Relative balance of the cost and benefit associated with carnivory in the tropical Utricularia foliosa

Investment by bladderwort (Utricularia foliosa) in carnivory, in terms of total C and N of bladders per leaf, was estimated in places with different nutrient concentrations from the Yahuarcaca Creek in the Colombian Amazon. The aims were to determine whether nutrient limiting conditions stimulate the investment in carnivory, and the relative balance between C and N invested in carnivory versus C and N obtained from prey. There were no significant differences either for phosphate (PO₄³⁻) concentration or for ammonia (NH₄⁺) concentration among five sampling areas, along approximately 5 km long stretch of the creek, with a pooled mean ± S.D. of 0.19 ± 0.06 and 8.6 ± 3.0 μM, respectively. However, there were significant differences in the nitrate (NO₃⁻) concentration ranging from 0.6 to 2.5 μM. Total C and N of bladders per leaf increased with decreasing NO₃⁻. This corroborates the hypotheses that the carnivorous plant U. foliosa optimises its investment in carnivory according to nutrient availability in the water, and that N is a limiting factor that stimulates the investment in carnivory. The numbers of prey per bladder were also higher under NO₃⁻ limitation, thus enhancing the input of nutrients toward the plant through the bladders. The ratio of total C of prey captured/total C invested in bladders was always lower than 1. However, the efficiency of N was higher since when NO₃⁻ concentration was lower than 1 μM, the ratio of total N of prey captured/total N invested in bladders ranged between 0.97 and 1.67.     

Genetic characterization of apospory in tetraploid Paspalum notatum based on the identification of linked molecular markers

Tetraploid Paspalum notatum (bahiagrass) is a valuable forage grass with aposporous apomictic reproduction. In a previous study, we showed that apospory in bahiagrass is under the control of a single dominant gene with a distorted segregation ratio. The objective of this work was to identify molecular markers linked to apospory in tetraploid P. notatum and establish a preliminary syntenic relationship with the genomic region associated with apospory in P. simplex. A F₁ population of 290 individuals, segregating for apospory, was generated after crossing a completely sexual plant (Q4188) with a natural aposporous apomictic plant (Q4117). The whole progeny was classified as sexual or aposporous by embryo sacs analysis. A bulked segregant analysis was carried out to identify molecular markers co-segregating with apospory. Four hundred RAPD primers, 30 AFLP primers combinations and 85 RFLP clones were screened using DNA from both parental genotypes and aposporous and sexual bulks. Linkage analysis was performed with cytological and genetic information from the complete progeny. Cytoembryological analysis showed 219 sexual and 71 aposporous F₁ individuals. Seven different molecular markers (2 RAPD, 4 AFLP and 1 RFLP) were found to be completely linked to apospory. The RFLP probe C1069, mapping to the telomeric region of the long arm of rice chromosome 12, was one of the molecular markers completely linked to apospory in P. notatum. This marker had been previously associated with apospory in P. simplex. A preliminary map of the chromosome region carrying the apospory locus was constructed.     

Effect of pollen source and pollen ploidy on endosperm formation and seed set in pseudogamous apomictic Paspalum notatum

 It is generally accepted that most angiosperms require an accurate balance between maternal and paternal genome contribution for endosperm development. The endosperm balance number (EBN) hypothesis postulates that each species has an effective number which must be in a 2:1 maternal to paternal ratio for normal endosperm development and seed formation. The aim of this work was to investigate the effect of different sources and ploidy levels of pollen donors on endosperm formation and seed production of aposporous tetraploid (2n=4×=40) Paspalum notatum. Hand-emasculated spikelets of an apomictic 4× plant were dusted with pollen of 2×, 4×, 5×, 6× and 8× races of the same species; 3× and 4× races of a phylogenetically closely related species, P. cromyorrhizon; and 2× and 4× races of P. simplex, a species of a different subgenus. Experiments including self-pollination as well as emasculation without pollination were conducted for controls. Results indicated that apomictic 4×P. notatum is a pseudogamous species with effective fertilization of the two unreduced (2n) polar nuclei by a reduced (n) sperm. Endosperm development and seed production occurred independently of the species or the ploidy level of the pollen donor. However, seed germination rates were significantly lower than in the self-pollinated control when the pollen donor was 3×P. cromyorrhizon or 2× and 4×P. simplex. Aposporous embryo sacs in Paspalum contribute to endosperm formation with two unreduced (2n) polar nuclei, while the male contribution is the same as in sexual plants (n). Since sexual Paspalum plants fit the EBN hypothesis, the EBN insensitivity observed in apomictic plants might be a prerequisite for the spread of pseudogamous apomixis. The EBN insensitivity could have arisen as an imprinting consequence of a high maternal genome contribution. Received: 20 February 1998 / Revision accepted: 21 October 1998     

Prediction of Oncogenic Interactions and Cancer-Related Signaling Networks Based on Network Topology

Cancer has been increasingly recognized as a systems biology disease since many investigators have demonstrated that this malignant phenotype emerges from abnormal protein-protein, regulatory and metabolic interactions induced by simultaneous structural and regulatory changes in multiple genes and pathways. Therefore, the identification of oncogenic interactions and cancer-related signaling networks is crucial for better understanding cancer. As experimental techniques for determining such interactions and signaling networks are labor-intensive and time-consuming, the development of a computational approach capable to accomplish this task would be of great value. For this purpose, we present here a novel computational approach based on network topology and machine learning capable to predict oncogenic interactions and extract relevant cancer-related signaling subnetworks from an integrated network of human genes interactions (INHGI). This approach, called graph2sig, is twofold: first, it assigns oncogenic scores to all interactions in the INHGI and then these oncogenic scores are used as edge weights to extract oncogenic signaling subnetworks from INHGI. Regarding the prediction of oncogenic interactions, we showed that graph2sig is able to recover 89% of known oncogenic interactions with a precision of 77%. Moreover, the interactions that received high oncogenic scores are enriched in genes for which mutations have been causally implicated in cancer. We also demonstrated that graph2sig is potentially useful in extracting oncogenic signaling subnetworks: more than 80% of constructed subnetworks contain more than 50% of original interactions in their corresponding oncogenic linear pathways present in the KEGG PATHWAY database. In addition, the potential oncogenic signaling subnetworks discovered by graph2sig are supported by experimental evidence. Taken together, these results suggest that graph2sig can be a useful tool for investigators involved in cancer research interested in detecting signaling networks most prone to contribute with the emergence of malignant phenotype.     

Ploidy effects on the relationship between floral phenotype,reproductive investment,and fitness in an autogamous species complex

Premise

The relationships between reproductive investment, phenotype, and fitness have been broadly studied in cross-pollinated plants in contrast to selfing species, which are considered less interesting in this area because they are supposed to be a dead end in any evolutionary pathway. Still, selfing plants are unique systems to study these questions since the position of reproductive structures and traits related to flower size play an important role in female and male pollination success.

Methods

Erysimum incanum s.l. is a selfing species complex that has three levels of ploidy (diploids, tetraploids, and hexaploids) and traits that are typically associated with the selfing syndrome. Here, we used 1609 plants belonging to these three ploidies to characterize the floral phenotype and spatial configuration of reproductive structures, reproductive investment (pollen and ovule production), and plant fitness. Then, we used structural equation modelling to analyze the relationship between all these variables across ploidy levels.

Results

An increase in ploidy level leads to bigger flowers with anthers exserted farther and more pollen and ovules. In addition, hexaploid plants had higher absolute values for herkogamy, which is positively correlated with fitness. Ovule production significantly mediated the natural selection acting on different phenotypic traits and pollen production, a pattern that is maintained across ploidies.

Conclusions

The changes in floral phenotypes, reproductive investment, and fitness with ploidy level suggest that genome duplication can be a driver for transitions in reproductive strategy by modifying the investment in pollen and ovules and linking them with plant phenotype and fitness.     

Short-term manganese pretreatment partially protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that induces parkinsonism in human and non-human primates. Its mechanism of action is not fully elucidated.Recently, the participation of trace metals, such as manganese, on its neurotoxic action has been postulatted. In this work, we studied the effect of manganese administration on the neurochemical consequences of MPTP neurotoxic action. Male Swiss albino mice were treated with manganese chloride (MnCl₂ ·4H₂O; 0.5 mg/ml or 1.0 mg/ml of drinking water) for 7 days, followed by three MPTP administrations (30 mg/Kg, intraperitoneally). Seven days after the last MPTP administration, mice were sacrificed and dopamine and homovanillic acid contents in corpus striatum were analyzed. Striatal concentration of dopamine was found increased by 60% in mice pretreated with 0.5 mg/ml and 52% in the group treated of 1.0 mg/ml as compared versus animals treated with MPTP only. Hornovanillic acid content in both groups treated with manganese was the same as those in control animals. The results indicate that manganese may interact with MPTP, producing an enhancement of striatal dopamine turnover, as the protective effect of manganese was more pronounced in the metabolite than in the neurotransmitter.     

Quinolinic acid is a potent lipid peroxidant in rat brain homogenates

In this study, we describe the lipoperoxidative effect of quinolinic acid (QUIN) in vitro. The formation of thiobarbituric acid reactive products (TBA-RP), an index of lipid peroxidation, was measured in rat brain homogenates after incubation at 37°C for 30 min in the presence of QUIN and some structurally and metabolically related compounds such as Kynurenine, Kynurenic acid, Glutamate, Aspartate and Kainate. Concentrations of QUIN in the range of 20 to 80 M increased lipid peroxidation in a concentration-dependent manner from about 15% to about 50%. Kynurenic acid, a compound metabollically related to QUIN that can block its neurotoxic actions in vivo, also inhibited completely the QUIN-induced TBA-RP formation in our system. Lipid fluorescent material, another index of lipid peroxidation was also found increased by 49% after incubation with 40 M QUIN. It is concluded that lipid peroxidation may be a damaging process involved in the neurotoxicity of QUIN.     

Quantitation and characterization of the microtubule associated MAP2 in porcine tissues and its isolation from porcine (PK15) and human (HeLa) cell lines

A radioimmunoassay developed for the microtubule associated protein MAP₂ shows that this protein, or related polypeptides are present in all the porcine tissues studied. Nervous tissues (brain, 11 μg MAP₂/mg protein; cerebellum, 9.7 μg MAP₂/mg protein) contain much higher levels of MAP₂ than non-nervous tissues (kidney, 104 ng MAP₂/mg protein; lung 89 ng MAP₂/mg protein; spleen 66 ng MAP₂/mg protein; thyroid 21 ng MAP₂/mg protein; liver 9.7 ng MAP₂/mg protein). A heat resistant protein doublet of 300,000 with the ability to promote microtubule polymerization has been purified from pig kidney cells by affinity chromatography using MAP₂ antibodies. Using a similar purification method a protein of 200,000 daltons has been isolated from Hela cells.     

Assessing species traits and landscape relationships of the mammalian carnivore community in a neotropical biological corridor

Mammalian carnivores play an important role in regulating food webs and ecosystems. While many carnivore populations are facing various threats such as habitat loss and fragmentation, poaching, and illegal trade, others have adapted to human-dominated landscapes. Information about Neotropical carnivore communities in particular is limited, especially in disturbed landscapes. We conducted a camera trap survey at 38 sites across the San Juan–La Selva Biological Corridor in Costa Rica to assess occupancy and detection probabilities of the carnivore community. We developed hypotheses within a likelihood-based framework in order to determine the landscape features and species traits (diet and size) that influenced their occupancy. We detected nine of the 13 native carnivores predicted to occur in the corridor. When modeled separately, each species responded to land cover changes differently, suggesting no strong community-wide predictors of occupancy. We then modeled three separate guilds within the carnivore community: omnivorous mesopredators, obligate carnivorous mesopredators, and apex predators. These community guild models revealed a negative relationship between omnivorous mesopredators and increasing forest and tree plantation cover, suggesting omnivores utilize forest fragments and edge habitats in agricultural landscapes. Obligate carnivorous mesopredator models did not reveal any strong habitat relationships, but landscape effects tended to contradict our a priori predictions. Apex predators were positively associated with increasing forest and tree plantation cover, protected areas, and increasing distances to villages. Alarmingly, apex predators and obligate carnivorous mesopredators were generally rare within the biological corridor. A lack of top-down control alone might result in heightened occupancy for all mesopredators, but because the community is dominated by omnivorous species, bottom-up release from human-induced land cover changes and resource provision may better explain their high occupancy.