Effects of monovalent cations on phosphate accumulation and storage of the ectomycorrhizal fungus Suillus bovinus

Abstract

Comparative in vivo (31)P-NMR studies of the fungus Suillus bovinus (L.: Fr.) O. Kuntze in pure culture have produced interesting new data. To investigate the response of phosphate metabolism to a change in external monovalent cations, samples were exposed to a Hoagland solution containing different monovalent cations Li+, Na+, K+, or Rb+ at 10 mM concentration. A method of nutrient cycling during analysis where the cation was changed and the phosphate kept constant allowed us to determine the kinetics of phosphate accumulation, storage and incorporation into polyphosphate following exposure to the range of test cations. Different external monovalent cations had different effects upon changes in the content of both phosphate and polyphosphate. Treatment with Li+, Na+, or Rb+ resulted in a change in phosphate accumulation to 60, 73, and 107% and in content of the intracellular mobile polyphosphate (polyP) to 119, 112, and 94%, respectively, compared with the control taken as 100%. The effect of each cation is related to its position in the periodic table. Reversing this process, i.e., exchanging with K+, returned phosphate metabolism to normal. Although, the increase in depolarization of the cell membrane should affect the internal pH, fungal metabolism using energy requiring mechanisms appeared necessary to maintain the intracellular pH. Thus, increasing contents of mobile polyP were the consequence of an increasing energy demand. On the other hand, the increasing depolarization of the cell membrane following the sequence Rb+ < K+ < Na+ < Li+ inhibited the net P(i) accumulation. Furthermore, it is postulated that the Pi accumulation was also regulated by the intracellular content in polyP.