Biochemical and genetic characterization of wheat (Triticum spp.) kernel polyphenol oxidases

Genetic variability of polyphenol oxidase (PPO) activity was evaluated in hexaploid, tetraploid, and aneuploid wheat (Tritictan spp.). A DNA probe to kernel-specific PPO hybridized to PPO clones from an immature wheat kernel cDNA library but not to clones from a seedling cDNA library. Recombinant protein and antibody were developed from the kernel-specific PPO. PPO transcript and antigenic proteins were most abundant during kernel development and decreased rapidly at physiological maturity. PPO proteins were more abundant in immature kernels, but PPO activity was greater in mature kernels. Wheat kernel antigenic protein bands of similar to 58, 60, 62, and 75kD were identified; immunoprecipitated proteins of similar to 60 and similar to 62kD were confirmed to be PPOs by LC-MS/MS. The 2D chromosome was implicated as a major locus of PPO activity in cultivar (cv.) 'Chinese Spring' based on antigenic staining intensity of similar to 60-62 kD proteins and kernel PPO activity in aneuploid lines. The similar to 58 kD protein was not well-correlated with kernel PPO activity, while the similar to 75 kD protein was likely a PPO precursor. Tropolone completely inhibited PPO activity extracted from mature kernels but not from immature kernels. Total PPO activity in mature kernels is thus a function of specific PPO isoforms present, their abundance, and activation levels. (c) 2006 Elsevier Ltd. All rights reserved.