THE SHIBATA SHIFT - EFFECTS OF IN-VITRO CONDITIONS ON THE SPECTRAL BLUE-SHIFT OF CHLOROPHYLLIDE IN IRRADIATED ISOLATED PROLAMELLAR BODIES

The spectral blue-shift of chlorophyllide (Chlide) in flash irradiated isolated prolamellar bodies (PLBs) of dark-grown wheat (Triticum aest ivum) was analysed. The fluorescence emission at -196 degrees C of Chl ide varied depending on the composition of the medium. NADPH-protochlo rophyllide oxidoreductase (Pchlide reductase) activity was taken as an indication that a general protein denaturation had not occurred. The results indicate that the spectral blue-shift of Chlide is in part owi ng to conformational changes of the Chlide-Pchlide reductase complexes induced by the phototransformation of Pchlide to Chlide. The Chlide s pectral blue-shift decreased with increasing concentrations of sucrose or glycerol. At high concentration of glycerol (87%) there was neithe r a Chlide blue-shift nor any esterification of Chlide, while the phot otransformation of Pchlide to Chlide was not affected. Phototransforma tion of Pchlide to Chlide may induce changes in the pigment-Pchlide re ductase interactions that cannot be transduced into a molecular rearra ngement of the enzyme protein in the presence of high concentrations o f osmotic agents. EDTA and Ca2+ caused effects which in part could be explained as an enhanced disaggregation of the oligomeric Chlide-Pchli de reductase complexes. Addition of BSA enhanced the blue-shift of Chl ide even at high sucrose concentrations. It also inhibited a reformati on of Pchlide-Pchlide reductase complexes and reduced the esterificati on of Chlide. The effect of BSA on the blue-shift was suppressed by ad dition of NADPH. The possibility that BSA interacted with the Chlide-P chlide reductase complexes is discussed.