MECHANISMS OF ACCLIMATION TO LOWERED GROWTH TEMPERATURES IN ISOLATES OF ARCTIC AND TEMPERATE ECTOMYCORRHIZAL FUNGI.

摘要

The structure, respiration, and quantity of mycorrhizae associated with Salix rotundifolia Trautv. were studied for coastal tundra sites at Barrow and Cape Simpson, Alaska. All of the rootlets of S. rotundi-folia examined from both sites proved to be ectomycorrhizal. Straight line responses were noted for S. rotundifolia from both sites when the effects of temperature on oxygen uptake rates were presented in the form of Arrhenius plots. These results indicated that S. rotundifolia mycorrhizae taken from soil behaved in a manner typical of chilling insensitive plants. Root tip counts conducted during the summer of 1977 indicated that the number of mycorrhizae per ml of soil were higher at Cape Simpson than at Barrow. In addition, the percentage of mycorrhizae formed by the fungus Cenococcum graniforme was about four times as great in tarry soils near the Cape Simpson oil seep as in normal tundra soils at Barrow.; During the summers of 1976 and 1977, attempts were made to isolate fungi suspected of being mycorrhizal with S. rotundifolia. Isolates of Hebeloma pusillum, Entoloma sericeum, C. graniforme from Barrow, and C. graniforme from Cape Simpson were obtained in axenic culture during this time period. All of these isolates were proven capable of forming ectomycorrhizae with S. rotundifolia in controlled environment resynthesis experiments. An isolate of C. graniforme obtained from Maryland did not form ectomycorrhizae with S rotundifolia in resynthesis experiments.; The effects of acclimation temperature on these mycorrhizal fungi were studied in detail by using liquid cultures grown at 12(DEGREES) and 20(DEGREES)C of H. pusillum, C. graniforme (Cape Simpson), and C. graniforme (Maryland). All of these isolated demonstrated maximal growth rates at 12(DEGREES) which equalled those obtained at 20(DEGREES)C, however, growth at 12(DEGREES)C was marked by distinct lag phases of varying duration. Growth of these fungi at 12(DEGREES)C resulted in an adaptive response of oxygen uptake rates. All of the isolates examined demonstrated ideal compensation of oxygen uptake with growth at 12(DEGREES)C, that is, oxygen consumption at 12(DEGREES) for 12(DEGREES)C grown cells equalled oxygen consumption at 20(DEGREES) for 20(DEGREES)C grown cells.; Further studies were conducted to determine the mechanistic basis for this ideal compensation of oxygen uptake. Examinations were conducted into the effects of growth temperatue on specific activities; enthalpy of activation (Ea), and Km of certain enzymes.; Growth temperature did not have a statistically significant effect on the specific activities of glucokinase, phosphoglucose isomerase, 6 phosphogluconate dehydrogenase, and glucosel-6-phosphate dehydrogenase from any of the siolates. Specific activity estimates of the two C. graniforme isolates were more similar to each other than to those of H. pusillum. Hebeloma pusillum was the only isolate to show the predicted trend towards higher specific activities at the lower growth temperature.; Growth temperature did not have a significant effect on Ea for glucokinase from any of the isolates. Values of Ea for the C. graniforme isolates were similar to each other and were lower than those obtained for H. pusillum.; For the isolates the Km of glucokinase decreased with decreasing assay temperature, at least over a portion of temperature range examined. This decrease in Km with temperature (thermal modulation) tended to be greater for enzyme from 12(DEGREES)C grown cells in two out of the three isolates examined.