PARENT SESSION
Posters P5C Biosynthesis and assembly: Pigments. Abstracts (643-659)

Effects of light on localization of NADPH-protochlorophyllide oxidoreductase (POR)-pigment complexes in barley etioplasts. Dragan Kovacevic^*,1, David Dewez¹, Radovan Popovic¹, ¹ UQAM, CP 8888, succursale Centre-ville, Montreal, Quebec, Canada

ABSTRACT- Light-dependent step of chlorophyll biosynthesis is catalyzed by the POR photoenzyme accumulated in the etioplast prolamellar body membranes (PLB) of dark-grown angiosperms. The effects of light on the localization of pigment-POR complexes after photoreduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide) have been examined. Light-induced reversible decrease of the POR polypeptide content was observed in isolated etioplast inner membranes (EPIMs) of illuminated etiolated barley leaves. Analysis of different etioplast compartments indicated that this decrease may be attributed to different processes such as dispersal of the PLBs, solubilization of POR and the formation of POR dimer and oligomer forms. After illumination of etiolated barley leaves the evident decrease of the nonphotoactive Pchl(ide) fluorescence band (633 nm) of the EPIMs was observed, while at the same time a Chl(ide) band at 677 nm was noticed. This may provide evidence that the nonphotoactive Pchl(ide) dissociated from the EPIMs attached to the POR enzyme. However, the newly formed Chl(ide) may remain associated with the EPIMs. In etioplasts of illuminated etiolated leaves a stroma-located Chl(ide) emitting at 677.5 nm was found to be concomitantly present with the 683-nm Chl(ide) located in the PLB membrane. These results indicate that the Chlide transformation process in the PLB fraction of etioplasts was complete.

KEY WORDS: protochlorophyllide, etioplast, protochlorophyllide reductase