Editing Chloroplast (section)

=== Cellular location ===
{{plain image with caption|File:Chloroplast movement.svg|When chloroplasts are exposed to direct sunlight, they stack along the [[wikt:anticlinal|anticlinal cell walls]] to minimize exposure. In the dark they spread out in sheets along the [[wikt:periclinal|periclinal walls]] to maximize light absorption.|460px|right|bottom|triangle|#3fbceb}}

==== Chloroplast movement ====
{{See also|Cytoplasmic streaming}}

The chloroplasts of plant and algal cells can orient themselves to best suit the available light. In low-light conditions, they will spread out in a sheet—maximizing the surface area to absorb light. Under intense light, they will seek shelter by aligning in vertical columns along the plant cell's [[cell wall]] or turning sideways so that light strikes them edge-on. This reduces exposure and protects them from [[photooxidative damage]].<ref name="Wells-1979">{{Cite journal |last1=Wells |first1=C. |last2=Balish |first2=E. |year=1979 |title=The mitogenic activity of lipopolysaccharide for spleen cells from germfree, conventional, and gnotobiotic rats |journal=Canadian Journal of Microbiology |volume=25 |issue=9 |pages=1087–93 |doi=10.1139/m79-166 |pmid=540263}}</ref> This ability to distribute chloroplasts so that they can take shelter behind each other or spread out may be the reason why land plants evolved to have many small chloroplasts instead of a few big ones.<ref name="Glynn-2007" />
Chloroplast movement is considered one of the most closely regulated stimulus-response systems that can be found in plants.<ref name="Dong-1998">{{cite journal |vauthors=Dong XJ, Nagai R, Takagi S |year=1998 |title=Microfilaments Anchor Chloroplasts along the Outer Periclinal Wall in Vallisneria Epidermal Cells through Cooperation of PFR and Photosynthesis |journal=Plant and Cell Physiology |volume=39 |issue=12 |pages=1299–306 |doi=10.1093/oxfordjournals.pcp.a029334 |doi-access=free}}</ref> [[Mitochondrion|Mitochondria]] have also been observed to follow chloroplasts as they move.<ref name="Takagi-2003">{{cite journal |vauthors=Takagi S |date=June 2003 |title=Actin-based photo-orientation movement of chloroplasts in plant cells |journal=The Journal of Experimental Biology |volume=206 |issue=Pt 12 |pages=1963–9 |doi=10.1242/jeb.00215 |pmid=12756277 |doi-access=free|bibcode=2003JExpB.206.1963T }}</ref>

In higher plants, chloroplast movement is run by [[phototropins]], blue light [[Photoreceptor protein|photoreceptors]] also responsible for plant [[phototropism]]. In some algae, [[moss]]es, [[fern]]s, and [[flowering plant]]s, chloroplast movement is influenced by red light in addition to blue light,<ref name="Wells-1979" /> though very long red wavelengths inhibit movement rather than speeding it up. Blue light generally causes chloroplasts to seek shelter, while red light draws them out to maximize light absorption.<ref name="Takagi-2003" />

Studies of ''[[Vallisneria gigantea]]'', an aquatic [[flowering plant]], have shown that chloroplasts can get moving within five minutes of light exposure, though they don't initially show any net directionality. They may move along [[microfilament]] tracks, and the fact that the microfilament mesh changes shape to form a honeycomb structure surrounding the chloroplasts after they have moved suggests that microfilaments may help to anchor chloroplasts in place.<ref name="Dong-1998" /><ref name="Takagi-2003" />