Snow algae and lichen algae differ in their resistance to freezing temperature: An ice nucleation study
| Authors | |
|---|---|
| Year of publication | 2009 |
| Type | Article in Periodical |
| Magazine / Source | Phycologia |
| MU Faculty or unit | |
| Citation | |
| Web | http://www.ec-inc.co.jp/ipc9/ |
| Field | Botany |
| Keywords | snow algae; lichen algae; freezing temperature; ice nucleation spectrometry; Trebouxia; resistance |
| Description | Introduction: Cryoresistance of snow algae and lichens surviving at extreme environments (i.e. freezing temperature) includes ice nucleation activity. However, interspecific differences in cryoresistance exist according to physiological adjustment of the species to in situ conditions. Objectives: We focused on differences in freezing temperatures of snow (Chlamydomonas nivalis, Chloromonas nivalis) and lichen symbiotic algae (Trebouxia erici, T.assymetrica, T.glomerata). The green mesophilic flagellate Chlamydomonas reinhardtii was used as an inner standard. We also focused on growth temperature optimum. Methods: Ice nucleation spectrometry (INS) was used to quantify the number and activity of ice nucleating agents. Temperature optimum was measured using a cross gradient cultivator (temperature x light). Results: Pooled data showed that snow algae had higher value of freezing temperature (minus 9.8 deg C) than lichen symbiotic algae (minus 14.7 deg C). Surprisingly, the freezing temperature of a mesophilic Chlamydomonas reinhardtii (minus 12.6 deg C) did not differ significantly from the snow algae. The INS analysis showed that snow algae had lower capacity of ice nucleation than lichen symbiotic algae. Growth optima were 18.5 deg C (Trebouxia sp.), and below 10 deg C (Chlamydomonas and Chloromonas). Conclusions: From the results follows that snow algae are bad ice nucleators with the exception of Chloromonas nivalis in which the fungal contamination cannot be excluded. However, these algae tolerate low temperatures and survive repeated freezethaw cycles. Therefore, other mechanisms preventing ice crystal formation must be involved. The mechanisms likely include either decrease of the freezing temperature by antifreeze proteins or osmoticly active compound synthesis. Acknowledgements: GAAV KJB601630808, GAAV KJB60050708, CAREX Knowlege Grants |
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