Primary Thermostability of Cells and a Problem of Adaptation of Plants to Conditions of Cold Climate

Abstract

The primary thermostability of leaf cells of flowering plants from the arctic, subarctic and boreal zones was determined on the basis of either cessation of protoplasmic streaming in cells or cellular loss of the capacity for plasmolysis after heating. 227 species belonging to 95 genera and to 25 families were studied. The thermostability of cells in most arctic and arctic-alpine plants (defined by cessation of protoplasmic streaming after 5 min of heating) was found to range from 42 to 43 °C, while that in the majority of boreal species ranged between 44 and 45 °C. Subarctic species occupy an intermediate position. A comparison of cell thermostabilities of closely related species (belonging to 35 genera) from different climatic zones shows that 59 % of the arctic and arctic-alpine species have a much lower heat resistance than do subarctic species of the same genera, and that 73 % of the species exhibit a lower cell thermostability compared to related species from the taiga. This difference in cell thermostability is also observed in subspecies of different latitudinal distribution. In the rest of the cases the cell thermostability of arctic plants does not differ from that of related species of the more southern subarctic and boreal zones. Boreal species, which do not differ in their thermostability from related species of more northern zones, are mainly arcto-boreal in distribution, i.e. boreal elements of the arctic flora The primary thermostability of cells is determined largely by the resistance of protein components of the cell and is regarded as indirect evidence of the conformational flexibility of protein macromolecules. That a great number of northern species prove to have a low cell thermostability permits the assumption that the increase of flexibility of protein macromolecules providing for a high metabolic rate at low temperatures is, as maintained by A lexandrov , one of the main mechanisms of plant adaptation to cold climate