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

Abstract 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 μg L −1 MC-LR and Mic -CE revealed strong increases of α- and β-tocopherol content, whereas the influence on β-tocopherol was far stronger than on α-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.