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  • Author or Editor: Margaret J McMahon x
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Similarities exist between the effects of phytochrome and cytokinins on plant growth and development (e.g., chloroplast development, amaranthin synthesis. seed germination, photomorphogenesis). It is unclear, however, if and how these two systems interact.

As a beginning step to determine cytokinin-phytochrome interactions, we developed a strategy utilizing ipt -transgenic tobacco in phytochrome/light treatment investigations. The sour-cc of the ipt gene was Agrobacterium tumefaciens Ti plasmid 15955. This gene encodes for isopentenyl transferase which is an enzyme active in cytokinin biosynthesis.

Ipt -transgenic tobacco cultures (grown on MS medium supplemented with kanamycin but no plant growth regulators) were treated with end-of-day red or far-red light for 15 minutes. After 30 days of treatment, the plant tissue was harvested and either homogenized for SDS-PAGE or fixed for transmission electron microscopic analysis.

Results from immuno-gold labelling using polyclonal antibodies specific to iptase will he used to Indicate the influence of phytochrome on cytokinin activity. Also, structural changes at the ultra-cellular level will be determined.

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Experiments were conducted to correlate the response of chrysanthemum [Dendrathema ×grandiflorum (Ramat.) Kitamura] plants to light environment based on various quantitative light quality parameters by growing plants under 6% or 40% CuSO4 and water spectral filters. Using a narrow band width (R = 655-665 and FR = 725-735 nm) or a broad band width (R = 600-700 and FR = 700-800 nm) for R: FR ratio calculation, 6% CuSO4 filter transmitted light with a higher R: FR ratio than 40% CuSO4 or water filters. Light transmitted through 40% CuSO4 and water filters had similar narrow band R: FR ratios (≈1.2), but the broad band R: FR ratio (2.0) of 40% CuSO4 filter was higher than that of water filters. The estimated phytochrome photoequilibrium (ϕ) value varied considerably with the photochemical properties of phytochrome used for estimations. Final height and internode length of plants grown in 6% or 40% CuSO4 chambers was ≈30% less than of plants in corresponding control chambers. Leaf and stem dry weights were reduced by light transmitted through CuSO4 filters. The results suggest that broad band R: FR ratio correlated more closely to above plant responses than the narrow band R: FR ratio. Blue (B): R and B: FR ratios (not absolute amount of blue wavelengths) correlated well with plant response, suggesting that involvement of blue light should not be ignored in expressing plant response to light transmitted through CuSO4 filters. At present, the presentation of complete spectral data would be the most useful in explaining plant response to light environment.

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The interest in using nonchemical alternatives for growth control of horticultural crops has recently increased due to public concerns for food safety and environmental pollution. Several research teams around the world are investigating alternative growth control measures, such as genetic manipulation, temperature, water and nutrient management, mechanical conditioning, and light quality manipulation. This review discusses the recent developments in light quality manipulation as a nonchemical alternative for greenhouse plant height control.

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Commercially available polyethylene mulches were evaluated for their influence on spectral properties (absorption, reflection, and transmission) and soil temperature during the growing season. Vegetative growth and yield of bell pepper (Capsicum annuum cv. Keystone Resistant Giant No. 3) plants were evaluated for each mulch. Black plastic had the greatest absorption (95%) of photosynthetic photon flux (PPF; 400-700 nm). White plastic had the greatest reflection (6575%) of PPF and blue (400-500 nm) light. The Alor selective mulch had the greatest reflective far-red/red ratio (730-740/640-650 nm) of light. Clear plastic had the greatest transmission (90%) of PPF and blue light. Soil temperature was coolest under the white mulch (32 C) and warmest under the clear mulch (52 C) when measured at maximum soil temperature in the early afternoon (1400 to 1800 hrs). Vegetative growth and yield were greatest for plants grown on the white mulch treatment and lowest for plants grown on the clear mulch treatment.

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Currently, in the United States, the greenhouse industry covers more than 15,000 acres and is supported by a diverse number of firms with employee expertise that includes greenhouse manufacturing, engineering, irrigation, horticulture, IPM, sales, marketing, and business management. The growing greenhouse industry continues to be in need of highly trained undergraduates that have mastered an amalgam of scientific and business concepts necessary to be competitive in today's agricultural marketplace. Using a multidisciplinary approach we are creating a multimedia instrument for utilization in a variety of greenhouse related courses. This instrument ultimately will be available on the web for anyone to access. To ensure that our vision matches need, we have reviewed the courses offered throughout the United States at 1862, 1890, and 1994 land grant institutions. Course information collected includes; college, Dept., title, level, description, website (if available) and instructor e-mail (if available). Interestingly, there are at least 84 courses offering some aspect of greenhouse science in the U.S. Most are offered in Colleges of Agriculture or Engineering, but are housed in 17 diverse Dept.s. Examples include Dept.s of Horticulture; Agronomy and Horticulture; Agricultural Biosystems and Engineering; Plant, Soil, and Entomological Science; and Horticulture, Forestry, Landscape & Parks. This information will be utilized to focus the instructional design phase of the multimedia instrument, to contact current course instructors for feedback, and to frame future development of the resource.

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Using a multidisciplinary approach, we are creating an instrument for utilization in a variety of greenhouse related courses. We now have over 3 hours of edited and titled video segments that were obtained at different locations by the same videographer. The greenhouse businesses in Arizona, Vermont, Ohio, and Florida were chosen due to their unique business strategies, level of computerization, type of greenhouse construction, management philosophies, and climate challenges. Individual video segments are based on nine topics that were covered at each location including computers, structure, plant life cycle, and labor. The videos have been placed on a streaming media server and will be burned to a DVD. An interactive Flash-based greenhouse environment simulator is nearly complete. This instrument allows students to model greenhouse environments based on climate data from each of the four video locations. Additionally, a searchable digital repository has been established that will allow other participants to submit materials for educational use. This open source software (DSpace) has an integrated distribution license which streamlines compliance with the Digital Millennium Copyright Act. Several hundred high quality images have already been uploaded, described and tagged. Learning assessment tools based on numerical self-evaluation and verification narratives are also being developed in conjunction with the multimedia tools. We have created a database of all the greenhouse courses at 1862, 1890, and 1994 institutions and hope to build a community of teachers that will utilize and contribute to the multimedia greenhouse collection. This community has already grown to include two international greenhouse experts who contributed interactive software for educational use.

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