The Duckweed Experiment: Effects of Lowering Light Intensity on the Rate of Per Capita Growth of Lemna Minor

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Iran. J. Environ. Health. Sci. Eng., 2010, Vol. 7, No. 2, pp. 299-306

GROWTH, PHOTOSYNTHESIS AND RESPIRATORY RESPONSE TO COPPER IN LEMNA MINOR: A POTENTIAL USE OF DUCKWEED IN BIOMONITORING Downloaded from http://journals.tums.ac.ir/ on Thursday, February 23, 2012 * N. Khellaf, M. Zerdaoui Laboratory of Environmental Engineering, Faculty of Engineering, Badji Mokhtar University, Annaba, Algeria Received 3 February 2010; revised 21 Jully 2010; accepted 20 August 2010

ABSTRACT

Aquatic macrophytes are known to accumulate various heavy metals in their biomass. This accumulation is often accompanied by physiological changes which can be used in biomonitoring for aquatic pollution. In this study, the impact of copper (Cu) on the growth of the duckweed Lemna minor, followed by its removal, was studied with 0.1–1.0 mg/L of Cu in a quarter Coïc and Lesaint solution at pH=6.1. In order to verify duckweed tolerance to Cu, photosynthesis was measured at the maximal concentration which caused no effect on the plant growth. The results showed that copper inhibited Lemna growth at concentrations ≥ 0.3 mg/L. At 0.2 mg/L, the final biomass was approximately four times greater than the initial biomass. Analysis of metal concentration in water showed that Lemna minor was responsible for the removal of 26% of Cu from the solution. In the presence of Cu, respiration was reduced, while photosynthesis increased considerably. Net photosynthesis approximately increased three times compared to the control. Copper was responsible for 130-290% increase in the photosynthetic activities. These results suggested that Lemna minor could be a good tool for the evaluation of copper pollution in biomonitoring programs. Key words: Aquatic pollution; Bioindicator; Lemna minor; Physiological modifications; Growth; Photosynthesis

INTRODUCTION

Copper (Cu) is an essential element for organisms and is involved in numerous physiological processes (Teisseire and Guy, 2000). However, it is toxic at higher concentrations by causing deleterious effects to human, animals and plants (Vinodhini and Narayanan, 2009). Excess of Cu may reach living organisms as a result of environmental pollution caused by anthropogenic activities (mining operations, manufacturing industries and agricultural technologies) which can modify the biogeochemical cycles of the metal. Several studies demonstrated that many species of duckweed, a group of free-floating freshwater plants of the family Lemnaceae, are able to *Corresponding author: E-mail: khellafdaas@yahoo.fr Tel/Fax: +213 38 87 60 65

absorb and accumulate high amount of copper in their biomass producing an internal concentration several fold greater than the nutrient medium (Jain et al., 1989; Zayed et al., 1998; Miretzky et al., 2004; Ater et al., 2006). This accumulation has, in some ways, a relationship with the tolerance phenomena which is defined as the cell capability to protect plant tissues against injury caused by the metal (Sabreen and sugiyama, 2008). At metal concentration greater than the tolerated concentration, toxicity symptoms and physiological changes are induced. Cupric ions are responsible for many alterations of plant cells and inhibition of enzymatic activities (Teisseire and Guy, 2000). They also cause significant changes in respiration, photosynthetic CO2 fixation and photosynthetic pigments by 299

N. Khellaf et al., a comparatIVE aNaLytIcaL Study ...

Downloaded from http://journals.tums.ac.ir/ on Thursday, February 23, 2012

increasing oxidation of chloroplast membranes (Prasad et al., 2001; Hattab et al., 2009). These physiological modifications, evaluated by biotoxicity tests, can be used as an indicator of metal pollution and offer data in biomonitoring (Movahedian et al., 2005). Sedentary macrophytes as bioindicators have some advantages such as high tolerance to aquatic metal pollution, convenience for sampling, large individuals and easy to realize laboratory raise (Zhou et al.,...
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