The effects of excess copper sulfate on the metabolism of the duckweed Lemna minor

Abstract

Several parameters of growth and metabolism of axenic cultures of the duckweed Lemna minor L. were evaluated for effects of a 60% elevation of the copper sulfate concentration in standard Hutner's medium (2.50 vs. 3.94 mg 1 −1). All cultures were grown for 20 days at 24°C in a 14-h photoperiod (120 μE). Relative to controls, presence of the excess copper sulfate resulted in the following effects: chlorophyll a decreased from 0.962 to 0.346 mg g wet wt. −1; phot synthetic CO 2 uptake from the water decreased from 0.101 to 0.003 mg C g dry wt. −1;h −1; heterotrophic uptake of glucose in the dark decreased from 0.46 to 0.075 mg glucose g dry wt. −1 h −1. No significant changes occurred in the rates of dark respiration or release of organic carbon in the dark, but photorespiratory CO 2 release increased from 2.09 to 20.4% of recently fixed 14CO 2h −1, and organic carbon release in the light increased from 1.19 to 8.88% of recently fixed 14CO 2h −1. The results indicate that the high toxicity of a relatively small excess of copper sulfate is manifested in several ways in L. minor.