Influence of glyphosate an Mastigocladus laminosus.

A laboratory study on the effects of commonly field-sprayed herbicide, glyp hosate ('Roundup') on the nitrogen-fixing biofertilizer cyanobacterium, Mas tigocladus laminosus Cohn. were studied. This herbicide, operating through inhibition of Shikimic acid pathway, caused significant decrease in chlorop hyll and phycobilin pigments even at 10 mu M concentrations within 24 hours leading to bleaching of cultures. Photosynthesis was also drastically affe cted, indicated by the low carbohydrate content of cells. Carotenoid conten t of cells remained unaffected. The levels of total cellular nitrogen and p rotein declined steadily inspite of maintenance of constant heterocyst coun ts. Eventhough, the herbicide inhibits shikimic acid pathway of amino acid biosynthesis, the total cellular amino acid registered a high level leading to the inhibition of ammonia assimilation (Glutamine Synthetase) activity. It is suggested that the greater amino acid pools of the cells could have been possible by the break down of cellular proteins, including the major p igment, phycobiliprotein.