Cylindrospermopsin induces biochemical changes leading to programmed cell death in plants

In the present study we provide cytological and biochemical evidence that the cyanotoxin cylindrospermopsin (CYN) induces programmed cell death (PCD) symptoms in two model vascular plants: the dicot white mustard (Sinapis alba) and the monocot common reed (Phragmites australis). Cytological data include chromatin fragmentation and the increase of the ratio of TUNEL-positive cells in roots, the latter being detected in both model systems studied. The strongest biochemical evidence is the elevation of the activity of several single-stranded DNA preferring nucleases-among them enzymes active at both acidic and alkaline conditions and are probably directly related to DNA breaks occurring at the initial stages of plant PCD: 80 kDa nucleases and a 26 kDa nuclease, both having dual (single- and double-stranded nucleic acid) specificity. Moreover, the total protease activity and in particular, a 53-56 kDa alkaline protease activity increases. This protease could be inhibited by PMSF, thus regarded as serine protease. Serine proteases are detected in all organs of Brassicaceae (Arabidopsis) having importance in differentiation of specialized plant tissue through PCD, in protein degradation/processing during early germination and defense mechanisms induced by a variety of biotic and abiotic stresses. However, knowledge of the physiological roles of these proteases and nucleases in PCD still needs further research. It is concluded that CYN treatment induces chromatin fragmentation and PCD in plant cells by activating specific nucleases and proteases. CYN is proposed to be a suitable molecule to study the mechanism of plant apoptosis.