Seasonal dynamics of dehydrins and water freezing temperatures in the thalli of the lichen Lobaria pulmonaria in the middle taiga zone

Seasonal changes in the content of dehydrin proteins, water content, and freezing point of water in the lichen Lobaria pulmonaria have been studied. Two dehydrins with mol. weight of 40 and 43 kDa have been identified for the first time. They are available in the thalli throughout the year, which indicates the constitutive expression of these proteins. The lowest content of these dehydrins has been identified for the spring period, which is the most favorable time for the lichen growth. Desiccation of the thalli in warm summer days increases the content of the proteins. The change for the cold year period also provokes an increase in their concentration. The relative water content ranges from 45 % to 70 % fresh weight of the thalli. The water crystallisation temperature varies depending on the season and is minus 10–11 °C for the coldest period. As the temperature decreases, 25–45 % of the total water content in the thalli undergoes a phase transition from water to ice. It has been suggested that the level of dehydrins correlates with the water content and freezing point of the water, and that dehydrins contribute to the formation of a fraction of the strongly bound water.