Editing Chloroplast (section)

==== Plastoglobuli ====

Plastoglobuli ('''singular''' ''plastoglobulus'', sometimes spelled ''plastoglobule(s)''), are spherical bubbles of [[lipid]]s and [[protein]]s<ref name="Wise-2006b" /> about 45–60 nanometers across.<ref name="Austin-2006" /> They are surrounded by a [[lipid monolayer]].<ref name="Austin-2006" /> Plastoglobuli are found in all chloroplasts,<ref name="Burgess-1989a" /> but become more common when the chloroplast is under [[oxidative stress]],<ref name="Austin-2006">{{cite journal | vauthors=Austin JR, Frost E, Vidi PA, Kessler F, Staehelin LA |author5-link=Lucas Andrew Staehelin | title=Plastoglobules are lipoprotein subcompartments of the chloroplast that are permanently coupled to thylakoid membranes and contain biosynthetic enzymes | journal=The Plant Cell | volume=18 | issue=7 | pages=1693–703 | date=July 2006 | pmid=16731586 | pmc=1488921 | doi=10.1105/tpc.105.039859 |bibcode=2006PlanC..18.1693A }}</ref> or when it ages and transitions into a [[gerontoplast]].<ref name="Wise-2006b" /> Plastoglobuli also exhibit a greater size variation under these conditions.<ref name="Austin-2006" /> They are also common in [[etioplasts]], but decrease in number as the etioplasts mature into chloroplasts.<ref name="Austin-2006" />

Plastoglobuli contain both structural proteins and enzymes involved in [[lipid synthesis]] and [[metabolism]]. They contain many types of [[lipid]]s including [[plastoquinone]], [[vitamin E]], [[carotenoid]]s and [[chlorophylls]].<ref name="Austin-2006" />

Plastoglobuli were once thought to be free-floating in the [[stroma (fluid)|stroma]], but it is now thought that they are permanently attached either to a [[thylakoid]] or to another plastoglobulus attached to a thylakoid, a configuration that allows a plastoglobulus to exchange its contents with the thylakoid network.<ref name="Austin-2006" /> In normal green chloroplasts, the vast majority of plastoglobuli occur singularly, attached directly to their parent thylakoid. In old or stressed chloroplasts, plastoglobuli tend to occur in linked groups or chains, still always anchored to a thylakoid.<ref name="Austin-2006" />

Plastoglobuli form when a bubble appears between the layers of the [[lipid bilayer]] of the thylakoid membrane, or bud from existing plastoglobuli—though they never detach and float off into the stroma.<ref name="Austin-2006" /> Practically all plastoglobuli form on or near the highly curved edges of the [[thylakoid]] disks or sheets. They are also more common on stromal thylakoids than on [[granum|granal]] ones.<ref name="Austin-2006" />

{{plain image with caption|File:Chlamydomonas TEM 07.jpg|[[Transmission electron micrograph]] of ''[[Chlamydomonas reinhardtii]]'', a green alga that contains a pyrenoid surrounded by starch.|300px|right|bottom|triangle|#aaa}}