Abstract
The composition of the growth medium has a major influence on the physiological properties of microalgae. We have previously shown that addition of the trace elements Zn and I enhances desiccation-induced fluorescence quenching (qdes) in the lichen phycobiont Trebouxia asymmetrica. qdes is likely to be an important factor of the tolerance against drought, as it has a protective function against photoinhibition in the dehydrated state of this poikilohydric organism. The influence of the presence of iodine and/or zinc ions in culture media on growth of T. asymmetrica and its ability to show qdes were investigated. T. asymmetrica was able to grow in seawater and showed enhanced qdes as compared to when grown in the usual Bold’s basal growth medium. While artificial seawater had no effect, addition of Zn and I in the concentrations present in natural seawater enhanced qdes to almost the same level as observed in natural seawater. The presence of Zn and I also increased growth by the factor of almost 2, thus approximating the growth rate reached in enriched seawater. Both effects, enhancement of qdes and of the growth rate were dependent on the simultaneous presence of both elements. Adding only one element at any concentration resulted in no or very little effect on either growth rate or qdes. The mechanism of the action of both elements is unknown. It is possible that the simultaneous presence of I and Zn has a profound effect on the fitness of lichens containing T. asymmetrica in nature.
Published Version
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