Origin of cellular asymmetries in the pre-implantation mouse embryo: a hypothesis

The first cell fate decision during mouse development concerns whether a blastomere will contribute to the inner cell mass (ICM; which gives rise to the embryo proper) or to trophectoderm (TE; which gives rise to the placenta). The position of a cell within an 8- to 16-cell-stage embryo correlates with its future fate, with outer cells contributing to TE and inner cells to the ICM. It remains unknown, however, whether an earlier pre-pattern exists. Here, we propose a hypothesis that could account for generation of such a pre-pattern and which is based on epigenetic asymmetry (such as in histone or DNA methylation) between maternal and paternal genomes in the zygote.     

向日葵螟对不同向日葵品种的寄主选择性

通过田间选择性试验结合室内黑色素鉴定,研究向日葵螟Homoeosoma nebulellum Denis et Schiffermüller对35个不同向日葵品种的寄主选择性。向日葵螟对不同供试向日葵品种的选择性存在显著差异,选择性最强的是大黑片,其次是S47,再则是5135和RH316,选择性较弱的有T25和天葵503等18个品种,对TO12244和GT110等13个品种无选择性。寄主选择性可以用开花盛期的花盘被害率、每盘可见幼虫数、每盘虫粪指数与籽粒成熟期的籽粒被害率、籽粒被害虫情指数5个指标中的任何一个来评价。相关性分析表明,向日葵螟的寄主选择性与向日葵花盘直径呈显著正相关关系。     

向日葵籽实产量预测数学模型的研究

根据2年10个点次的田间试验结果建立了由数粒法、盘重法和盘径法预测向日葵籽实产量的回归数学模型,并根据1994年4个点次的产量实测结果对各模型的可靠性进行了验证．结果表明,三种方法建立的模型均有效、可靠．但在我国向日葵科研和生产实践中,以盘径法最为实用,建议推广应用．     

Seed yield,head characteristics and oil content in sunflower varieties as influenced by seeds from single and multiple headed plants under humid tropical conditions

Field trials were conducted during 2004 and 2005 to determine the effect of sowing seeds from plants with multiple heads and seeds from single headed plants of sunflower on seed yield, head characteristics and oil content of three widely grown open pollinated varieties (Funtua, Record and Isaanka) in the humid forest—savanna transition zone which is outside the current growing areas with a view to improving stability and sunflower productivity in this region. Seeds from multiple headed plants produced plants that flowered and matured 2–3 days later than plants from single headed plants. Apart from days to flowering in 2004, number of days to maturity and plant height were affected independently by variety and seed source factors. However, the seeds from single headed plants produced plants that recorded significantly (P < 0.01) higher head weight, head diameter, achene weight and number per head than plants from seeds of plants with multiple heads. Seed source had little effect on sunflower seed yield and oil content. However, Funtua produced significantly (P < 0.05) high seed yield (1956.0 kg ha^?1 ± 76.06) when seeds from plants with multiple heads were sown, while Isaanka recorded comparatively high seed yield from seeds of plants from either multiple (1221.0 kg ha^?1 ± 165.90) or single heads (1388.0 kg ha^?1 ± 135.84) and Record (1201.0 kg ha^?1 ± 96.97) when seeds from single headed plants were sown. Therefore, it is recommended that prospective sunflower growers who wish to cultivate Isaanka, can sow seeds from either the multiple or single head and preferably the multiple head for Funtua, and single head for Record.     

Development of avascularity during cartilage differentiation in the embryonic limb

The differentiation of cartilage and muscle in limb-bud mesenchyme has been interpreted by some investigators in terms of a vascular pre-pattern model. It has been argued that a pre-pattern of the early limb vasculature compartmentalises the mesenchyme into specific microenvironmental areas in which, depending on the oxygen tension and nutrient supply, cartilage or muscle will differentiate. However, recent analyses of the development and differentiation of blood vessels in limbs have shown that regional variations in vascularization develop co-incidentally with the earliest indication of cartilage formation or mesenchymal condensation. The simple model described in the present study suggests that the mechanical compression/tension forces generated by the condensing mesenchyme are sufficient to constrict and eventually close off the thin-walled undifferentiated vessels caught in the condensation foci, thus leading to the avascularity of cartilage rudiments. This view suggests that the vasculature has no major function in governing the pattern of cartilage differentiation.     

The genetic basis of a mutation that alters the floral symmetry in sunflower

The indeterminate inflorescence of sunflower (Helianthus annuus) is heterogamous with zygomorphic ray flowers in the outer whorl of the head and actinomorphic disc flowers arrayed in arcs radiating from the centre of the head. The Chrysanthemoides (Chry) mutant is characterised by a change of the radially symmetric corolla of tubular disc flowers into a monosymmetric ligulate‐like corolla. Zygomorphy is pronounced in the disc flowers placed on the peripheral whorls of inflorescences, while the monosymmetry is less marked toward the centre of the inflorescence. Although the Chry phenotype was one of first known morphological mutants in plants, studies on the genetic control of this trait are scarce and contradictory. Our results indicate that the Chry mutation is semidominant and exclude a maternal influence. Moreover, the data gathered in F₂, BC₁ and F₃ progenies support a genetic model involving one major locus and an unknown number of modifiers. The improved knowledge on genetic control of the Chry mutation should enhance the introduction of this trait in crossbreeding programmes designed to produce new varieties of ornamental sunflower.     

Morphometric and mating compatibility of Dectes texanus texanus (Coleoptera: Cerambycidae) from soybean and sunflower

The cerambycid Dectes texanus texanus LeConte that infests soybean, Glycine max (L.) Merr., is thought to be the same Dectes that damages sunflower, Helianthus annuus L. However, morphometric characteristics and mating compatibility between individuals from soybean and sunflower fields have not been assessed. Eight hundred eighty stalks of soybean and sunflower residues infested with Dectes were collected from Texas and Kansas. Outside stalk diameter of sunflower (22.6 mm) was 3.2 times greater than that of soybean. Diameters of tunnels by Dectes in sunflower and soybean were 7.0 and 3.4 mm, respectively. Widths of head capsules and pronotums were approximately 1.3 times greater for Dectes larvae from sunflower than soybean. Larval, pupal, and adult Dectes from sunflower were approximately 2.5 times heavier and 1.3 times longer than from soybean. Adults reared from residues of soybean and sunflower were paired to evaluate mating compatibility. Although individuals collected and reared from different crop residues differed significantly in size, percentage of mating success by Dectes from the two crops (26.2%) did not differ significantly from that by adults from the same kind of crop (34.9%). Results indicated that Dectes that infest soybean and sunflower are the same species and reconfirmed that farmers should not plant soybean and sunflower in rotation or in adjacent fields.     

Enhanced crop productivity and compatibility through intercropping of sesame and sunflower varieties

Field trials were conducted during 2002 and 2003 to determine the productivity and compatibility of the cropping systems obtained from intercropping varieties of sesame (E8, PBTil and 530-6-1) and sunflower (Funtua, Record and Isaanka) in the humid forest–savanna transition zone which is outside the current growing areas. Intercropping did not affect the number of branches per plant, number and weight of capsules per plant, weight of seeds per plant, 1000 seed weight or seed production efficiency (SPE) of all sesame varieties in both years, except SPE in 2003. In both years, intercropping sesame with sunflower varieties significantly reduced grain yield of PBTil and E8. However, 530-6-1 produced grain yield similar to the monocrop when intercropped with Record and Funtua in 2002 and 2003, and Record in 2003. In both years, intercropping significantly depressed the grain yield of the three sunflower varieties because of reduction in their head diameter, head weight, number and weight of seeds per head and lower number of plants per unit area relative to their monocrops. E8, 530-6-1 and PBTil intercropped with the three sunflower varieties recorded land equivalent ratio values in the range of 1.13–1.37, 1.32–1.46 and 1.22–1.35, respectively. Based on competitive ratio values, E8 demonstrated the greatest ability to compensate for intercrop competition with taller sunflower varieties. It was concluded that growers can successfully cultivate sesame (530-6-1 and PBTil) under intercropping with sunflower in the humid forest–savanna transition zone.     

Transductions for the Expression of Structural Pattern: Analysis in Sunflower

The transductions to initiate and propagate pattern were investigated in the sunflower head. The spiral pattern emerges as new florets form in regular centripetal sequence on the flat disc. The spiral lines of florets arise as rows of simple bumps. Each bump splits to become a small bract and a circular disc flower. This topographical progression was described by a scanning electron microscopic technique applied to living tissue. The suitability of various theories to explain the progression was examined. Because no periodic cell specialization was seen by scanning electron microscopy prior to pattern emergence, a mechanism that produces pattern in uniform tissue by spontaneous physical buckling (folding) was examined further. Key configurational changes of development were reproduced in models using the buckling assumptions. In further testing, a young head was physically constrained to cause it to grow as an oval. Pattern was modified as predicted. Unexpectedly, organ character changed as well. In localized regions, the folding was abnormal; the typical dyad floret, bract and flower, was replaced by a single large bract. This anomaly is known in mutants of sunflower; hence, the physical treatment induced a phenocopy. We concluded that (1) buckling is a strong candidate to be the process producing organ pattern, and (2) the accompanying topographical changes can be prerequisite to organ differentiation.     

Impact of planting dates on a seed maggot, Neotephritis finalis (Diptera: Tephritidae), and sunflower bud moth (Lepidoptera: Tortricidae) damage in cultivated sunflower

Neotephritisfinalis (Loew) (Diptera: Tephritidae), and sunflower bud moth, Suleima helianthana (Riley) (Lepidoptera: Tortricidae) are major head-infesting insect pests of cultivated sunflower (Helianthus annuus L.). Planting date was evaluated as a cultural pest management strategy for control of N. finalis and S. helianthana in several production regions of North Dakota during 2009 and 2010. Results of the nine site-year study revealed that late planting date (early to mid-June) reduced damage ratings and percentage of damaged heads for N. finalis compared with early planting dates (mid- to late May). Visual observations of adult N. finalis found that the majority of flies were found in the early planted sunflower (78.2%) compared with the late planted sunflower (21.8%). Late planting date also reduced the percentage of S. helianthana damaged heads compared with early planting dates. Yield losses were reduced with late planting date when populations of N. finalis and S. helianthana were high enough to cause damage. Results of this study showed that delayed planting is an effective integrated pest management strategy that can reduce head damage caused by N. finalis and S. helianthana and mitigate yield losses.     

Early development of the gut: new light on an old hypothesis

This review deals with the early development of the gut. It draws largely on information provided from the study of avian embryos. Evidence that concerns the early determination of the regional fate of the endoderm and mesoderm of the gut is reviewed. Gut endoderm can undergo a limited degree of differentiation from a remarkably early age when cultured in the absence of mesoderm and there is evidence that points to the establishment of a pre-pattern in the early mesoderm before the genes responsible for patterning in gut are active. Initially, at least at cranial levels, those parts of the mesoderm and endoderm that are in contact are not those parts that will ultimately be in apposition; the consequence of this for any signalling between these layers is considered. In the light of the above information, the probable role of mesenchyme in gut development is re-examined.     

Specific dynamic action in the sunflower star, Pycnopodia helianthoides

The effects of meal size and meal type on specific dynamic action (SDA) were investigated in a large, active asteroid, the sunflower star, Pycnopodia helianthoides. When the sunflower stars were fed clam flesh totalling 5%, 10%, or 20% of their body weight there was a step-wise increase in the scope, time to peak oxygen consumption, duration of the response and total SDA. The change in the rate of oxygen consumption was slower than other organisms, and oxygen uptake remained elevated for over 12 d following consumption of the largest meal. There were also differences in the characteristics of the SDA if sunflower stars consumed a whole clam versus the shucked flesh of a clam. The time to reach peak oxygen consumption was greater for sunflower stars consuming a whole clam. This occurred because the clam had to be opened before they could digest the flesh; a smaller initial peak comprising 3.5% of the total SDA represented the energy require to open the clam valves. When the sunflower stars were fed different prey items (e.g. butter clam, purple urchin and herring) of similar wet organic mass, there was no difference in the time to peak, peak oxygen uptake or total SDA despite the fact that the prey items differed in protein, lipid and caloric content. There was an increased duration for which oxygen uptake remained elevated for sea stars that consumed the urchin meal. Five of the seven sunflower stars that consumed urchins exhibited a smaller second peak in oxygen uptake, totalling approximately 8.5% of the SDA energy budget. This likely represented the energy required to eject the urchin test from the stomach. Although the sunflower star is much larger and more active than other sea stars, it displayed similar SDA responses to other members of the Asteroidea, indicative of the low metabolic rate of this class.     

Selection and estimation of the heritability of sunflower (Helianthus annuus) pollen collection behavior in Apis mellifera colonies

We selected honey bee colonies (Apis mellifera L.) with a high tendency to collect sunflower pollen and estimated the heritability of this trait. The percentage of sunflower pollen collected by 74 colonies was evaluated. Five colonies that collected the highest percentages of sunflower pollen were selected. Nineteen colonies headed by daughters of these selected queens were evaluated for this characteristic in comparison with 20 control (unselected) colonies. The variation for the proportion of sunflower pollen was greater among colonies of the control group than among these selected daughter colonies. The estimated heritability was 0.26 +/- 0.23, demonstrating that selection to increase sunflower pollen collection is feasible. Such selected colonies could be used to improve sunflower pollination in commercial fields.     

Formation of cone mosaic of zebrafish retina.

In the zebrafish retina, four types of cone photoreceptor cells (or cones) with different sensitive frequencies are arranged in a regular pattern, named "cone mosaic". A pair of small cones, one sensitive to red and the other sensitive to green, is in close contact and forms a "double cone". In addition, there are two kinds of single cones, sensitive to blue and to UV, respectively. We study characteristics of cell-differentiation rules that realize stable formation of cone mosaic. Assumptions are: undifferentiated cells are arranged in a regular square lattice, and they are one of the three types (B, U, and D cells). A D cell has two parts (G and R-parts) and takes one of the four directions. The cells change their cell type and orientation following a continuous-time Markovian chain. The state transtion occurs faster if it increases the stabilities of the focal cell, in which the stability is the sum of affinities with neighboring cells. After the transient period, the system may reach a stable pattern (pre-pattern). The pattern becomes fixed later when the cells are fully differentiated in which B cells, U cells, and D cells become blue-sensitive, UV-sensitive, and double cones, respectively. We search for the combinations of affinities between cell states that can generate the same cone mosaic patterns as in zerbrafish retina. Successful transition rules give (1) zero or small affinity with the pairs of cell states that are absent in the zebrafish cone mosaic (lambda(UR), lambda(BG)and the contact of two cells of the same type); (2) a large affinity between a part of D cells and a non-D cell (lambda(UG)and lambda(BR)); and (3) a positive affinity of an intermediate magnitude between two non-D cells (lambda(BU)) and between two parts of D cells (lambda(GR)). The latter should be of a magnitude of about 60-90% of the former. The time needed to form a regular pattern increases with the lattice size if all the cells start pre-pattern formation simultaneously. However, the convergence time is shortened considerably if the pre-pattern formation occurs only in a narrow band of morphogenetic cell layer that sweeps from one end of the lattice to the other.     

Metamorphosis ofHydractinia echinata Insights into pattern formation in Hydroids

Summary Hydractinia echinata is a marine, colony-forming coelenterate. Fertilized eggs develop into freely swimming planula larvae, which undergo metamorphosis to a sessile (primary) polyp. Metamorphosis can be triggered by means of certain marine bacteria and by Cs⁺. Half a day after this treatment a larva will have developed into a polyp. The induction of metamorphosis can be prevented by addition of inhibitor I, a substance partially purified from tissue ofHydra. The larvae ofH. echinata also appear to contain this substance. Inhibitor I appliedafter the onset of metamorphosis blocks its continuation as long as it remains in the culture medium. Cs⁺ applied within the same period of time also blocks the continuation of metamorphosis. However, these two agents have opposite effects on the body pattern of the resultant polyps. The experiments indicate that application of Cs⁺ triggers the generation of the pre-pattern. Inhibitor I appears to be a factor of this prepattern. A model is proposed which describes the basic features of head and foot/stolon formation not only forHydractinia but also for other related hydroids.     

Models for the morphogenesis of the molluscan shell

We give a review of current theories of morphogenesis of both the general coiling and the ornamentation of molluscan shells. These two aspects of shell growth are closely connected, as ornamentation is primarily due to local perturbations of the general apertural growth field controlling coiling. Also, a new, generalized, free-form apertural growth map model is presented in this paper, illustrating some aspects of the regulation of logarithmic spiral growth. This model is used to simulate the formation of megastriae in ammonoids. We emphasize the importance of damaged specimens and how they regenerated, as illustrated with examples from ammonoids. The phenomenon of ornamental compensation can be explained by a mechanism involving a pre-pattern in the mantle. However, simple reaction-diffusion models for ornamental pattern formation should be regarded only as useful abstractions.     

Models for pattern formation in somitogenesis: a marriage of cellular and molecular biology

Somitogenesis, the process by which a bilaterally symmetric pattern of cell aggregations is laid down in a cranio-caudal sequence in early vertebrate development, provides an excellent model study for the coupling of interactions at the molecular and cellular level. Here, we review some of the key experimental results and theoretical models related to this process. We extend a recent chemical pre-pattern model based on the cell cycle Journal of Theoretical Biology 207 (2000) 305-316, by including cell movement and show that the resultant model exhibits the correct spatio-temporal dynamics of cell aggregation. We also postulate a model to account for the recently observed spatio-temporal dynamics at the molecular level.     

Partial hybridization in wide crosses between cultivated sunflower and the perennial Helianthus species H. mollis and H. orgyalis

To obtain introgressed sunflower lines with improved disease resistance, interspecific crosses were performed with foreign perennial species. We report on several unusual features displayed by these hybrid plants. The methods used to produce the kernels affected yield and genotypes of progeny. Phenotypic traits and DNA markers were investigated in 97 plants derived from cross-pollination between annual diploid cultivated sunflower (Helianthus annuus) and the perennial diploid species H. mollis or H. orgyalis, and the reverse reciprocal crosses. The level of hybridization in progeny was determined using RAPD and RFLP markers. Hybridization was performed by leaving embryos to develop normally on the head (classical crossing) or using embryo rescue. All observed plants derived from H. mollis were diploid (2n = 34). Phenotypes were predominantly similar to the female when cultivated sunflower was the female parent. Progeny from crosses using a wild species as the female parent resembled that parent. Thus, reciprocal crosses led to different progeny. F1 sister progeny shared different sets of molecular markers representing a few of those of the wild species used as the pollen donor. Our results indicate mechanisms leading to the unusual event of partial hybridization. Possible mechanisms behind these unusual events and their possible impact on evolution are discussed.