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T.J. Miesle, A. Proctor, and L.M. Lagrimini

The activity, isoenzymes, and histochemical location of peroxidase were studied in developing highbush blueberries (Vaccinium corymbosum L.). Total peroxidase activity increased during development when expressed on a fresh-weight basis, reaching a maximum in red berries and then declining. When peroxidase activity was expressed per berry it did not decline after the red-berry stage. Most of the enzyme was ionically bound to cell walls throughout development, with the number of isoenzymes increasing with maturity. Histochemical localization of peroxidase showed that enzyme activity spread throughout the berry during development.

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Ruth C. Martin, Machteld C. Mok, and David W.S. Mok

Cytokinins are widely used in tissue culture and transformation systems; however, little is known of their mode of action or the mechanisms regulating their levels in plant tissues. We are studying enzymes responsible for the metabolism of zeatin in immature seeds of Phaseolus. Selective expression of genes encoding such enzymes may regulate the level of active cytokinins during seed development as well as in in vitro systems. A zeatin O-xylosyltransferase, which mediates the formation of O-xylosylzeatin from trans-zeatin and UDP-xylose, has been isolated and monoclonal antibodies specific to the enzyme have been produced. Tissue print analyses demonstrated that the enzyme is primarily localized in the endosperm. ln situ localization and EM studies indicated that the enzyme is present in the cytoplasm and the nucleus. cDNA libraries were constructed from immature seed mRNA and immunopositive clones were selected. The products of these clones are being analyzed in E. coli and baculovirus expression systems.

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Rumphan Koslanund, Douglas D. Archbold, and Kirk W. Pomper

Pawpaw fruit were harvested at the advent of the ripening process and were ripened at room temperature. Based on fruit firmness and respiration and ethylene production rates at harvest and during ripening, fruit were classified into one of four categories: preripening (no to very slight loss of firmness; preclimacteric), early ripening (some softening; increasing rates of ethylene and CO2 production), mid-ripening (soft; at or just past climacteric), and late ripening (very soft; postclimacteric). The activities of the cell-wall degrading enzymes polygalacturonase (PG), endo-(1→4)ß-D-glucanase (EGase), and endo-ß-1,4-mannanase (MAN) were low in the preripening and early ripening stages, increased dramatically by mid-ripening coincident with the respiratory and ethylene climacterics, and decreased at late ripening. However, pectin methylesterase (PME) activity per milligram protein was highest at the green stage when the fruit firmness was high and decreased as ripening progressed. Tissue prints indicated both EGase and MAN increased as ripening proceeded. The EGase activity was evident near the seeds and the surface of the fruit at preripening and eventually spread throughout, while MAN activity was evident near the fruit surface at preripening and was progressively expressed throughout the flesh as fruit ripened. The greatest decline in fruit firmness occurred between pre- and early ripening, before the peak activities of PG, EGase, and MAN, although MAN exhibited the greatest relative increase of the three enzymes in this period. The data suggest that PME may act first to demethylate polygalacturonate and may be followed by the action of the other enzymes resulting in cell wall disassembly and fruit softening in pawpaw.

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Sophie Rochefort, Yves Desjardins, David J. Shetlar, and Jacques Brodeur

this instance, a 2-mm cross-section of a tiller was analyzed using a commercial tissue print immunoblot test kit (Agrinostics Ltd. Co., Watkinsville, Ga.). Tissue print immunoblot technique for detection of N. coenophialum mycelial proteins was first

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different dates, from a commercial watermelon field showing symptoms of SqVYV, CuLCrV and PRSV-W and possibly CYSDV. This was followed by a smaller sampling of five plants in a different commercial planting. Tissue prints were made from cross sections of