Changes of leaf antioxidant system, photosynthesis and ultrastructure in tea plant under the stress of fluorine

Seedlings of Camellia sinensis were grown hydroponically for 30 d in order to study the effect of fluorine (F) on growth parameters, antioxidant defence system, photosynthesis and leaf ultrastructure. Fresh and dry mass, chlorophyll (Chl) content and net photosynthetic rate (P-N) decreased with increasing F concentration. Superoxide dismutase (SOD) activity decreased significantly, catalase (CAT) and guaiacol peroxidase (GPX) activities reached maximun under 0.21 and 0.32 mM F, respectively. Proline, malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents increased significantly. These results suggested, that antioxidant defence system of leaves did not sufficiently scavenge excessive reactive oxygen species. The cell ultrastructure was not changed under 0.11-0.21 mM F, however, it was destroyed at 0.32-0.53 mM F. So tea plants tolerated F in concentration less than 0.32 mM.