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Gamma-irradiation effect: variation of photosynthetic activity of Euglena
T Sakashita1, M Doi, Y Nakamura
1National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan. tetsuya@nirs.go.jp
Objective:
To study the effects of gamma-ray irradiation on carbon fixation (Specific production rate: SPR), CO2 utilization efficiency (CUE) and electron transfer rate (ETR) in the photosynthetic flagellate Euglena gracilis strain Z in a dose-response dependent manner.
Methods:
Euglena cells were cultured in an inorganic nutrient medium containing ammonium chloride or proteose peptone. Cells were exposed to gamma-ray at 5 doses (0, 100, 250, 350, 500 Gy for water). Five days after irradiation, three photosynthetic activities were measured. SPR, which is a carbon uptake rate per unit carbon mass, was determined by 13C tracer methodology. CUE was evaluated using a relation of carbon isotope fractionation in Calvin cycle. ETR in photosystem II (PS II) was measured by a chlorophyll fluorescence analysis.
Results:
Even at a dose of 500 Gy, 80% of ETR of the non-irradiated control (0 Gy) was sustained, while SPR and CUE were about half the level in the non-irradiated control at 500 Gy. Furthermore, the dose response of ETR was considerably different from the others.
Conclusion:
Our findings suggest that not only PS II but also the Calvin cycle in the photosynthetic system is affected by gamma ray irradiation.