Is Glc a significant product of starch mobilization?
Two leaves on a spinach plant were subjected to steady-state labelling with an atmospheric concentration of 14CO2 during the preceding light period to label the starch pool uniformly. Thirty minutes before the start of the photoentrained night period, these leaves were removed and chloroplasts isolated. At various times, chloroplasts were separated from the external medium by centrifugation through a single layer of silicone oil, terminated in 25% (v/v) CH3OH, and immediately frozen. The concentrations of starch and soluble basic, acidic, and neutral products (Glc, fructose, sucrose, and maltose) were measured in the aqueous medium above the silicone oil layer (Fig. 5A) and in the chloroplast pellet (Fig. 5B) using enzyme coupled assays and radioactivity measurement. For comparison, these same metabolites were measured in leaf discs removed at various times during the day and night periods from an intact spinach leaf adjacent to those used for preparing chloroplasts (Fig. 6). Starch le
