Influence of microcystin-RR on growth and photosynthetic capacity of the duckweed Lemna minor L.

The influence of microcystins on animal physiology and pathology has been studied intensively but there is only little information about toxic effects on growth and physiological processes in higher plants. In the present study the duckweed Lemna minor L. was exposed to microcystin-RR, a well known hepatotoxic cyclic heptapeptide produced by several cyanobacterial species. Axenic plants of Lemna minor L. were cultivated for 6 days in a nutrient solution supplemented with 0.1, 0.5, 1.0, 3.0 and 5.0 mg microcystin-RR l(-1), respectively. There was no effect of microcystin-RR on growth of Lemna minor. L. at concentrations between 0.1 and 1.0 mg microcystin-RR l(-1). Concentrations of 3 and 5 mg microcystin-RR l(-1) decreased the formation of fronds already 3 days after treatment, significantly After 6 days most of the plants grown at 5 mg microcystin-RR l(-1) formed only dwarfish, partially malformed fronds, and some of these showed chlorosis compared to the: control plants. Moreover, the maximum electron transport rate as an indicator of photosynthetic capacity was reduced up to 16 % compared to the values obtained from control plants. Furthermore, the contents of chlorophyll a, b and the total amount of carotenoids were significantly reduced by more than 50 %.