If potassium is obtained from sea-water by precipitation with calcium dipicrylamine, potassium fertilizers and sea-water will be contaminated with a little dipicrylamine. The influence of calcium dipicrylamine on metabolism of Chlorella and some other aquatic and terrestrial plants was therefore studied. It inhibited photosynthesis even at lower concentrations (10 -6-10 -5M), than other inhibitors such as ethyl urethane, phenyl urethane, hydroxylamine, 2,4-dinitrophenol and sodium azide. Autotrophic growth was inhibited at almost the same concentration. But heterotrophic growth of Chlorella was less inhibited. Respiration was stimulated by up to 60 %, even at 10 -2M. At this concentration, glucose-stimulated respiration was 50 % inhibited but at least partly reversibly. The same degree of inhibition (not reversible by washing) was observed with light saturation as with light limitation in Chlorella photosynthesis. This suggested a specific enzyme- inhibitor, influencing certain dark reactions as well as the energy transfer in photosynthesis. Lower temperatures severely increased inhibition of photosynthesis in Chlorella.Despite inhibition of growth and photosynthesis at low concentrations in water culture, the compound was less harmful in the field through the high adsorptive capacity of soil, especially of humus. Only with extreme artificial contamination was there a decrease in yield.
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