Night Interruption Treatments Research Articles

Intermittent Light from a Rotating High-pressure Sodium Lamp Promotes Flowering of Long-day Plants

A technology for long-day (LD) lighting was evaluated for commercial production of ornamentals using a stationary high-pressure sodium (HPS) lamp with an oscillating aluminum parabolic reflector (rotating HPS lamp). We performed an experiment with four LD species (Campanula carpatica Jacq., Coreopsis grandiflora Hogg ex Sweet, Petunia ×hybrida Vilm.-Andr., and Rudbeckia hirta L.) to compare the efficacy of a rotating HPS lamp in promoting flowering with night-interruption (NI) lighting using incandescent (INC) lamps. Seedlings were grown under natural short-day (SD) photoperiods (12 h or less) and NI treatments were delivered from a 600-W rotating HPS lamp mounted at one gable end of the greenhouse or from INC lamps that were illuminated continuously for 4 h or cyclically for 6 min every 30 min for 4 h. Plants were grown at lateral distances of 1, 4, 7, 10, or 13 m from the rotating HPS lamp, which provided a maximum photosynthetic photon flux of 25.4 μmol·m−2·s−1 (at 1 m) to 0.3 μmol·m−2·s−1 (at 13 m). Control plants were grown under an uninterrupted 15-h skotoperiod. Within 16 weeks, 80% or greater of the plants within each species that received NI lighting had a macroscopic visible flower bud or inflorescence, whereas all species but Petunia ×hybrida remained vegetative under the SD. Flowering of all species grown at 13 m from the rotating HPS lamp was delayed by 14 to 31 d compared with those under continuous INC. The weekly operational costs to provide NI lighting to a 139-m2 greenhouse with one 600-W rotating HPS lamp or a standard cyclic INC lamp installation was estimated to be 80% to 83% lower compared with INC lighting for the entire 4-h NI. These results indicate that a rotating HPS lamp can be used to efficiently deliver LD lighting, but flowering time was delayed and flower number reduced in some species when the maximum NI light intensity was less than 2.4 μmol·m−2·s−1.

Reproductive Response of Okra and Native Rosella to Long-day Treatment with Red, Blue, and Green Light-emitting Diode Lights

We investigated the reproductive responses of three cultivars of short-day plants to day-extension and night-break treatment with red, blue, and green light-emitting diodes (LEDs). The plants examined were all Malvaceae species: two cultivars of okra [Abelmoschus esculentus (L.) Moench.] and a cultivar of native rosella [Abelmoschus moschatus ssp. tuberosus (Span.) Borss.]. To create day extension or night break, we provided supplemental light from LED panels with peak photon emissions of 470 (blue), 520 (green), or 650 (red) nm. Day-extension treatment using red or blue LEDs inhibited flower and bud appearances; the response was especially pronounced with red LEDs. Night-break treatment with red LEDs also delayed flower bud appearance, but night break with blue LEDs did not produce a clear effect. Night break with green light delayed flowering more strongly than blue light but a little less than red light. We concluded that the dark period-regulated reproductive processes of these plants are most sensitive to disruption by red light, closely followed by green light, but that they are insensitive to blue light, especially when the exposure period is short.

Red:far-red light ratio and far-red light integral promote or retard growth and flowering in Eustoma grandiflorum (Raf.) Shinn

Night break treatment was applied to Eustoma grandiflorum ‘Nail Peach Neo’ using light sources with different red (R: 660 ± 30 nm): far-red (FR: 730 ± 30 nm) ratios or FR light intensities in order to investigate growth and flowering responses. Flower initiation and induction were promoted by night break treatment with a low R:FR light source, but was delayed by a high R:FR ratio. The promotion or delay of flower bud formation was accompanied by a decrease or an increase, respectively, in the number of nodes on the main stem at anthesis to the first floret. The difference between date of visible bud with plants under night break treatment and that of the control was approximated with high accuracy by a sigmoid function of the logarithms of R:FR ratio. The threshold R:FR ratio demarcating the promotion and delay of date of visible bud was about 5.3 under the experimental conditions used. The critical R:FR ratios for promotion or delay of visible bud would be about 0.5 and 50.0, respectively. In addition, the time from planting to visible bud was approximated with an exponential function of FR light intensity. The maximum acceleration of date of visible bud by long-day treatment would be 20 days, and the critical FR light intensity would be 2.0 μmol m −2 s −1. It is concluded that growth and flowering of E. grandiflorum can be regulated by long-day treatment using light sources with different R:FR ratios or FR light intensities.

Night Break Treatment Using Different Light Sources Promotes or Delays Growth and Flowering of Eustoma grandiflorum (Raf.) Shinn.

Night break treatment was applied to Eustoma grandiflorum ‘Neilpeach Neo’ using different light sources to investigate growth and flowering responses. The seedlings were grown in a greenhouse and treated with night break treatment using a far-red fluorescent lamp, a plant growth fluorescent lamp, a daylight-type fluorescent lamp or an incandescent lamp, or were grown under non-treated conditions (control). Photosynthetic photon flux density (PPFD) at the top of the plant was 5 μmol·m−2·s−1 under each light source. The red (660 ± 30 nm): far-red (730 ± 30 nm) ratio of the light sources was 0.01, 0.43, 5.00, and 0.65, respectively. The time from planting to flower budding was 46 days for plants grown under a far-red light fluorescent lamp, compared with 66 days in the control. The incandescent lamp and plant growth fluorescent lamp also reduced the time to flower budding; however, the daylight-type fluorescent lamp delayed flower budding by 4 days compared with the control. The light source regimes had little or no effect on the time to flowering after flower budding. The far-red fluorescent lamp, incandescent lamp and plant growth fluorescent lamp reduced the number of nodes on the main stem at the anthesis of the first floret, while the daylight-type fluorescent lamp increased the number of nodes. The far-red fluorescent lamp and incandescent lamp promoted internode elongation, while the daylight-type fluorescent lamp reduced internode length. Moreover, a red fluorescent lamp with a R: FR ratio of 105 delayed flower budding and flowering, and increased the number of nodes of the plants as compared with the control, regardless of the long day lengths in July and August. Thus, it is considered that the growth and flowering time of Eustoma grandiflorum can be controlled by long-day treatment carried out with the proper type of light source.

Improvement of Eustoma grandiflorum (Raf.) Shinn. Cut Flower Quality for Early-Autumn Shipping with Long-Day Treatment Using Light Sources That Delay Flower Bud Formation

Eustoma grandiflorum (Raf.) Shinn. was subjected to long-day treatment using four types of light sources with a high red (R; 660 ± 30 nm) to far-red (FR; 730 ± 30 nm) light ratio to improve cut flower quality for early-autumn shipping. The R:FR ratios of a red-light fluorescent lamp, a color fluorescent lamp (R-type), a bulb-type red-light fluorescent lamp, and a bulb-type daylight fluorescent lamp were 62.0, 100.0, 8.8, and 8.5, respectively. As a control, plants were grown under ambient daylight. Flower budding of ‘Double Pink’ seedlings, planted on July 11 and treated with night-break treatment from planting to budding using these four light sources, was delayed 2–5 days compared with the control. Night-break treatment using each light source increased the number of nodes on the main stem, number of lateral branches, and number of flower buds, and increased the cut flower length of plants at anthesis of the first floret, compared with the control. Three cultivars were treated with night break using a color fluorescent lamp (R-type) and a bulb-type red-light fluorescent lamp. Although these two light sources did not delay the flowering of ‘King of Snow’ compared with the control, the mean flowering date of ‘Double Pink’ and ‘Piccolosa Snow’ under both light sources was 3–6 days later than that of the control. These light sources increased the number of nodes of the main stem, and increased the stem length and cut flower length compared with the control in each cultivar. As the most practical application, the bulb-type red-light fluorescent lamp was used for long-day treatment of ‘Double Pink’ under four lighting periods: pre-dawn lighting for 6 h, end-of-day lighting for 6 h, all-night lighting, and night break for 6 h during the night. All-night lighting delayed flowering more than the other treatments. Cut flower length of the plants at anthesis of the first floret was longest in the pre-dawn lighting treatment. We concluded that long-day treatment using a bulb-type red-light fluorescent lamp from 0:00 to 6:00 just after planting until flower budding is most effective to improve cut flower quality for early-autumn shipping of Eustoma cultivars.

Flowering of cyclamen is accelerated by an increase in temperature, photoperiod, and daily light integral

SummaryCyclamen (Cyclamen persicum Mill.) crop production times can be reduced by increasing the greenhouse temperature, but alternative methods to accelerate crop development are desirable when energy costs for heating are high. The effects of photoperiod and increasing daily light integral (DLI) on cyclamen remain unclear. We performed experiments to examine the effect of DLI using two temperatures (16°C or 20°C) and three photoperiods (8, 12, or 16 h) delivering DLI values of 4.9, 7.3, or 9.8 mol m–2 d–1, respectively, and the effect of night interruption (NI) lighting from incandescent lamps (IL), on the flowering of cyclamen ‘Metis Purple Flame’. Plants grown at 20°C reached the visible flower bud (VB) stage earlier than plants grown at 16°C under all photoperiods. NI hastened flower bud initiation by 22 – 29 d compared with an 8-h photoperiod at both temperatures. Plants grown under the 8-h photoperiod with an NI treatment (DLI = 4.9 mol m–2 d–1) flowered at a similar time as plants grown under the 12-h photoperiod (DLI = 7.3 mol m–2 d–1). In addition, plants grown at 16°C with an NI reached the VB stage in a similar time to plants grown at 20°C with an 8-h photoperiod. Therefore, the effects of increasing the DLI, providing NI lighting, or increasing the temperature can be compared, so that growers can determine which strategies can reduce the greenhouse production time of cyclamen most cost-effectively.

Magnesium localization in shoot apices during flower induction in Pharbitis nil

We present the potential involvement of Mg2+ in the flowering mechanism in the shoot apex of the short-day plant Pharbitis nil (L.). To analyze elemental distribution in shoot apical meristems, fluorescence staining methods with Mag-fluo-4 AM and Fluo-3 AM were used. The former is sensitive to both Mg2+ and Ca2+, and the latter is a specific Ca2+ indicator. When plants were grown under continuous light conditions, some cells with intensive fluorescence of Mg2+ appeared in the top layers of the shoot apical meristem. During growth in the vegetative phase, cells in the center of the top layers accumulated large amounts of Mg2+. Exposure to a single 16 h short-day treatment induced the flowering process and dramatically reduced the fluorescence associated with Mg2+ accumulation in the top layers, suggesting that Mg2+ contributes to the flower induction process. The fluorescence associated with Ca2+ did not show this distribution difference between growth phases. A night-break treatment also influenced the fluorescence pattern. It was suggested for the first time that Mg2+ plays an important role in flower induction.

(74) Winter Greenhouse Performance and Photoperiod Responses of 51 Cultivars of Seed-grown Trailing Petunias

Long days are known to hasten flowering of Petunia hybrida. However, breeding of modern standard-type petunia cultivars has reduced this response. With the introduction of new genetics involved in the creation of trailing-type petunias, many cultivars have been observed to have a strong photoperiodic response to the point that it is an issue for late winter or early spring flowering cropping cycles. In order to characterize this photoperiodic response in modern seed-grown trailing-type petunia cultivars, seed of 51 cultivars of trailing petunias (Petunia hybrida) were sown in November in 288 plug trays. When established about 4 weeks later, uniform plants were selected and transplanted individually to 15-cm pots. Plants were exposed to either natural days or a 4-hour night interruption using incandescent light from 2200 to 0200 HR each day until flowering. A minimum night temperature of 17 °C was maintained. Days to first flower from sowing ranged from 72 to 117 days. Generally, the night interruption treatment hastened flowering. However, the degree of hastening ranged from 4 and 5 days for `Ramblin' Burgundy Chrome' and `Ramblin' Lilac Glo', respectively, to 27 and 32 days for `Tidal Wave Cherry' and `Tidal Wave Hot Pink', respectively. Effects of night interruption treatment on plant architecture will also be presented.

Budding Response of Horticultural Crops to Night Break with Red Light on Alternate Days

To investigate whether night break (i.e., the interruption of the dark period by artificial lighting) controls plant flowering sufficiently with treatment on alternate days, we compared the reproductive responses of seven horticultural crop species under a daily night-break treatment, an alternate-day treatment, and no night-break treatment during the short-daylength season. Longday crops of spinach (Spinacia oleracea), petunia (Petunia×hybrida), and godetia (Godetia cvs.) and short-day crops of cosmos (Cosmos bipinnatus), perilla (Perilla ocymoides), zinnia (Zinnia elegans), and Japanese morning glory (Pharbitis nil) were used. The night-break treatment was supplied for 2 hours starting at midnight using red light-emitting diodes. The effect of the alternate-day treatment was much smaller than the effect of the daily treatment in zinnia and Japanese morning glory; was smaller in spinach, godetia and cosmos; and was only slightly smaller in petunia. Budding in perilla was inhibited by both night-break treatments.

Calcium and pH patterning at the apical meristem are specifically altered by photoperiodic flower induction in Chenopodium spp.

ABSTRACTThe apical meristem of the short‐day plant Chenopodium rubrum responds to photoperiodic flower induction with specific changes of pH and Ca2+ patterning immediately after the inductive dark span. The red–far‐red reversibility of the pH and Ca2+ patterning in response to night break treatments was measured in order to distinguish between the effect of the prolonged dark span per se and the specific effect of photoperiodic flower induction. In addition, the pH and Ca2+ patterning in C. rubrum was compared with the long‐day plant Chenopodium murale. The pH was visualized using the fluorescent probe carboxy SNARF‐1. Calcium ion concentrations were studied using a combination of Ca2+‐probes Fluo‐3 and Fura Red. It was observed that the specific changes in pH and Ca2+ patterning at the apical meristem of C. rubrum were abolished by the red‐light break. This effect was fully reversed with a subsequent single far‐red treatment. These observations infer the influence of phytochrome on both pH and Ca2+ patterning. Changes in pH and Ca2+ patterning upon flower induction were observed in both long‐day and short‐day plants. These results support the hypothesis that changes of pH and [Ca2+] in cells of the apical meristem are part of the pathway in signal transduction triggering flower initiation.

Budding and Bolting Responses of Horticultural Plants to Night-break Treatments with LEDs of Various Colors

We investigated the use of light-emitting diodes (LEDs) of particular wavelength emissions as light sources for night-break treatment of plants. We used the long-day plants godetia (Godetia cvs.), petunia (Petunia×hybrida Vilm.), and spinach (Spinacia oleracea L., two cultivars); and the short-day plants perilla (Perilla ocymoides L.), cosmos (Cosmos bipinnatus Cav.), yellow cosmos (Cosmos sulphureus Cav.), zinnia (Zinnia elegans Jacq.), and Japanese morning glory (Pharbitis nil Choisy). The plants were exposed daily to LED irradiation from 2300 to 0100h during the short-day season (late autumn to early spring). Red and orange LED lights were effective in controlling flowering in all plants used in this study. Yellow and green LEDs were almost as effective. Far-red LED was effective in some, but not all, cases. One spinach cultivar bolted in response to far-red night-break treatment, but the other cultivar did not. Blue LED was effective in only one trial with perilla, but not so effective in other cases.

Modifications in Aster response to long-day conditions caused by overexpression of phytochrome A or B

We studied the role of phytochromes A and B in the regulation of critical day length, night-break signal and the quantitative effects of sunlight on inflorescence development, a long-day induced process, in Aster. We used transgenic plants overexpressing either PHY A or PHY B, different natural daylight conditions, and day extension and night break treatments by low-fluence-rate fluorescent or incandescent lighting with a red to far-red ratio of 7.3 and 0.6, respectively. Wild-type plants had a higher sensitivity to day extension with fluorescent than incandescent lighting and a quantitative response to natural daylight conditions. Their response to a day extension with either incandescent or fluorescent lighting and to a night break with incandescent, but not fluorescent, lighting was subject to the quantitative effect of daylight conditions during the natural short day. Overexpression of PHY A shortened the critical day length for inflorescence development from 14 to 8 h. Overexpression of PHY B shortened the length of the night break needed to induce inflorescence development from 2 h to 15 min. Overexpression of either PHY A or B reduced the quantitative effect of natural daylight. For Aster plants grown under commercial conditions, from autumn through spring, the overexpression of either PHYA or PHYB substantially increased the yield of flowering shoots.

Elimination of POR expression correlates with red leaf formation in Amaranthus tricolor.

Amaranthus tricolor L. tricolor cv. Earlysplendor, an ornamental amaranth, generates red leaves instead of green leaves in late summer to early autumn. Red leaf formation was promoted under short-day conditions and delayed by night-break treatments. Red leaves were characterized by lower levels of chlorophyll accumulation rather than higher levels of red pigment (betacyanin) accumulation. However, the metabolic activity toward the production of Mg-protoporphyrin, an intermediate in the biosynthesis pathway for chlorophyll, was detected in red leaves as well as in green leaves. RNA gel blot analysis was performed to assess the expression of nine genes encoding eight enzymes involved in chlorophyll biosynthesis. Among these enzymes, red-leaf-specific reduction of gene expression was observed only for NADPH-protochlorophyllide oxidoreductase (POR), a key enzyme catalyzing a later step of chlorophyll biosynthesis. In addition, immunoblot analysis showed no accumulation of POR protein(s) in red leaves. These data indicate that the repression of POR gene expression and resultant loss of chlorophyll synthesis activity plays a role in red leaf formation of A. tricolor.

The poplar bark storage protein gene (Bspa) promoter is responsive to photoperiod and nitrogen in transgenic poplar and active in floral tissues, immature seeds and germinating seeds of transgenic tobacco.

In Populus, seasonal nitrogen storage involves the accumulation of a 32 kDa bark storage protein (BSP) in the inner bark parenchyma and xylem rays. Poplar BSPs are encoded by a multigene family and one member, bspA, has been cloned and sequenced. The regulation of bspA was investigated by transforming either hybrid poplar or tobacco with a chimeric gene consisting of the 2.8 kb bspA promoter fused to the coding region of beta-glucuronidase (uidA). In transformed poplar, the bspA 2.8 kb promoter conferred both short-day (SD) and nitrogen (N) inducibility to GUS and activity was localized to the bark (primary and secondary phloem, and cortex) and xylem rays. Night-break treatments inhibited SD induction of GUS. Deletion of the 1.6 kb distal DNA sequences from the bspA promoter eliminated SD induction of GUS while some N induction was retained. These results indicate that although poplar BSP is encoded by a multigene family, transcriptional activation of bspA per se can account for bsp expression in bark and xylem rays in response to either SD or N treatment. These results also show that the elements responsible for SD or N induction are separable. Because of the long generation intervals associated with trees, the developmental regulation of bspA in flowers, developing seeds, and germinating seeds was investigated by transforming the 2.8 kb bspA-promoter::uidA chimeric gene into tobacco. The bspA promoter was active in developing tobacco floral tissues and in seeds during early stages of embryogenesis, decreased progressively during seed maturation and regained activity upon seed germination. Although seed storage proteins of poplar share some similarities to poplar BSP, the observed developmental expression patterns in tobacco are consistent with a role for bspA in vegetative rather than seed storage protein storage.

Flowering of Herbaceous Perennials under Various Night Interruption and Cyclic Lighting Treatments

Six long-day species of herbaceous perennials were grown under six night-interruption (NI) photoperiod treatments to determine their relative effectiveness at inducing flowering. Photoperiods were 9-hour natural days with NI provided by incandescent lamps during the middle of the dark period for the following durations: 0.5, 1, 2, or 4 hours; 6 minutes on, 54 minutes off for 4 hours (10% or 6/54 cyclic lighting); or 6 minutes on, 24 minutes off for 4 hours (20% or 6/24 cyclic lighting). For five species, the experiment was repeated with more mature plants; for the sixth, Rudbeckia fulgida Ait. `Goldsturm', following a cold treatment of 8 weeks at 5 °C. The species generally showed a quantitative flowering response to the NI duration until a saturation duration was reached; as the length of the uninterrupted night break increased, flowering percentage, uniformity, and number and plant height increased and time to flower decreased. Minimum saturation durations of NI were 1 hour for Coreopsis grandiflora Hogg ex Sweet `Early Sunrise' and Hibiscus moscheutos L. `Disco Belle Mixed', 2 hours for Campanula carpatica Jacq. `Blue Clips' and Coreopsis verticillata L. `Moonbeam', and 4 hours for unchilled R. fulgida `Goldsturm'. Echinacea purpurea Moench `Bravado' flowered similarly across all lighting treatments. The 6/24 cyclic lighting regimen induced flowering comparable to that under a continual 4-hour NI for four of the six species and the cold-treated R. fulgida `Goldsturm'. Flowering under the 6/54 regimen was generally incomplete, nonuniform, and delayed compared to that under saturation duration treatments. Three of five species flowered earlier when more mature plants were placed under the NI treatments. Cold-treated R. fulgida `Goldsturm' flowered more rapidly than unchilled plants and the saturation duration of NI decreased to 1 hour.

Accumulation of a clock-regulated transcript during flower-inductive darkness in pharbitis nil

To clarify the molecular basis of the photoperiodic induction of flowering in the short-day plant Pharbitis nil cv Violet, we examined changes in the level of mRNA in cotyledons during the flower-inductive photoperiod using the technique of differential display by the polymerase chain reaction. A transcript that accumulated during the inductive dark period was identified and a cDNA corresponding to the transcript, designated PnC401 (P. nil C401), was isolated. RNA-blot hybridization verified that levels of PnC401 mRNA fluctuated with a circadian rhythm, with maxima between 12 and 16 h after the beginning of the dark period) and minima of approximately 0. This oscillation continued even during an extended dark period but was damped under continuous light. Accumulation of PnC401 mRNA was reduced by a brief exposure to red light at the 8th h of the dark period (night-break treatment) or by exposure to far-red light at the end of the light period (end-of-day far-red treatment). These results suggest that fluctuations in levels of PnC401 mRNA are regulated by phytochrome(s) and a circadian clock and that they are associated with photoperiodic events that include induction of flowering.

Effect of Night-interruption Duration and Cyclic Lighting on Flowering of Obligate Long-day Herbaceous Perennial Plants

Six obligate long-day species of herbaceous perennials were grown under six night-interruption treatments to determine their relative effectiveness at inducing flowering. Photoperiods were 9 hours natural days with night interruptions provided by incandescent lamps during the middle of the dark period for the following durations: 0.5, 1, 2, or 4 hours; 6 minutes on, 54 minutes off for 4 hours (10% cyclic lighting); or 6 minutes on, 24 minutes off for 4 hours (20% cyclic lighting). Response to night interruptions varied by species, but five of the six species flowered most rapidly and uniformly under 4-hour night interruption. Few or no Campanula carpatica `Blue Clips', Rudbeckia fulgida `Goldsturm', or Hibiscus ×hybrida `Disco Belle Mixed' plants flowered with 1 hour or less of continuous night-break lighting. All Coreopsis ×grandiflora `Early Sunrise' flowered, but flowering was hastened as the duration of night interruption increased. Echinacea purpurea `Bravado' flowered similarly across all treatments. In general, the effectiveness of the night-interruption treatments at inducing flowering was 4 hours > 2 hours > 20% cyclic > 1 hour > 10% cyclic > 0.5 hour.

Determining the Critical Photoperiod for Flowering of Several Herbaceous Perennial Species

Twenty-four herbaceous perennial species were treated at 5C for 0 or 15 weeks. Critical photoperiods for flower initiation and development with and without a cold treatment were determined. Photoperiods were 10, 12, 14, 16, and 24 h of continuous light and 9 h plus a 4-h night interruption. Continuous photoperiodic treatments consisted of 9-h natural days extended with light from incandescent lamps. Response to cold and photoperiod varied by species; Scabiosa caucasica `Butterfly Blue' flowered without a cold treatment under all photoperiods after 8 to 10 weeks of forcing, but plant height increased from 14 to 62 cm as daylength increased. Rudbeckia fulgida `Goldsturm' flowered without cold after 13 to 15 weeks of forcing, but only under 16 hours of continuous light and night interruption treatments. Heuchera sanguinea `Bressingham Hybrids' did not flower without cold under any photoperiod but did flower under all photoperiods with cold. The only Lavendula angustifolia `Munstead Dwarf' plants that flowered without cold were those under 24-h continuous light; ≈60% flowered. After cold, some lavender plants flowered under all photoperiods, and the flowering percentage increased with increasing daylength.

Appearance of peroxidase isozymes in floral‐initiated shoot apices of Pharbitis nil

A novel biochemical assay system for detecting the early stage of flowering is reported. Peroxidase isozymes in shoot apices of Pharbitis nil plants that had been exposed to flower‐inducing or non‐inducing conditions were analyzed by isoelectric focusing in polyacrylamide gels and activity staining for peroxidase. Several isozymes with pH 8.5–8.8 appeared for the first time 7 days after the beginning of short‐day treatment, but not after nightbreak (non‐inducing) treatment. When shoot tips were cultured in vitro, these same isozymes also appeared after short‐day treatment but not after night‐break treatment. The extent of the appearance of these isozymes was reduced by exposure to high or low temperature during the inductive dark period and removal of cotyledons after the inductive dark period. Such treatments also reduced the extent of flowering. The appearance of an isozyme with pH 8.5 was more closely correlated with flowering than that of the other isozymes. From these results, the appearance of this peroxidase isozyme in shoot apices is discussed as a biochemical marker of flowering in intact plants and in cultured shoot tips.

Changes in in vitro translated polypeptides of Pharbitis nil Chois., strain Violet cotyledons during the first flower-inductive and non-inductive photoperiods

Two-dimensional gel electrophoresis was used to compare the changes between the in vitro translated polypeptides of cotyledons of Pharbitis nil Chois., strain Violet under different conditions. Seedlings were grown under short day (flower-inductive), or night break (non-inductive), or long day (non-inductive) conditions. Cotyledons were harvested every 2 h for 24 h commencing from the beginning of the dark period. Total RNA samples extracted from cotyledons were translated in vitro with a reticulocyte lysate containing [ 35S]methionine. The translation products were analyzed by two-dimensional polyacrylamide gel electrophoresis. Several differences were observed between the short day or night break treatment and long day treatment, but only two differences were detected between short-day(SD)- and night break(NB)-treated cotyledons. Their significance in the control of flowering is discussed.