Seasonal acclimatization of thallus proline contents of Mastocarpus stellatus and Chondrus crispus: intertidal rhodophytes that differ in freezing tolerance.

Mastocarpus stellatus and Chondrus crispus often co-occur in the lower intertidal of Northern Atlantic rocky shorelines. At our field site along the Maine coast (USA), Mastocarpus stellatus thalli possessed greater contents of proline when compared with thalli of Chondrus crispus. In addition, M. stellatus thalli acclimated to colder growth conditions in winter/early spring by increasing proline content several fold; no seasonal acclimation in proline content was observed in C. crispus. Proline accumulates in the tissues of a broad diversity of freezing-tolerant organisms and is among the most common cryoprotectant molecules. Thus, our observations provide a basis for the previously well-documented greater freezing tolerance of Mastocarpus stellatus when compared with Chondrus crispus.