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Acid phosphatase activity fluctuates in mature epidermal guard cells of Campanula persicifolia in response to changing light conditions. As demonstrated both by Gomori's method and by Burstone's simultaneous coupling azo dye technique in both unfixed and aldehyde-fixed epidermal strips, the enzyme is active in the spherosomes when the guard cells are flaccid and the stomata are either partially or fully closed. It is inactive when the cells are turgid and the stomata are fully open, regardless of whether opening had resulted from a photoactive or scotoactive process. In living preparations, such inactive spherosomes will gradually become active for acid phosphatase if turgid guarde clls are subjected to partial plasmolysis. Marked activity for acid phosphatase becomes manifest in the vacuoles as well as in the spherosomes of the guard cells if the plants are kept in the dark for many days. In senescent leaves the vacuoles of the guard cells are reactive even though the plants are grown in the light. The walls of the epidermal cells exhibit sporadic activity for the enzyme, but the walls of guard cells have not been observed to react. Nuclear staining sometimes is present after tissues are incubated in the Gomori medium, but it is considered to result from nonenzymic binding of lead on the nuclear surface. The spherosomes evidently are among the principal sites for acid phosphatase activity in plant cells. In guard cells the spherosomes are considered to be enzymically active when the cells are in a relatively catabolic phase of metabolism and to become inactive when the cells enter a relatively anabolic phase.

FLUCTUATIONS IN THE ACID PHOSPHATASE ACTIVITY OF SPHEROSOMES IN GUARD CELLS OF CAMPANULA PERSICIFOLIA