BIOLOGICAL EFFECTS OF A HERBICIDE ON A NITROGEN‐FIXING CYANOBACTERIUM (BLUE‐GREEN ALGA): AN ATTEMPT FOR INTRODUCING HERBICIDE‐RESISTANCE

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Abstract
Summary: The herbicide monuron [3‐(4‐chlorophenyl)‐1, 1‐dimethylurea] inhibits growth and heterocyst formation in the nitrogen‐fixing cynobacterium Nostoc muscorum. These inhibitory effects are glucose‐reversible in both N2 (nitrogen‐free) and NO3− media. A spontaneous mutant of this cyanobacterium, resistant to a dose of monuron normally applied to the rice‐fields of North India, has been isolated and preliminarily characterized as having no requirement for an organic carbon source for its normal physiology under monuron‐treated conditions. The behaviour of the mutant has been tentatively explained as resulting from a permeation mutation preventing monuron entry into N. muscorum.