Microcystin-LR, a Cyanobacterial Toxin, Induces DNA Strand Breaks Correlated with Changes in Specific Nuclease and Protease Activities in White Mustard (Sinapis alba) Seedlings

Abstract

There is increasing evidence for the induction of programmed cell death (PCD) in vascular plants by the cyanobacterial toxin microcystin-LR (MC-LR). Our aim was to detect the occurrence of PCD-related DNA strand breaks and their possible connections to specific nuclease and protease activities. DNA breaks were studied by the deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method in the photoperiodically grown dicot model of white mustard (Sinapis alba). In-gel nuclease and protease activity assays showed changes in the activities of specific isoenzymes during treatments with MC-LR. Strand breaks occurred both in the developing root epidermis and cortex. Several isoenzyme activities were related to these breaks, for example: an increase in the activity of neutral 80–75 kDa, acidic high MW (100–120 kDa) and, most importantly, an increase in the activity of neutral 26–20 kDa nucleases, all of them having single-stranded DNA cleaving (SSP nuclease) activities. Increases in the activities of alkaline proteases in the 61–41 kDa range were also detected and proved to be in relation with MC-LR-induced PCD. This is one of the first pieces of evidence on the correlation of PCD-related DNA strand breaks with specific hydrolase activities in a model dicot treated with a cyanobacterial toxin known to have environmental importance.

Cyanobacteria: A Natural Source for Controlling Agricultural Plant Diseases Caused by Fungi and Oomycetes and Improving Plant Growth

“…This study suggested that microcystin affected photosynthesis with a reversible, short-term effect at a single application of low concentration and with an irreversible, long-term effect at high concentration with a single application or when multiple applications at low concentrations are used [74]. In most cases, the alterations may be directly related to the specific biochemical effects of cyanotoxins as inhibition of protein phosphatases 1 and 2A and of protein synthesis [70,75]. Cyanotoxins cause spindle abnormalities and mitotic spindle disruptions in several plant species leading to distorted organs and growth inhibition [69][70][71]76].…”

“…Cyanotoxins cause spindle abnormalities and mitotic spindle disruptions in several plant species leading to distorted organs and growth inhibition [69][70][71]76]. These alterations were triggered by a change in the phosphorylation status of proteins (e.g., microtubule associated proteins) that regulates spindle assembly and leads to abnormal segregation of sister chromatids in mitosis [70,76]. Subcellular alterations induced by cyanotoxins, as shown above, generally anticipate the plant cell death [69].…”

“…This issue may raise concerns about possible effects on crop growth and development due to bioaccumulation of toxins in the crops and thereby, the food security. Regarding the effects of cyanotoxins on plants, large amount of recent scientific articles have been published to explain the biochemical and physiological alterations induced by microcystins and cylindrospermopsins [65,[68][69][70][71]. Structural and physiological alterations have crucial consequences on plant growth and on the crop productivity.…”

“…In most cases, the alterations may be directly related to the specific biochemical effects of cyanotoxins as inhibition of protein phosphatases 1 and 2A and of protein synthesis [70,75]. Cyanotoxins cause spindle abnormalities and mitotic spindle disruptions in several plant species leading to distorted organs and growth inhibition [69][70][71]76]. These alterations were triggered by a change in the phosphorylation status of proteins (e.g., microtubule associated proteins) that regulates spindle assembly and leads to abnormal segregation of sister chromatids in mitosis [70,76].…”