Differential sensitivity of three cyanobacteria to the rice field herbicide Machete

Abstract

The effect of the rice field herbicide Machete (2‐chloro‐2′6′‐diethyl‐N‐(Butoxymethyl)acetanilide) on the growth and cell composition of Anacystis nidulans, Nostoc muscorum and Anabaena doliolum was investigated. Growth of these cyanobacteria was completely inhibited at 2.5, 5.0 and 20 μg/ml, respectively, while a slight stimulation of growth was observed at lower concentrations. Stimulation of cyanobacterial growth in the presence of low concentrations of Machete was associated with an increase in the cellular levels of phycobilins and RNA while there was little impact on the levels of chlorophyll a and DNA. Photosynthetic pigments were degraded at lethal concentrations. The toxicity of the herbicide towards N. muscorum and A. doliolum could be reversed by supplementing the growth medium with either nitrate, nitrite or ammonia. This did not apply for A. nidulans. It is suggested that Machete inhibited nitrogen fixation in the former two strains while availability of nutrients was affected in the latter strain. In either case death of the organisms was most likely due to nitrogen starvation. Copyright © 1986 Wiley‐VCH