The lower limit of photon fluence rate for phototrophic growth: the significance of 'slippage' reactions |
| |
Authors: | JOHN A RAVEN JOHN BEARDALL |
| |
Institution: | Department of Biological Sciences, University of Dundee, Dundee DD1 4HN, Scotland |
| |
Abstract: | Abstract. The role of 'slippage' reactions, in the form of passive H+ uniport through CF0-CF1, ATP synthetase and breakdown of the S2 and S3 intermediates of O2 evolution, is considered in relation to the growth of phototrophic organisms at low photon fluence rates. Analysis of the limited data available suggests that adaptation (phenotypic or genotypic) to low photon fluence rates is accompanied by an increase in the ratio of light-absorbing pigments to the (potentially slippage-inducing) photosystem two units and CF0-CF1 ATP synthetases. Furthermore, organisms which are genotypically adapted to high photon fluence rates do not, when grown at low photon fluence rates, achieve the same low ratio of reaction centres to total light-harvesting pigments as is found in phototrophs genotypically adapted to low photon fluence rates. The limits to, and energy costs of, such a mechanism of adaptation to low photon fluence rates are also discussed. |
| |
Keywords: | Shade adaptation S-statcs H+ permeability photosynthetic unit CF0-CF1 ATPase |
|
|