Influence of the cyanotoxin microcystin-LR on tocopherol in Alfalfa seedlings (Medicago sativa)

Spray irrigation of crop plants can represent a risk if the water is contaminated with cyanotoxins. These secondary metabolites produced by many cyanobacteria can have adverse effects on organisms, among others the induction of excess oxygen radicals, so-called oxidative stress. Thereby tocopherol as a lipid antioxidant is essential to maintain membrane integrity. In this study the effects of the cyanotoxin microcystin-LR (MC-LR), and a Microcystis crude extract (Mic-CE) containing MC-LR on tocopherol content and gene expression of Homogentisate phytyltransferase (HPT), involved in tocopherol synthesis, were investigated in seedlings of the crop plant Medicago sativa. Exposures to environmental relevant concentrations showed that Mic-CE affects the tocopherols at a lower concentration than the pure toxin. Changes during a 3-day exposure using 0.5 mu g L-1 MC-LR and Mic-CE revealed strong increases of alpha- and beta-tocopherol content, whereas the influence on beta-tocopherol was far stronger than on a-tocopherol. The HPT mRNA was elevated after 24 and 72 h exposure to MC-LR. These results show that also low concentrations of cyanobacterial toxins in the water have strong influence on tocopherol in M. sativa seedlings and therefore represent a stress for the plants. (C) 2010 Elsevier Ltd. All rights reserved.