Light filtering by epidermal flavonoids during the resistant response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity |
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Authors: | Edwards W Ray Hall Judy A Rowlan Alan R Schneider-Barfield Tama Sun Tzeli Julia Patil Mohini A Pierce Margaret L Fulcher R Gary Bell Alois A Essenberg Margaret |
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Institution: | a Department of Biochemistry and Molecular Biology, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, OK 74078-3035, United States b Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108-6099, United States c USDA/ARS National Cotton Pathology Research Unit, Southern Crops Research Laboratory, College Station, TX 77845, United States |
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Abstract: | 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-β-glucoside and quercetin-3-O-β-glucoside, respectively. |
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Keywords: | Gossypium hirsutum L Malvaceae Upland cotton Xanthomonas campestris pv malvacearum Ecological biochemistry Anthocyanin Flavonol glycoside Phytoalexin Sesquiterpene Cyanidin-3-O-β-glucoside Chrysanthemin 2 7-Dihydroxycadalene Isoquercitrin Lacinilene C Quercetin-3-O-β-glucoside UV damage UV protection |
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