In vivo influence of cyanobacterial toxins on enzyme activity and gene expression of protein phosphatases in Alfalfa (Medicago sativa)

Abstract Irrigation of crop plants with surface water can be a threat if cyanobacterial toxins are present in the water. Cyanotoxins are known to cause adverse effects in plants. Microcystin (MC), a cyclic heptapeptide, with more than 70 structural variants, is a frequently occurring toxin. MC is a specific inhibitor of serine/threonine protein phosphatases 1 and 2A (PP1 and 2A), important regulatory enzymes in eukaryotic cells. Protein phosphatases consist of a catalytic subunit and one or more regulatory subunits. In Alfalfa several isoforms of the catalytic subunit of PP1 ( Ms PP1α, Ms PP1β, Ms PP1γ, Ms PP1δ, Ms PP1ɛ) and PP2A ( Ms PP2A Cα/β/γ) are known along with isoforms of the regulatory subunits of PP2A ( Ms PP2A Aα/β, Ms PP2A Bα/β). The in vivo effect of environmentally relevant concentrations of cyanobacterial components on the mRNA transcript level of the subunits of protein phosphatases 1 and 2A in Alfalfa ( Medicago sativa ) was examined using semi-quantitative RT-PCR. Plants were exposed for one week to 5 μg L −1 microcystin-LR, microcystin-LW, okadaic acid and to cell-free cyanobacterial crude extracts from Microcystis aeruginosa containing 5 μg L −1 microcystin-LR and a toxin-free crude extract from Synechocystis spp. The protein phosphatase activity in vivo was inhibited when exposed to toxins and crude extract containing microcystin-LR, no change was induced by Synechocystis crude extract. The gene expression of the Ms PP1γ subunit and the Ms PP1ɛ subunit was induced in plants exposed to MC-LW.