Environmental variations mediate duckweed (Lemna minor L.) sensitivity to copper exposure through phenotypic plasticity

Biomonitoring of heavy metals and their phytoremediation by duckweeds: Advances and prospects

Heavy metals (HMs) contamination of water bodies severely threatens human and ecosystem health. There is growing interest in the use of duckweeds for HMs biomonitoring and phytoremediation due to their fast growth, low cultivation costs, and excellent HM uptake efficiency. In this review, we summarize the current state of knowledge on duckweeds and their suitability for HM biomonitoring and phytoremediation. Duckweeds have been used for phytotoxicity assays since the 1930s. Some toxicity tests based on duckweeds have been listed in international guidelines. Duckweeds have also been recognized for their ability to facilitate HM phytoremediation in aquatic environments. Large-scale screening of duckweed germplasm optimized for HM biomonitoring and phytoremediation is still essential. We further discuss the morphological, physiological, and molecular effects of HMs on duckweeds. However, the existing data are clearly insufficient, especially in regard to dissection of the transcriptome, metabolome, proteome responses and molecular mechanisms of duckweeds under HM stresses. We also evaluate the influence of environmental factors, exogenous substances, duckweed community composition, and HM interactions on their HM sensitivity and HM accumulation, which need to be considered in practical application scenarios. Finally, we identify challenges and propose approaches for improving the effectiveness of duckweeds for bioremediation from the aspects of selection of duckweed strain, cultivation optimization, engineered duckweeds. We foresee great promise for duckweeds as phytoremediation agents, providing environmentally safe and economically efficient means for HM removal. However, the primary limiting issue is that so few researchers have recognized the outstanding advantages of duckweeds. We hope that this review can pique the interest and attention of more researchers.

Terrestrial and Floating Aquatic Plants Differ in Acclimation to Light Environment

The ability of plants to respond to environmental fluctuations is supported by acclimatory adjustments in plant form and function that may require several days and development of a new leaf. We review adjustments in photosynthetic, photoprotective, and foliar vascular capacity in response to variation in light and temperature in terrestrial plants. The requirement for extensive acclimation to these environmental conditions in terrestrial plants is contrasted with an apparent lesser need for acclimation to different light environments, including rapid light fluctuations, in floating aquatic plants for the duckweed Lemna minor. Relevant features of L. minor include unusually high growth rates and photosynthetic capacities coupled with the ability to produce high levels of photoprotective xanthophylls across a wide range of growth light environments without compromising photosynthetic efficiency. These features also allow L. minor to maximize productivity and avoid problems during an abrupt experimental transfer of low-light-grown plants to high light. The contrasting responses of land plants and floating aquatic plants to the light environment further emphasize the need of land plants to, e.g., experience light fluctuations in their growth environment before they induce acclimatory adjustments that allow them to take full advantage of natural settings with such fluctuations.

Physiological Response of Nutrient-Stressed Lemna gibba to Pulse Colloidal Silver Treatment

Wastewater is a source of many environmental pollutants and potentially high concentrations of essential plant nutrients. Site-specific nutrient levels may influence the response of exposed plants to a chemical stressor. In the present study, we focused on the responses of model aquatic macrophyte swollen duckweed (Lemna gibba L.) to a short pulse exposure and a commercially available colloidal silver product as a potential environmental chemical stressor, combined with two levels of total nitrogen and phosphorus nutrition. Treatment with the commercially available colloidal silver product caused oxidative stress in L. gibba plants under both high and low nutrient levels. Plants grown and treated under high nutrient levels showed lower levels of lipid peroxidation and hydrogen peroxide accumulation, as well as higher levels of photosynthetic pigment content in comparison to treated plants under low nutrient levels. Higher free radical scavenging activity for plants treated with silver in combination with high nutrient levels resulted in better overall protection from silver-induced oxidative stress. The results showed that external nutrient levels significantly affected the L. gibba plant's response to the colloidal silver presence in the environment and that nutrient levels should be considered in the assessment of potential environmental impact for contaminants.

Combined action of gamma radiation and exposure to copper ions on Lemna minor L

PURPOSE

Under natural conditions, the reaction of living organisms to the action of acute gamma radiation depends on other stressors, including heavy metals. The aim of this work was to study changes in morphometric parameters, the content of photoassimilation pigments and the level of oxidative stress in irradiated duckweed at various copper concentrations in the culture medium.

MATERIALS AND METHODS

As a model organism, we used Lemna minor L. Duckweed was exposed to acute γ-radiation at doses of 18, 42, 63 Gy. After irradiation, the plants were transferred into a medium containing 3, 5, 6.3 μmol/L Cu. On the 4th day of exposure, the levels of chlorophyll, carotenoids, malondialdehyde (MDA) were measured; after 7 days, the specific growth rate, the level of damage, the change in the frond area, copper concentration in plant tissues were determined.

RESULTS

The action of γ-radiation (18, 42, 63 Gy) and copper ions (3, 5, 6.3 μmol/L) reduced the growth rate, increased the membrane lipid peroxidation, reduced the area of the fronds more significantly than under the separate action of the factors. The factors acted antagonistically on the specific growth rate. The content of copper in the tissues of irradiated plants (42, 63 Gy) increased.

CONCLUSION

Irradiation of duckweed with acute doses of gamma radiation reduced the resistance of plants to excess copper in the environment.

The change of accumulation of heavy metal drive interspecific facilitation under copper and cold stress

Plant diversity has important functions in ecosystem productivity overyielding and community stability. Little is known about the mechanism causing productivity overyielding and stability under harsh conditions. This study investigated the photosynthetic response and subcellular distribution of uni- and co-cultured duckweeds (Lemna aequinoctialis and Spirodela polyrhiza) under excess copper (1.0 mg/L) and low temperature (5 °C) conditions. The results showed that the growth of uni-cultured L. aequinoctialis was not different from that of uni-cultured S. polyrhiza across copper treatments at control temperature (25 °C). The growth rate of L. aequinoctialis increased by 55.5 % under excess copper concentration when it coexisted with S. polyrhiza, compared with uni-culture. Subcellular distributions of copper were predominantly distributed in cell walls. S. polyrhiza accumulated more copper in cell walls than L. aequinoctialis under uni-cultured condintion at excess copper concentration. Co-cultured S. polyrhiza increased copper accumulation in cell walls of co-cultured L. aequinoctialis to decrease toxicity at excess copper concentration, compared with L. aequinoctialis. Low temperature increased copper toxicity, with duckweeds having lower growth rate and photosynthetic activities (Fv/Fm). The L. aequinoctialis growth rate in co-culture was higher than in uni-culture under excess copper concentration and low temperature conditions, indicating that S. polyrhiza decreased the copper toxicity for L. aequinoctialis. The photosynthetic activity (Fv/Fm) of co-cultured L. aequinoctialis was higher than that of uni-cultured L. aequinoctialis exposed to excess copper concentration at low temperature. The community that formed by co-culturing S. polyrhiza and L. aequinoctialis produced more biomass by avoiding the toxicity of excess copper through heavy metal compartmentalization and photosynthetic activities.