Do flavonoids and tannins have a role in photoprotection in mangroves?

Abstract

In previous work, based on the apparent disparity between CO2 fixation rates and electron transport, we suggested that molecular O2 was a significant sink for electrons in Rhizophora mangroves. We also reported high levels of superoxide dismutase (SOD) both in and outside chloroplasts, which were not matched by equivalent activities of APx, GSR or other potential chloroplast enzymes to process the H2O2. We indicated this as further suggesting that additional downstream processing, perhaps related to tannin or flavonoid production, was an important feature of the antioxidant system in these trees. In this study, we have examined photosynthesis and fluorescence in the neotropical R. mangle at a site off Belize, Central America, and quantified the levels of tannins and flavonoids, and the activities of SOD and phenolic peroxidase in leaves from several different habitats. The results indicate several significant differences between these studies and the previous ones undertaken in Australia, including lower concentrations of the phenolics and greater sensitivity of øII to light at irradiances less than 500 µmol m-2s-1. Overall, both the phenolics and the peroxidase enzyme show remarkable stability even under high temperature conditions and during leaf senescence. The results will be discussed with respect to the Yamasaki flavonoid cycling model for H2O2 detoxification (Yamasaki et al. 1997, Plant Physiology 115: 1405-1412).