Validation of a Photosynthesis Model through the Use of the CO2Balance of a Greenhouse Tomato Canopy

Several leaf photosynthesis models were developed from wellcontrolled experiments in growth chambers. However, only a fewhave been validated under greenhouse conditions for their quantitativeand qualitative adequacy. In this paper, rates of net photosynthesisfor a tomato crop (Lycopersicon esculentum Mill) were measuredin a semi-commercial greenhouse (615 m³) for a significant timeperiod. Concomitant measurements of climatic conditions andLAI were used for simulation of net photosynthesis using theTOMGRO model which integrates Acock's model for photosynthesiscalculations. From simulations and from sensitivity analysis,the prediction of net photosynthesis appeared to be very sensitiveto the quantum use efficiency. The Acock model with originalparameters underestimated the net photosynthesis rate, but anincrease in the quantum use efficiency by 10% gave a good fit.In an effort to generalize the validity of the model, a residualanalysis was performed and showed a systematic bias relatedto light intensity intercepted by the canopy. The Marquardtalgorithm was used to adjust our data to the model but did noteliminate residual heterogeneity of variance with new parametervalues. On the basis of collected data, the criteria of goodnessof fit used showed that the photosynthesis model is inadequatein describing the CO₂-balance of the greenhouse agrosystem.However, it was determined that it could be used as a submodelwithin a more complex model for predicting growth and development.Copyright 1999 Annals of Botany Company Greenhouse, CO₂-balance, photosynthesis, TOMGRO model, Acock's model, residuals, tomato Lycopersicon esculentum Mill.     

Cell location and partial characterization of Brochothrix thermosphacta and Lactobacillus curvatus lipases

The lipases of Brochothrix thermosphacta and Lactobacillus curvatus were in the soluble fraction of the cell and not membrane- or wall-bound. Their optimal activities were around pH 6mD5 and at 37°C. Enzymes were stable between 4 and 30°C and at freezing temperatures (— 20°C and —60°C). The lipase of Lact. curvatus was stable in the pH range of 4mD0 to 11mD0, whereas that of B. thermosphacta was denatured at pH lower than 5mD0 and greater than 9mD0. Among triglycerides tested, maximal activity was found with tributyrin and hydrolysis of other triglycerides decreased as the length of fatty acid increased.     

Ecological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell

Abstract.  1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.
2.  Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed.
3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next.
4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources.
5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches.     

Evolution of the population structure of Venturia inaequalis,the apple scab fungus,associated with the domestication of its host

Evaluating the impact of plant domestication on the population structure of the associated pathogens provides an opportunity to increase our understanding of how and why diseases emerge. Here, we investigated the evolution of the population structure of the apple scab fungus Venturia inaequalis in response to the domestication of its host. Inferences were drawn from multilocus microsatellite data obtained from samples collected on (i) the Central Asian Malus sieversii, the main progenitor of apple, (ii) the European crabapple, Malus sylvestris, a secondary progenitor of apple, and (iii) the cultivated apple, Malus×domestica, in orchards from Europe and Central Asia. Using clustering methods, we identified three distinct populations: (i) a large European population on domesticated and wild apples, (ii) a large Central Asian population on domesticated and wild apples in urban and agricultural areas, and (iii) a more geographically restricted population in M. sieversii forests growing in the eastern mountains of Kazakhstan. Unique allele richness and divergence time estimates supported a host‐tracking co‐evolutionary scenario in which this latter population represents a relict of the ancestral populations from which current populations found in human‐managed habitats were derived. Our analyses indicated that the domestication of apple induced a significant change in the genetic differentiation of populations of V. inaequalis in its centre of origin, but had little impact on its population dynamics and mating system. We discuss how the structure of the apple‐based agrosystem may have restricted changes in the population structure of the fungus in response to the domestication of its host.     

Parasite-mediated sexual selection and species divergence in Lake Victoria cichlid fish

We investigate the role of parasite-mediated sexual selection in the divergence of two species of Lake Victoria cichlids. Pundamilia pundamilia and Pundamilia nyererei represent a common pattern of male nuptial colour divergence between haplochromine sister species: metallic grey–blue in P. pundamilia and bright yellow and red in P. nyererei . Female mating preferences for different male colours maintain the genetic and phenotypic differentiation of the two species in clear water. Previous work indicated that the red coloration of P. nyererei males, which is subject to directional sexual selection, may be a carotenoid-dependent signal of parasite infestation rate. In the present study, we find a parallel result for P. pundamilia : bright blue males are infected with fewer species of parasites. We also find that parasite infestation rates differ quantitatively between the two species in a way that is consistent with species differences in diet and microhabitat. We conclude that parasite-mediated sexual selection may have contributed to the divergence of female mating preferences between P. pundamilia and P. nyererei , and may currently strengthen reproductive isolation between these species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 53–60.     

Facts and Hypotheses Concerning the Control of Odontoblast Differentiation

Numerous studies using amphibians have demonstrated that preodontoblasts emerging from the dental papilla are derived from cranial neural crest cells [4, 12, 46, 64]. However this has not been established for mammals. The history of odontogenesis begins during the early stages of cranial-facial development when the maxillary and mandibular processes develop. Continuous epithelio-mesenchymal interactions condition the histogenesis and morphogenesis of the teeth [24–26, 43, 44, 49, 51,58] as well as the terminal differentiation of odontoblasts and ameloblasts [23, 47, 52, 54, 59, 61, 67].
During recent years a considerable amount of experimental data relating to differentiation of odontoblasts has been published. We summarize these data and attempt to integrate them in deductive hypotheses concerning the control of odontoblast differentiation.