Phosphate Limitation in Isochrysis Galbana

Abstract

The effect of steady-state phosphorus limitation on photosynthetic characteristics was examined in the marine haptophyte Isochrysis galbana Green. Phosphate-limited chemostates were maintained at four dilution rates, ranging from 0.13 – 0.78 d⁻¹, under continuous irradiance levels of 175 μmole quanta m⁻² s⁻¹, which saturated photosynthesis at all growth rates. Phosphate limitation led to an overall reduction in pigmentation and a decrease in the cellular concentration of reaction centers; however, the optical absorption cross-section, normalized to chlorophyll a, increased. Light-saturated photosynthetic rates normalized to chlorophyll a remained relatively constant. The PSII/PSI ratio increased from 2.18 to 2.66 over the dilution rates, and PSI decreased much faster than PSII. The average turnover time for light-saturated photosynthetic electron transport from water to carbon dioxide increased from 6.76 to 8.51 ms.