Phil L. Bruckner

Evaluation of Wheat Polyphenol Oxidase Genes

ABSTRACT Polyphenol oxidases (PPOs) present in mature wheat (Triticum aestivum L.) kernels have been implicated in the undesirable darkening of cereal products such as Asian noodles. To accelerate the functional characterization of wheat PPOs and allow the identification of those PPO genes that are primarily involved in food biochemistry, several basic local alignment search tool (BLAST) searches of expressed sequence tag (EST) databases were performed using a known wheat PPO sequence as a search argument; identified ESTs were resequenced and aligned. Results from this study suggest the presence of at least six PPO genes in hexaploid wheat, falling into two clusters with three similar sequences each. Based on the tissues used for cDNA library preparation, three genes (all members of one cluster) are expressed during kernel development and may therefore influence cereal product quality; the remaining three genes (belonging to the second cluster) were isolated from nonkernel cDNA libraries and may not be ex...

Molecular and biochemical characterisation of polyphenol oxidases in developing kernels and senescing leaves of wheat (Triticum aestivum)

Polyphenol oxidases (PPOs) have been implicated in plant defence reactions. From an applied point of view, high PPO activity is associated with browning / darkening of fresh and processed food. Owing to its complex genome and economic importance, wheat (Triticum aestivum L.) represents an interesting system to advance our understanding of plant PPO function. We have previously shown that wheat PPOs are organised in a multigene family, consisting of two distinct phylogenetic clusters with three members each. In this study, we demonstrate that members of one cluster are not expressed in developing kernels or senescing flag leaves. Transcriptional regulation of one major gene in the other cluster largely controls PPO levels in these tissues, at least in the wheat varieties used for this study. Our data further indicate that the product of this gene is present as a latent enzyme during early kernel development, and that the latent enzyme is activated during later developmental phases. Enzyme activation can be achieved in vitro by limited tryptic digestion, but our data do not indicate activation by a proteolytic mechanism in vivo. Together, results presented in this study provide important insights into the regulation of wheat PPO function.

Extraction and Activation of Wheat Polyphenol Oxidase by Detergents: Biochemistry and Applications

ABSTRACT Polyphenol oxidases (PPOs) from several plant species, including wheat, have been implicated in undesirable brown discolorations of food products. It has been demonstrated that these enzymes are often present in a latent form or are membrane-associated, necessitating detergent or other treatments to obtain fully active preparations. Here, the influence of different detergents on wheat meal and flour PPOs was investigated. Extraction in presence of 50 mM SDS led to a 5- to 15-fold increase in PPO activity, making quantitative assays in flour from low-PPO lines more robust. Among a series of additional nonionic, anionic, and cationic detergents tested, only n-lauroylsarcosine increased extractable PPO activity to a degree comparable to that of SDS. Additional experiments suggested that a large fraction of wheat meal PPOs may be membrane-associated and that SDS is able to activate PPOs extracted from high-activity but not from low-activity wheat lines. PPO activities assayed after SDS extraction of ...

Using Agronomic Traits and Semiochemical Production in Winter Wheat Cultivars to Identify Suitable Trap Crops for the Wheat Stem Sawfly

Abstract Trap crops are a plausible control strategy for the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), especially in alternate wheat—fallow cropping systems. Identifying the most suitable winter wheat (Triticum aestivum L., Poaceae) cultivars is necessary to further improve the effectiveness of winter wheat trap crops. We compared cultivars suitable for cultivation in Montana to identify those that exhibit the greatest potential as trap crops. To accomplish this we used nine winter wheat cultivars to analyze plant characteristics that influence the oviposition behavior of the WSS: stem height, stem diameter, rate of plant development, and emission of the WSS attractant (Z)-3-hexenyl acetate. Data on sawfly-induced stem cutting collected from these cultivars in field nurseries were analyzed to evaluate the potential of each cultivar to attract sawflies. Based on these criteria, five cultivars with good potential as trap crops are ‘Norstar’, ‘Neeley’, ‘Morgan’, ‘Rampart’, and ‘BigSky’. More data from laboratory preference tests and detailed measurement of semiochemical production from these cultivars are required for selecting optimal cultivars for trap-cropping.