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Sandra L. Barbour and Dennis R. Decoteau

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.

To determine the effects of phytochrome activity on cytokinin synthesis and ultracellular plant development, we utilized tobacco transformed with the Agrobacterium tumefaciens isopentenyl transferase (ipt) gene. This gene encodes for isopentenyl transferase (iptase) which is an enzyme active in cytokinin biosysthesis.

Ipt-transgenic tobacco cultures were treated with end-of-day red or far-red light for 15 minutes. After 15-30 days of treatment, the plant tissue was harvested and ipt expression was verified by SDS-PAGE and western blot analysis. Polyclonal antibodies specific to iptase were used as a primary antibody. Colloidal gold conjugated to goat. anti-rabbit antiserum served as an electron dense, secondary antibody and a probe to light-influenced iptase synthesis and distribution within the cell.

A Hitachi 600AB transmission electron microscope was used to determine the influence of phytochrome/light treatments on the ultrastructure of ipr-transgenic cells.

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E. Mergenthaler, Gy. Bisztray, and D.P. Coyne

As ancestors of higher plants, mosses offer advantages as simple model organisms in studying complex processes. The moss Physcomitrella patens became a powerful model system in the last few years (Cove and Knight, 1993). Adaptation of PEG-mediated DNA uptake procedure has permitted the establishment of efficient molecular genetic approaches. To study possible effects of a Type I phytochrome, the potato phyA gene was introduced into the moss P. patens. Stabile transformants exhibited a range of similar phenotypes (Schaefer et al., 1991). The aim was to differentiate the wild type from the transgenic moss plants with simple, quick measurements providing data suitable for analyzing offspring populations. Ten different morphological and biochemical methods were used to investigate the phenotype in order to choose the best phenotypical category to indicate the presence and the effect of the phytochrome transgene. Two selected strains were used with the most and the least intensive phenotypical features (3*, 29), along with their selfed progenies, as well as progenies from crosses with the nicotinic-acid auxotrophic mutant. The best methods to differentiate between wild type and transgenic plants were the statistical analysis of the number of gametophores, photometric measurement of pigment contents and composition under different light conditions, color evaluation by PC-based vision system, and visual observation of morphogenetic changes. Our investigations support that the potato phytochrome transgene has a pleiotropic effect in the moss P patens. The methods used would be applicable for the characterization of mosses with different transgenes.

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Sandra B. Wilson and Dennis R. Decoteau

Similarities exist between the effects of phytochrome and cytokinins on plant growth and development (e.g., chloroplast development, amaranthin synthesis, seed germination). It is unclear, however, if and how these two systems interact. The coaction between phytochrome and cytokinins was investigated by using Nicotiana plumbaginifolia plants transformed with the isopentenyl transferase (ipt) cytokinin gene and treated with end-of-day (EOD) red (R) and far-red (FR) light. The ipt gene was under control of either a constitutive cauliflower mosaic virus promoter (35S-plants) or an inducible, heat shock promoter (HS-plants). When treated with EOD FR light, whole plants were characterized by decreased chlorophyll concentrations and increased fresh weights. When treated with EOD R light, 35S-plants contained high concentrations of zeatin riboside (ZR) compared to plants treated with EOD FR light. When treated with EOD FR light, HS-plants contained high concentrations of ZR compared to plants treated with EOD R light. Both cytokinin responses were photoreversible. The reasons for the differences between the 35S- and HS-plant responses are not known. Results appear to implicate interactions between phytochrome and cytokinins in plant growth and development.

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Joan John, William Courtney, and Dennis R. Decoteau

The effects of light spectral quality on Discorea alata cv, Oriental in vitro grown plantlets were investigated. Cultured nodes were treated with red (R) or far-red (FR) light at the end of a 14 hr photoperiod. End-of-day (EOD) light treatments did not affect organogenesis. EOD FR light increased average internode lengths as compared to plantlets treated with EOD R light. The EOD FR enhancement of internode elongation was reversed by following the FR with R suggesting the involvement of phytochrome. There were no residual light effects on subsequent plantlet development from subcultured nodes or potted plantlets after EOD light treatments were terminated.

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N.K. Damayanthi Ranwala and Dennis R. Decoteau

End-of-day (EOD) red (R) or far-red (FR) light treatments were used to study phytochrome-regulated growth and dry matter distribution in 2-week-old watermelon plants. Plants were exposed to low-intensity R or FR light for 15 min at the end of photoperiod for 9 consecutive days. End-of-day FR increased the petiole elongation in the first two leaves, which was accompanied by higher dry matter partitioning to the petioles after 3 days of treatments. However, total plant dry mass (above ground) in FR-treated plants increased significantly after 6 days of treatments. This indicates EOD FR regulated dry matter compensation among plant parts at the early stages of EOD light treatments, allowing plants to better adapt to the environment. Net CO2 assimilation rate in the second leaf of FR-treated plants also increased. Phytochrome involvement in these processes is suggested, since growth and dry matter distribution patterns were reversible when plants were treated with FR immediately followed by R.

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Nihal C. Rajapakse, Margaret J. McMahon, and John W. Kelly

The response of `Bright Golden Anne' and `Spears' chrysanthemum plants to EOD-R or FR light was evaluated to determine the involvement of phytochrome in regulation of plant morphology under CuSO4 filters. Light transmitted through the CuSO4 filter significantly reduced height, internode length and stem dry weight of `BGA' and `Spears' chrysanthemum plants. However, the degree of response varied with the cultivar. Exposure to EOD-FR reversed the reduction of plant height, internode length and the stem dry weight caused by the light transmitted through CuSO4 filters to a level comparable with control plants. Exposure to EOD-FR did not significantly alter height and stem dry weight under control filter Exposure to EOD-R light reduced the height and stem dry weight of `BGA' plants grown under control filter but EOD-R had no effect under CuSO4 filters. In `Spears' plants, EOD-R caused stem dry weight reduction under control filters, but did not reduce stem or internode elongation. The results suggest phytochrome may be involved in controlling plant response under CuSO4 filters. However, there are evidence to indicate that an additional mechanism may be acting on stem/internode elongation.

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David G. Clark and John W. Kelly

Potted miniature roses (Rosa × hybrida `Confection ' & `Meijikatar') were treated at the end of each 8 hour photoperiod with 30, min of red (R) or far-red (FR) light for 21 days. These light treatments convert phytochrome to the Pfr and Pr forms respectively. Plants were paper sleeved and stored in cardboard boxes at 16°C for 5 days to simulate postharvest shipping conditions. `Meijikatar' plants treated with FR light showed more postharvest leaf chlorosis than plants treated with R light or controls.

`Meijikatar' plants treated at the end of each 12 hour photoperiod with FR light exhibited more postharvest leaf chlorosis than plants treated with R light. There were no differences in postharvest leaf chlorosis between plants treated with FR light followed by R light or plants treated with R light followed by FR light. These results suggest that an avoidance of end-of-day FR light will result in less postharvest leaf chlorosis in potted roses.

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A. Cutlan, G. Nordwig, R. Warner, and J.E. Erwin

Variation in red/far red leaf and photosynthetically active radiation (PAR) absorption by an individual leaf of various ornamental hanging basket species was measured. Red/far red ratios varied from 0.30 to 0.83 for Syngonium podophyllum Schott. and Chlorophytum comosum Thunb. `vittatum', respectively. Reduction in PAR varied from 86% to 61% for those same species, respectively. Estimated state of phytochrome photoequilibria for understory crops when grown under each species was calculated. Cucumis sativus L. seedling hypocotyl elongation was measured under different species to validate hypothesized differences in stem elongation associated with differences in red/far red filtering through individual leaves. Implications with respect to light quality effects on stem elongation and dry weight accumulation of plants grown under different species are discussed.

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Nihal C. Rajapakse and John W. Kelly

The response of chrysanthemum plants to varying R:FR ratios and phytochrome photoequilibrium values (Ø = Pfr/Ptot) was evaluated 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) and a broad bandwidth (R = 600-700 and FR = 700-800 nm) for R:FR calculation, 6% CUSO4 filter transmitted light with greater R:FR (3.9) and grater Ø (0.81) than 40% CuSO4 or water filters. Light transmitted through 40% CuSO4 and water filters had a similar narrow band R:FR ratio (1.2), but the broad band R:FR ratio (2.1) of 40% CuSO4 filter was higher than water filter. Estimated Ø value was similar for both water and 40% CuSO4 filters. Final height of plants grown in CuSO4 chambers was about 30% less than the plants in control chambers. The results suggest that broad band R:FR ratio correlated more closely to plant response than the narrow band R:FR ratio.

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David L. Bubenheim, Raman Sargis, and David Wilson

Electronic dimming of high intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400 W metal halide (MH) and high pressure sodium (HPS) lamps were equipped with a dimmer system using silicon controlled rectifiers (SCR) as high speed switches. Phase control operation turned the line power off for some period of the AC cycle. At full power the electrical input to HPS and MH lamps was 480 W (RMS) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased the 589 nm peak remained constant while the 595 nm peak decreased, equalling the 589 nm peak at 345 W input, and was almost absent at 270 W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another, smaller peak, at 545 nm. As input power to the MH lamps decreased the 589 nm peak diminished to equal the 545 nm peak. As input power approached 428 W the 589 nm peak shifted to 570 nm. While a spectral change was observed as input power was decreased in both MH and HPS lamps, the phytochrome equilibrium ratio (Pfr/Ptot) remain unchanged for both lamp types.