Characterisation of peroxidase activity in bird-of-paradise (Strelitzia reginae Ait.) stems

Abstract

SummaryBird-of-of-paradise (Strelitzia reginae Ait.) is an exotic tropical ornamental species from the family Strelitziaceae used as a cut flower and as a perennial plant in gardens. During ageing, the inflorescences show symptoms of wilting and discolouration, and a decrease in stem fresh weight. These symptoms are correlated with an increase in peroxidase (POX) activity at the base of the cut stem. A POX was extracted and partially purified from the base of ageing stems of cut inflorescences to determine its biochemical properties. The highest POX enzyme activity was evident at pH 5.0, while activity was greatly reduced at pH 2.5 and pH 9.0. Furthermore, pre-incubation of the enzyme preparation in a buffer at pH 2.5 was efficient at inhibiting POX activity when the activity was later determined at the optimum pH of 5.0. We also found that the highest POX activity occurred at 60ºC, followed by heat inactivation at ≥ 70ºC. However, inactivation of bird-of-paradise stem POX by the application of extreme pH or high temperature is not practical. The responses of POX enzymes to anti-oxidant inhibitors and surfactant substances varied widely. Nevertheless, complete inactivation of bird-of-paradise stem POX was obtained in 1.0 mM dithiothreitol or 1.0 mM 2-mercaptoethanol, which may offer a means to control the action of this enzyme.