Seasonal and diurnal changes in photochemistry and antioxidant responses, and phenolic metabolism in evergreen Jasminum fruticans

In this study, seasonal and diurnal changes in photosynthesis and phenolic metabolism in evergreen jasmin (Jasminum fruticans L.) were examined over a 12-month period. We found the differences in pigment and phenolic contents between the values determined during the autumn and winter months and the values determined during the spring and summer months. During the autumn and winter months, the low seasonality of Chla was accompanied by increases in both carotenoids and phenol levels which play a major role in photoprotection processes. While the maximal quantum efficiency of PSII (Fv/Fm) showed diurnal changes during the winter months, such diurnal changes were not observed for the other seasons. These diurnal changes reflected dynamic photoinhibition, as an adaptation mechanism, which may actually protect the leaves against photodamage under cold conditions. During the winter months, increased O–J phase (from the OJIP chlorophyll fluorescence curve) and decreased I–P phase in parallel with the reduction of Fv/Fm, revealed that the cold stress influenced both the donor and acceptor sides of PSII. Interestingly, we found the relationship between diurnal changes of Fv/Fm and those of hydrogen peroxide (H2O2) levels and catalase (CAT) activity during the winter months. Diurnal changes in CAT activity represented the differences between the values determined in warm and cold seasons. Compared with the diurnal changes during the spring and summer months, the maximum activity of CAT was observed at 15:00 h during the winter months, which indicated that CAT may play an effective role in protection of photosystems under a high photosynthetically active radiation (PAR) during cold days.