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Metabolism and Enzymology

Comparison of Polyphenol Oxidase Expression in Glandular Trichomes of Solanum and Lycopersicon Species ¹

Department of Plant Breeding and Biometry, Cornell University, Ithaca, New York 14853-1901

Tetralobulate glandular trichomes are present on the foliage of many solanaceous species. Resistance of many of these species to insects is conditioned by the ability of trichomes to rupture upon contact and to rapidly polymerize their contents, resulting in entrapment of insects in hardened trichome exudate. In the wild potato, Solanum berthaultii, polymerization of trichome exudate is initiated by a soluble M_r 59,000 polyphenol oxidase (PPO), which is a dominant protein constituent of the organ. PPOs, although ubiquitous in angiosperms, typically display great heterogeneity in molecular weight and are found at low levels in plant cells. Because of the unusually high accumulation and tissue-specific expression of the M_r 59,000 PPO in S. berthaultii glandular trichomes, we analyzed trichome proteins of a number of Lycopersicon and Solanum species to assess the extent to which possession of the M_r 59,000 PPO is conserved. Trichomes were collected manually and examined for PPO activity, immuno-cross-reactivity with S. berthaultiiM_r 59,000 PPO, and protein content. In addition, N-terminal amino acid sequences were obtained for five trichome PPOs. All species analyzed possessed trichome PPOs similar in structure and level of expression to that of S. berthaultii. The relationship between sequences and structures of these conserved PPOs and the variable PPOs of leaf is discussed.

³ Present address: Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843.

¹ This work was supported in part by Hatch Project NYS 149417, the International Potato Center, and by a grant from the Cornell Biotechnology Program, which is sponsored by the New York State Science and Technology Foundation, a consortium of industries, the U.S. Army Research Office, and the National Science Foundation.

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