EFFECTS OF OSMOTIC-STRESS AND GROWTH STAGE ON CELLULAR PH AND POLYPHOSPHATE METABOLISM IN NEUROSPORA-CRASSA AS STUDIED BY P-31 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY
Yc. Yang et al., EFFECTS OF OSMOTIC-STRESS AND GROWTH STAGE ON CELLULAR PH AND POLYPHOSPHATE METABOLISM IN NEUROSPORA-CRASSA AS STUDIED BY P-31 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY, Biochimica et biophysica acta, 1179(2), 1993, pp. 141-147
High-resolution P-31-NMR was employed to investigate the effects of gr
owth stage and environmental osmolarity on changes of polyphosphate me
tabolism and intracellular pH in intact Neurospora crassa cells. Our s
tudy showed that changes of these parameters were growth-dependent. Th
e ratio of polyphosphate to orthophosphate in vacuoles increased from
2.4 to 13.5 in N. crassa as cells grew from early log phase to station
ary phase. Cytoplasmic pH and vacuolar pH changed, respectively, from
6.91 and 6.49 in early log phase cells to 7.25 and 6.84 in stationary
phase cells. Hypoosmotic shock of N. crassa produced growth-dependent
changes including: (i) a rapid hydrolysis of polyphosphate with a conc
omitant increase in the concentration of the cytoplasmic phosphate, (i
i) an increase in cytoplasmic pH, and (iii) an increase in vacuolar pH
. Early log phase cells produced the most dramatic response whereas th
e stationary phase cells appeared to be recalcitrant to the osmotic st
ress. Thus, 95% and 60% of polyphosphate in the early log phase and mi
d-log phase cells, respectively, disppeared in response to hypoosmotic
shock, but little or no hydrolysis of polyphosphate occurred in stati
onary cells. The cytoplasmic pH and the vacuolar pH increased in respo
nse to hypoosmotic shock by 0.4 and 0.53 unit, respectively, in early
log phase cells; and by 0.22 and 0.27 unit, respectively, in the mid-l
og phase cells. In contrast, hypoosmotic shock of the stationary phase
cells did not cause any change in intracellular pH. The osmotic stres
s-induced polyphosphate hydrolysis and pH changes in early log and mid
-log phase cells were reversible, suggesting that these changes were r
elated environment osmolarity. Addition of polyamines or basic amino a
cids which are known to be sequestered in vacuoles did not affect poly
phosphate metabolism.