No abstract

A method is described for cell-free studies of lipid release from be involved, stroma and envelope were independently or toisolated chloroplast envelope. The isolated membrane fraction gether incubated with [-32 P]GTP or [-32 P]GTP. Stroma and envelope proteins were phosphorylated and the envelope frac-incorporated radiolabeled galactose into galactolipids, predominantly monogalactosyldiacylglycerol, prior to immobi-tion contained GMP/GDP binding proteins as well. When the fractions were co-incubated, the patterns of protein phospho-lization of the membrane vesicles onto strips of nitrocellulose. The strips with immobilized membrane were individually incu-rylation and guanine nucleotide binding was different compared to the additive effects of the separate fractions, bated with various co-factors and the incubations were terminated by removing the strips. Radioactivity was determined suggesting that guanine nucleotides may have roles in galactolipid release in addition to providing energy. The results for the strips with immobilized membrane as well as for the point to several similarities between the regulation of galac-material released during the assay. The release of galactolipids from immobilized chloroplast envelope was time-and tolipid release from isolated chloroplast envelope and the temperature dependent, required stroma protein(s) and was regulation of vesicular trafficking among animal and yeast cytosolic membranes, although other mechanisms for lipid further stimulated by hydrolysable ATP, GTP and 5 50 mM release cannot, at this stage, be ruled out. acyl-CoAs, of which 16:1-CoA was the most stimulative. To investigate whether guanine nucleotide-binding proteins could

I., Ryberg, M. and Sundqvist, C. 1996. Protochlorophyllide transformations and chlorophyll accumulation in epicotyls of pea (Pisum sativum). -Physiol. Plant. 96; 706-713, Low-temperature fluorescence emission spectra of cpieotyls of 6.5-day-old darkgrown seedlings of pea (Pisum saiivum L.) showed the dominance of short-wavelength protochlorophyllide forms with emission maxima at 629 and 636 nm, respectively. The presence of long-wavelength protochlorophyllide with emission maxima around 650 nm was just detectable. Accordingly, irradiation witli millisecond flashes gave a minute formation of chlorophyllide. The chlorophyll(ide) formation varied along the epicotyl. hradiation with continuous light for 1,5 h resulted in an evident accumulation of chlorophyU(ide) in the upper part of the epicotyl. Only small amounts accumulated in the middle section. The conversion of protochlorophyllide to chlorophyllide was temperature dependent and almost arrested at O^C, The chlorophyll(ide) formed had one dominating fluorescence peak at 681 nm. Irradiation for 24 h gave almost 100 times more ehlorophyll in the upper part of the epicotyl than in the lower part. Electron micrographs from the upper part of the epicotyl irradiated for 6 h showed plastid.s with several developing thylakoids, while the plastids in the lower part of the epicotyl had only a few thylakoids. The dominance of short-wavelength protochlorophyllide forms indicaled the presence of protochlorophyllide not bound to the active site of NADPH-protochlorophyllide oxidoreductase (EC 1.3.1.33). The inability of the short-wavelength form to transform into ehlorophyllide with flash hght denotes a dislocation from the active site. The time and temperature dependenee of the ch!orophyll(ide) foimation in continuous light indicates that a relocation is required of the short-wavelength protochlorophyllide before chlorophyllide formation can occur.