| Autor: |
Heber, Ulrich, Neimanis, Spidola, Siebke, Katharina, Schönknecht, Gerald, Katona, Eva |
| Zdroj: |
Photosynthesis Research; Dec1992, Vol. 34 Issue 3, p433-447, 15p |
| Abstrakt: |
Chlorophyll fluorescence, light scattering, the electrochromic shift P and levels of some photosynthetic intermediates were measured in illuminated leaves. Oxygen and CO concentrations in the gas phase were varied in order to obtain information on control of Photosystem II activity under conditions such as produced by water stress, when stomatal closure restricts access of CO to the photosynthetic apparatus. Light scattering and energy-dependent fluorescence quenching indicated a high level of chloroplast energization under high intensity illumination even when linear electron transport was curtailed in CO-free air or in 1% oxygen with 35 μll CO. Calculations of the phosphorylation potential based on measurements of phosphoglycerate, dihydroxyacetone phosphate and NADP revealed ratios of intrathylakoid to extrathylakoid proton concentrations, which were only somewhat higher in air containing 35 μl l CO than in CO-free air or 1% oxygen/35 μl l CO. Anaerobic conditions prevented appreciable chloroplast energization. Acceptor-limitation of electron flow resulted in a high reduction level of the electron transport chain, which is characterized by decreased oxidation of P, not only under anaerobic conditions, but also in air, when CO was absent, and in 1% oxygen, when the CO concentration was reduced to 35 μll. Efficient control of electron transport was indicated by the photoaccumulation of P at or close to the CO compensation point in air. It is proposed to require the interplay between photorespiratory and photosynthetic electron flows, electron flow to oxygen and cyclic electron flow. The field-indicating electrochromic shift (P) measured as a rapid absorption decrease on switching the light off followed closely the extent of photoaccumulation of P in the light. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
Full text from SpringerLink