A novel response of wild‐type duckweed (Lemna paucicostata Hegelm.) to heavy metals

Abstract

The responses of wild-type Lemna paucicostata, used as the experimental stock, to seven heavy metals were investigated with a hydroponic culture in a culture facility. The results showed that six of the metals could induce L. paucicostata to release daughter fronds from the mother frond before maturity, resulting in breakup of the colony. This phenomenon is novel and has not been reported before. Six of the heavy metals investigated-copper, cadmium, nickel, zinc, mercury, and chromium-could induce this response, but sensitivity and response of the plant varied. When Cu(2+) at a concentration of 0.2 micromol/L was added, the response was significantly different from that of the control after a 2-h exposure. The response to cadmium (0.8 micromol/L) was significantly different after a 6-h exposure; to zinc (10 micromol/L) and nickel (5 micromol/L), after 5 and 7 h, respectively. But for lead, even at a concentration of 80 micromol/L for 96 h, no colony breakup was induced. The response to heavy metals occurred within 24 h; increasing the exposure by another 24 h had nearly no additional effect on the colony breakup. When the response was over, the number of colonies with fronds varied with the inducement capacity of the metal. Nutrients could affect the sensitivity of L. paucicostata to some heavy metals, such as mercury, chromium, zinc, and nickel, but not to copper and cadmium. Sensitivity was also changed when CuCl(2) was used as the copper source instead of CuSO(4). These results indicate that some heavy metals could serve as a toxicant for inducing L. paucicostata to release daughter fronds in advance. This change might involve a stress response such as ethylene production. Also discussed is the possibility of this response as a biomarker in a bioassay.

Effects of nanomolar copper on water plants—Comparison of biochemical and biophysical mechanisms of deficiency and sublethal toxicity under environmentally relevant conditions

“…Earlier studies on Ni and Cd were performed at several higher concentrations than in our study, reaching several hundreds of micromolar concentrations and performed only seldom with aquatic macrophytes and multicellular algae (Li and Xiong, 2004). In one such study, authors found that Ni treatment with concentrations above 9 mg l -1 (= 150 µM) were toxic to the duckweed, and when above 1 mg l -1 (=17 µM) towards higher concentrations, there was a gradual decrease in contents of Chl a, b and carotenoids with a reduction in the multiplication rate (Singh et al, 2011).…”

“…Li and Xiong (2004) found that colonies of Lemna paucicostata collapsed when treated with 5 µM of Ni. Another species of duckweed, Spirodela polyrhiza, showed reduced multiplication rate with increasing concentrations of Ni (Singh et al, 2011).…”

Phytoremediation of Cu, Cr and Pb Mixtures by Lemna minor

“…While essential for plant metabolism, Cu is known to adversely affect L. minor in concentrations as low as 0.05 lmol/L (Li and Xiong 2004). EC 50 values for L. minor have previously been determined by Wang (1986) (1.1 mg/L for 48 h of exposure), Khellaf and Zerdaoui (2009) (0.45 mg/L for 4 days of exposure) and Drost et al (2007) (9.7 lM for 7 days of exposure).…”

Nickel in the Environment and Its Role in the Metabolism of Plants and Cyanobacteria

“…Subtle changes in physiology, which may still be signifi cant for survival in the natural environment, may occur at much lower concentrations. For example, a break-up of colonies of the fl oating higher aquatic plant Lemna was observed already at 5 µM Ni 2ϩ (or 0.2 µM Cu 2ϩ ) within 6 h of exposure [101]. And a 15% decrease of root growth was observed at 2.5 µM Ni 2ϩ in a particularly sensitive strain of Silene paradoxa growing on nutrient solution in sand culture [102].…”