LUXURY PHOSPHATE UPTAKE AND VARIATION OF INTRACELLULAR METAL CONCENTRATIONS IN HETEROSIGMA AKASHIWO (RAPHIDOPHYCEAE)

ABSTRACT

The effectr of phosphate starvation and subsequent uptake on distribution and concentration of phosphate metabolic intermediates and metals were studied in Heterosigma akashiwo (Hada) Hada by ³¹P-NMR spectroscopy, neutron activation analysis and ESR spectroscopy. Excess orthophosphate (4.5 μM P_i, as NaH₂PO₄) added to a medium with P-depleted H. akashiwo cells was rapidly taken up resulting in an increase in P cell quota (q_p)from 68.2 to 99.6 fmol. cell-¹in 2 h and to 156.3 fmol. cell-¹in 6 h. After three days, q_p approached about 190 fmol. cell⁻¹. Polyphosphate (PP_i) rapidly increased from 0 to 11.4 fmol· cell⁻¹in 2 h and to 24.7 fmol·cell⁻¹in 6 h. Diel variation of cell quota indicated that cellular P_i increase was synchronized with cellular PP_i decrease and vice versa. The average chain length of PP_i increased from ca. 0 to ca. 10.2 phosphate residues in 2 h after addition of P_i and one day later, from ca. 9.8 to ca. 12.5.

The cell quota of Mn (q_Mn), and to a lesser extent Co, increased rapidly from 4.87 fg. cell⁻¹in the P- starved condition to 50.48 fg·cell⁻¹2 h afer addition of P_i but decreased to 8.63 fg. Cell⁻¹by 6 h. Concentrations of Zn, As, Hf, Cu and sometimes Al, Mg, K, and Ca changed in a manner opposite to that of Mn and Co. The excretion of these cations, which was synchronized with the uptake of Mn and Co, may be important for a charge balancing in the cells. The ESR spectra showed that the high cellular Mn observed at 2 h after P addition was Mn²⁺which was taken up by the cells rather than adsorbed on the cell surface. These data combined with PP_i data suggested that the behavior of q_Mn is synchronized with the behavior of average chain length of PP_i.