Effect of glyphosate on nitrogen assimilatory system in the wild type and mutant strains of Anabaena doliolum

Growth of the wild type and glyphosate-tolerant mutant of Anabaena, measured as a function of graded concentration of glyphosate in presence of exogenous combined nitrogen sources, showed that reduced form of nitrogen was best, followed by NO₂⁻ and NO₃⁻. The mutant strain was relatively less susceptible to glyphosate than the wild type irrespective of the type of nitrogen source used. Glyphosate induced stimulation in the nitrate reductase (NR) and reduction in glutamine synthetase (GS) activity indicated nitrogen starvation conditions. However, the rate of GS and NR activity in the glyphosate tolerant mutant was found to be higher than the wild type. Further, the glyphosate dependent efflux of nitrite was higher in the wild type than the mutant. The results suggested that reduced susceptibility of nitrogen assimilatory system of the mutant strain might be responsible for higher glyphosate tolerance.