Long-day Photoperiod Research Articles

FRIGIDA-Independent Variation in Flowering Time of Natural Arabidopsis thaliana Accessions

FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) are two genes that, unless plants are vernalized, greatly delay flowering time in Arabidopsis thaliana. Natural loss-of-function mutations in FRI cause the early flowering growth habits of many A. thaliana accessions. To quantify the variation among wild accessions due to FRI, and to identify additional genetic loci in wild accessions that influence flowering time, we surveyed the flowering times of 145 accessions in long-day photoperiods, with and without a 30-day vernalization treatment, and genotyped them for two common natural lesions in FRI. FRI is disrupted in at least 84 of the accessions, accounting for only approximately 40% of the flowering-time variation in long days. During efforts to dissect the causes for variation that are independent of known dysfunctional FRI alleles, we found new loss-of-function alleles in FLC, as well as late-flowering alleles that do not map to FRI or FLC. An FLC nonsense mutation was found in the early flowering Van-0 accession, which has otherwise functional FRI. In contrast, Lz-0 flowers late because of high levels of FLC expression, even though it has a deletion in FRI. Finally, eXtreme array mapping identified genomic regions linked to the vernalization-independent, late-flowering habit of Bur-0, which has an alternatively spliced FLC allele that behaves as a null allele.

Feeding glucose or sucrose, but not trehalose, suppresses the starvation-induced premature pupation in the yellow-spotted longicorn beetle, Psacothea hilaris

Under 25 °C and a long-day photoperiod, starvation induces premature pupation in 4th instar Psacothea hilaris larvae exceeding a threshold weight of 180 mg, resulting in the formation of small but morphologically normal adults. To investigate possible mechanisms underlying this phenomenon, we first measured the hemolymph trehalose and glucose levels of starved larvae. When larvae were starved after 4 days of feeding (attaining the threshold weight), glucose levels decreased 4-fold within the next 24 h, while trehalose levels, after a temporary slight decrease, increased remarkably to reach a peak just before the prepupa stage. The effects of ingesting various nutrients on the developmental fate and the hemolymph sugar titers of starving larvae were then examined. Feeding on agar blocks containing sucrose or glucose totally suppressed the occurrence of premature pupation, while trehalose, fructose, casein and starch were ineffective. Feeding on glucose or trehalose resulted in a 6-fold decrease in hemolymph glucose levels and remarkably elevated trehalose levels. Since feeding on glucose and trehalose induced similar changes in hemolymph sugar titers but trehalose was not effective in suppressing premature pupation, glucose may have exhibited its effects via gustatory mechanisms.

Selectivity of Canary HVC Neurons for the Bird's Own Song: Modulation by Photoperiodic Conditions

To what extent seasonal factors modify the neuronal functional properties within the nuclei of the avian song system remains an open question. In adult songbirds, neurons of the song premotor nucleus HVC (used as a proper name) exhibit selective responses for the bird's own song (BOS). Here we examine whether, outside the breeding season, when songs are less stereotyped, HVC neurons of male canaries still respond selectively to the BOS produced during this period. In an initial experiment, single-unit recordings (n = 114) revealed that the neuronal selectivity for the current BOS was attenuated in males exposed to a short-day photoperiod (typical of the nonbreeding season) compared with that found in males exposed to a long-day photoperiod. In long-day conditions, 35% of the cells responded to the BOS, whereas only 12% did in short-day conditions; there were four times more selective cells (d' > 1) in long-day than in short-day conditions. To determine whether these effects were the consequence of differences in acoustic features between breeding and nonbreeding songs, neurons (n = 72) recorded in short-day conditions were tested with both a short-day BOS and a long-day BOS. A low percentage of neurons exhibited responses to short-day or to long-day BOS (11% for each song). Responses of putative interneurons (spike duration < 0.4 ms) and of putative relay cells were similarly attenuated by the short-day conditions. These results strongly suggest that, in canary, rather than being a fixed property, the selectivity for the BOS moves along a continuum and peaks when the day length mimics the breeding conditions.

A test of absolute photorefractoriness and photo-induced neural plasticity of song-control regions in black-capped chickadees (Poecile atricapillus)

We tested whether male and female black-capped chickadees, Poecile atricapillus (L., 1766), were absolutely photorefractory according to Hamner's (1968) criteria of (i) spontaneous regression of gonads during prolonged long-day exposure and (ii) no subsequent recrudescence of gonads in response to constant light. We initially exposed black-capped chickadees to constant long-day photoperiods. Gonads regressed spontaneously, demonstrating that the birds met Hamner's first criterion for absolute photorefractoriness. Once their gonads fully regressed and the birds were in advanced prebasic moult, we exposed them to one of three photoperiods for an additional 2 weeks: constant light (24 h L), short days (8 h L), and controls (15 h L). Constant light challenge had no effect on gonadal condition or rate of moult, confirming that the birds met Hamner's second criterion for absolute refractoriness. We also compared volumes of song-control nuclei in the three groups and found that males overall had larger HVC, robust nucleus of arcopallium, and area X than females, but that longer days (24 h L) did not increase volumes and that shorter days (8 h L) did not decrease volumes compared with controls (15 h L). These data support the inference that black-capped chickadees do indeed become absolutely photorefractory, and that photorefractoriness precludes photo-induced plasticity of the song-control system.

The Arabidopsis Pseudo-response Regulators, PRR5 and PRR7, Coordinately Play Essential Roles for Circadian Clock Function

In Arabidopsis thaliana, a number of clock-associated protein factors have been identified. Among them, TOC1 (TIMING OF CAB EXPRESSION 1) is believed to be a component of the central oscillator. TOC1 is a member of a small family of proteins, designated as ARABIDOPSIS PSEUDO-RESPONSE REGULATOR, including PRR1/TOC1, PRR3, PRR5, PRR7 and PRR9. It has not been certain whether or not other PRR family members are also implicated in clock function per se. To clarify this problem, here we constructed a double mutant line, which is assumed to have severe lesions in both the PRR5 and PRR7 genes. Resulting homozygous prr5-11 prr7-11 young seedlings showed a marked phenotype of hyposensitivity to red light during de-etiolation. In addition, they displayed a phenotype of extremely late flowering under long-day photoperiod conditions, but not short-day conditions. The rhythms at the level of transcription of certain clock-controlled genes were severely perturbed in the double mutant plants when they were released into continuous light (LL) and darkness (DD). The observed phenotype was best interpreted as 'arrhythmic in both LL and DD' and/or 'very short period with markedly reduced amplitude'. Even under the light entrainment (LD) conditions, the mutant plants showed anomalous diurnal oscillation profiles with altered amplitude and/or phase with regard to certain clock-controlled genes, including the clock component CCA1 (CIRCADIAN CLOCK-ASSOCIATED 1) gene. Such events were observed even under temperature entrainment conditions, suggesting that the prr5-11 prr7-11 lesions cannot simply be attributed to a defect in the light signal input pathway. These pleiotropic circadian-associated phenotypes of the double mutant were very remarkable, as compared with those observed previously for each single mutant. Taking these results together, we propose for the first time that PRR5 and PRR7 coordinately (or synergistically) play essential clock-associated roles close to the central oscillator.

Hypothalamic responses to peripheral glucose infusion in food-restricted sheep are influenced by photoperiod

Nutritional feedback provided by systemic hormones, such as insulin and leptin, influences reproductive neuroendocrine output within the hypothalamus, yet the mechanisms and their interaction with photoperiodic cues remain unresolved in seasonal species. Here, peripheral glucose (G) infusion was used to increase endogenous concentrations of insulin and leptin in food-restricted sheep kept in either long-day (LD) or short-day (SD) photoperiod, and responses were examined in terms of pulsatile luteinising hormone (LH) (gonadotrophin-releasing hormone by inference) output and hypothalamic gene expression for nutritionally sensitive neuropeptides and receptors. We addressed the hypothesis that these hypothalamic responses were correlated and influenced by photoperiod. Oestradiol-implanted, castrated male sheep were kept 16 weeks in SD (8 h light/day) or LD (16 h light/day) and then transferred to the opposite photoperiods for 8 weeks, during which food was restricted to 90% requirement to maintain body weight (maintenance). For the final 6 days, food was reduced to 75% maintenance, and sheep in both photoperiods were infused intravenously with G (60 mM/h) or saline (S) (n = 8/group). G-infused sheep had higher mean plasma concentrations of G, insulin and leptin than S-infused sheep, with no effect of photoperiod. In LD, but not in SD, G infusion increased LH pulse frequency and pulse amplitude. In LD, but not in SD, gene expression in the hypothalamic arcuate nucleus was lower in G- than S-infused sheep for neuropeptide Y (NPY) and agouti-related peptide (AGRP) and was higher in G- than S-infused sheep for pro-opiomelanocortin (POMC). Gene expression for leptin and insulin receptors was not affected by photoperiod or infusion. These results are consistent with the involvement of NPY, AGRP and POMC in mediating the reproductive neuroendocrine response to increased systemic nutritional feedback, and they support the hypothesis that hypothalamic responses to nutritional feedback are influenced by photoperiod in sheep.

Response to selection for photoperiod responsiveness on the density and location of mature GnRH-releasing neurons

Natural variation in neuroendocrine traits is poorly understood, despite the importance of variation in brain function and evolution. Most rodents in the temperate zones inhibit reproduction and other nonessential functions in short winter photoperiods, but some have little or no reproductive response. We tested whether genetic variability in reproductive seasonality is related to individual differences in the neuronal function of the gonadotropin-releasing hormone network, as assessed by the number and location of mature gonadotropin-releasing hormone-secreting neurons under inhibitory and excitatory photoperiods. The experiments used lines of Peromyscus leucopus previously developed by selection from a wild population. One line contained individuals reproductively inhibited by short photoperiod, and the other line contained individuals nonresponsive to short photoperiod. Expression of mature gonadotropin-releasing hormone (GnRH) immunoreactivity in the brain was detected using SMI-41 antibody in the single-labeled avidin-biotin-peroxidase-complex method. Nonresponsive mice had 50% more immunoreactive GnRH neurons than reproductively inhibited mice in both short- and long-day photoperiods. The greatest differences were in the anterior hypothalamus and preoptic areas. In contrast, we detected no significant within-lines differences in the number or location of immunoreactive GnRH neurons between photoperiod treatments. Our data indicate that high levels of genetic variation in a single wild population for a specific neuronal trait are related to phenotypic variation in a life history trait, i.e., winter reproduction. Variation in GnRH neuronal activity may underlie some of the natural reproductive and life history variation observed in wild populations of P. leucopus. Similar genetic variation in neuronal traits may be present in humans and other species.

Effects of Hypothyroidism on Gonadal Function after Transition of Short Day Photoperiod in Male Golden Hamsters (Mesocricetus auratus)

Thyroid hormones permit the annual reproductive transition of seasonal breeders. Although, precise function of thyroid hormones in seasonal breeding is not well understood. In the present study, we examined effects of hypothyroidism on the hypothalamus-pituitary-gonadal axis in adult male golden hamsters after transition of the short-day photoperiod (SD; 8 h light: 16 h dark) condition. We confirmed that hypothyroid, which had been induced by administration of thiouracil in drinking water for 4 weeks, did not have direct effects on testes in male hamsters under the long-day photoperiod. Plasma concentrations of free T3 and T4 decreased 15 weeks after transition of SD condition. Plasma concentrations of testosterone in the hypothyroid group decreased earlier than in the control group after the transition from LD to SD. In animals treated with testosterone after castration, plasma concentrations of LH in the hypothyroid group decreased earlier than in the control group after the transition of SD. On the other hand, pituitary response to GnRH for LH release did not change in castrated hamsters as a result of hypothyroidism. These results suggest that thyroid hormones act the hypothalamus and might be required to maintain GnRH secretion in male golden hamsters.

Photoperiodic Response and Vase Life of Ornamental Sunflower Cultivars

Photoperiodic response and vase life of 28 cultivars of ornamental sunflower (Helianthus annuus) were evaluated. Plants were grown in a glasshouse under 16-hour long-day (LD) or 11.5-hour shortday (SD) conditions. Most cultivars (82%) reached visible flower bud stage earlier under SD than LD. All cultivars flowered under both SD and LD conditions, but in 26 cultivars (92.9%) flowering was significantly delayed under LD, demonstrating them to be quantitative SD plants. The delay was variable among the cultivars. A 14-day or greater hastening of flowering was found under SD in 18 cultivars. Photoperiod had no effect on flowering of `Lemon Eclair' and `Moonshadow'; these cultivars are day-neutral (DN) plants. For some cultivars the LD photoperiod increased plant height and the number of nodes and leaves. Vase life varied from 6.8 to 11.2 days depending on the cultivar, but no photoperiodic effect was found.

Short-Day Potentiation of Low Temperature-Induced Gene Expression of a C-Repeat-Binding Factor-Controlled Gene during Cold Acclimation in Silver Birch

Development of winter hardiness in trees is a two-stage process involving sequential perception of distinct environmental cues, short-day (SD) photoperiod and low temperature (LT). We have shown that both SD and LT are recognized by leaves of silver birch (Betula pendula cv Roth) leading to increased freezing tolerance, and thus leaves can be used as an experimental model to study the physiological and molecular events taking place during cold acclimation. To obtain a molecular marker for the acclimation process in birch we cloned a gene, designated Bplti36, encoding a 36-kD acidic SK2 type of dehydrin. The gene was responsive to LT, drought, salt, and exogenous abscisic acid. This responsiveness to abiotic stresses and abscisic acid was retained when Bplti36 was introduced to Arabidopsis (Arabidopsis thaliana). The LT induction of the gene appeared to be under the control of the C-repeat-binding factor pathway as suggested by the presence of several C-repeat/dehydration-responsive element/LT-responsive elements in the Bplti36 promoter and its constitutive expression in C-repeat-binding factor overproducing Arabidopsis. In birch SD photoperiod at normal-growth temperature did not result in significant induction of Bplti36. However, preexposure to SD followed by LT treatment resulted in a remarkable increase in Bplti36 transcript accumulation as compared to LT-treated plants grown at long-day photoperiod. This suggests that SD photoperiod potentiates the LT response by conditioning the leaf tissue to be more responsive to the LT stimulus.

Direct Effect of Melatonin on Syrian Hamster Testes: Melatonin Subtype 1a Receptors, Inhibition of Androgen Production, and Interaction with the Local Corticotropin-Releasing Hormone System

Besides the hypothalamus and pituitary, melatonin action at the testicular level has been recently suggested. Therefore, we investigated in the Syrian hamster, a well-characterized seasonal breeder, melatonin action on Leydig cells, testicular expression of melatonergic receptors, and possible interactions between melatonin receptors and the previously identified testicular serotoninergic and CRH systems. In isolated Leydig cells from active testes of adult hamsters kept in a long-day (14 h light, 10 h dark) photoperiod and from regressed testes of adult animals exposed to a short-day photoperiod during 16 wk (6 h light, 18 h dark), melatonin significantly reduced human chorionic gonadotropin-stimulated production of cAMP and the main androgens: testosterone and androstane-3alpha,17beta-diol, respectively, and decreased the expression of steroidogenic acute regulatory protein, P450 side chain cleavage, 3beta-hydroxysteroid dehydrogenase and 17beta-hydroxysteroid dehydrogenase. In Leydig cells exposed to a short-day photoperiod during 16 wk, melatonin stimulated the conversion of testosterone into 5alpha-reduced androgens by inducing 5alpha-reductase isoform 1, and controlled androstane-3alpha,17beta-diol production by inhibiting 3alpha-hydroxysteroid dehydrogenase expression. Melatonin subtype (mel1a) receptors were detected in Leydig cells. Although the local serotonin system did not mediate melatonin action on androgen production, melatonergic effect on steroidogenesis involved the interaction between mel1a receptors and the inhibitory CRH system. Moreover, melatonin significantly increased CRH mRNA levels and production in hamster Leydig cells expressing CRH subtype 1 receptors. Our studies indicate that melatonin may act as a local inhibitor of human chorionic gonadotropin-stimulated cAMP and androgen production through mel1a receptors, down-regulation of steroidogenic acute regulatory protein, and key steroidogenic enzymes expression and its interaction with the local CRH system.

Endocrine changes associated with metamorphosis and diapause induction in the yellow-spotted longicorn beetle, Psacothea hilaris

At 25°C and under a long-day photoperiod, all 5th instar Psacothea hilaris larvae pupate at the next molt. Under a short-day photoperiod, in contrast, they undergo one or two additional larval molts and enter diapause; the 7th instar larvae enter diapause without further molt. The changes in hemolymph juvenile hormone (JH III) titers, JH esterase activity, and ecdysteroid titers in pupation-destined, pre-diapause, and diapause-destined larvae were examined. JH titers of the 5th instar pupation-destined larvae decreased continuously from 1.3 ng/ml and became virtually undetectable on day 13, when JH esterase activity peaked. Ecdysteroids exhibited a small peak on day 8, 1 day before gut purge, and a large peak on day 11, 2 days before the larvae became pre-pupae. The two ecdysteroid peaks are suggested to be associated with pupal commitment and pupation, respectively. JH titers of the 5th instar pre-diapause larvae were maintained at ∼1.5 ng/ml for 5 days and then increased to form a peak (3.3 ng/ml) on day 11. JH esterase activity remained at a low level throughout. Ecdysteroid levels exhibited a large peak of 40 ng/ml on day 18, coincident with the larval molt to the 6th instar. JH titers of the 7th instar diapause-destined larvae peaked at 1.9 ng/ml on day 3, and a level of ∼1.1 ng/ml was maintained even 30–60 days into the instar, when they were in diapause. Ecdysteroid titers remained ∼0.02 ng/ml. Diapause induction in this species was suggested to be a consequence of high JH and low ecdysteroid titers.

Genetic analyses of a seasonal interval timer.

Seasonal clocks (e.g., circannual clocks, seasonal interval timers) permit anticipation of regularly occurring environmental events by timing the onset of seasonal transitions in reproduction, metabolism, and behavior. Implicit in the concept that seasonal clocks reflect adaptations to the local environment is the unexamined assumption that heritable genetic variance exists in the critical features of such clocks, namely, their temporal properties. These experiments quantified the intraspecific variance in, and heritability of, the photorefractoriness interval timer in Siberian hamsters (Phodopus sungorus), a seasonal clock that provides temporal information to mechanisms that regulate seasonal transitions in body weight. Twenty-seven families consisting of 54 parents and 109 offspring were raised in a long-day photoperiod and transferred as adults to an inhibitory photoperiod (continuous darkness; DD). Weekly body weight measurements permitted specification of the interval of responsiveness to DD, a reflection of the duration of the interval timer, in each individual. Body weights of males and females decreased after exposure to DD, but 3 to 5 months later, somatic recrudescence occurred, indicative of photorefractoriness to DD. The interval timer was approximately 5 weeks longer and twice as variable in females relative to males. Analyses of variance of full siblings revealed an overall intraclass correlation of 0.71 +/- 0.04 (0.51 +/- 0.10 for male offspring and 0.80 +/- 0.06 for female offspring), suggesting a significant family resemblance in the duration of interval timers. Parent-offspring regression analyses yielded an overall heritability estimate of 0.61 +/- 0.2; h(2) estimates from parent-offspring regression analyses were significant for female offspring (0.91 +/- 0.4) but not for male offspring (0.35 +/- 0.2), indicating strong additive genetic components for this trait, primarily in females. In nature, individual differences, both within and between sexes, in the timekeeping properties of seasonal interval timers, and a strong heritable basis thereof, would provide ample substrate for selection to rapidly influence seasonal clocks. Balancing selection in environments where the onset of spring conditions varies from year to year could maintain genetic variance in interval timers and yield interval timers tuned to the local environment.

Prolactin mediates photoperiodic immune enhancement: effects of administration of exogenous prolactin on circulating concentrations, receptor expression, and immune function in steers.

Changes in photoperiod can significantly impact the physiology of many species. For example, we have observed an improvement in cellular immune function in cattle on short-day photoperiod (SDPP) relative to long-day photoperiod (LDPP). In addition, prolactin (PRL) and PRL receptor (PRL-R) are affected by photoperiod management. Our hypothesis is that the inverse relationship observed between PRL and PRL-R mRNA expression during photoperiod treatment alters the sensitivity of the animal to PRL, thereby affecting the changes in their cellular immune function. The objective of this study was to determine the effects of exogenous PRL on photoperiodic-mediated immune responses. Eight Holstein steers received each of four treatments: LDPP (16L:8D), SDPP (8L:D), SDom (SDPP plus PRL via osmotic minipump for 10 days), and SDinj (SDPP plus PRL via 3x daily injections for 10 days). Steers on SDPP had decreased PRL relative to the other treatments. Expression of PRL-R mRNA was increased in SDPP animals relative to LDPP, SDom, and SDinj. Prior to PRL treatment, SDPP animals had greater lymphocyte proliferation and neutrophil chemotaxis relative to LDPP animals. Following PRL treatment, cellular immune function of SDom and SDinj animals was reduced to the level of LDPP animals. Addition of PRL to the in vitro lymphocyte proliferation did not alter response of LDPP animals but increased proliferation of lymphocytes from SDPP animals. The results of these experiments suggest that an animal's responsiveness to PRL correlate to changes in cellular immune function that occur with photoperiod manipulation.

Isolation and characterization of PHYC gene from Stellaria longipes: differential expression regulated by different red/far-red light ratios and photoperiods.

We have cloned and characterized the phytochrome C ( PHYC) gene from Stellaria longipes. The PHYC gene is composed of a 110-bp 5'-untranslated leader sequence, a 3,342-bp coding region, and a 351-bp 3'-untranslated sequence. The Stellaria PHYC contains three long introns within the coding region at conserved locations as in most angiosperm PHY genes. DNA blot analysis indicates that the Stellaria genome contains a single copy of PHYC. Stellaria PHYC shares 60%, 58%, and 57% deduced amino acid identities with rice, Sorghum, and Arabidopsis PHYC, respectively. Phylogenetic analysis indicates that Stellaria PHYC is located in the dicot branch, but is divergent from Arabidopsis PHYC. The Stellaria PHYC is constitutively expressed in different plant organs, though the level of PHYC gene transcript in roots is slightly higher than in flowers, leaves, and stems. When 2-week old seedlings grown in the dark were exposed to constant white light, PHYC mRNA quickly accumulates within 1-12 h. When plants grown in darkness for 7 days were exposed to different red/far-red light (R/FR) ratios, the levels of PHYC mRNA at R/FR = 0.7 are much lower than under R/FR = 3.5. The levels of PHYC mRNA under short-day (SD) photoperiod are higher than under long-day (LD) photoperiod. Plants under SD conditions do not elongate, and are only about 1.7 cm tall at 19 days. In contrast, plants under LD conditions elongate with an average height of 21.2 cm at 19 days. The plants do not flower under SD conditions, but do so at 18-19 days under LD conditions. These results indicate that under SD conditions the high level of PHYC mRNA may inhibit stem elongation and flower initiation. In contrast, under LD conditions the high level of PHYC mRNA may promote stem elongation and flowering.

The effects of long-day photoperiod on growth, body composition and skin colour in immature gilthead sea bream (Sparus aurata L.)

Immature gilthead sea bream (Sparus aurata L.) with a mean initial weight of 25.6 g were reared over 11 months to market size under different photoperiods: 16L:8D; 24L:0D and a control. Differences in final mean weight were significant between the three treatments (P<0.001): 16L:8D, 465.0 g; 24L:0D, 445.9 g; control, 402.6 g. Fish from the 24L:0D consumed most while 16L:8D fish converted it most efficiently. The lipid content of fillets was lower (P<0.05) for the 24L:0D (5.37±0.16 g 100 g−1 of fillet) than for the control (6.02±0.12 g), and the moisture content lower for the control than for either treatment groups. Skin luminosity (L*) was directly related to the number of hours of light exposure.

Diapause Termination in Overwintering Larvae of a Greek Strain ofAdoxophyes orana(Lepidoptera: Tortricidae)

The course of diapause development under field conditions for diapausing larvae of Adoxophyes orana (F.v.R.) (Lepidoptera: Tortricidae) was investigated. Larvae of A. orana were collected during the winter and early spring from 1996 to1999 from peach and cherry trees in the area of Naousa in northern Greece. Each larva was placed individually in a plastic cylindrical cell with a piece of artificial diet at 20°C under long-day (16:8 L:D) or short-day photoperiods (8:16 L:D). Photoperiod had a significant influence on diapause development. Duration in days, from transfer from the orchard to the laboratory until first molt and pupation of larvae, was also significantly affected by sampling date. Photoperiodic sensitivity was no longer detected after late January. Short-day photoperiod maintained diapause for larvae sampled until late January. Thus, A. orana may complete diapause development in late January, but it will not break diapause until spring, when temperatures are sufficiently high to induce diapause break.

Characterization of circadian-associated APRR3 pseudo-response regulator belonging to the APRR1/TOC1 quintet in Arabidopsis thaliana.

In higher plants, there are wide ranges of biological processes that are controlled through the circadian clock. In this connection, we have been characterizing a small family of proteins, designated as ARABIDOPSIS PSEUDO-RESPONSE REGULATORS (APRR1, APRR3, APRR5, APRR7, and APRR9), among which APRR1 is identical to TOC1 (TIMING OF CAB EXPRESSION1) that is believed to be a component of the central oscillator. Through previous genetic studies, several lines of evidence have already been provided to support the view that, not only APRR1/TOC1, but also other APRR1/TOC1 quintet members are important for a better understanding of the molecular links between circadian rhythm, control of flowering time, and also photomorphogenesis. However, the least characterized one was APRR3 in that no genetic study has been conducted to see if APRR3 also plays an important role in the circadian-associated biological events. Here we show that APRR3-overexpressing transgenic plants (APRR3-ox) exhibited: (i). a phenotype of longer period (and/or delayed phase) of rhythms of certain circadian-controlled genes under continuous white light, (ii). a phenotype of late flowering under long-day photoperiod conditions, (iii). a phenotype of hypo-sensitiveness to red light during early photomorphogenesis of de-etiolated seedlings, supporting the current idea as to the APRR1/TOC1 quintet described above.

Influence of photoperiod and temperature on vegetative growth and development of Florida betony (Stachys floridana)

Experiments were conducted in environmental chambers to the evaluate effects of photoperiod and temperature on Florida betony growth and development. Plants were exposed to two photoperiods, short day (9 h) and long day (9 + 3 h night interruption), and three day/night temperature regimes, 18/14, 22/18, and 26/22 C. After 10 wk of growth, shoot length and weight were 3.4 and 3.5 times greater, respectively, in the long-day photoperiod and with the 26 and 22 than with the 22 and 18 C day and night temperature regime, respectively. Shoot number, however, was greatest in the short-day photoperiod and at a lower temperature of 22/18 C. Shoot number in long day 22/18 C and 26/22 C environments increased asymptotically. No difference in root weight was observed between long- and short-day environments, but root weight increased with increasing temperature. Flowering and tuber production only occurred in long-day environments, with greater production of both at higher temperatures. Results provide a general framework for understanding Florida betony growth and development characteristics in the field and provide insights that should be considered in developing control strategies.

Photoperiod Effects upon Shoot Growth and Color of Bermudagrass Fertilized with Slow-release Nitrogen Sources

Total plant biomass, shoot growth rate, and the periodicity in shoot growth and color of hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy `Tifgreen'] in response to slow-release fertilizer N sources, rates, and application frequencies were studied in two, 120-day greenhouse studies. Plugs were planted in plastic cylinders filled with a growing medium of 93 sand: 7 peat moss (w/w). The first experiment was completed under progressively increasing photoperiod (13.1 to 14.9 hours) typical of the long-day requirements for bermudagrass growth. The second experiment occurred under progressively decreasing photoperiod (13.7 to 10.7 hours) representative of autumnal growing conditions and declining growth and N demand. Urea (URE), sulfur-coated urea (SCU), and hydroform (HYD, methylene urea polymers) were broadcast at N rates of 100 or 200 kg·ha-1 and at frequencies of 20 or 40 days. Bermudagrass was clipped at 3-day intervals and the average daily clipping growth rate (increase in shoot dry matter; DM) reached a maximum of 11.5 g·m-2 per day. Use of the least soluble source, HYD, produced the lowest total clipping DM, and at low HYD rate and frequency, leaf color intensity was frequently below the accepted standard of 7, in the scale from 1 “tan” to 9 “dark green”. A greater responsiveness of bermudagrass to N rate and application frequency (increased clipping growth rate and color intensification upon N application) occurred under increasing photoperiodic conditions as compared to decreasing photoperiodic conditions. Both clipping growth and color changed cyclically through time and mainly under long-day photoperiod (&gt;12 hours), with greater oscillation at longer fertilization interval (40 days). With either SCU or URE, at low N rate and frequency (total N application of 0.25 g·m-2 per day), clipping growth rates were above 4 g·m-2 per day, and turf color was at or above the minimum quality standard through most of the growing period. Higher total SCU and URE application rates, previously shown to increase N leaching losses in these experimental conditions, produced significantly more clipping growth and did not appear to intensify color sufficient to warrant the increased risk of N loss.