Macromolecular Physiology of Plastids

Abstract

Dispersal of the prolamellar body tubules into primary lamellar layers has been studied in leaves of dark-grown bean seedlings (Phaseolus vulgaris L.). Following complete photoconversion of protochlorophyllide the dispersal process can proceed in either light or darkness. The dispersal is reversibly inhibited in leaves at o °C. Above o °C the time course for the dispersal is temperature dependent. The spectral shift of the in vivo absorption maximum of newly formed chlorophyllide from 684 to 672 nm is also inhibited at o °C and the time course is temperature-dependent in a manner similar to that of the membrane dispersal. A causal connexion between the 2 phenomena can thus be suggested. Derangement of the tubular membranes produced by heat treatment or by freezing and thawing in darkness causes the appearance of photoactive protochlorophyllide absorbing at 635 nm. Photoconversion of protochlorophyllide 635 nm results in chlorophyllide absorbing at 672 nm and further dissociation of the membranes. Denaturation of the prolamellar body membranes by heating or by slow thawing results in the formation of photoinactive protochlorophyllide absorbing at 632 nm.