On the basis of the biological compounds that they metabolize, plant peroxidases have long been implicated in plant growth, cell wall biogenesis, lignification, and host defenses. Transgenic tobacco (Nicotiana tabacum L.) plants that underexpress anionic peroxidase were generated using antisense RNA. The antisense RNA was found to be specific for the anionic isoenzyme and highly effective, reducing endogenous transcript levels and total peroxidase activity by as much as 1600-fold. Antisense-transformed plants appeared normal at initial observation; however, growth studies showed that plants with reduced peroxidase activity grow taller and flower sooner than control plants. In contrast, previously transformed plants overproducing anionic peroxidase were shorter and flowered later than controls. Axillary buds were more developed in antisensetransformed plants and less developed in plants overproducing this enzyme. It was found that the lignin content in leaf, stem, and root was unchanged in antisense-transformed plants, which does not support a role for anionic peroxidase in the lignification of secondary xylem vessels. However, studies of wounded tissue show some reduction in wound-induced deposition of lignin-like polymers. The data support a possible role for tobacco anionic peroxidase in host defenses but not without a reduction in growth potential.

Al~trlct. Red oaks (Quercus rubra L.) were regenerated via direct and indirect asexual embryogenesis from immature zygotic embryo tissues. Late heart and early cotyledonary explants cultured in light on modified MS medium proved to be most embryogenic. Embryoids arose from explants cultured on various combinations of 2,4-D and BA. However, the highest percentages of normal polar embryoids were produced by. explants cultured on growth-regulator-free media. Epicotyl dormancy of embryoids was overcome by desiccation (air drying and use of an osmoticum) and rehydration treatments. Asexual plantlet development paralleled developmental changes associated with seed germination. White oak (Quercus alba L.) embryoids were also regenerated, but failed to germinate.

Partially expanded male catkins at the pre-pollen shedding stage of Quercus rubra L. and Quercus bicolor Willd. were cultured on MS medium supplemented with BA or 2,4D Explants on 2,4D produced a yellow embryogenic callus, seeming to originate from the pedicels. Subsequent transfers to BA and then, MS without growth regulators, resulted in callus proliferation. After ten weeks in culture, white embryoids developed from the callus of Q. bicolor. Separated and individually cultured embryoids underwent direct, repetitive embryogenesis. Upon transfer to ½-strength MS, embryoid germination and plant regeneration occurred, Callus of Q. rubra degenerated after five months in culture, failing to produce embryogenic structures.

The objective of this study was to develop an asexual embryogenic regeneration system for Rubus, even though previous attempts had proved unsuccessful (Fiola and Swartz, 1986). In an initial experiment, fruits of fieldgrown R. occidentalis 'Bristol' and 'Jewel' and R. idaeus 'Exp-72' plants were collected at the early green, late-green or early yellow, and the red stages of ripeness. Seeds were extracted and disinfested in a 0.5% sodium hypochlorite and 0.5% Alconox solution for 15 min followed by two 30-sec sterile distilled water rinses. Cotyledon explants (0.5 to 1.0 mm) were excised from embryos that had been aseptically dissected from the seeds and cultured on a modified MS medium (Murashige and Skoog, 1962) containing 200 mg casein hydrolysate/liter, 3% sucrose, and 0, 0.45, or 4.5 µM (2,4-dichlorophenoxy)acetic acid (2,4-D). For the three stages of ripeness, we used 133, 56, and60 explants for 'Bristol'; 143, 60, and 77 for 'Jewel'; and 64, 166, and 60 for 'Exp-72', with each group divided equally among growth regulator treatments. The pH of the medium was adjusted to 5.7 before adding 0.25% Gelrite (Scott Laboratories, Atlanta) and autoclaving. Cultures were incubated at 24C under cool-white fluorescent illumination (70 µmol•m-2 •s-1). About 70% of all 'Bristol' and 'Jewel' explants extracted from seed of late-green or early yellow fruit were highly embryogenic regardless of 2,4-D concentration. Most embryoids originated directly from explant tissue and not through callus. Repetitive embryogenesis (Tulecke and McGranahan, 1985) was common in all of these cultures. Even though the initiation of embryogenesis occurred sooner on explants cultured on media containing 2,4-D, embryoids developed on such media exhibited many abnormalities, including polycotyledony, "rooty" masses, and increased anthocyanin production. Sixty-nine 'Jewel' and 14 'Bristol' normal embryoids (parallelling

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