The Effect of Vanadate on Phosphate Transport in Aged Potato Tuber Tissue 2Solarium tuberosum)

The effect of orthovanadate on the uptake of phosphate by agedpotato tuber tissue was investigated to study the relationshipwith plasma membrane ATPase activity. Vanadate inhibited therate of phosphate uptake by aged discs with a maximum effectat 500 µM (58% inhibition). When vanadate was added tothe ageing medium for 24 h, the subsequent rate of phosphateuptake was also markedly decreased (68% inhibition). The resultsshow that the inhibition by vanadate was not due to enhancedleakage of phosphate nor to a non-specific toxic effect. Furthermore,complementary experiments with erythrosin B and molybdate wereconsistent with the hypothesis that vanadate acts specificallyon the plasma membrane ATPase and that this enzyme is involvedin maintaining the driving force for active uptake of phosphate(via co-transport with protons) by storage cells of potato tubers. Key words: Proton-phosphate co-transport, vanadate, plasma membrane ATPase, unloading     

Population structure in Mediterranean islands and risk of genetic invasion in Culexpipiens L. (Diptera: Culicidae)

The mosquito Culex pipiens is subjected to organophosphate treatments in both Corsica and southern Sardinia, but the resistance gene A2-B2, which is currently in a worldwide expansion, has only reached Sardinia. In order to understand this situation, the genetic structure of populations sampled in Sardinia and Corsica was assessed using 15 isozymes. Two loci (HK1 and HK2) were not taken into account because of the possibility of selection. For trie other loci, statistical independence was not rejected for all possible pairs, and no deviation from Hardy-Weinberg expectations was apparent. Low but significant genie differentiation was present between Corsica and Sardinia, as well as between northern and southern Sardinia, despite a large number of effective migrants per generation. These results are discussed in the context of the high probability of extinction/recolonization of breeding sites, the flight migration ability of this mosquito, and the pleiotropic cost of insecticide resistances genes. It is concluded that A2-B2 resistance is unlikely to reach Corsica from southern Sardinia, unless accidental human transportation occurs.     

Cleavage Furrow Establishment--A Preliminary to Cylindrical Shape Change

The predictable pattern of cell shape changes characterizinganimal development must be a consequence of control mechanismsthat are at least analogous to those operating in dividing cells.When cells change shape by an internal mechanism, it is impliedthat they also contain systems that will activate and deactivatethe mechanism, localize it within the cell, insure proper timing,and impart the proper vectoral qualities. Experimental investigationsdesigned to elucidate similar processes in dividing cells revealthat the physical mechanism that accomplishes cytokinesis isestablished at or near the equatorial cell surface by the mitoticapparatus. The process is completed by late metaphase or earlyanaphase. In cleaving eggs a pair of asters can substitute forthe intact mitotic apparatus. The nature of the stimulus whichapparently passes from the mitotic apparatus to the surfaceis presently unknown. It moves toward the surface at about 6microns per minute and requires about 1 minute to establishthe mechanism. The resulting equatorial contractile activityis initially isotropic but becomes anisolropic at the beginningof visible constriction.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.     

Microsatellite markers developed from Theobroma cacao L. expressed sequence tags

Theobroma cacao L. expressed sequence tags (ESTs) were converted into useful genetic markers for fingerprinting individuals and genetic linkage mapping. Primers were designed to microsatellite‐containing ESTs. Twenty‐two T. cacao accessions, parents of various mapping populations segregating for disease resistance and crop yield characteristics, were tested. Twenty‐seven informative loci were discovered with 26 primer pairs. The number of detected alleles ranged from two to 11 and averaged 4.4 per locus. All 27 markers could be mapped into at least one of the existing F₁ or F₂ populations segregating for agronomically important traits.     

Role of terpenes from aphid-infested potato on searching and oviposition behavior of Episyrphus balteatus

To cope with pathogen and insect attacks, plants develop different mechanisms of defence, in both direct （physical and chemical） and indirect ways （attractive volatiles to entomophagous beneficials）. Plants are then able to express traits that facilitate ＂top-down＂ control of pests by attracting herbivore predators. Here we investigate the indirect defence mechanism of potato plants by analyzing the volatile patterns of both healthy and aphid- infested plants. Important changes in the emitted terpene pattern by the Myzus persicae infested host plant were observed. Using Solid Phase MicroExtraction （SPME） and GC-MS, the （E）-fl-farnesene （EBF） appeared to be emitted by aphid-infested potato and not by healthy plants. To assess the infochemical role of these volatile releases after aphid damage on the aphidophagous predators Episyrphus balteams, the hoverfly foraging behavior was assessed using the Observer 5.0 software （Noldus, Wageningen, The Netherlands）. Aphidfree potato plants were also used as a control volatile source in the predator behavioral study. While aphid-infested plants induced efficient searching and acceptation behaviors leading to egg-laying, no kairomonal effect of healthy potato plants was observed, leading to longer immobility durations and shorter searching periods in the net cage. High oviposition rate of E. balteatus was observed when aphid-infested potato was used （mean of 48.9 eggs per laying and per female）. On the other hand, no egg was produced by the hoverfly on healthy aphid-free plants. The E. balteatus foraging and reproductive behaviors according to the volatile emission from aphid-infested plants are discussed in relation to the potential use of active infochemical molecules in integrated aphid pest management.     

Testing the Adaptive Significance of Acclimation: A Strong Inference Approach

Acclimation is a common phenotypic response to environmentalchange. Acclimation is often thought to enhance performanceand thus to be adaptive. This view has recently been formalizedas the "Beneficial Acclimation Hypothesis" and predicts thatindividuals acclimated to one environment perform better inthat environment than do individuals acclimated to a differentenvironment. Although Beneficial Acclimation is appealing andwidely supported, recent studies with E. coli and Drosophilahave challenged its general validity. Although these challengescould be dismissed as mere exceptions, they encourage a re-evaluationof the adaptive significance of acclimation. Our philosophicalapproach differs from that of most previous studies of acclimation,in which the prediction derived from a Beneficial Acclimationperspective (e.g., heat tolerance is positively correlated withacclimation temperature) is tested against the null hypothesis("single hypothesis approach"). Instead, we follow Huey andBerrigan (1996) in advocating a strong inference approach (sensuPlatt, 1964), which recognizes that Beneficial Acclimation isactually one of a set of competing hypotheses that make differentpredictions as to how developmental temperature influences thethermal sensitivity of adults ("developmental acclimation").Using this perspective, Huey and Berrigan proposed a factorialexperimental design (3 developmental by 3 adult temperatures)designed to discriminate among all competing hypotheses. Wenow derive a formal statistical model (ANOVA with orthogonalpolynomial contrasts) for this experimental design and use itto evaluate simultaneously the relative impact of each competinghypothesis. We then apply this model to several case studies(Drosophila, Volvox, Trichogramma), and we review also a recentstudy with E. coli. The influence of Beneficial Acclimationis supported (albeit often weakly) in most cases. Nevertheless,other hypotheses (especially the Optimal Developmental TemperatureHypothesis) often have a greater impact. Even so, however, BeneficialAcclimation usually predicts relative performance at extremetest temperatures. We conclude that, although rumors of itsdeath are premature, Beneficial Acclimation cannot be viewedas the dominant expectation, at least with regard to developmentaltemperature acclimation. Moreover, our findings reinforce theview that a strong inference approach provides a more comprehensiveportrait of complex biological responses than do single-hypothesisapproaches.