Deposition of Cytokinesis‐Related Callose in Riella helicophylla and Arabidopsis thaliana. Effects of Photolytically Altered Nifedipine1

Abstract: The cytokinesis‐related callose deposition in cell plates and juvenile cross walls of meristematic cells was investigated in the liverwort Riella helicophylla and seedlings of Arabidopsis thaliana. The β‐1,3‐glucan callose was detected by its specific staining properties with sirofluor and aniline blue by fluorescence microscopy. The photo‐labile calcium antagonist nifedipine (NIF) exerted a specific promotive effect when the substance was exposed to light. The nitroso derivative of photolysed NIF was found to be the active compound which was responsible for the enhancement in callose deposition. The nitroso derivative was isolated after photolysis of NIF by UV light (365 nm) and its structure was verified with ¹H‐nuclear magnetic resonance and infrared spectroscopy. The characteristic absorption maximum at 770 nm in dimethyl sulfoxide was employed to determine the concentration of the nitrosopyridine in solutions by use of the molar absorption coefficient of the isolated substance. In addition, the nitro derivative of nifedipine was prepared. This nitropyridine was ineffective with respect to the stimulation of callose deposition in dividing cells. The possible mechanism of this cytotoxic effect and its implications for symplastic growth in meristems is discussed.