Light filtering by epidermal flavonoids during the resistant response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity.
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.
Edwards
W Ray
WR
Department of Biochemistry and Molecular Biology, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, OK 74078-3035, United States.
Hall
Judy A
JA
Rowlan
Alan R
AR
Schneider-Barfield
Tama
T
Sun
Tzeli Julia
TJ
Patil
Mohini A
MA
Pierce
Margaret L
ML
Fulcher
R Gary
RG
Bell
Alois A
AA
Essenberg
Margaret
M
D005419:Flavonoids / Q000502:physiology*; D003368:Gossypium / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D010858:Pigmentation / Q000187:drug effects; D010935:Plant Diseases; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D012717:Sesquiterpenes; D013053:Spectrophotometry; D013472:Sunlight; D013729:Terpenes / Q000737:chemistry / Q000633:toxicity*; D000094162:Phytoalexins
D005419:Flavonoids; D012717:Sesquiterpenes; D013729:Terpenes; D000094162:Phytoalexins