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Dennis R. Decoteau and Heather H. Friend

Phytochrome-regulated growth of watermelon [Citrulls lanatus (Thunb.) Matsum & Naki cv. Sugar Baby] was investigated by treating plants with brief exposures of red (R) or far-red (FR) light at the end of the daily photoperiod. Light treatments were initiated when the plants were 2 weeks old (two true-leaf stage). After 4 days of treatment, petiole lengths of leaf 1 (first leaf above the cotyledon) and leaf 2 (second leaf above the cotyledon) were longer, and the angle formed between these two petioles was more acute in plants treated with end-of-day (EOD) FR than in plants treated with EOD R light or non-EOD-treated plants (control). After 7 days of treatment, internodes 2 and 3 and petioles from leaves 1, 2, and 3 were longer from plants treated for 7 days with EOD FR light than from plants treated with EOD R light or from controls. The EOD FR light promotion of internode, petiole angle, and petiole elongation was reversible by immediately following the FR with R, implicating the involvement of phytochrome in the regulation of these growth processes of watermelon. After 21 days of treatment, most of the internodes (six of eight) from the EOD FR-treated plants were longer than the corresponding internodes from the EOD R-treated plants. Plants that were treated with EOD light for 21 days and then grown for an additional 14 days without EOD light treatments exhibited no residual EOD light effect on internode elongation (as compared to plants not exposed to EOD light). Residual EOD FR light treatment effects on elongation of petioles 1, 2, 3, and 4 were suggested for plants treated with EOD light for 21 days and then grown for 14 days without EOD treatments.

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Gary W. Stutte

provide a brief review of phytochrome physiology; 3) to discuss basic concepts in selecting LEDs for horticulture; and 4) to discuss two examples from the horticultural literature of how LEDs have been used to alter crop development. Background on Light

Open access

Paul Kusuma and Bruce Bugbee

responses: phytochrome photoequilibrium (PPE) and the R:FR ratio. Issues with these metrics are exacerbated under light-emitting diodes (LEDs), which are important to photobiology because of their narrow bandwidth. Furthermore, the high efficiency output of

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Andrew Schofield* and Gopinadhan Paliyath

The accumulation of carotenoids such as lycopene and beta-carotene greatly influences the quality of ripe tomato (Lycopersicon esculentum) fruit because cellular levels of these compounds determine the intensity of red color. As well, lycopene has anti-cancer properties and beta-carotene is a Vitamin A precursor. Recent work has demonstrated phytochrome regulation of the carotenoid pathway but the mechanism is not completely understood. This work investigates phytochrome regulation of 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and phytoene synthase (PSY), two key enzymes of carotenogenesis. A simple procedure for the assay of PSY from crude pericarp extracts was developed and mRNA levels of DXS and PSY1 genes were measured by relative RT-PCR. Discs from mature green tomatoes were ripened in total darkness, or in darkness interrupted by brief daily treatments of red light, or red light followed by far red light. After ten days of incubation, lycopene levels of red light-treated discs had reached ≈12 mg/100 g fresh weight; nearly a 50% increase over discs ripened in total darkness. This increase was not observed in discs treated with red light followed by far red light, demonstrating the red/far red reversibility (and thus phytochrome control) of carotenoid accumulation. Similar patterns of phytochrome control are observed for PSY activity but not for DXS and PSY1 transcript levels, suggesting the mechanism of control may be at the level of post-translational modification of PSY. Potential applications of this regulation of carotenoid accumulation will be discussed.

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Yoshiko Yambe, Kiyotoshi Takeno, and Takashi Saito

Seed germination percentage of multiflora rose (Rosa multiflora Thunh.) was much higher under continuous white light than in complete darkness. Red light was the most effective in inducing germination, and far-red light was ineffective. Exposure to red light for 1 min increased germination; this effect was saturated at an exposure of2 min. The red-light effect was reversed by subsequent exposure to far-red light. The results indicate that rose seeds are positively photoblastic, and that the photoreceptor involved is most likely phytochrome.

Open access

Tomohiro Jishi, Ryo Matsuda, and Kazuhiro Fujiwara

), durations of blue light and red light irradiation, and average phytochrome photostationary state (PSS) of each treatment. The units for average PPFD and DLI are µmol·m −2 ·s −1 and mol·m −2 d −1 , respectively. Cultivation experiments. A total

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Po-Lung Chia and Chieri Kubota

Phytochromes are photoreceptor proteins making possible the perception of the external light environment by plants. The light reception region within phytochrome is the chromophore that has two interconvertible isoforms with different peak light

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Grete Grindal Patil, Vibeke Alm, Roar Moe, and Olavi Junttila

The role of phytochrome in control of stem elongation by daily temperature alternations is unclear. The aim of this work was to study the involvement of phytochrome B in thermoperiodism in cucumber (Cucumis sativus L.), and the interaction with gibberellin (GA). The wild type and the phytochrome B deficient, long-hypocotyl (lh) cucumber mutant were grown under alternating day (DT) and night temperature (NT) and either with or without an exposure to end-of-day far-red light (EOD-FR). Without EOD-FR, hypocotyl and internodes of the wild type plants were shorter under a low DT (19 °C)/high NT (25 °C) (negative DIF) compared with a high DT/low NT regime (positive DIF), while the number of leaves was reduced by 12%. EOD-FR enhanced elongation of hypocotyl and internodes. However, EOD-FR reduced the effect of alternating temperature on hypocotyl elongation. The lh cucumber mutant did not respond to EOD-FR treatments, but internode length was slightly increased by positive compared with negative DIF. The results suggest that phytochrome B is required for a maximum effect of daily temperature alternations on stem elongation in cucumber. Additional GA4 reduced the difference between positive and negative DIF, but it had a minor effect only on the difference between EOD-FR and EOD red light (EOD-R) in the wild type. Plants depleted for endogenous GA by the GA biosynthesis inhibitor paclobutrazol, did not respond at all to DIF or EOD treatments. When seedlings were treated with prohexadione-calcium, which blocks both biosynthesis and inactivation of GA4, response to applied GA4 was enhanced by EOD-FR. The present results suggest that, in cucumber, EOD-FR, and probably also positive DIF, enhances tissue sensitivity to GA4. In addition, catabolism of GA4 can be enhanced by negative DIF.

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Paul H. Henry and Frank A. Blazich

Two experiments investigated the relationship of light and temperature in seed germination of Fraser fir [Abies fraseri (Pursh) Poir.]. Irradiation during the warm portion of 9/15 hr thermoperiod of 20/10C and 30/20C increased germination percentages after 42 days, and the degree of stimulation depended on the timing of the light exposures. A 1-hr exposure was most effective during the latter part of the warm portion of the thermoperiods, and varying the time of irradiation had the greatest effect at 20/10C. The involvement of phytochrome in this photomorphogenic response was ascertained by demonstration of red/far-red reversibility.

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N.K. Damayanthi Ranwala, D.R. Decoteau, and R.T. Fernandez

End-of-day (EOD) light treatments were used to study phytochrome involvement in photosynthesis and photosynthate partitioning in watermelon plants. Two-week-old plants were treated with brief low-intensity red (R) or far-red (FR) light for 9 days at the end of daily light period. Petiole elongation in the first two leaves was the first significant growth change in FR-treated plants compared to other plants after 3 days of treatments. This petiole elongation was accompanied by significantly higher photosynthate partitioning to petioles, even without increase in above-ground dry weight of plants. Net CO2 assimilation rate in the second leaf was significantly higher in FR treated plants on a weight basis after 3 days of treatments. Far-red-treated plants had lower chlorophyll content per leaf area and higher stem specific weight compared to R-treated plants after 3 and 6 days of treatments, respectively. Transpiration and stomatal conduction were higher in FR-treated plants compared to other treatments after 3 days of treatments. The EOD FR regulated growth and photosynthate partitioning patterns were reversible when FR treated plants were immediately followed by R. This implies EOD R: FR ratio acting through the phytochrome regulates the growth and development processes in watermelon plants.