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

Author
item EDWARDS, W. RAY - OKLAHOMA STATE UNIVERSITY
item HALL, JUDY - OKLAHOMA STATE UNIVERSITY
item ROWLAN, ALAN - OKLAHOMA STATE UNIVERSITY
item BARFIELD-SCHNEIDER, TAMA - OKLAHOMA STATE UNIVERSITY
item SUN, TZELI JULIA - OKLAHOMA STATE UNIVERSITY
item PATIL, MOHINI - OKLAHOMA STATE UNIVERSITY
item PIERCE, MARGARET - OKLAHOMA STATE UNIVERSITY
item FULCHER, R. GARY - UNIVERSITY OF MINNESOTA
item Bell, Alois - Al
item ESSENBERG, MARGARET - OKLAHOMA STATE UNIVERSITY

Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2008
Publication Date: 7/9/2008
Citation: Edwards, W., Hall, J.A., Rowlan, A.R., Barfield-Schneider, T., Sun, T., Patil, M.A., Pierce, M.L., Fulcher, R., Bell, A.A., Essenberg, M. 2008. Light filtering by epidermal flavonoids during the resistant response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity. Phytochemistry. 69:2320-2328.

Interpretive Summary: When infected with bacteria or fungi, cotton plants produce antibiotics that kill the invading organisms. The antibiotics are also toxic to cotton cells but in inact leaves do little damage. In this paper the scientists show that cells next to those producing the antibiotic produce colored compounds that prevent activation of the antibiotic by light. These protective compounds were identified as cyanidin-3-0-beta-glucoside and quercetin-3-0-beta-glucoside. This basic information is important for scientists designing experiments to manipulate natural defense systems by introduction of foreign genes or chemical treatments.

Technical 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- to 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 ipidermal 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.