No abstract

No abstract

Summary• Oxidative stress arises when desiccation restricts photosynthesis and light energy is transferred from photo-excited pigments onto ground state oxygen. We tested whether a highly desiccation tolerant lichen, Pseudevernia furfuracea , displays better protection against oxidative stress than more sensitive species, Lobaria pulmonaria and Peltigera polydactyla .• We rehydrated lichens after desiccation periods of 2, 7 and 9 weeks and assessed their viability by measuring CO 2 exchange using IRGA. During desiccation and rehydration, photosynthetic pigments and the antioxidant α -tocopherol were analysed by HPLC, and peroxidases by spectrophotometry.• Pseudevernia furfuracea contained considerably lower chlorophyll, α -tocopherol and β -carotene concentrations and peroxidase activity than the two other lichens. However, it recovered photosynthesis rapidly, even after remaining in the desiccated state for 2 months while there was a significant delay in the onset of photosynthesis in L. pulmonaria and P. polydactyla .• We conclude that high antioxidant concentrations do not necessarily indicate better adaptation to desiccation. Rather, the ability to rapidly re-establish the speciesspecific normal antioxidant concentrations during rehydration, even after longer desiccation times, is a characteristic of well-adapted species.

Photosynthetic irradiance response of vegetative and reproductive structures of the green-flowered deciduous perennial green hellebore was studied by the comparative use of chlorophyll (Chl) fluorescence techniques and gas exchange measurements. All the Chl-containing organs (leaves, sepals, stalks, and fruits) examined were photosynthetically active showing high intrinsic efficiencies of photosystem 2 (F v /F m : 0.75-0.79) after dark adaptation. Even in the smaller fertile and sterile parts of the flower (nectaries and anthers) a remarkable photosynthetic competence was detected. With increasing photon flux densities (PFD) electron transport rates, actual quantum yields, and photochemical quenching coefficients of the main photosynthetic organs decreased in the order: leaf>sepal>fruit>stalk. At moderate to high PFDs the sepals achieved maximum electron transport rates corresponding to about 80 % of concomitant mature leaves. In contrast, maximum net photosynthetic rate of the sepals [2.3 µmol(CO 2 ) m -2 s -1 ] were less than one fourth of the leaves [10.6 µmol(CO 2 ) m -2 s -1 ]. This difference is explained by a 70-80 % lower stomatal density of sepals in comparison to leaves. As the basal leaves emerge late during fruit development, the photosynthetically active sepals are a major source of assimilates, contributing more than 60 % of whole-plant CO 2 gain in early spring. The ripening dehiscent fruits are characterized by an effective internal re-fixation of the respirational carbon loss and thus additionally improve the overall carbon budget.

No abstract