Yutaka Nasu

Lemna (duckweed) as an indicator of water pollution. I. The sensitivity ofLemna paucicostata to heavy metals

The environmental conditions affecting the growth and multiplication ofLemna paucicostata in the presence of heavy metals were examined to establish a phytometer method for water pollution using the duckweed,Lemna. The pH of the medium, concentration, and composition of the nutrient in the medium, and the temperature at which cultures were maintained, were found to affect the sensitivity ofLemna to heavy metals. Therefore, if the growth and multiplication ofLemna is maintained by a Bonner-Devirians medium (pH 6.1, 7.1) above 25°C, heavy metals can be detected in water.

Comparative studies on the absorption of cadmium and copper in Lemna paucicostata

Abstract The absorption of copper or cadmium in Lemna paucicostata 6746 was suppressed by the addition of EDTA to the medium. Only 30 μm of EDTA was sufficient to prevent the absorption of copper at a concentration of 5–10 μ m whereas 400 μ m of EDTA was necessary to prevent the absorption of cadmium at the same concentration as copper. Ammonium ion added to the medium also greatly suppressed copper absorption. Cadmium absorption was, however, only slightly suppressed by this means. The growth of Lemna under these experimental conditions was inhibited in proportion to the amount of copper or cadmium absorbed. The absorption of cadmium was higher, the higher the initial pH of the medium, but that of copper was not significantly affected by the initial pH between 3·6 and 5·1. Nonetheless, both cadmium and copper inhibited plant growth more strongly at pH 5·1 than at pH 4·1. The absorption mechanism and the mode of action of cadmium seem to differ from those of copper in Lemna paucicostata 6746.

Effects of cadmium and copper co-existing in the medium on the growth and flowering of Lemna paucicostata in relation to their absorption

Abstract Copper ion added to M-sucrose medium suppressed both frond multiplication and frond growth (wet weight increase of each frond) of Lemna paucicostata 6746, but cadmium ion suppressed only frond multiplication not affecting frond growth. Such ion specific actions of copper and cadmium were evident even in the medium containing both metal ions, the degree of their effects depending on the concentration of each metal ion absorbed. The absorption of copper was not influenced by the presence of cadmium but that of cadmium was reduced considerably with increasing concentrations of copper in the medium. The flower-inducing activity of copper ion in this plant was nullified by simultaneous application of cadmium which does not suppress either copper absorption or short-day induced flowering.

LEMNA AS AN INDICATOR OF WATER POLLUTION AND THE ABSORPTION OF HEAVY METALS BY LEMNA

ABSTRACT To determine the potential for use of Lemna paucicostata 6746 as an indicator of water pollution, and for its utilization as a purifier of waste water, and to study the biokinetics of heavy metals, the sensitivity of Lemna to heavy metals and the mode of metal absorption by Lemna were studied. The concentration factor of cadmium for Lemna was from approximately 100 to 500 at the 24th hour after the start of culture on Bonner-Devirian medium containing cadmium (pH6.1). Seven days after the start of culture, 70% of cadmium in 25ml of medium was absorbed by Lemna on 0.01ppm cadmium-containing medium, 50% on 0.1ppm, and 2% on 1ppm cadmium-containing medium. Those factors which make Lemna more sensitive to cadmium–the high pH value of the medium, dilution of the medium, and high temperature– were also effective in causing the rapid absorption of cadmium by Lemna. The frond multiplication of Lemna for 7 days was inhibited 50% by 0.1ppm of cadmium or copper, and by 1ppm of zinc, manganese or arsenic. Arsenic and copper inhibited the growth of each frond more effectively than frond multiplication, whereas zinc, manganese and cadmium primarily inhibited frond multiplication.