Etiolated sunflower cotyledons developed in complete darkness and lacking photosystem (PS) 2 were exposed to continuous 200 µmol(photon) m-2 s-1 "white light" for 1, 3, 6, 12, and 18 h prior to evaluations of excitation-energy dissipation using modulated chlorophyll a fluorescence. Photochemical potential of PS2, measured as the dark-adapted quantum efficiency of PS2 (FV(M)/FM), and thermal dissipation from the antenna pigment-protein complex, measured as the Stern-Volmer non-photochemical quenching coefficient (NPQ), increased to 12 h of irradiation. Following 12 h of irradiation, thermal dissipation from the antennae pigment-protein complex decreased while the efficiency of excitation capture by PS2 centers (F'V/F'M) and light-adapted quantum efficiency of PS2 (ΦPS2) continued to increase to 18 h of irradiation. The fraction of the oxidized state of QA, measured by the photochemical quenching coefficient (qP), remained near optimal and was not changed significantly by irradiation time. Hence during the development of maximum photochemical potential of PS2 in sunflower etioplasts, which initially lacked PS2, enhanced thermal dissipation helps limit excitation energy reaching PS2 centers. Changes of the magnitude of thermal dissipation help maintain an optimum fraction of the oxidized state of QA during the development of PS2 photochemistry. and J. G. Lebkuecher ... [et al.].
External morphology of the nematode Pterygodermatites bovieri (Blanchard, 1886), a very rare parasite of bats in the Palaearctic region, was studied by scanning electron microscopy. Special attention was paid to the cephalic end structure and cutieular armament, which are of great systematic importance in this group of nematodes. The mouth opening of P. bovieri is subterminal and oriented dorsally. Numerous sclerotized denticles, arranged in two rows, are situated in the buccal cavity around the mouth opening. They are better developed in its ventral part. In females there are 12-14 ventral denticles. Cephalic papillae are arranged in two rows: internal (six papillae - two dorsal, two lateral and two ventral) and external (four papillae). Amphids are small, situated close to lateral cephalic papillae of the internal row. Males possess 40-41 cutieular combs in each ventro-lat-eral plate row, and, in addition, a short row of four ventral, unpaired precloacal fans. Females in our material possessed 68 cu-ticular elements represented by combs and spines, in each row. Changes of the cutieular elements shape along the nematode body length are described. Results of SEM observations are compared with previous descriptions of P. bovieri based on the light microscopical observations.