PHOTOSYNTHETICA

Photosynthetica 2005, 43(1):55-64 | DOI: 10.1007/s11099-005-5064-x

Photosynthetic performance of vegetative and reproductive structures of green hellebore (Helleborus viridis L. agg.)

G. Aschan¹, H. Pfanz¹, D. Vodnik², F. Batič²

¹ Applied Botany, University of Duisburg-Essen, Essen, Germany

² Agronomy Department, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia

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(CO₂) m^-2 s^-1] were less than one fourth of the leaves [10.6 μmol(CO₂) 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 CO₂ 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.

Additional key words: carbon budget; chlorophyll fluorescence; CO₂ re-fixation; floral photosynthesis; nectaries; sepals

Received: February 16, 2004; Accepted: September 23, 2004; Published: March 1, 2005  Show citation