Intracellular pH of spores in an S. pombe ascus.
Upon nitrogen starvation and sporulation most free GFP including
phluorin is scavenged and destroyed. To prevent this,
phluorin was targeted to the nucleus using an NLS and the cells then
sporulated by nitrogen starvation.  The photograph shows an ascus
containing 4 spores. The blue image is the nucleus containing the
phluorin-NLS. The cytoplasm of the spore does not contain detectable
phfluorin. Some phluorin-NLS remains in the region outside the spores as
they mature. Note that this phluorin is indicating a different
pH from that of the nucleus. Nuclear pH is indistinguishable from cytoplasmic
pH in vegetative cells.

Karagiannis and Young. 2001. J. Cell Sci. 114, 2929.