Influence of exogenous urea on photosynthetic pigments, (14)CO 2 uptake, and urease activity in Elodea densa-environmental implications.

This paper analyzes the effect of exogenous urea in increased concentration gradient (0, 100, 500 and 1,000 mg L(-1)) on photosynthetic pigments (measured spectrophotometrically), uptake of (14)CO2 (using radioisotope), and urease activity (by measuring ammonia with Nessler's reagent) in leaves of Elodea densa Planch. We have observed that low concentration of urea (100 mg L(-1)) stimulates the accumulation of photosynthetic pigments and intensifies photosynthesis in E. densa, whereas high concentration (1,000 mg L(-1)) suppresses these processes.

Ecophysiological tolerance of Elodea canadensis to nickel exposure.

Biological accumulation of nickel and concomitant ecophysiological responses were studied in the leaves of Elodea canadensis treated with different concentrations of Ni (1-50 microM) for 5d. In low concentrations nickel was accumulated mainly in the soluble protein fraction, which correlated with its highest observed accumulation coefficient. In higher concentrations, Ni binding in the non-protein soluble fraction was observed.