Abstract
To study the regulation of lipid transport from the chloroplast envelope to the thylakoid, intact chloroplasts, isolated from fully expanded or still-expanding pea (Pisum sativum) leaves, were incubated with radiolabeled lipid precursors and thylakoid membranes subsequently were isolated. Incubation with UDP[(3)H]Gal labeled monogalactosyldiacylglycerol in both envelope membranes and digalactosyldiacylglycerol in the outer chloroplast envelope. Galactolipid synthesis increased with incubation temperature. Transport to the thylakoid was slow below 12 degrees C, and exhibited a temperature dependency closely resembling that for the previously reported appearance and disappearance of vesicles in the stroma (D.J. Morré, G. Selldén, C. Sundqvist, A.S. Sandelius [1991] Plant Physiol 97: 1558-1564). In mature chloroplasts, monogalactosyldiacylglycerol transport to the thylakoid was up to three times higher than digalactosyldiacylglycerol transport, whereas the difference was markedly lower in developing chloroplasts. Incubation of chloroplasts with [(14)C]acyl-coenzyme A labeled phosphatidylcholine (PC) and free fatty acids in the inner envelope membrane and phosphatidylglycerol at the chloroplast surface. PC and phosphatidylglycerol were preferentially transported to the thylakoid. Analysis of lipid composition revealed that the thylakoid contained approximately 20% of the chloroplast PC. Our results demonstrate that lipids synthesized at the chloroplast surface as well as in the inner envelope membrane are transported to the thylakoid and that lipid sorting is involved in the process. Furthermore, the results also indicate that more than one pathway exists for galactolipid transfer from the chloroplast envelope to the thylakoid.
Highlights
To study the regulation of lipid transport from the chloroplast envelope to the thylakoid, intact chloroplasts, isolated from fully expanded or still-expanding pea (Pisum sativum) leaves, were incubated with radiolabeled lipid precursors and thylakoid membranes subsequently were isolated
The fractional purity of thylakoid fractions were assayed in thylakoid fractions isolated from chloroplast batches corresponding in size to those later used for lipid transport assays
The first issue to be met in undertaking an in organello study of lipid transfer from the envelope to the thylakoid membrane is the isolation of highly purified thylakoids from intact chloroplasts
Summary
To study the regulation of lipid transport from the chloroplast envelope to the thylakoid, intact chloroplasts, isolated from fully expanded or still-expanding pea (Pisum sativum) leaves, were incubated with radiolabeled lipid precursors and thylakoid membranes subsequently were isolated. Structures apparently resembling fusions between the inner envelope membrane and the thylakoid have been observed in chloroplasts of expanding leaves (Carde et al, 1982; Morreet al., 1991b) and membrane vesicles have been observed in the stroma, close to the plastid envelope, both in embryonic leaf cells (Kaneko and Keegstra, 1996) and expanding leaves (Morreet al., 1991b). By analogy to the temperature dependence of vesicular trafficking between endoplasmic reticulum and the Golgi compartment in animal cells, it was proposed that the vesicles enriched in the stroma at low temperature represented transport vesicles that had blebbed off the envelope membrane, but which could not at the lowered temperature fuse with the thylakoid membrane (Morreet al., 1991b). Our objective with the present investigation was to determine whether the transfer of galactolipids from the chloroplast envelope to the thylakoid in organello showed temperature dependence resembling that of the previously reported appearance and disappearance of vesicles in the stroma compartment (Morreet al., 1991b). Lipid Transport from the Chloroplast Envelope to the Thylakoid wanted to assess whether the extent and regulation of lipid transport to the thylakoid depended on the stage of leaf development
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
