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

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 (MsPP1α, MsPP1β, MsPP1γ, MsPP1δ, MsPP1ɛ) and PP2A (MsPP2A Cα/β/γ) are known along with isoforms of the regulatory subunits of PP2A (MsPP2A Aα/β, MsPP2A 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 MsPP1γ subunit and the MsPP1ɛ subunit was induced in plants exposed to MC-LW.