Based on stable carbon isotope ratio (δ13C) measurements, photosynthetic pathway types were determined for 61 species in 54 genera and 24 families of flowering plants from the saline meadows of Northeastern China. Of these total vascular plants, 18 species in 17 genera from 6 families were found to have C4 photosynthesis; 43 species in 38 genera from 20 families had C3 photosynthesis. Six dicotyledonous species exhibited C4 pathway, 12 monocotyledonous species were found with C4 photosynthesis. The dicotyledonous C4 species had relative greater mean δ13C value and less total carbon content than both monocotyledonous C4 and C3 species. Most dicotyledonous C4 species were annual forbs and halophytes. Some C4 species had been previously documented, but their δ13C values varied remarkably from those of the present study. Even though there are some fluctuations for the δ13C values of some C4 species, δ13C value was still more reliable for C3 and C4 identification than the use of the enzyme ratio method and of low CO2 compensation concentration.
Plants have developed various photoprotective mechanisms to resist irradiation stress. One of the photoprotective mechanisms described in the literature for LHC2-containing organisms involves a down-regulation of photosystem (PS) 2 occurring simultaneously with the build-up of a proton gradient across the thylakoid membrane (ΔpH). It is often correlated with deepoxidation of xanthophylls located in LHC2. In Rhodophyta instead of LHC2, the peripheral antenna of PS2 consists of a large extramembrane complex, the phycobilisome (PBS), which transfers its excitation to the core antennae of PS2 composed of the CP43 and CP47 protein-chlorophyll complexes and there is no xanthophyll cycle. In the red alga Rhodella violacea a ΔpH-dependent chlorophyll (Chl) a fluorescence quenching can be formed. We characterised this quenching, studied the effects of various irradiances and inhibitors. Under photoinhibitory conditions, the ΔpH-dependent Chl fluorescence quenching exerts a photoprotective role and delays the kinetics of photoinhibition. It is the first time that such a photoprotective mechanism is described in PBS-containing organisms. and M. Ritz, K. V. Neverov, A.-L. Etienne.