final disintegration of the cell structures. High temperature obviously reinforced the toxic effects of the herbicide mixture.