Involvement of chloroplast peroxidase on chlorophyll degradation in postharvest broccoli florets and its control by UV-B treatment.

Chlorophyll (Chl)-degrading peroxidase (POX) was purified from green and green-yellow broccoli florets to elucidate the physiological role and cell localisation of Chl-degrading POX. Effect of UV-B treatment on Chl-degrading POX activity was also determined. The Chl-degrading POX activity was separated by an ion exchange chromatography into 3 fractions, Chl-POX1, Chl-POX2 and Chl-POX3. The activities of Chl-POX2 and Chl-POX3, but especially that of Chl-POX3, were found in green-yellow florets and were clearly suppressed by UV-B irradiation. The protein molecular sizes of cPOX1 and cPOX3 purified from Chl-POX1 and POX3 were 43 and 34kDa, respectively. The cPOX1 was not located within chloroplast fraction, whereas the cPOX3 was found in intact chloroplasts extracted from senescing broccoli florets. We propose that cPOX3 is a chloroplast POX and the activity was suppressed by UV-B treatment, suggesting that cPOX3 might be involved in Chl degradation in stored broccoli florets.