THE EFFECT OF PH ON MEIOSIS REINITIATION IN OOCYTES OF THE PROSOBRANCH MOLLUSK CELLANA-NIGROLINEATA (REEVES)

Prophase-blocked eggs obtained from a dissected ripe ovary of the prosobranch mollusc Cellana nigrolineata (Reeves) were exposed to various pH levels (6.0, 6.5, 6.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0). The mean percentage and mean time of occurrence of germinal vesicle breakdown (GVBD), a process involved in meiosis reinitiation, was used to assess the effects of the various levels of pH. Mean percent GVBD in control (untreated seawater), i.e., spontaneous maturation which began within 35 min, was 25%. Exposure of oocytes to NaOH-fortified filtered seawater initiated GVBD within 10 min. Mean percent GVBD at this time was 61 % at pH 8.0, 73 % at pH 8.5, 98 % at pH 9, 82 % at ph 9.5, and 7% at pH 10. At low and neutral pH, GVBD did not occur. These results verify previous studies showing that pH plays an intracellular role in the oocyte maturation process and that alkalinization increases intracellular pH. GVBD occurs because of the change in intracellular pH.