Growth inhibition and microcystin accumulation in bush bean (Phaseolus vulgaris L.) plant irrigated with water containing toxic Chrooccocus minutus

Abstract

Cyanobacterial blooms and microcystins (MCs) in irrigation waters have been recognized as an emergent environmental threat to many terrestrial plants. While several studies addressed the impacts of crude cyanobacterial extracts and dissolved MC-containing water on crop plants, less is known about the effects of irrigation water containing cyanobacterial blooms (i.e., intracellular plus extracellular toxins). In the present study, we investigated the effects of whole culture, cell-free culture filtrate and living cells of the toxic cyanobacterium Chroococcus minutus on growth, physiological parameters and MC accumulation in Phaseolus vulgaris (bush bean) plants. The plants were grown in pots containing agricultural soil, in order to mimic common agricultural practice. After 4 weeks of growth, treated plants exhibited substantial reduction in root and shoot growth, photosynthetic pigments, and protein contents compared to control plants. Treated plants also showed higher lipid peroxidation than control plants. The lowest inhibitory effects were observed in plants treated with culture filtrate containing extracellular MCs only (15.3 μg L−1). The highest inhibitory effects were recorded in plants treated with whole cyanobacterial culture containing both intra- and extracellular MCs (132 μg L−1), indicating the release of intracellular MCs from cells into the rizhosphere and their uptake by plant roots. MC concentrations in immature pods of P. vulgaris plants irrigated with whole culture and living cyanobacterial cells led to estimates of daily MCs intake (0.125–0.391 μg kg−1 body weight) that exceeded the total daily intake guidelines (0.04 μg kg−1 body weight) for human food consumption. This study suggests that irrigation water as well as plants used in human consumption should be regularly monitored for the presence of MCs and other cyanotoxins.