Stepwise adaptation to salinity in the green alga Nannochloris bacillaris

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Abstract
A severe inhibitory decrease in water potential owing to salinity increase (ψ = −0.2 to −5.5 MPa) was tolerated in Nannochloris bacillaris Naumann if an intermediate salinity step at ψ = −2.6 MPa was provided. Photosynthesis, respiration, and growth were all enhanced by the provision of an intermediate step. The length of time of the application of the intermediate salinity step was critical to the resulting abilities of the cells to exhibit substantial adaptation. Increasing the length of the intermediate step from 10 to 120 min resulted in a 168-fold increase in the rate of photoassimilation of bicarbonate. Adaptation of other functions (e.g., growth) took much longer. The effects of pulse shocks, downward then upward water potentials, indicated that when there was an inhibition of photosynthesis and it was irreversible over the short term. Pulse shocks to noninhibitory water potentials did not cause inhibition. These results were correlated with measurements of volume changes, rates of excretion of solutes, and ultrastructural changes.

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