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Jerry D. Cohen

An in vitro system was used for the production of tomato (Lycopersicon esculentum) fruit in culture starting from immature flowers. This system produced small parthenocarpic (seedless) fruit in response to 10-4 m indole-3-acetic acid (IAA) supplied in the medium. Other auxins, auxin conjugates and antiauxins tested were not effective or produced markedly fewer fruit. Additional IAA supplied to the fruit culture media before breaker stage resulted in an increase in the time period between breaker and red-ripe stages from 7 days without additional IAA to 12 days when 10-5 m IAA was added. These results suggest that significant changes in the ripening period could be obtained by alteration of auxin relationships in tomato fruit.

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Carol Auer, Jerry D. Cohen, and Todd Cooke

The uptake and metabolism of exogenous tritium-labelled benzyl adenine was studied during the shoot induction period of petunia leaf explants in tissue culture. Transfer experiments with Petunia `MD1' leaf explants (1 cm2) on MS media with 2.2 uM BA show that 27% and 100% of the leaf explants are committed to shoot induction on days 6 and 10, respectively. To study BA uptake and metabolism, leaf explants were placed on media containing tritium-labled BA for 1, 3, 6 and 10 days. BA was taken up from the media on days 1-6. BA metabolizes were analyzed using HPLC, a UV absorbancc detector and enzymatic techniques. Metabolizes produced include: BA, BAdo, BA 7G, BA 9G, BAdoMP, BAdoDP, BAdoTP and 3 unidentified compounds. BA and BAdo were detected on days 1 and 3 but not during day 6-10, the time of shoot induction. The pool of ribotide metabolites decreased from days 1 to 10, from 26.5% of all metabolites to 1.6%. Glucosylated compounds, BA 7G and BA 9G, increased continuously from 24.9% to 69.8% between days 1 and 10. An unidentified compound C increased from 13% on day 3 to 24.8% on day 10. In separate experiments, BA uptake and metabolism were compared in two Petunia hybrida lines, St40 and TLV1, with different shoot organogenic responses in tissue culture. These data show interesting patterns of BA metabolism in relationship to shoot induction and organogenesis.

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Jerry D. Cohen and Janet P. Slovin

The literature is full of different techniques and approaches to the isolation, purification and quantitative analysis of plant hormones. From this body of literature it is possible to deduce that 1) a lot of investigators are interested in how much of these compounds are in plants and 2) that the techniques for phytohormone analysis are still largely “under development”. This talk will discuss different approaches to hormone analysis, suitability of each approach, and criteria for the evaluation of techniques and results. The goal will be to highlight points that are important to obtaining reliable analytical information and knowing what to do when problems occur. Nevertheless, having reliable numbers is frequently only the first step in understanding hormonal systems involved in plant development, It is often the case that the expected results are not what is found in experiments involving plant hormone quantitation. We will consider experimental design, tissue localization, developmental stages, sampling and extraction procedures, and the limits of what to expect when “dogma confronts reality”. Work reported was supported by grants from the National Science Foundation DCB-8917378, USDA-CRGO 89-3721-4734, US-Israel BARD US-1362-87, and by funds from the USDA Argicultural Research Service,

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Fernando A. De Villena, Vincent A. Fritz, Jerry D. Cohen, and William D. Hutchison

Changes in the levels of gluconasturtiin (2-phenylethyl glucosinolate), an aromatic glucosinolate, was used to evaluate the response of ‘Green Rocket’ Chinese cabbage (Brassica campestris ssp. pekinensis L.) to the feeding of three and five cabbage looper (Trichoplusia ni Hübner) larvae per plant. Plants were harvested 0, 10, and 17 days after infestation. The change in gluconasturtiin concentration resulting from decreased light capture from diminished leaf area was also studied. All samples were assayed for gluconasturtiin concentration using high-performance liquid chromatography. The gluconasturtiin concentration of plants subjected to five larvae per plant showed a 59% increase 10 days after infestation compared with noninfested plants. Difference in gluconasturtiin concentration between three and five larvae per plant was nonsignificant. Seventeen days after initial infestation and 7 days after larvae were removed (final harvest), gluconasturtiin concentration did not decrease compared with the previous harvest. Reduced light or leaf area removal did not significantly affect gluconasturtiin concentration.

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Veronica L. Justen, Jerry D. Cohen, Gary Gardner, and Vincent A. Fritz

Glucosinolates (GSLs) are thioglucosides with important properties for plant defense and human health. The objective of this study was to quantify yield and GSL concentration in turnip (Brassica rapa subsp. rapa) roots and shoots as influenced by colored plastic mulches. Four turnip cultivars (‘Just Right’, ‘Purple Top’, ‘Royal Crown’, and ‘Scarlet Queen’) were grown over five mulch treatments: white, yellow, silver, red, blue, and a bare soil control in both a May and an August planting in 2006 and 2007. Yield varied by variety; however, there was no consistent relationship between mulch treatment and yield. Glucosinolate concentrations and profiles varied with tissue type, genotype, and environmental factors, including temperature and planting date. Mulch-dependent increases in GSL concentrations were not consistent across tissue types, cultivars, planting dates, and years of the study, possibly as a result of differences in climatic factors and mulch-dependent changes in soil temperature between planting dates and years of the study.

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Charles L. Rohwer, Lynette Y. Wong, David C. Zlesak, and Jerry D. Cohen

It may seem paradoxical that a teaching assistant (TA), whose involvement in a particular class may be limited to a single semester, can provide continuity in the classroom from year to year. Improvement in TA performance from one year to the next also seems difficult to achieve under such circumstances. However, when TAs are encouraged to document classroom activities, specific TA responsibilities, and student concerns, this documentation may be useful in achieving continuity, improved TA performance, and result in a better classroom experience for the students. In addition to the benefit of documentation, TAs, in conjunction with faculty, can together reflect upon how well the objectives of specific laboratories were met. TAs can contribute to generating and documenting ideas that may be implemented to help improve student learning in the future. Each TA comes to the course with a unique collection of horticultural and teaching experiences and has the potential to aid faculty in course refinement and improvement. We explain how TA-directed documentation can provide continuity and year-to-year improvement in horticulture classrooms using our experience with HORT 3005, a required plant physiology laboratory course specifically targeted to horticulture students at the University of Minnesota.