about 600 known
almost half from the family Rubiaceae
quinones are usually colored
exist in equilibrium with the "enolic" forms in many cases
some are ubiquitous in plants, e.g., ubiquinone and plastoquinones
a variety of pathways
Simple quinones
many interesting quinones in the Myrsinaceae
Salvia, a number of diterpenes from this genus contain interesting ortho-quinones
Striga is a parasitic plants; one species Striga asiatica is a serious pest of cereal grains, primarily Sorghum in Africa
A hydroquinone with a long side chain is a seed germination stimulant. The corresponding p-benzoquinone lacks this activity.
Haustorial formation
2,6-dimethoxy-p-benzoquinone induces haustorial formation. Haustoria (one is a haustorium) link the roots of the Striga parasite and the Sorghum host.
the root must be within 50 micrometers of the root to be successful
laccases from Striga oxidize syringic acid from Sorghum roots
Naphthoquinones
vitamin K1 is in all green plant tissues
two main pathways lead to naphthoquinones in higher plants
some are polyketides, e.g., plumbagin and 7-methyljuglone
others arise from the shikimic acid pathway (to be covered in more detail in the next lecture)
chorismic acid ----> iso-chorismic acid ----> reacts with α -ketoglutarate ----> ortho-succinylbenzoic acid
lawsone (in Impatiens balsamina and juglone (Juglans regia are both derived from these precursors. Note that in compounds that involve symmetrical intermediates, the label gets scrambled. The the label gets scrambled in juglone, but not in lawsone.
Naphthoquinones derived from iso-chorismic acid and α -ketoglutarate are found in plants and bacteria
in lapachol ... a portend of things to come ... prenylation occurs... cyclization of these prenyl units leads to anthraquinones
juglone and allelopathy
many "antifeedants" or allomones in wood are naphthoquinones
Anthraquinones
over 200 are known from plants
many occur as β-glycosides. β-Glycosidases also are present.
when these compounds are isolated from plant material, they frequently change from yellow ----> red. This is a result of hydrolysis
in base many go from deep red to blue
again, there are two main biosynthetic origins:
Polyketide
many of these compounds are produced in tissue cultures, e.g., emodin
aloesaponin and chrysophanol ... represent two different ways of folding the polyketide precursor
Iso-chorismic acid
alizarin is a well-known example of this group of compounds
these are especially common in the family Rubiaceae, closely related prenylnaphthoquinones also occur
madder, Rubia tinctoria is a well-known example of dye-stuffs from plants
a series of anthraquinones from Streptocarpus dunnii (Gesneriaceae) also has been extensively studied
Distribution: Anthraquinones from iso-chorismic acid are found in a number of closely related families including the Rubiaceae. They are not produced by most other plants or by fungi and bacteria.
Hypericum perforatum, Klamath weed or St. John's Wort, is an introduced weedy plant with anti-depressant activity. The plant is toxic to livestock and became a major problem in California and Oregon. Chrysolina beetles were introduced as an early biological control. Today, the plant is reduced to a fraction of it's former range in the American West. The plant is a powerful photosensitizer as well.
Assorted Quinones, Napthoquinones and Anthraquinones
Polyketide Anthraquinone Formation
Anthraquinones from the Rubiaceae
Anthraquinones from Rubia tinctoria
Plants with Quinones, Naphthoquinones,
and Anthraquinones
© David S. Seigler, Integrative Biology 425, Plant Secondary Metabolism, Department
of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana,
Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.
