PROTOCHLOROPHYLLIDE TRANSFORMATIONS AND CHLOROPHYLL ACCUMULATION IN EPICOTYLS OF PEA (PISUM-SATIVUM)

Low-temperature fluorescence emission spectra of epicotyls of 6.5-day- old dark-grown seedlings of pea (Pisum sativum L.) showed the dominanc e of short-wavelength protochlorophyllide forms with emission maxima a t 629 and 636 nm, respectively. The presence of long wavelength protoc hlorophyllide with emission maxima around 650 nm was just detectable. Accordingly, irradiation with millisecond flashes gave a minute format ion of chlorophyllide. The chlorophyll(ide) formation varied along the epicotyl. Irradiation with continuous light for 1.5 h resulted in an evident accumulation of chlorophyll(ide) in the upper part of the epic otyl. Only small amounts accumulated in the middle section. The conver sion of protochlorophyllide to chlorophyllide was temperature dependen t and almost arrested at 0 degrees C. The chlorophyll(ide) formed had one dominating fluorescence peak at 681 nm. Irradiation for 24 h gave almost 100 times more chlorophyll in the upper part of the epicotyl th an in the lower part. Electron micrographs from the upper part of the epicotyl irradiated for 6 h showed plastids with several developing th ylakoids, while the plastids in the lower part of the epicotyl had onl y a few thylakoids. The dominance of short-wavelength protochlorophyll ide forms indicated the presence of protochlorophyllide not bound to t he active site of NADPH-protochlorophyllide oxidoreductase (EC 1.3.1.3 3). The inability of the short-wavelength form to transform into chlor ophyllide with flash light denotes a dislocation from the active site. The time and temperature dependence of the chlorophyll(ide) formation in continuous light indicates that a relocation is required of the sh ort-wavelength protochlorophyllide before chlorophyllide formation can occur.