End-of-day Far-red Research Articles

The influence of plant growth regulators and light on microtuber induction and formation in Dioscorea alata L. cultures

The effects of plant growth regulators, light intensity, and end-of-day (EOD) light quality treatments on node and microtuber induction (% of cultures with microtubers) and development (fresh weight of microtubers) in yam (Dioscorea alata L. cv. Oriental) cultures were investigated. Nodal segments were excised from plantlets cultured on tuberization medium containing growth regulators and exposed to various light treatments. Absciscic acid (1 μM) stimulated and cytokinins (2.5 μM) inhibited microtuber development from yam nodal segments cultured on Mantell's and Hugo's full-strength tuberization medium under 8-h photoperiods. EOD far-red (FR) light inhibited microtuber induction and development and enhanced node formation. EOD FR light effects were nullified by immediately following the FR treatment with red light. This suggested the involvement of phytochrome in these processes. The lowest light intensity evaluated (12 μmol m−2 s−1) inhibited microtuber, root and shoot production as compared to light intensities of 42, 72 and 102 μmol m−2 s−1. Kinetin (2.5 μm) in half-strength tuberization medium inhibited microtuber induction and development but did not affect node production in the light intensity evaluation.

Photocontrol of Dioscorea alanta plantlet growth

Light quality evaluations were conducted on yam ( Dioscorea alata L. cultivar ‘Oriental’) plantlets to determine the potential usefulness of manipulation of the light environment in regulating growth. Eight-week old, in vitro grown yam plantlets were transferred to pots and treated in vivo with end-of-day (EOD) red (R) or far-red (FR) light. Also, nodal segments of D. alata plantlets were cultured on Murashige and Skoog basal medium and exposed in vitro to EOD R or FR light. EOD FR light increased internode elongation in both the in vivo and in vitro evaluations, but stimulated petiole elongation and protuber number and dry weight per plant only in the in vivo evaluation. EOD FR light enhancements of internode and petiole elongation and protuber development in these evaluations were reversed by immediately following far-red with red light, suggesting the involvement of phytochrome in these photoreversible processes. Photosynthetic photon flux density (PPFD) evaluations with white (fluorescent) light indicated that leaf, node, and root production per plant from D. alata segments on Murashige and Skoog basal medium was enhanced when subjected to higher PPFD (67 and 107 μmol m −2 s −1).

End of day far-red light reverses height reduction of chrysanthemum induced by CuSO 4 spectral filters

The response of cultivars ‘Bright Golden Anne’ (‘BGA’) and ‘Spears’ chrysanthemum plants to end of day-red (EOD-R) and end of day-far-red (EOD-FR) light was evaluated to determine the involvement of phytochrome in the regulation of plant morphology under CuSO 4 filters. The CuSO 4 spectral filters removed FR wavelengths and hence, increased the red:far-red (R:FR), blue:far-red (B:FR) and blue:red (B:R) ratios (R = 600–700 nm ; FR = 700–800 nm ; B = 400–500 nm) and ф of transmitted light compared with water (control) filter. Control plants were shaded with cheese cloth so as to attain the same photosynthetic photon flux (PPF) as in the CuSO 4 chamber. Light transmitted through the CuSO 4 filter significantly reduced height, internode length and stem dry weight of cvs. ‘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 CuSO 4 filters to a level comparable with plants that received no EOD treatment under control. Exposure to EOD-R light reduced the height and stem dry weight of ‘BGA’ plants grown under the control filter, but had no effect under the CuSO4 filter. Exposure to EOD-FR did not significantly alter height and stem dry weight under control 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 that phytochrome may be involved in controlling plant response under CuSO 4 filters. However, there is evidence to indicate that an additional mechanism may be acting on stem/internode elongation.

SENSITIVITY OF WATERMELON PLANT GROWTH TO PHOTOMORPHOGENIC SIGNALS DURING THE LIGHT OR DARK PHASE OF THE PHOTOPERIOD

Previous research has demonstrated that watermelon plants are sensitive to changes in light quality, as suggested by an individual treatment of plants with 15-min of end-of-day (EOD) red (R)and far-red (FR) light. FR-induced growth responses (i.e., petiole elongation, internode elongation, reduced petiole angles) were reversed by immediately following the FR light treatment with R light implicating phytochrome as the light quality perception mechanism. The objective of the present experiment was to determine the influence of individual and multiple FR light treatments (each treatment of 15-min duration) during the light and dark phase of the photoperiod on photomorphogenic growth responses of young watermelon plants. Light regulated growth responses of watermelon were influenced by the timing and the number of light quality exposures during the light or dark phase of the photoperiod. Individual FR treatments during the light phase except for the EOD exposure did not affect plant growth responses. In contrast, individual FR treatments at selected intervals during the dark period affected plant development. The most effective individual FR treatment to induce growth responses was at the beginning of the dark period, with decreasing responses as the FR treatment was delayed into the dark period. Multiple exposures of FR during the dark slightly increased growth responses as compared to a single EOD FR treatment.

Growth and Subsequent Yield of Tomatoes following End-of-day Light Treatment of Transplants

The influence of end-of-day (EOD) light treatments of tomato (Lycopersicon esculentum Mill. cv. Mountain Pride) transplants on growth and subsequent fruit production was investigated. In the first experiment, transplants were treated with EOD red (R) and far-red (FR) light for 2 weeks in a controlled environment and then placed in the greenhouse under ambient light conditions from November to March. Before transplanting to the greenhouse, transplants treated with EOD R light were shorter and had less total leaf length than plants that were not treated with EOD light (controls). EOD R light increased the number of flowers on the plants before first harvest but had no effect on subsequent fruit production (as compared to plants treated with EOD FR light or control plants). In the second experiment, cool-white fluorescent lights (a light source high in red wavebands) were used to supplement solar light that transplants received in a nonshaded glasshouse for 1 hour before the end of the natural photoperiod. The fluorescent light reduced transplant height and total leaf length as compared to plants not treated with supplemental light. Supplemental fluorescent light for transplants had no effect on subsequent fruit production in the field. These results suggest that EOD light treatments that affect tomato transplant growth do not affect subsequent fruit production.

Phytochrome-regulated Growth of Young Watermelon Plants

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.

PHOTOCONTROL OF DIOSCOREA ALATA PLANTLET GROWTH IN VITRO

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.