Photophosphorylation during Chloroplast Development in Red Kidney Bean: II. Photophosphorylation and Photoreduction Appear Concomitantly but Initially are Uncoupled.
Cyclic phosphorylation with phenazine methosulfate and noncyclic phosphorylation and reduction with ferricyanide were detected in isolated chloroplasts from greening bean leaves after 3 to 4 hours of illumination. Activity commenced when rapid synthesis of chlorophyll was initiated. Rates of photophosphorylation were comparable to mature levels by 15 to 18 hours of development. Photoreduction of ferricyanide attained a peak value by 12 hours of illumination and subsequently fell to normal levels by 15 to 18 hours. With ferricyanide, the P/e(2) ratios were initially less than 0.1 but were close to 1.0 after 18 hours of illumination. The data suggested that photosystems I and II appeared concomitantly in the chloroplast but were not fully operative until later in development. Proplastids and immature chloroplasts exhibited high capacities to reduce ferricyanide in the dark. The rates of dark reduction rapidly diminished to low levels by 15 hours of illumination when normal rates of photochemical activity were observed. After a 2-to 3-day lag, a rapid increase in leaf fresh weight was noted at the time total chlorophyll content reached steady state values on a fresh weight basis. With fresh weight as an index of growth, primary leaves completed their development after 6 to 7 days of illumination.
Howes
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Department of Botany, University of Massachusetts, Amherst, Massachusetts 01002.
Stern
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AI