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.
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
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
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.
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.
flowering time of chrysanthemum grown under natural short days. Although phytochrome photoreceptors primarily absorb both R and FR light to mediate flowering, R light is generally a more effective signal than FR light for short-day plants ( Thomas and Vince
), 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
Abstract
This study evaluates light quality and photoperiodic effects on vegetative growth on Cucurbita maxima Duch. In a growth chamber with fluorescent and incandescent lighting the quality of light prior to the dark period, rather than photoperiod, significantly affected internode elongation, and end-of-day red (R) and far-red (FR) treatments demonstrated phytochrome involvement. Internode elongation occurred primarily during the dark period. FR treatments at the beginning of the dark period were most promotive, but FR up to 12 hour into a 16 hour dark period promoted internode elongation significantly. Changes in the ratio of R to FR light at sunset are probably not of sufficient duration and intensity to elicit an end-of-day growth response. In the field, changes in light quality at sunset did not alter the growth habit of the bush or bush-vine phenotypes.
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
Abstract
Continuous, low intensity, far red (FR) irradiation prevented germination, and continuous, low intensity, red (R) irradiation decreased the rate of germination of seed of dw-2 dwarf watermelon [Citrullus lanatus (Thunb.) Matsumara and Nakai]. Intermittent, 15 minute light treatments with R or FR at 6 hour intervals affected germination similarly to continuous irradiations. Seeds germinated best in darkness and would germinate in darkness following prolonged incubation in FR light. A short exposure to R light following a prolonged FR treatment enhanced subsequent germination in darkness (D), and the effect of R light was reversed by a short exposure to FR light, indicating phytochrome control of germination. Responses to single, short exposures to FR light after different periods of incubation, and to different intervals of D and prolonged FR light, indicated that germination of dwarf watermelon seeds is regulated by phytochrome between about 6 to 24 hours of incubation at 29 to 30°C.