Transient state characteristics of changes in light conditions for the cyanobacterium Oscillatoria agardhii |
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Authors: | A F Post |
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Institution: | (1) Laboratorium voor Microbiologie, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands;(2) Present address: Department of Biological Chemistry, Hebrew University, 91904 Jerusalem, Israel |
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Abstract: | The cyanobacterium Oscillatoria agardhii was subjected to changes in irradiance and to changes in light period. During transient states parameters as growth rate, pigment contents, photosynthetic activities and pool sizes of carbohydrate and proteins were followed. The changes in pigments and photosynthesis were similar for irradiance transitions and transitions in light period length. Carbohydrates served for the supply of carbon and energy during adaptation to low light conditions until a basal level of 125 g · mg dry wt-1 was reached. After transfer to high light conditions excess carbon fixation led to the storage of carbohydrate reserve polymers up to 600 g · mg dry wt-1. During adaptation to longer light periods cells showed an overcapacity for carbohydrate accumulation even in the presence of a high carbohydrate content at the start of the light period. A model for the feed back repression of photosynthesis related to carbohydrate accumulation was presented. In all cases protein synthesis was directly maximized under the given conditions. Growth rate defined as specific rate of change in carbon showed the fastest response after a shift in light conditions. It was concluded that adaptation of O. agardhii to changes in light conditions was directed to the optimization of growth. The observation that carbohydrate is used to supply carbon and/or energy during adaptation leads to the conclusion that changes on survival in low light depend on carbohydrate level, the efficiency of its conversion in cell material and the maintenance requirements. Such a survival strategy enables cyanobacteria to cope succesfully with light limiting conditions.Abbreviations HL
high irradiance Em-2s-1
- LL
low irradiance Em-2s-1
- L/D
light-dark cycle h
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specific growth rate h-1
- e
specific maintenance coefficient h-1
- max
maximal specific growth rate h-1
- c
specific rate of change of carbon h-1
- protein
specific rate of change of protein h-1
- Chl a
chlorophyll a
- CPC
C-phycocyanin
- dry wt
dry weight mg
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light utilization efficiency nmol O2 · mg dry wt-1 · min-1/ Em-1 s-1
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P
max
photosynthetic capacity nmol O2 · mg dry wt-1 · min-1
- PSI
photosystem I
- PS II
photosystem II
- RC II
reaction center of PS II
- PQ
plastoquinone |
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Keywords: | Cyanobacteria Photosynthesis Light-shade adaptation Reserve polymers Carbohydrate accumulation Protein synthesis |
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