Using flowering times and leaf numbers to model the phases of photoperiod sensitivity in Antirrhinum majus L

A model has been developed that can be used to determine the phases of sensitivity to photoperiod for seedlings subjected to reciprocal transfers at regular intervals between long (LD) and short day (SD) conditions. The novel feature of this approach is that it enables the simultaneous analysis of the time to flower and number of leaves below the inflorescence. A range of antirrhinum cultivars were grown, all of which were shown to be quantitative long-day plants. Seedlings were effectively insensitive to photoperiod when very young (juvenile). However, after the end of the juvenile phase, SD delayed flowering and increased the number of leaves below the inflorescence. Plants transferred from LD to SD showed a sudden hastening of flowering and a decrease in leaf number once sufficient LD had been received for flower commitment. Photoperiod had little effect on the rate of flower development. The analysis clearly identified major cultivar differences in the length of the juvenile phase and the photoperiod-sensitive inductive phase in both LD and SD.     

Hd1, a major photoperiod sensitivity quantitative trait locus in rice, is closely related to the Arabidopsis flowering time gene CONSTANS

A major quantitative trait locus (QTL) controlling response to photoperiod, Hd1, was identified by means of a map-based cloning strategy. High-resolution mapping using 1505 segregants enabled us to define a genomic region of approximately 12 kb as a candidate for Hd1. Further analysis revealed that the Hd1 QTL corresponds to a gene that is a homolog of CONSTANS in Arabidopsis. Sequencing analysis revealed a 43-bp deletion in the first exon of the photoperiod sensitivity 1 (se1) mutant HS66 and a 433-bp insertion in the intron in mutant HS110. Se1 is allelic to the Hd1 QTL, as determined by analysis of two se1 mutants, HS66 and HS110. Genetic complementation analysis proved the function of the candidate gene. The amount of Hd1 mRNA was not greatly affected by a change in length of the photoperiod. We suggest that Hd1 functions in the promotion of heading under short-day conditions and in inhibition under long-day conditions.     

Mapping quantitative trait loci associated with days to flowering and photoperiod sensitivity in rice (Oryza sativa L.)

This study was undertaken to identify putative quantitative trait loci (QTLs) associated with days to flowering (DTF) and photoperiod response in rice. A population of 143 recombinant inbred lines derived from a cross between CO39 and Moroberekan was grown under greenhouse conditions and exposed to two different photoperiod regimes. DTF of individual plants was evaluated under 10 h and 14 h day lengths, and loci associated with photoperiod sensitivity were identified based on the delay in flowering under the 14 h photoperiod (DTF at 14 h minus DTF at 10 h). An RFLP data set consisting of 127 markers provided the basis for the QTL analysis. Both single marker and interval analysis were used and interactions between putative QTLs were estimated based on two-way ANOVA. Out of 15 QTLs associated with DTF, only 4 were identified as influencing the response to photoperiod. Interactions between flowering QTLs indicated the complex nature of the control of flowering in rice. The effectiveness of using a single recombinant inbred population to study a variety of complex phenotypes is discussed in relation to practical plant breeding.     

Tweaking biological switches through a better understanding of bistability behavior

Many biological events are binary. The switch between mutually exclusive OFF to ON state in response to a stimulus is frequently mediated by a control circuit with a positive and/or a negative feedback. Such a system typically exhibits hysteresis with its switching ON and OFF stimulus levels dependent on the current state of the system. The system can be shown to be bistable both experimentally and mathematically. Work to synthesize such switches by combining natural or engineered components has begun to illustrate the potential of such control circuits in many areas of applications.     

The genetic basis of flowering time and photoperiod sensitivity in rapeseed (Brassica napus L.)

The objective of this study was to dissect the genetic control of days to flowering (DTF) and photoperiod sensitivity (PS) into the various components including the main-effect quantitative trait loci (QTLs), epistatic QTLs and QTL-by-environment interactions (QEs). Doubled haploid (DH) fines were produced from an F1 between two spring Brassica napus cultivars Hyola 401 and Q2. DTF of the DH lines and parents were investigated in two locations, one location with a short and the other with a long photoperiod regime over two years. PS was calculated by the delay in DTF under long day as compared to that under short day. A genetic linkage map was constructed that comprised 248 marker loci including SSR, SRAP and AFLP markers. Further QTL analysis resolved the genetic components of flowering time and PS into the main-effect QTLs, epistatic QTLs and QEs. A total of 7 main-effect QTLs and 11 digenic interactions involving 21 loci located on 13 out of the 19 linkage groups were detected for the two traits. 3 main-effect QTLs and 4 pairs of epistatic QTLs were involved in QEs conferring DTF. One QTL on linkage group (LG) 18 was revealed to simultaneously affect DTF and PS and explain for the highest percentage of the phenotypic variation. The implications of the results for B. napus breeding have been discussed.     

Moving towards a better understanding of chemotaxis

Eukaryotic cells are thought to move across supporting surfaces through a combination of coordinated processes: polarisation; extension of dynamic protrusions from a leading edge; adhesion-associated stabilisation of some protrusions; centripetal pulling against those leading adhesions; and de-adhesion at the rear. Gradients of extracellular ligands can be detected by cells and then used to guide them either towards the source (in the case of a chemoattractant) or away from the source (in the case of a chemorepellent)--such migration is termed chemotaxis. Recent work suggests that chemotaxis probably emerges from the ability of cells to spatially encode extracellular gradients of ligands, a process for which phosphoinositide 3'-kinase (PI3K) signals alone are insufficient, and to use that vectorial information to bias movement by enhancing the survival, and not the formation, of the protrusions that experience the greatest stimulation.     

Nutritional sub-fertility in the dairy cow: towards improved reproductive management through a better biological understanding

There has been a significant decline in the reproductive performance of dairy cattle in recent decades. Cows, take longer time to return to the oestrus after calving, have poorer conception rates, and show fewer signs of oestrus. Achieving good reproductive performance is an increasing challenge for the dairy producer. In this study we focus on understanding the overall biological phenomena associated with nutritional sub-fertility rather than the underlying multiplicity of physiological interactions (already described in a number of recent studies). These phenomena are important because they represent the natural adaptations of the animal for dealing with variations in the nutritional environment. They can also be used to monitor and modulate reproductive performance on-farm. There is an underlying trade-off between two aspects of reproduction: investment in the viability of the current calf and investment in future offspring. As the investment in, and viability of, the current calf is related to maternal milk production, we can expect that level of milk production per se has effects on subsequent reproductive performance (investment in future offspring). Lactating cows have a lower proportion of viable embryos, which are of poorer quality, than do non-lactating cows. The same applies to high- compared to medium-genetic merit cows. Another important biological property is the adaptive use of body reserves in support of reproduction. Orchestrated endocrine changes in pregnancy and lactation facilitate the deposition of body lipid during pregnancy and mobilisation in early lactation. When the cow fails to accumulate the reserves she needs to safeguard reproduction she delays committing to further reproductive investment. But how does the cow ‘know’ that she is failing in energy terms? We argue that the cow does this by ‘monitoring’ both the body fat mobilisation and body fatness. Excessive body fat mobilisation indicates that current conditions are worse than expected. Body fatness indicates the future ability of the cow to safeguard her reproductive investment is compromised. Both delay further reproductive commitment. The relationship between reproductive performance and; milk production as an index of maternal investment, body fatness as an index of ability to safeguard reproductive investment, and body fat mobilisation as an index of the current nutritional environment – are examined. Nutritional strategies that seek to modulate body mobilisation and the endocrine environment by use of glucogenic and lipogenic diets, and the use of in-line progesterone profiles to monitor reproductive status are then discussed in this biological context.     

Development of in vitro models for a better understanding of the early pathogenesis of Batrachochytrium dendrobatidis infections in amphibians

Batrachochytrium dendrobatidis, the causal agent of chytridiomycosis, is implicated in the global decline of amphibians. This chytrid fungus invades keratinised epithelial cells, and infection is mainly associated with epidermal hyperplasia and hyperkeratosis. Since little is known about the pathogenesis of chytridiomycosis, this study was designed to optimise the conditions under which primary keratinocytes and epidermal explants of amphibian skin could be maintained ex vivo for several days. The usefulness of the following set-ups for pathogenesis studies was investigated: a) cultures of primary keratinocytes; b) stripped epidermal (SE) explants; c) full-thickness epidermal (FTE) explants on Matrigel?; d) FTE explants in cell culture inserts; and e) FTE explants in Ussing chambers. SE explants proved most suitable for short-term studies, since adherence of fluorescently-labelled zoospores to the superficial epidermis could be observed within one hour of infection. FTE explants in an Ussing chamber set-up are most suitable for the study of the later developmental stages of B. dendrobatidis in amphibian skin up to five days post-infection. These models provide a good alternative for in vivo experiments, and reduce the number of experimental animals needed.     

Improving the validation of finite element models with quantitative full-field strain comparisons

The techniques used to validate finite element (FE) models against experimental results have changed little during the last decades, even though the traditional approach of using single point measurements from strain gauges has major limitations: the strain distribution across the surface is not captured and the accurate determination of strain gauge positions on the model surface is difficult if the 3D surface topography of the bone surface is not measured. The full-field strain measurement technique of digital speckle pattern interferometry (DSPI) can overcome these problems, but the potential of this technique has not yet been fully exploited in validation studies. Here we explore new ways of quantifying and visualising the variation in strain magnitudes and orientations within and between repeated DSPI measurements as well as between the DSPI measurements and FEA results. We show that our approach provides a much more comprehensive and accurate validation than traditional methods. The measurement repeatability and the correspondence between measured and predicted strains vary to a great degree within and between measurement areas. The two models used in this study predict the measured strain directions and magnitudes surprisingly well considering that homogeneous and isotropic mechanical properties were assigned to the models. However, the full-field comparisons also reveal some discrepancies between measured and predicted strains that are most probably caused by inaccuracies in the models' geometries and the degree of simplification of the modelled material properties.     

Cell biology as the basis of a better understanding of cancer

Clinicians will argue that cancer can only really receive the treatment that is needed through thorough understanding of medicine. However, even empirical approaches to therapy result in experimental analysis of the agencies involved on test cells, usually in culture. From the obverse perspective, cell biologists will argue that until we fully understand cell cycle regulation, tumour management will be too imprecise to make the best advances. A forum is needed whereby the fundamental studies on cells prior to, during and after transformation in vitro can be freely reported (open access) and discussed. The action of anticancer agents and cancer preventative substances can more easily be studied in vitro before the often excessive complexity of making similar studies in experimental and human cancers is tackled. Cancer Cell International is committed to providing such a forum. Ironically within a few months of launching this open access journal, Elsevier had much the same idea, and there one has to pay for the privilege of downloading vital papers in this biomedical field.     

Towards a better understanding of carotenoid metabolism in animals

Vitamin A derivatives (retinoids) are essential components in vision; they contribute to pattern formation during development and exert multiple effects on cell differentiation with important clinical implications. All naturally occurring vitamin A derives by enzymatic oxidative cleavage from carotenoids with pro-vitamin A activity. To become biologically active, these plant-derived compounds must first be absorbed, then delivered to the site of action in the body, and metabolically converted to the real vitamin. Recently, molecular players of this pathway were identified by the analysis of blind Drosophila mutants. Similar genome sequences were found in vertebrates. Subsequently, these homologous genes were cloned and their gene products were functionally characterized. This review will summarize the advanced state of knowledge about the vitamin A biosynthetic pathway and will discuss biochemical, physiological, developmental and medical aspects of carotenoids and their numerous derivatives.     

The sorghum photoperiod sensitivity gene, Ma3, encodes a phytochrome B.

The Ma3 gene is one of six genes that regulate the photoperiodic sensitivity of flowering in sorghum (Sorghum bicolor [L.] Moench). The ma3R mutation of this gene causes a phenotype that is similar to plants that are known to lack phytochrome B, and ma3 sorghum lacks a 123-KD phytochrome that predominates in light-grown plants and that is present in non-ma3 plants. A population segregating for Ma3 and ma3 was created and used to identify two randomly amplified polymorphic DNA markers linked to Ma3. These two markers were cloned and mapped in a recombinant inbred population as restriction fragment length polymorphisms. cDNA clones of PHYA and PHYC were cloned and sequenced from a cDNA library prepared from green sorghum leaves. Using a genome-walking technique, a 7941-bp partial sequence of PHYB, was determined from genomic DNA from ma3 sorghum. PHYA, PHYB, and PHYC all mapped to the same linkage group. The Ma3-linked markers mapped with PHYB more than 121 centimorgans from PHYA and PHYC. A frameshift mutation resulting in a premature stop codon was found in the PHYB sequence from ma3 sorghum. Therefore, we conclude that the Ma3 locus in sorghum is a PHYB gene that encodes a 123-kD phytochrome.     

Toward a better understanding of the regional causes of local community richness

Despite widespread acknowledgement that local ecological communities are profoundly shaped by regional-scale influences, including evolutionary and biogeographic processes, this perspective has yet to be widely incorporated into ecological research. Drawing on recent research, we propose four steps towards making regional influences a stronger part of research on the richness of local communities: (1) identifying the regional-scale causes of variation in species richness in the systems ecologists study; (2) testing for effects of regional richness on local richness, using improved observational and experimental analyses to overcome earlier problems; (3) simultaneously analysing environmental influences on regional and local species richness as well as the influence of regional richness on local richness and (4) considering the potential reciprocal effects of local processes on regional richness. In conclusion, we suggest some ways that similar approaches could be applied to other aspects of community structure beyond species richness.