Autovaccination Confers Protection against Devriesea agamarum Associated Septicemia but Not Dermatitis in Bearded Dragons (Pogona vitticeps)

Devrieseasis caused by Devriesea agamarum is a highly prevalent disease in captive desert lizards, resulting in severe dermatitis and in some cases mass mortality. In this study, we assessed the contribution of autovaccination to devrieseasis control by evaluating the capacity of 5 different formalin-inactivated D. agamarum vaccines to induce a humoral immune response in bearded dragons (Pogona vitticeps). Each vaccine contained one of the following adjuvants: CpG, incomplete Freund''s, Ribi, aluminium hydroxide, or curdlan. Lizards were administrated one of the vaccines through subcutaneous injection and booster vaccination was given 3 weeks after primo-vaccination. An indirect ELISA was developed and used to monitor lizard serological responses. Localized adverse effects following subcutaneous immunization were observed in all but the Ribi adjuvanted vaccine group. Following homologous experimental challenge, the incomplete Freund''s as well as the Ribi vaccine were observed to confer protection in bearded dragons against the development of D. agamarum associated septicemia but not against dermatitis. Subsequently, two-dimensional gelelectrophoresis followed by immunoblotting and mass spectrometry was conducted with serum obtained from 3 lizards that showed seroconversion after immunisation with the Ribi vaccine. Fructose-bisphosphate aldolase and aldo-keto reductase of D. agamarum reacted with serum from the latter lizards. Based on the demonstrated seroconversion and partial protection against D. agamarum associated disease following the use of formalin-inactivated vaccines as well as the identification of target antigens in Ribi vaccinated bearded dragons, this study provides promising information towards the development of a vaccination strategy to control devrieseasis in captive lizard collections.     

Establishing a New Species Encephalitozoon pogonae for the Microsporidian Parasite of Inland Bearded Dragon Pogona vitticeps Ahl 1927 (Reptilia,Squamata, Agamidae)

The microsporidium parasitizing Inland Bearded Dragons Pogona vitticeps, and developing primarily in macrophages within foci of granulomatous inflammation of different organs, is described as a new species Encephalitozoon pogonae. Establishing the new species was based on sequencing the ITS‐SSUrDNA region of the ribosomal gene and consequent SSUrDNA‐inferred phylogenetic analyses, as well as on comparison of pathogenesis, host specificity, and ultrastructure among Encephalitozoon species and isolates. The new species is closely related to E. lacertae and E. cuniculi. Analysis of the literature suggests that this microsporidium has been reported previously as an unidentified microsporidian species or isolate of E. cuniculi and may represent a common infection in bearded dragons. All stages of E. pogonae develop in parasitophorous vacuoles. Uninucleate spores on methanol‐fixed smears measured 2.1 × 1.1 μm, range 1.7–2.6 × 0.9–1.7 μm; on ultrathin sections spores measured 0.8–1.1 × 1.8–2.2 μm. Ultrastructural study revealed 3–6 polar filament coils, a mushroom‐shaped polar disk, and a polar sac embracing half of the volume occupied by the lamellar polaroplast. In activated spores, polar filament everted eccentrically. The overall morphology and intracellular development of E. pogonae were similar to other Encepahalitozoon spp. We also review the existing data on microsporidia infecting reptiles.     

Regulation of pulmonary surfactant secretion in the developing lizard,Pogona vitticeps

Pulmonary surfactant is a mixture of lipids and proteins that is secreted by alveolar type II cells in the lungs of all air-breathing vertebrates. Pulmonary surfactant functions to reduce the surface tension in the lungs and, therefore, reduce the work of breathing. In mammals, the embryonic maturation of the surfactant system is controlled by a host of factors, including glucocorticoids, thyroid hormones and autonomic neurotransmitters. We have used a co-culture system of embryonic type II cells and lung fibroblasts to investigate the ability of dexamethasone, tri-iodothyronine (T(3)), adrenaline and carbamylcholine (carbachol) to stimulate the cellular secretion of phosphatidylcholine in the bearded dragon (Pogona vitticeps) at day 55 (approx. 92%) of incubation and following hatching. Adrenaline stimulated surfactant secretion both before and after hatching, whereas carbachol stimulated secretion only at day 55. Glucocorticoids and triiodothyronine together stimulated secretion at day 55 but did not after hatching. Therefore, adrenaline, carbachol, dexamethasone and T(3), are all involved in the development of the surfactant system in the bearded dragon. However, the efficacy of the hormones is attenuated during the developmental process. These differences probably relate to the changes in the cellular environment during development and the specific biology of the bearded dragon.     

Prostaglandins are important in thermoregulation of a reptile (Pogona vitticeps)

The effectiveness of behavioural thermoregulation in reptiles is amplified by cardiovascular responses, particularly by differential rates of heart beat in response to heating and cooling (heart-rate hysteresis). Heart-rate hysteresis is ecologically important in most lineages of ectothermic reptile, and we demonstrate that heart-rate hysteresis in the lizard Pogona vitticeps is mediated by prostaglandins. In a control treatment (administration of saline), heart rates during heating were significantly faster than during cooling at any given body temperature. When cyclooxygenase 1 and 2 enzymes were inhibited, heart rates during heating were not significantly different from those during cooling. Administration of agonists showed that thromboxane B(2) did not have a significant effect on heart rate, but prostacyclin and prostaglandin F(2alpha) caused a significant increase (3.5 and 13.6 beats min(-1), respectively) in heart rate compared with control treatments. We speculate that heart-rate hysteresis evolved as a thermoregulatory mechanism that may ultimately be controlled by neurally induced stimulation of nitric oxide production, or maybe via photolytically induced production of vitamin D.     

Modulation of prey capture kinematics and the role of lingual sensory feedback in the lizard Pogona vitticeps

Most organisms feed on a variety of prey that may differ dramatically in their physical and behavioural characteristics (e.g. mobility, mass, texture, etc.). Thus the ability to modulate prey capture behaviour in accordance with the characteristics of the food appears crucial. In animals that use rapid tongue movements to capture prey (frogs and chameleons), the coordination of jaws and tongue is based on visual cues gathered prior to the prey capture event. However, most iguanian lizards have much slower tongue-based prey capture systems suggesting that sensory feedback from the tongue may play an important role in coordinating jaw and tongue movements. We investigated the modulation of prey capture kinematics in the agamid lizard Pogona vitticeps when feeding on a range of food items differing in their physical characteristics. As the lizard is a dietary generalist, we expected it to be able to modulate its prey capture kinematics as a function of the (mechanical) demands imposed by the prey. Additionally, we investigated the role of lingual sensory feedback by transecting the trigeminal sensory afferents. Our findings demonstrated that P. vitticeps modulates its prey capture kinematics according to specific prey properties (e.g. size). In addition, transection of the trigeminal sensory nerves had a strong effect on prey capture kinematics. However, significant prey type effects and prey type by transection effects suggest that other sources of sensory information are also used to modulate the prey capture kinematics in P. vitticeps.     

The influence of hypoxia on the thermal sensitivity of skin colouration in the bearded dragon, Pogona vitticeps

One physiological mechanism used by reptiles to remain within thermal optima is their ability to reversibly alter skin colour, imparting changes in overall reflectance, and influencing the rate of heat gain from incident radiation. The ability to lighten or darken their skin is caused by the movement of pigment within the dermal chromatophore cells. Additionally, lizards, as ectotherms, significantly lower their preferred body temperatures when experiencing stressors such as hypoxia. This decrease in preferred temperature has been proposed to be the result of a downward adjustment of the thermal set-point, the temperature around which the body temperature is typically defended. We tested the hypothesis that lightening of the skin in lizards would be modified by hypoxia in a manner consistent with the known reduction in preferred temperatures. Skin colouration values of the dorsal skin of bearded dragons were analysed at three different levels of oxygen (20.8, 9.9 and 4.9 kPa) and at temperatures spanning the preferred temperature range (30, 32, 34, 36, 38 and 40 C). Hypoxic lizards lightened their skin at lower ambient temperatures more than normoxic ones, and in an oxygen-dependent fashion. The orchestrated adjustment of skin reflectance suggests that this physiological trait is being regulated at a new and lower set-point. Evidence from this study demonstrates that skin colouration plays a role in body temperature regulation and that the reduction in temperature set-point so prevalent in hypoxia is also manifested in this physiological trait.     

Ethylene Stimulation During the Hypersensitive Reaction of Soybean to Tobacco Necrosis Virus under Different Photoperiods

Abstract The production of stress ethylene was increased in soybean leaves hypersensitively responding to tobacco necrosis virus, independently of photoperiod. However, only little increase occurred under continuous darkness, whereas most occurred under continuous darkness, whereas most occurred under continuous light. Ethylene stimulation paralleled accumulation of 1-aminocyclopropane-1-carboxylic (ACC) and its conversion to ethylene. Continuous darkness substantially inhibited viral antigen accumulation but not lesion area in comparison to continuous light. Ethylene release, viral lesion area and antigen accumulation were substantially increased when darkened leaf tissues were fed with glucose, this suggesting that dark inhibition was due to energy and/or, metabolic depletion. Co²⁺ and aminoethoxyvinylglycine, which completely inhibited stress ethylene, and ACC, which conspicuously increased it, had no effect on both viral lesion and antigen accumulation.
These results indicate that stress ethylene developing during a HR to virus does not affect the localizing mechanism operating during it.     

外源ABA对低温不同光周期下四季秋海棠叶片花色素苷的诱导机理

以‘超级奥林匹克’四季秋海棠(‘Super Olympia’ Begonia semperflorens)为材料,于常温（25 ℃/15 ℃）等日照条件下用0、5、10、50、100、500 μmol/L脱落酸(ABA)和低温（15 ℃/6 ℃）不同光周期下用10 μmol/L ABA分别喷施各处理植株,对不同处理下植株的色素含量、内源激素含量及其酶活性进行比较分析,探讨ABA对其叶片花色素苷合成的调控作用及其机理。结果显示：（1）常温等日照条件下,四季秋海棠叶片在5和10 μmol/L ABA处理后的第3~5天有明显变红趋势,且花色素苷含量和内源ABA含量显著增加,而内源赤霉素（GA）含量的下降幅度较为显著,相应的花色素苷合成关键酶和运输酶活性也显著提高。（2）低温条件下,四季秋海棠叶片花色素苷积累量与光周期密切相关,短日照处理的花色素苷积累量最大并显著高于等日照和长日照,但等日照与长日照下花色素苷积累量无显著差异;外源10 μmol/L ABA处理均可显著提高低温不同光周期下四季秋海棠叶片的花色素苷含量。（3）外施10 μmol/L ABA增加了低温下长日照和等日照处理中DFR（二氢黄酮醇 4 还原酶）还原反应中H供体NADPH的含量,促使DFR和UFGT（糖苷转移酶）的活性上调进而增加了花色素苷的含量;外施ABA处理均能够提高低温不同光周期处理组的内源ABA含量,降低内源GA的含量,与花色素苷的生成量相一致。研究表明,外源ABA能够通过调节花色素苷合成的关键酶来影响花色素苷的合成,外施适宜浓度ABA能够促进四季秋海棠叶片花色素苷的积累,可用于实际生产中的叶片着色调控管理。     

不同光周期对西红花开花和花丝品质的效应比较

为筛选促进西红花开花和提高花丝品质的最佳光周期,以3种不同规格(20～25 g、25～30 g、30～35 g)西红花种球为材料,设置4种光周期处理(8 h/16 h、10 h/14 h、12 h/12 h、14 h/10 h),考察光周期对西红花种球鲜重变化、主芽生长、展叶数量、开花后营养物质含量以及花朵性状和花丝品...     

Influence of Temperature on the Flowering of Lemna perpusilla 6746 Grown under Skeleton Photoperiods

The flowering of Lemna perpusilla Torr. strain 6746 grown under 24-hour skeleton photoperiods consisting of 13- and 10.5-hour dark periods separated by 0.25-hr light pulses is strongly dependent on temperature. When plants are cultured in 50-ml Erlenmeyer flasks containing 20 ml of half-strength Hutner's medium supplemented with 1% (w/v) sucrose maximum, per cent, flowering occurs at 23 C. At temperatures above and below 23 C a marked decline in per cent flowering is seen.     

不同光周期对德国鸢尾‘Royal touch’的花芽分化和光合作用的影响

以德国鸢尾‘Royal touch’为试验材料,研究了5种光周期对其花芽分化和光合作用的影响。结果表明:(1)短日照加速了植株花芽分化的进程,而长日照促进了单花序上花芽数目的增加;(2)长日照下植株单位叶面积的光合能力较强(;3)植株的花芽分化与其叶面积、叶干重、地上部分与地下部分的干重比值之间呈显著的正相关关系。这些结果说明了光周期对德国鸢尾‘Royal touch’花芽分化时间和数量的影响与光周期对其植株生物量和光合作用的影响有关。     

Testosterone-Induced Expression of Male Colour Morphs in Females of the Polymorphic Tawny Dragon Lizard,Ctenophorus decresii

Many colour polymorphisms are present only in one sex, usually males, but proximate mechanisms controlling the expression of sex-limited colour polymorphisms have received little attention. Here, we test the hypothesis that artificial elevation of testosterone in females of the colour polymorphic tawny dragon lizard, Ctenophorus decresii, can induce them to express the same colour morphs, in similar frequencies, to those found in males. Male C. decresii, express four discrete throat colour morphs (orange, yellow, grey and an orange central patch surrounded by yellow). We used silastic implants to experimentally elevate testosterone levels in mature females to induce colour expression. Testosterone elevation resulted in a substantial increase in the proportion and intensity of orange but not yellow colouration, which was present in a subset of females prior to treatment. Consequently, females exhibited the same set of colour morphs as males, and we confirmed that these morphs are objectively classifiable, by using digital image analyses and spectral reflectance measurements, and occur in similar frequencies as in males. These results indicate that the influence of testosterone differs for different colours, suggesting that their expression may be governed by different proximate hormonal mechanisms. Thus, caution must be exercised when using artificial testosterone manipulation to induce female expression of sex-limited colour polymorphisms. Nevertheless, the ability to express sex-limited colours (in this case orange) to reveal the same, objectively classifiable morphs in similar frequencies to males suggests autosomal rather than sex-linked inheritance, and can facilitate further research on the genetic basis of colour polymorphism, including estimating heritability and selection on colour morphs from pedigree data.     

Biases in Studying the Diet of the Bearded Vulture

Abstract: We compared methods of assessing the diet of the bearded vulture (Gypaetus barbatus) during the nestling period in the Pyrenees, northeast Spain. We determined diet from direct observations of food items delivered to the nest, recent prey remains present in the nest, remains collected in the nests after fledging, and remains collected in the ossuaries (bone-breaking sites). Data suggest that direct observation (food items delivered and recent prey remains present in the nest) is the only valid method of assessing the bearded vulture's diet accurately. Remains overestimated the presence of large mammals, such as cows (Bos taurus) and horses (Equus caballus), Suidae, and birds; delivered samples contained a higher proportion of small mammals, medium-sized mammals, micromammals, and reptiles. Ossuaries also differed from delivered samples because remains collected there overestimated large and medium-sized mammals. Concerning the skeletal parts, ossuaries, compared to all other methods, underestimated extremities and overestimated long bones, such as femur, humeri and tibiae, scapulae, vertebrae, and skulls. Remains samples, which overestimated scapulae, also differed from delivered and present samples. Our results suggest that bearded vultures favor extremities of prey (78% of the mammal remains, which make up 95% of the diet). The prevalence of small carcasses (almost 17%) suggests that vultures select small animals for food for the young. Because food quality may influence breeding success, future conservation projects based on the selective provision of food to breeding pairs should add to food stations meat remains and small carcasses consistent with our assessment of the birds’ dietary needs.     

Carbohydrate Metabolism and Frost Hardiness in Pine and Spruce Seedlings Grown at Different Photoperiods and Thermoperiods

Large changes occur in carbohydrate contents of pine (Pinus silvestris L.) and spruce (Picea abies (L.) Karst.) seedlings cold-hardened by photoperiod or by combined photo- and thermo-period. The largest change is in sucrose content, which is almost doubled after six weeks short-day (6/18 h) treatment; and more than doubled (spruce) or more than tripled (pine), when also temperature is lowered (10/5°C). Development of frost hardiness is strongly correlated with the change in carbohydrate contents. At dehardening, the carbohydrate content decreases rapidly, especially in pine, and the raffinose formed during the rest period disappears within 2–4 weeks. Frost hardiness decreases in parallel. The content of soluble carbohydrates may thus play a role in frost hardiness, although it is not the only factor. Bud formation at cold acclimation is not directly correlated with the changes in carbohydrate content and hardiness.     

温度对紫色不结球白菜外观和营养品质的影响

以紫色不结球白菜品种‘紫衣’为试验材料,利用人工气候箱,采用盆栽法,研究3个不同温度(5℃、25℃和35℃)条件对紫色不结球白菜叶片颜色和营养品质等指标的影响,为优质紫色不结球白菜设施栽培温度的选择提供依据。结果显示:(1)紫色不结球白菜在受到5℃低温处理时,叶片紫色会随着处理时间的延长而加深,最终呈深紫色;反之,当受到35℃高温时,叶片颜色逐渐变浅,直至叶片呈绿色,该现象与叶片中花青素含量的变化规律一致。(2)与正常25℃相比,紫色不结球白菜叶片中的还原糖、可溶性糖和总糖含量在受到高温胁迫(35℃)后逐渐降低,而在低温(5℃)处理下,先增后减,且高温降低幅度大于低温;可溶性蛋白、还原性抗坏血酸和氨基酸含量也随着高温胁迫的延长而降低,但低温处理下则逐渐增加;抗坏血酸-过氧化物酶活性(APX)、纤维素和硝酸盐含量在高温胁迫下逐渐增加,低温条件下则显著降低。研究发现,不同温度明显影响着紫色不结球白菜叶片紫色深浅,低温促进花青素积累,高温抑制或是加速花青素的降解;低温能促进叶片可溶性蛋白、抗坏血酸和氨基酸等品质指标的积累,同时降低纤维素含量,从而提高紫色不结球白菜的外观和营养品质,高温胁迫则降低以上品质指标。     

Regulatory Properties of ADP Glucose Pyrophosphorylase Are Required for Adjustment of Leaf Starch Synthesis in Different Photoperiods

Arabidopsis (Arabidopsis thaliana) leaves synthesize starch faster in short days than in long days, but the mechanism that adjusts the rate of starch synthesis to daylength is unknown. To understand this mechanism, we first investigated whether adjustment occurs in mutants lacking components of the circadian clock or clock output pathways. Most mutants adjusted starch synthesis to daylength, but adjustment was compromised in plants lacking the GIGANTEA or FLAVIN-BINDING, KELCH REPEAT, F BOX1 components of the photoperiod-signaling pathway involved in flowering. We then examined whether the properties of the starch synthesis enzyme adenosine 5′-diphosphate-glucose pyrophosphorylase (AGPase) are important for adjustment of starch synthesis to daylength. Modulation of AGPase activity is known to bring about short-term adjustments of photosynthate partitioning between starch and sucrose (Suc) synthesis. We found that adjustment of starch synthesis to daylength was compromised in plants expressing a deregulated bacterial AGPase in place of the endogenous AGPase and in plants containing mutant forms of the endogenous AGPase with altered allosteric regulatory properties. We suggest that the rate of starch synthesis is in part determined by growth rate at the end of the preceding night. If growth at night is low, as in short days, there is a delay before growth recovers during the next day, leading to accumulation of Suc and stimulation of starch synthesis via activation of AGPase. If growth at night is fast, photosynthate is used for growth at the start of the day, Suc does not accumulate, and starch synthesis is not up-regulated.Many plants store starch as a product of photosynthesis in leaves during day then degrade it to provide sugar for continued metabolism and growth at night. It is well established that rates of starch synthesis adjust to changes in daylength. Adjustments occur in plants acclimated to different daylengths: the shorter the day, the greater the proportion of photosynthate allocated to starch and hence available for metabolism at night (Chatterton and Silvius, 1979; Baysdorfer and Robinson, 1985; Hewitt et al., 1985; Lorenzen and Ewing, 1992; Lu et al., 2005; Gibon et al., 2009; Sulpice et al., 2014). In Arabidopsis (Arabidopsis thaliana), starch synthesis is also accelerated in the light period following a single, unexpected extension of the night (Gibon et al., 2004a). The mechanisms that adjust the rate of starch synthesis to daylength are not known. Neither the nature of the signals from daylength nor the manner in which they influence starch synthesis are understood, and it is not known whether the acclimation of the rate of starch synthesis to different daylengths involves the same mechanisms as its immediate adjustment following an unexpected extension of the night.By contrast, the short-term control of starch synthesis is well understood. Partitioning of photosynthate into starch in the chloroplast is largely determined by the balance between the rate of photosynthetic carbon assimilation and the rate of Suc synthesis. Assimilate for Suc synthesis is exported from the chloroplast as triose phosphate, in exchange for inorganic phosphate (Pi) released during its cytosolic conversion to Suc. The rate of Suc synthesis is regulated via action of Fru 2,6-bisphosphate on the cytosolic Fru 1,6-bisphosphatase and allosteric and posttranslational regulation of Suc phosphate synthase (Stitt and Quick, 1989; Stitt et al., 2010). If the rate of Suc synthesis falls, for example in response to feedback from decreased utilization by sink organs, the amount of Pi available for exchange with triose phosphate is decreased, leading to retention of a larger proportion of the triose phosphate in the chloroplast and its use for starch synthesis. Conversely, if the rate of photosynthetic carbon assimilation falls, for example as a result of shading or stomatal closure, the concentration of triose phosphate in the chloroplast tends to fall, and the rate of starch synthesis decreases. Thus, a change in either the rate of photosynthetic carbon assimilation or the rate of Suc synthesis can rapidly bring about a change in the amount of photosynthate allocated to starch synthesis.These short-term adjustments of starch synthesis are brought about by modulation of the activity of adenosine 5′-diphosphate-glucose pyrophosphorylase (AGPase). This enzyme catalyzes the first committed step in starch biosynthesis: the synthesis of ADP-Glc and pyrophosphate from ATP and Glc 1-P. It is composed of large and small subunits and is subject to several levels of posttranslational regulation. The allosteric properties of the enzyme potentially allow it to regulate flux into starch in response to the rate of cytosolic Suc synthesis. High levels of triose phosphate in the chloroplast result in high 3-phosphoglyceraldehyde (3-PGA) levels, which activate the enzyme. Low levels of triose phosphate result in low 3-PGA and high Pi levels, which inhibit the enzyme (Heldt et al., 1977; Stitt et al., 1987). AGPase is also activated in the light and by sugars through reduction via NADP-thioredoxin reductase C and the thioredoxin Trx f1, which causes the loss of a disulfide bond between the two small subunits. Redox activation greatly increases the sensitivity of the enzyme to allosteric regulation by 3-PGA and Pi (Preiss, 1988; Kavakli et al., 2002; Tiessen et al., 2002; Hendriks et al., 2003; Michalska et al., 2009; Thormählen et al., 2013). Both large and small subunits are reported to be phosphorylated (Reiland et al., 2009, 2011; Nakagami et al., 2010; Umezawa et al., 2013; Wu et al., 2013), but the functional significance of these modifications is not known. Flux control analysis using Arabidopsis mutants with reduced activities of starch biosynthetic enzymes shows that AGPase can exert strong control over the rate of starch synthesis during photosynthesis, although the degree of control varies with environmental conditions (Neuhaus and Stitt, 1990; Sun et al., 1999; Hädrich et al., 2011). These mechanisms enable coordinated control of the use of Calvin-Benson cycle metabolites for starch and Suc synthesis, preventing the depletion of cycle intermediates and the inhibition of photosynthesis.It is not clear whether the mechanism that mediates short-term regulation of starch synthesis forms part of the unknown mechanism(s) by which starch synthesis is adjusted to daylength. One possibility is that a daylength-dependent signal sets an underlying default level of partitioning between Suc and starch or a target quantity of starch to be accumulated by the anticipated end of the day and that the short-term control described above operates on top of this default setting. We showed recently that the rate of starch degradation in leaves at night is controlled in part by the circadian clock (Graf et al., 2010; Scialdone et al., 2013): perhaps an analogous, clock-based mechanism ensures that sufficient starch is synthesized during the day to meet the carbon demands of the plant during the night. Daylength-dependent signals might affect partitioning through modulation of the abundance or properties of key enzymes of starch and/or Suc synthesis. Consistent with this idea, plants grown in short days have higher maximum catalytic activities of AGPase relative to Suc phosphate synthase than plants grown in long days (Gibon et al., 2009; Sulpice et al., 2014), due, in particular, to a rise of AGPase activity and protein before dawn in short but not in long days (Gibon et al., 2004b). Modulation of the redox sensitivity of AGPase can also affect partitioning: complementation of an AGPase-deficient Arabidopsis mutant with a mutagenized AGPase that is redox insensitive and mimics a constitutively redox-activated enzyme resulted in faster rates of starch accumulation in short days and low irradiance and the maintenance of slightly higher starch levels throughout the diel cycle in long day or high light regimes. However, these plants were still able to adjust the rate of starch synthesis in response to changes in daylength, indicating that redox modulation of activity is not essential for the response to photoperiod (Hädrich et al., 2012).A second possibility is that the general relationship between starch synthesis and daylength is determined indirectly by daylength-dependent variation in the demand for photosynthate for growth. We showed recently that the temporal pattern of growth varies with daylength (Sulpice et al., 2014): our data are consistent with growth rates at night and at the start of the day being high in long days but lower in short days. Differences in growth rate impose different demands for Suc, hence different rates of Suc synthesis at the start of the day. Such differences are expected to influence the rate of starch synthesis via the AGPase-dependent mechanism described above.To shed further light on mechanisms that gear the rate of starch synthesis to daylength in Arabidopsis, we first examined the importance for this relationship of components of the circadian clock and related photoperiod-signaling pathways. We then examined whether the properties of AGPase that are crucial for adjustment of starch synthesis over a single photoperiod are also important for the relationship between starch synthesis and the length of the photoperiod. This was achieved by replacing the endogenous Arabidopsis AGPase with a deregulated bacterial AGPase and examining the impact upon the response of starch synthesis to daylength and to an unexpected extension of the night.