Assessment of the allelochemical activity of Ostreopsis cf. ovata and the ovatoxins towards competitive benthic microalgae

Aquatic Ecology - Recurrent blooms of the toxic dinoflagellate Ostreopsis cf. ovata are frequently reported in the Northwestern Mediterranean Sea. The impact of these proliferations on other...     

Grass consensus STS markers: an efficient approach for detecting polymorphism in Lolium

For ryegrass and many forage crops, characterization of varieties is often difficult for two reasons: few of discriminant morphological traits and a great within-varieties variation. Futhermore, few molecular markers are publicly accessible. In this paper we describe two approaches for the development of 42 sequence-tagged-site (STS) markers. Firstly, 14 STS markers were developed from Lolium sequences found in data bases. Secondly, 28 STS markers were developed from sequences found in related species of Gramineae. Out of 42 STS markers developed, 85.8% yielded successfull amplification and 62% revealed a high level of polymorphism with an average of five alleles per locus. The analysis of amplicons reveals a high STS marker specificity, a high conservation in gene structure and a strong intron sequence homology between allelic forms. Moreover, the majority of the STS markers can be considered as "universal markers" because 81% of these STS markers amplified successfully across 20 related grass species. These results permit us to consider the use of these markers in synteny studies.Communicated by G. Wenzel     

Piecing together the timetable for visual transduction with transgenic animals

Transgenic mice bearing null or functional mutations are being used to define the roles of specific elements in phototransduction and also to time the molecular interactions. Genetic manipulation of the collision frequency between rhodopsin and transducin molecules identified this parameter as rate-limiting for the photoresponse onset. Genetic interference with rhodopsin phosphorylation and arrestin binding, transducin shut-off and calcium feedback has revealed their respective roles in shaping the response waveform. The timetable for all of these molecular events determines the amplitude, kinetics and reproducibility of the photoresponse.     

Selection in the making: a worldwide survey of haplotypic diversity around a causative mutation in porcine IGF2

Domestic species allow us to study dramatic evolutionary changes at an accelerated rate due to the effectiveness of modern breeding techniques and the availability of breeds that have undergone distinct selection pressures. We present a worldwide survey of haplotype variability around a known causative mutation in porcine gene IGF2, which increases lean content. We genotyped 34 SNPs spanning 27 kb in 237 domestic pigs and 162 wild boars. Although the selective process had wiped out variability for at least 27 kb in the haplotypes carrying the mutation, there was no indication of an overall reduction in genetic variability of international vs. European local breeds; there was also no evidence of a reduction in variability caused by domestication. The haplotype structure and a plot of Tajima's D against the frequency of the causative mutation across breeds suggested a temporal pattern, where each breed corresponded to a different selective stage. This was observed comparing the haplotype neighbor-joining (NJ) trees of breeds that have undergone increasing selection pressures for leanness, e.g., European local breeds vs. Pietrain. These results anticipate that comparing current domestic breeds will decisively help to recover the genetic history of domestication and contemporary selective processes.     

Abnormal sympathoadrenal development and systemic hypotension in PHD3-/- mice

Cell culture studies have implicated the oxygen-sensitive hypoxia-inducible factor (HIF) prolyl hydroxylase PHD3 in the regulation of neuronal apoptosis. To better understand this function in vivo, we have created PHD3(-/-) mice and analyzed the neuronal phenotype. Reduced apoptosis in superior cervical ganglion (SCG) neurons cultured from PHD3(-/-) mice is associated with an increase in the number of cells in the SCG, as well as in the adrenal medulla and carotid body. Genetic analysis by intercrossing PHD3(-/-) mice with HIF-1a(+/-) and HIF-2a(+/-) mice demonstrated an interaction with HIF-2alpha but not HIF-1alpha, supporting the nonredundant involvement of a PHD3-HIF-2alpha pathway in the regulation of sympathoadrenal development. Despite the increased number of cells, the sympathoadrenal system appeared hypofunctional in PHD3(-/-) mice, with reduced target tissue innervation, adrenal medullary secretory capacity, sympathoadrenal responses, and systemic blood pressure. These observations suggest that the role of PHD3 in sympathoadrenal development extends beyond simple control of cell survival and organ mass, with functional PHD3 being required for proper anatomical and physiological integrity of the system. Perturbation of this interface between developmental and adaptive signaling by hypoxic, metabolic, or other stresses could have important effects on key sympathoadrenal functions, such as blood pressure regulation.     

Dugong grazing and turtle cropping: grazing optimization in tropical seagrass systems?

Grazing by dugongs and cropping by green turtles have the capacity to alter the subsequent nutritional quality of seagrass regrowth. We examined the effects of simulated light and intensive grazing by dugongs and cropping by turtles on eight nutritionally relevant measures of seagrass chemical composition over two regrowth periods (short-term, 1–4 months; long-term, 11–13 months) at two seagrass communities (a mixed species community with Zostera capricorni, Halophila ovalis, Halodule uninervis, Cymodocea rotundata and C. serrulate; and a monospecific bed of Halodule uninervis) in tropical Queensland, Australia. The concentrations of organic matter, total nitrogen, total water-soluble carbohydrates, total starch, neutral detergent fiber, acid detergent fiber, acid lignin, as well as the in vitro dry matter digestibility (IVDMD) were measured in the leaves and below-ground parts of each species using near-infrared reflectance spectroscopy (NIRS). Regrowth of preferred species such as H. ovalis and H. uninervis from simulated intensive dugong grazing after a year exhibited increased (by 35 and 25%, respectively, relative to controls) whole-plant N concentrations. Similarly, regrowth of H. ovalis from simulated turtle cropping showed an increase in the leaf N concentration of 30% after a year. However, these gains are tempered by reductions in starch concentrations and increases in fiber. In the short-term, the N concentrations increased while the fiber concentrations decreased. These data provide experimental support for a grazing optimization view of herbivory in the tropical seagrass system, but with feedback in a different manner. Furthermore, we suggest that in areas where grazing is the only major source of natural disturbance, it is likely that there are potential ecosystem level effects if and when numbers of dugongs and turtles are reduced.     

Genotypic and environmental variations in root morphology in rice genotypes under upland field conditions

Improving the water capturing capacity of its large and deep root system is required to stabilize the yield of upland rice in drought-prone areas in the tropics. For the improvement of the root system through breeding and soil management, it is critical to understand the relative importance of genotypic and environmental effect and their interaction on the root development under various soil conditions and agronomic management. This study aimed to quantify and characterize the effect of genotype and environment, soils and N application levels (0 and 90 kg N ha^–1) in the variations of the traits related to the size and distribution of the root system at the flowering stage using 11 rice genotypes in upland fields in southern Luzon in the Philippines. The results indicated that, among the root traits, the genotypic factor accounted for the largest portion of variation for the number of nodal roots, specific root weight (SRW), and R/S ratio, whereas the environmental effect was relatively large for deep root length ratio (DRR) and total root dry weight (RDW). Especially, the DRR, the ratio of root length at deeper than 30 cm per unit area to the RDW, was strongly affected by the site. Nitrogen application increased RDW without a substantial change in the R/S ratio and DRR. On the other hand, significant genotypic variations of RDW and DRR were obtained, which may imply the opportunity for the genetic improvement. Japonica upland varieties showed a large RDW (90–111 g m^–2) associated with high R/S ratio (0.18–0.23) and a high SRW (0.26–0.27 mg cm^–1), whereas aus (Dular) and indica (Vandana) upland varieties had a large DRR (12.5–13.8 m g^–1) with a medium R/S ratio (0.14–0.17), suggesting an efficient formation of a deep root system with a limited biomass allocation to the roots. In addition, the analysis of G × E interaction term for RDW by an Additive Main Effects and Multiplicative Interaction (AMMI) model indicated that the response to soil conditions also differed between these groups. This indicated that proper deployment of genotype to the given soil conditions is also important to maximize the expression of genotypic potentials.