AGGREGATION OF NADPH-PROTOCHLOROPHYLLIDE OXIDOREDUCTASE-PIGMENT COMPLEXES IS FAVORED BY PROTEIN-PHOSPHORYLATION

The greening of dark-grown leaves is initiated by the phototransformat ion of protochlorophyllide (Pchlide) to chlorophyllide (Chlide). Pchli de, NADPH-Pchlide oxidoreductase (Pchlide reductase, EC 1.3.1.33) and NADPH are associated in a ternary complex, which in an aggregated form is localized in the prolamellar bodies. Upon illumination, the newly formed Chlide shows a spectral blue-shift (the Shibata shift), the Chl ide-protein aggregates dissociate, Chlide is esterified, the prolamell ar bodies are transformed and Pchlide reductase is relocalized to the prothylakoids. The causality of these events is not fully understood. Treatment of dark-grown leaves of wheat (Triticum aestivum L.) with th e phosphatase inhibitor fluoride inhibited the Shibata shift and the e sterification of Chlide. ATP, as well as ATP-gamma-S, delayed the spec tral blue-shift of Chlide of isolated etioplast inner membranes in a s imilar manner as did fluoride. ATP or ATP-gamma-S promoted, while AMP or GTP did not, the reformation of phototransformable Pchlide in isola ted etioplast inner membranes, provided NADPH was present. P-32 was in corporated into Pchlide reductase from P-32-alpha-ATP as well as from P-32-gamma-ATP. Together, our results show that conditions which favou r protein phosphorylation or prevent protein dephosphorylation favoure d the formation/preservation of pigment-Pchlide reductase aggregates. Accordingly, phosphorylation would favour the formation of prolamellar bodies, while dephosphorylation would be connected to their transform ation. A dephosphorylation of Pchlide reductase may thus be an importa nt factor in the etioplast to chloroplast development.