Editing Self-incompatibility (section)

====The S-glycoprotein mechanism====
In this mechanism, pollen growth is inhibited within minutes of its placement on the stigma.<ref name="franklin-tong2003"/> The mechanism is described in detail for ''[[Papaver rhoeas]]'' and so far appears restricted to the plant family [[Papaveraceae]]. {{cn|date=July 2024}}

The female determinant is a small, extracellular molecule, expressed in the stigma; the identity of the male determinant remains elusive, but it is probably some [[cell membrane]] [[Receptor (biochemistry)|receptor]].<ref name="franklin-tong2003"/> The interaction between male and female determinants transmits a cellular [[signal transduction|signal]] into the pollen tube, resulting in strong influx of [[calcium]] [[cation]]s; this interferes with the intracellular [[concentration]] gradient of calcium [[ion]]s which exists inside the pollen tube, essential for its elongation.<ref>{{cite journal |doi=10.1046/j.1365-313X.1993.04010163.x | vauthors = Franklin-Tong VE, Ride JP, Read ND, Trewavas AJ, Franklin FC |title=The self-incompatibility response in ''Papaver rhoeas'' is mediated by cytosolic free calcium |journal=Plant J. |volume=4 |pages=163–177 |year=1993 |doi-access=free }}</ref><ref>{{cite journal |doi=10.1046/j.1365-313x.1997.12061375.x | vauthors= Franklin-Tong VE, Hackett G, Hepler PK |title=Ratioimaging of Ca21 in the self-incompatibility response in pollen tubes of ''Papaver rhoeas'' |journal=Plant J. |volume=12 |pages=1375–86 |year=1997 |issue=6 |doi-access=free }}</ref><ref>{{cite journal | vauthors = Franklin-Tong VE, Holdaway-Clarke TL, Straatman KR, Kunkel JG, Hepler PK | title = Involvement of extracellular calcium influx in the self-incompatibility response of Papaver rhoeas | journal = The Plant Journal | volume = 29 | issue = 3 | pages = 333–345 | date = February 2002 | pmid = 11844110 | doi = 10.1046/j.1365-313X.2002.01219.x | s2cid = 954229 | doi-access = free }}</ref> The influx of calcium ions arrests tube elongation within 1–2 minutes. At this stage, pollen inhibition is still reversible, and elongation can be resumed by applying certain manipulations, resulting in ovule fertilization.<ref name="franklin-tong2003"/>

Subsequently, the [[cytosol]]ic protein '''p26''', a [[pyrophosphatase]], is inhibited by [[phosphorylation]],<ref>{{cite journal | vauthors = Rudd JJ, Franklin F, Lord JM, Franklin-Tong VE | title = Increased Phosphorylation of a 26-kD Pollen Protein Is Induced by the Self-Incompatibility Response in Papaver rhoeas | journal = The Plant Cell | volume = 8 | issue = 4 | pages = 713–724 | date = April 1996 | pmid = 12239397 | pmc = 161131 | doi = 10.1105/tpc.8.4.713 }}</ref> possibly resulting in arrest of [[Biosynthesis|synthesis]] of molecular building blocks, required for tube elongation. There is [[polymerization|depolymerization]] and reorganization of [[actin]] filaments, within the pollen [[cytoskeleton]].<ref>{{cite journal | vauthors = Geitmann A, Snowman BN, Emons AM, Franklin-Tong VE | title = Alterations in the actin cytoskeleton of pollen tubes are induced by the self-incompatibility reaction in Papaver rhoeas | journal = The Plant Cell | volume = 12 | issue = 7 | pages = 1239–1251 | date = July 2000 | pmid = 10899987 | pmc = 149062 | doi = 10.1105/tpc.12.7.1239 | bibcode = 2000PlanC..12.1239G }}</ref><ref>{{cite journal | vauthors = Snowman BN, Kovar DR, Shevchenko G, Franklin-Tong VE, Staiger CJ | title = Signal-mediated depolymerization of actin in pollen during the self-incompatibility response | journal = The Plant Cell | volume = 14 | issue = 10 | pages = 2613–2626 | date = October 2002 | pmid = 12368508 | pmc = 151239 | doi = 10.1105/tpc.002998 | bibcode = 2002PlanC..14.2613S }}</ref> Within 10 minutes from the placement on the stigma, the pollen is committed to a process which ends in its death. At 3–4 hours past pollination, fragmentation of pollen [[DNA]] begins,<ref>{{cite journal | vauthors = Jordan ND, Franklin FC, Franklin-Tong VE | title = Evidence for DNA fragmentation triggered in the self-incompatibility response in pollen of Papaver rhoeas | journal = The Plant Journal | volume = 23 | issue = 4 | pages = 471–479 | date = August 2000 | pmid = 10972873 | doi = 10.1046/j.1365-313x.2000.00811.x | doi-access = free }}</ref> and finally (at 10–14 hours), the cell dies [[apoptosis|apoptotically]].<ref name="franklin-tong2003"/><ref>{{cite journal | vauthors = Thomas SG, Franklin-Tong VE | title = Self-incompatibility triggers programmed cell death in Papaver pollen | journal = Nature | volume = 429 | issue = 6989 | pages = 305–309 | date = May 2004 | pmid = 15152254 | doi = 10.1038/nature02540 | name-list-style = amp | s2cid = 4376774 | bibcode = 2004Natur.429..305T }}</ref>