Micronutrient tolerance and accumulation in the duckweed, Lemna.

Abstract

Vegetative growth of the aquatic monocotyledon Lemna minor L. (duckweed) under continuous irradiation in photoheterotrophic medium is log‐linear with a frond doubling‐time of about 1.4 d. This steady‐state frond multiplication rate was not altered (through six days) by concentrations of micronutrients (Fe,Mn,B,Cu, Zn,Mo) between 28 and 1000 times that contained in the routine growth medium. Using high but not inhibitory concentrations, the effect on steady‐state growth of all possible 2‐, 3‐, 4‐, 5‐, and 6‐way combinations has been studied. Lerma growing in the presence of high concentrations of any other micronutrient is least tolerant to the addition of Mo. Growth inhibition due to 2‐way combinations of certain elements (eg. MnMo) was prevented by the presence of a third (eg. MnMoZn) in patterns suggesting selective interaction between the elements. Moreover, in the absence of Mo in high concentration the combination of the other 5 micronutrients was not inhibitory even though separate 2‐, 3‐, and 4‐way combinations were.

The accumulation of micronutrients during steady‐state growth showed that each was absorbed against a chemical gradient at high external concentration (no data for B). In the absence of growth inhibition, Fe accumulated to 65 μg/g fresh weight, Mn to 221, Cu to 40, Zn to 139, and Mo to 705. Multiplying each by approximately 8 converts to μg/g dry weight.

Key words:

• duckweed
• micronutrients
• element tolerance/accumulation