Search

Effects of rice-field herbicide benthiocarb (S(4-chlorobenzyl)-N,N-diethyl thiolcarbamate) was studied on the nitrogen-fixing blue-green alga Nostoc linckia. The herbicide caused inhibition of growth and heterocyst formation, an increase in intensity of photoacoustic signals, and a four-fold reduction in oxygen evolution, but did not affect dark O2-uptake. The inhibition of growth and heterocyst formation was relieved by 500 micrograms/ml glucose. A Het-Nif- mutant of Nostoc muscorum failed to show an increase in reversion, frequency after treatment with 10 micrograms/ml benthiocarb for 1 hr.

Nitrogen-fixation by two species of Nostoc, one of them a lichen phycobiont, was generally stimulated by low concentrations of arsenic, cadmium, nickel, lead, palladium, and zinc. Higher concentrations (0.025 to 0.125 ppm) of arsenic, nickel, and palladium were also stimulatory; however, higher concentrations of cadmium, lead, and zinc tended to inhibit fixation. With the exception of palladium and zinc at low concentrations these six tested elements tended to inhibit nitrogen-fixation in Chlorogloea fritschii and Westiellopsis sp.

The effect of lanthanum sulphate on five Azotobacter strains (4A7, 10, 5A2, 5A1, and 3A3) isolated from Allahabad soil consists in a considerable increase in the nitrogen fixation, carbon consumption and in the amount of nitrogen fixed in mg per g of carbon consumed. The presence of 200 microM, 300 microM and 400 microM lanthanum sulphate in culture media increases the fixation of nitrogen by all the nitrogen fixers significantly.

The effect of 0, 100, 200, 300, 400, and 500 microM concentrations of sodium molybdate in the culture media of the five Azotobacter species isolated from Allahabad soil was studied. It was observed that the presence of molybdenum in the culture media of all the bacterial samples increased the fixation of nitrogen indicating that molybdenum is essential for increasing the efficiency of the nitrogen fixers for nitrogen fixation.

The effects of the pesticide hexachlorocyclohexane (HCH) on the nitrogen fixing blue-green algae Anabaenopsis raciborskii and Anabaena aphanizomenoides commonly found as blooms in fish ponds were studied. These algae were very sensitive to HCH, and a distinct decrease in growth rate was observed on prolonged incubation. Lower concentrations (10 microgram/ml) were algistatic and higher concentrations (60 microgram/ml) were algicidal. The inhibition of nitrogen fixation indicated that the presence of HCH might affect overall nitrogen economy of inland waters.

IAA was found to stimulate growth, nitrogen fixation and pigment synthesis in Anabaena doliolum in all concentrations tested. Heterocyst frequency was stimulated up to a concentration of 50 ppm IAA. NAA stimulated growth and nitrogen fixation up to 10 ppm. GA promoted growth, pigment synthesis, heterocyst frequency and nitrogen fixation only up to a concentration of 2 ppm. Kinetin promoted growth up to 100 ppm and synthesis of pigments, while nitrogen fixation was stimulated up to 5 ppm.

Growth and fixation of nitrogen were retarded in Anabaena doliolum when grown on elemental nitrogen in presence of four different herbicides. The alga was found to be intolerant to these chemicals under nitrogen fixing conditions even in low concentrations. An inhibition of photosynthesis has been regarded as the main basis of herbicidal activity besides other interactions.