The Properties of Betacyanin Leakage in Redbeet Discs Exposed to tert.-Butylhydroperoxide

Abstract

In order to obtain information on the mechanism of leakage which is often observed at the onset of plant senescence or some physiological disorders, a model experimental system has been established, which examines the kinetics and properties of betacyanin leakage from red beet discs treated with tert.-butylhydroperoxide (t-BHP).
1. No leakage of betacyanin was observed even after 4 days when red beet discs (φ13mm×1.5mm) were incubated in MES-NaOH (pH 5.8) buffer containing 0.2 M mannitol and streptomycin (0.5μg/ml) in the absence of t-BHP in the dark at 20°C.
2. In this experimental system, changing the concentration (2-10mM) of t-BHP and the duration (2-8 hours) of the treatment enabled the time when the betacyanin leakage occurred to be easily controlled.
3. As well as betacyanin, potassium ions, reducing sugars, UV-absorbing components and proteins also leaked out from red beet discs after the t-BHP treatment, but the extent of leakage appeared to be related to the molecular size.
4. The leakage showed a remarkable pH dependence between pH 5.05 and 7.43; the leakage of betacyanin occurred much faster below pH 5.8 than near pH 7.
5. Addition of calcium ion and spermine to the medium effectively prevented the leakage of betacyanin until t-BHP treatment caused leakage. Glutathione was effective only when it was used before treatment with t-BHP. Their mechanisms of prevention seem to differ.
This experimental system, using red beet discs, appears to be very useful for investigating the mechanism of leakage.