Photoacclimation in the marine alga Nannochloropsis sp. (Eustigmatophyte): A kinetic study

Exponentially growing cultures of Nannochloropsis sp. were transferred from high light (650 μmol quanta m^-2 s^-1) to low light (30 μmol quanta m^-2 s^-1). The kinetics of changes in the various parameters of the photoacclimation process were followed until steady state was reached. In this organism, the observed 4.25 increase in cellular chlorophyll a in the low-light-acclimated cells was linearly correlated with an increase in the number of photosynthetic units (PSU), while the PSU size remained constant. The new steady stale was reached after a transition period of 87 h and following an initial overshoot in the chlorophyll a concentration. During the process of photoacclimation, harvested and utilized light was increased due to a combination of increased cellular chlorophyll and an increase of the quantum yield. These improvements in efficiency were coupled with the reduction of respiration. The overall effect of photoacclimation, therefore, amounted to reducing the impact of low light on the growth rate of the algae. Our study demonstrates the importance of the photoacclimation process in the context of the planktonic way of life. An index of the 'effectiveness of photoacclimation' is proposed.