Inhibition by Purines of the Production of Fronds in Lemna perpusilla

Abstract

WHILE examining the herbicidal properties of a variety of compounds using a modified duckweed test¹, we noted that several purine derivatives showed marked inhibition of the production of fronds of L. perpusilla growing in a chemically defined medium². In these experiments 10 ml. of sterile Hillman's medium² (with sucrose) was added to 1 × 4 in. test-tubes (capped with Morton stainless steel closures). Dilutions of the test substances were added to the tubes and three fronds of L. perpusilla were then added. The inoculated tubes were placed on slanting boards in a room with a constant temperature of 75° F which was illuminated for 14 h each day. The number of fronds in each tube was determined after 3, 5, 7 and 9 days of incubation. Four replicate tubes were started for each concentration of test compound, and the average number of fronds in each tube was plotted in the dose–response curve. The concentration of inhibitor needed to reduce growth to 50 per cent of that of the untreated controls was determined graphically. In these conditions a ten-fold increase in the number of fronds was rioted in the control tubes during the 9 days.