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Mengzi Zhang and Erik S. Runkle

phytochrome photoreceptors, which have two forms: an R light–absorbing (Pr) form and an FR light–absorbing (Pfr) form ( Butler et al., 1959 ). The interconversion between these two forms of each phytochrome in plants is known as photoreversibility and can at

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Fumiko Kohyama, Catherine Whitman, and Erik S. Runkle

elicit a photoperiodic response from conventional light sources such as INC or high-pressure sodium (HPS) lamps ( Whitman et al., 1998 ). The phytochrome family of photoreceptors mediates perception of the ratio of R light (600 to 700 nm) and FR light

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Toshio Shibuya, Ryosuke Endo, Yoshiaki Kitaya, and Mizuki Tsuchida

using an SS-110 spectroradiometer (Apogee Instruments, Logan, UT), and their phytochrome photostationary state (PSS), which represents the ratio of active phytochrome to total phytochrome, was calculated according to the method of Sager et al. (1988

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Isabel Pimentel and Samuel Contreras

photoblastic lettuce seeds, while FR may inhibit germination and induce secondary dormancy in lots that did not have positive photoblasticity ( Contreras et al., 2008 ; Górski et al., 2013 ; Kendrick and Russell, 1975 ). Seeds sense light through phytochromes

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

field, providing a means to potentially influence processes regulated by phytochrome and cryptochrome mechanisms ( Kasperbauer, 1992 ). Colored plastic mulches can alter secondary metabolite concentrations and flavor profiles in several crops including

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Nihal C. Rajapakse, Robert K. Pollock, Margaret J. McMahon, John W. Kelly, and Roy E. Young

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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Qinglu Ying, Yun Kong, and Youbin Zheng

elongation response to FR is a typical shade-avoiding response mediated by phytochromes, which are photoreceptors activated mainly by R but deactivated by FR ( Sager et al., 1988 ). End-of-day FR treatments were reported to enhance stem elongation in tomato

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Frank M. Maas and Edwin J. Bakx

Growth and flowering of shoots of `Mercedes' rose was investigated as a function of the level and spectral quality of photosynthetic photon flux (PPF). Experiments were performed with single-shoot plants decapitated above the two most basal leaves with five leaflets. The development of the two lateral shoots emerging from the axillary buds of these leaves was studied for 4 to 6 weeks. To discriminate between the effects of irradiance and light quality, plants were grown in growth chambers in which PPF and its spectral composition could be controlled. At a photoperiod of 12 hours, the length, weight, and flowering of the shoots strongly increased with irradiance. The growth and number of flowering shoots were always higher for the uppermost than for the second shoot. At the highest PPF (270 μmol·m-2·s-1), flowering occurred in 89% and 33% of the uppermost and second shoots, respectively. At an irradiance level of 90 μmol·m-2·s-1, these percentages were 6% and 0%. Although length and dry weight of both types of shoots were significantly increased by reducing the amount of blue light at constant PPF, flower development was not affected. In a second experiment, plants grown in white light (12 h/day) received a short treatment with low-intensity red or far-red `light at the end of each photoperiod. An end-of-day treatment with red light resulted in significantly more flowering shoots than far-red. The red far-red reversibility of this flowering response indicates the involvement of the photoreceptor phytochrome.

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Heather A. Hatt Graham and Dennis R. Decoteau

The influence of end-of-day (EOD), supplemental, cool-white fluorescent light on pepper (Capsicum annuum L. cv. Keystone Resistant Giant No. 3) seedling growth and fruit production after transplanting to the field was investigated. Seedlings were exposed to this light source, which is high in the red wavebands, from one (1988) or two bulbs (1989) for 1 hour before the end of the natural photoperiod. Each year control plants were exposed to ambient light and received no supplemental fluorescent light. Before transplanting to the field, seedlings exposed to two bulbs were shorter and had smaller leaves than plants in the control treatment. Supplemental fluorescent light treatment, regardless of number of bulbs, reduced plant height, leaf area, fruit weight, and fruit count at the first harvest. Total fruit production was not affected by supplemental light, suggesting no residual effect of the light treatment during transplant production on total subsequent fruit production.