Localization and quantification of cell wall phenolics in European corn borer resistant and susceptible maize inbreds

Abstract

Three maize inbreds (MBR 6796-15, B86, and CI31A) resistant to leaf feeding by the European corn borer Ostrinia nubilalis, and one susceptible inbred (MS72), were evaluated for insect resistance and phytochemical composition to gain a better understanding of maize-resistance mechanisms. Insect resistance was evaluated using laboratory bioassays that demonstrated that immature leaf tissue is the preferred feeding substrate. Phytochemical analyses were conducted for leaf protein, hydroxamic acid content, and hydroxycinnamic acids bound to the cell wall for both immature and mature leaf tissue. Hydroxycinnamic acid distribution in cell walls was examined using five stains, autofluorescence, and microspectrophotometry. Phloroglucinol, azure B, diazotized salts of p-nitroaniline and sulfanilic acid, and chlorine sulfite allowed visualization of phenolic localization but were not quantitative. Microspectrophotometer readings of epidermal, phloem, and xylem cell walls confirmed staining results, showing extremely low cell wall hydroxycinnamic acid levels in epidermal cell walls of immature leaf tissue. Foliar nitrogen content was not related to insect feeding preference. Hydroxycinnamic acid fortification of epidermal cell walls appears to correlate best with corn borer feeding preference, accounting for differential resistance between inbred lines and between tissue maturities. Microspectrophotometry may be useful as a technique for monitoring phytochemical resistance mechanisms in breeding programs. Key words: maize, Ostrinia nubilalis, phenolic, hydroxycinnamic acids, cell wall, microspectrophotometry, resistance.