|Systematic IUPAC name
Physcion(e), rheochrysidin, methoxyemodin
|Molar mass||284.26348 g/mol|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Parietin is the predominant cortical pigment of lichens in the genus Caloplaca, a secondary product of the lichen Xanthoria parietina, and a pigment found in the roots of Curled Dock (Rumex crispus). It has an orangy-yellow color and absorbs blue light.
It reacts with KOH to form a deep, reddish-magenta compound.
It has also been shown to protect against UV-B light, for lichens at high altitudes in Alpine regions. The UV-B light stimulates production of parietin and the parietin protects the lichens from damage. Lichens in arctic regions such as Svarlbard retain this capability though they do not encounter damaging levels of UV-B, a capability that could be help protect the lichens in case of Ozone layer thinning.
- "Xanthoria parietina is a widespread lichen coloured by the orange cortical pigment parietin (= physcion). We studied the pigment content in 60 thalli sampled in 4 habitats along a sun–shade gradient from evergreen boreal forests through open deciduous stands to sea cliffs. The significant positive regression between contents of parietin per unit area and site factors (reflecting the openness of the canopy relative to an open sky) across sampled habitats suggested a photoprotective role of parietin at UV-B and/or blue wavelengths, the two absorbance maxima of parietin. UV-B susceptibility of X. parietina, measured as permanent reductions in photosystem II, decreased highly significantly with increasing parietin content per thallus area. However, as much as three-fold greater UV-B irradiances than ambient daily summer maxima, maintained continuously for 240 h were required to cause UV-B damage even in thalli of shaded habitats. Since a previous study has documented a high PAR susceptibility of parietin-deficient X. parietina in the absence of UV-B, there are reasons to believe that the blue light screening of parietin is functionally more important than the UV-B screening. A strong positive relationship between parietin content per unit area and reflectance at 500 nm allows the parietin content in X. parietina thalli to be assessed non-destructively by reflectance measurements" [Is parietin a UV-B or a blue-light screening pigment in the lichen Xanthoria parietina?]Yngvar Gauslaa and Elin Margrete Ustvedt, Photochem. Photobiol. Sci., 2003, 2, 424–432
- "This study reports UV screening pigments in the upper cortices of two widespread lichens collected in three sun-exposed locations along a latitudinal gradient from the Arctic lowland to alpine sites of the Central European Alps. Populations from the Alps receive 3–5 times higher UV-B irradiance than their Arctic counterparts from Svalbard because of latitudinal and altitudinal gradients in UV-B irradiance.... This implies that Arctic populations maintain a high level of screening pigments in spite of low ambient UV-B, and that the studied lichen species presumably may tolerate an increase in UV-B radiation due to the predicted thinning of the ozone layer over polar areas" The lichens Xanthoria elegans and Cetraria islandica maintain a high protection against UV-B radiation in Arctic habitats Line Nybakken, Knut Asbjørn Solhaug, Wolfgang Bilger, Yngvar Gauslaa, Oecologia July 2004, Volume 140, Issue 2, pp 211-216
- UV-induction of sun-screening pigments in lichens Knut Asbjørn Solhaug, Yngvar Gauslaa, Line Nybakken and Wolfgang Bilger, New Phytologist Volume 158, Issue 1, pages 91–100, April 2003 DOI: 10.1046/j.1469-8137.2003.00708.x
- Caloplaca coralloides chemistry
- Choi, Gyung Ja; Seon-Woo Lee, Kyoung Soo Jang, Jin-Seog Kim, Kwang Yun Cho and Jin-Cheol Kim (December 2004). "Effects of chrysophanol, parietin, and nepodin of Rumex crispus on barley and cucumber powdery mildews". Crop Protection 23 (12): 1215–1221. doi:10.1016/j.cropro.2004.05.005.
- Edwards, Howell G. M.; Emma M. Newton; David D. Wynn-Williams; Steven R. Coombes (2003-03-12). "Molecular spectroscopic studies of lichen substances 1: parietin and emodin". Journal of Molecular Structure 648 (1–2): 49–59. doi:10.1016/S0022-2860(02)00384-8.
- Solhaug, Knut A.; Yngvar Gauslaa (November 1996). "Parietin, a photoprotective secondary product of the lichen Xanthoria parietina". Oecologia 108 (3): 412–418. doi:10.1007/BF00333715.