Early physiological and biochemical responses of rice seedlings to low concentration of microcystin-LR

Abstract

Microcystin-leucine and arginine (microcystin-LR) is a cyanotoxin produced by cyanobacteria like Microcystis aeruginosa, and it's considered a threat to water quality, agriculture, and human health. Rice (Oryzasativa) is a plant of great importance in human food consumption and economy, with extensive use around the world. It is therefore important to assess the possible effects of using water contaminated with microcystin-LR to irrigate rice crops, in order to ensure a safe, high quality product to consumers. In this study, 12 and 20-day-old plants were exposed during 2 or 7 days to a M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations, 0.26-78 lg/L. Fresh and dry weight of roots and leaves, chlorophyll fluorescence, glutathione Stransferase and glutathione peroxidase activities, and protein identification by mass spectrometry through twodimensional gel electrophoresis from root and leaf tissues, were evaluated in order to gauge the plant's physiological condition and biochemical response after toxin exposure. Results obtained from plant biomass, chlorophyll fluorescence, and enzyme activity assays showed no significant differences between control and treatment groups. How-ever, proteomics data indicates that plants respond to M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations by changing their metabolism, responding differently to different toxin concentrations. Biological processes most affected were related to protein folding and stress response, protein biosynthesis, cell signalling and gene expression regulation, and energy and carbohydrate metabolism which may denote a toxic effect induced by M. aeruginosa extract and microcystin-LR. The implications of the metabolic alterations in plant physiology and growth require further elucidation.

Cyanobacterial Toxins Emerging Contaminants in Soils: A Review of Sources, Fate and Impacts on Ecosystems, Plants and Animal and Human Health

“…However, in a study performed by Gutiérrez-Praena et al [102] in which tomato plants were exposed to MC-LR at 100 µg L−1 , changes were detected in the function of various proteins related to ATP synthesis, carbon fixation, photosynthesis and carbohydrate metabolism that appear to be linked with the observed decrease in photosynthetic efficiency. A decrease in the expression of some proteins involved in photosynthesis was also observed by Azevedo et al [128] in rice plants exposed to 13 µg MC-LR L −1 . The contradictory results obtained in these different studies may be associated with differences in the microcystin concentrations used in each study and the nature of the toxin pure or present in a cyanobacterial crude extract.…”

Effects of microcystin-LR, cylindrospermopsin and a microcystin-LR/cylindrospermopsin mixture on growth, oxidative stress and mineral content in lettuce plants (Lactuca sativa L.)

“…The sGST activity was determined according to the method of Habig et al (1974), whereas GPx activity was determined according to the method of Lawrence and Burk (1976). GST and GPx activities were performed with 0.1 mg protein/mL, and the enzymatic activities were calculated according to Azevedo et al (2014) and expressed in nkat/mg protein. In were used as internal standards.…”

Evaluation of phytotoxicity and ecotoxicity potentials of a cyanobacterial extract containing microcystins under realistic environmental concentrations and in a soil–plant system

“…However, a significant increase in the dry weight of the aerial part of the tomato seedling was registered from the lowest MCs concentration (0.005 mg L À1 ). In a recent study performed by Azevedo et al (2014) in hydroponic conditions and at low concentrations of MCs (0-0.078 mg eq. MC-LR L À1 ), no significant differences on the dry and the fresh weight of roots and leaf of 20-day-old rice plants exposed for 7 d were registered.…”