Gamma-irradiation effect: variation of photosynthetic activity of Euglena.
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.


CONCLUSIONS
Our findings suggest that not only PS II but also the Calvin cycle in the photosynthetic system is affected by gamma ray irradiation.
Sakashita
T
T
National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan. tetsuya@nirs.go.jp
Doi
M
M
Nakamura
Y
Y
Fuma
S
S
Ishii
N
N
Takeda
H
H
D000818:Animals; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000032:analysis; D005055:Euglena / Q000502:physiology*; D005720:Gamma Rays / Q000009:adverse effects*; D010788:Photosynthesis
D002245:Carbon Dioxide; D002244:Carbon