Sporopollenin

Pollen grains with different surfaces from different plants: Lilium auratum with monocolpate pollen grains; the others have tricolpate pollen grains: sunflower ( Helianthus annuus ), morning glory ( Ipomoea purpurea ), Sildalcea malviflora , evening primrose ( Oenothera fruticosa ) and castor bean ( Ricinus communis ).

Sporopollenin is the plant substance that forms the building material of the exospore in spores and the exine of pollen grains . Sporopollenin is a highly polymeric heteropolymer of related biomolecules that is built up from simple aromatic carboxylic acids such as p -umaric acid (4-hydroxy- cinnamic acid ) and long-chain, unbranched aliphatics and aliphatic polyhydroxy components; the cross-linked molecular structure has ether bridges. Sporopollenin is chemically very resistant ( inert to acids, bases, solvents). An oxidative polymerization of carotenoids and carotenoid esters was assumed to be the origin . But tracer experiments suggest an involvement of lipid - and phenylpropanoid - metabolism in the biosynthesis out of sporopollenin. The exact chemical composition was not known for a long time, precisely because of the chemical resistance. Due to this property, pollen grains are not broken down in the absence of air and thus become microfossils .

Sporopollenin is a deposit (accretion) on the cell wall. The main function is to protect against UV radiation but not against dehydration.

Occurrence

Sporopollenin-like substances (e.g. algaenans ) occur in some air algae in the group of Chlorophyta : the Trentepohliophyceae and in some Chlorococcales . The main occurrence, however, is the Embryophyta : the mosses , fern-like and seed plants . Sporopollenin is considered to be a key feature of land plants that has contributed to the successful colonization of land. The spore (later: pollen) resistance was increased. Sporopollenin is also found in chandelier algae (Characeae), whose line of development is considered to be the sister group of the Embryophyta.

literature

• G. Bohne, H. Woehlecke, R. Ehwald: Water relations of the pine exine . Annals of Botany. Volume 96, 2005, pages 201-208.
• Guido Bohne: Selected properties of pine sporopollenin ; Dissertation, 2007, Humboldt University Berlin, Faculty of Mathematics and Natural Sciences I.
• J. Doyle, M. O'Leary, Pollination in Pinus , Scientific Proceedings of the Royal Dublin Society Volume 21 [20], 1935, pages 181-191.
• Peter Sitte , Elmar Weiler , Joachim W. Kadereit , Andreas Bresinsky , Christian Körner : Textbook of botany for universities . Founded by Eduard Strasburger . 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010-X .
• Gerhard Wagenitz : Dictionary of botany. The terms in their historical context . 2nd expanded edition. Spectrum Academic Publishing House, Heidelberg / Berlin 2003, ISBN 3-8274-1398-2 .
• R. Wiermann, S. Gubatz: Pollen wall and sporopollenin . International Review of Cytology - a Survey of Cell Biology, Volume 140, 1992, pages 35-72.
• R. Wiermann, F. Ahlers, I. Schmitz-Thom: Sporopollenin . In: M. Hofrichter, A. Steinbüchel: Biopolymers Volume 1. Pages 209-229, Wiley-VCH, Weinheim 2001.

Individual evidence

1. ^ Paul Kenrick & Peter R. Crane (1997): The origin and early evolution of plants on land. Nature 389, 33-39.
2. ↑ CF Delwiche, LE Graham, N. Thomson (1989): lignin-like compounds and sporopollenin in Coleochaete, plans to algal model for the country. Science 245, 399-401.