Light filtering by epidermal flavonoids during the resistant response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity

Phytochemistry. 2008 Sep;69(12):2320-8. doi: 10.1016/j.phytochem.2008.05.021. Epub 2008 Jul 9.


2,7-Dihydroxycadalene and lacinilene C, sesquiterpenoid phytoalexins that accumulate at infection sites during the hypersensitive resistant response of cotton foliage to Xanthomonas campestris pv. malvacearum, have light-dependent toxicity toward host cells, as well as toward the bacterial pathogen. Adaxial epidermal cells surrounding and sometimes covering infection sites turn red. The red cells exhibited 3-4-fold higher absorption at the photoactivating wavelengths of sunlight than nearby colorless epidermal cells. Red epidermal cells protected underlying palisade mesophyll cells from the toxic effects of 2,7-dihydroxycadalene plus sunlight, indicating a role for epidermal pigments in protecting living cells that surround infection sites from toxic effects of the plant's own phytoalexins. A semi-quantitative survey of UV-absorbing substances extracted from epidermal strips from inoculated and mock-inoculated cotyledons indicated that the principal increase in capacity to absorb the photoactivating wavelengths was due to a red anthocyanin and a yellow flavonol, which were identified as cyanidin-3-O-beta-glucoside and quercetin-3-O-beta-glucoside, respectively.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Flavonoids / physiology*
  • Gossypium / drug effects
  • Gossypium / physiology*
  • Gossypium / radiation effects
  • Light
  • Pigmentation / drug effects
  • Plant Diseases
  • Plant Leaves / drug effects
  • Plant Leaves / physiology*
  • Plant Leaves / radiation effects
  • Sesquiterpenes
  • Spectrophotometry
  • Sunlight*
  • Terpenes / chemistry
  • Terpenes / toxicity*


  • Flavonoids
  • Sesquiterpenes
  • Terpenes
  • phytoalexins