Phosphorylase in Guard Cells

Abstract

Using a histochemical method to detect phosphorylase in plant cells (Yin and Sun, Science 105: 650. 1947), leaves of tobacco and Broad bean were starved in darkness to free them of starch, and the epidermis was stripped off and treated with glucose-1-phosphate. Very intense starch formation was found in the guard cells after 4-5 hrs. of incubation, indicating strong phosphorylase activity. Little or no reaction was shown by the epidermal cells. Incubation with glucose instead of glucose-1-phosphate with or without Mg salts and adenosine-triphosphate failed to produce starch even after 24 hrs. The guard cells have no detectable phosphorylating mechanism even though they show some phosphatase activity. Phosphorylase activity is exclusively localized in the chloroplasts. It is very clear in cells which have been incubated for but a short time before too much starch has been accumulated. No activity was found in the nucleus and cytoplasm. Each chloroplast had one or more active loci. These enlarged and merged so that the whole plastid appeared to be filled with starch.