Effects of picloram on growth and on chlorophyll, RNA, and protein content of plants

Abstract

Foliar application of picloram (4-amino-3,5,6-trichloropicolinic acid) markedly inhibited the growth of soybean (Glycine max (L.) Merr., cv. Harosoy 63) and Canada thistle (Cirsium arvense (L.) Scop.). The rates of picloram which caused death of soybean (0.14 kg/hectare) and Canada thistle (0.56 kg/hectare) in 2 weeks caused no marked injury symptoms to barley (Hordeum vulgare L. cv. Parkland). ED50 values of picloram (doses required to reduce growth by half) were 16.1 g/hectare for soybean, 18.2 g/hectare for Canada thistle, and 3.64 kg/hectare for barley.Picloram (250 mg/liter, about 0.30 kg/hectare), both 1 and 3 days after treatment, markedly reduced the chlorophyll content of soybean and Canada thistle plants. RNA (ribonucleic acid) and protein contents of such picloram-treated plants, on the other hand, were increased up to 30% over controls. In barley, picloram had very little effect on chlorophyll, RNA, and protein content.