Nadia Bertin

Major Proteome Variations Associated with Cherry Tomato Pericarp Development and Ripening

Tomato (Solanum lycopersicum) is a model plant for studying fleshy fruit development. Several genetic and molecular approaches have been developed to increase our knowledge about the physiological basis of fruit growth, but very few data are yet available at the proteomic level. The main stages of fruit development were first determined through the dynamics of fruit diameter and pericarp cell number. Then, total proteins were extracted from pericarp tissue at six relevant developmental stages and separated by two-dimensional gel electrophoresis. Protein patterns were markedly different between stages. Proteins showing major variations were monitored. We identified 90 of 1,791 well-resolved spots either by matrix-assisted laser-desorption ionization time-of-flight peptide mass fingerprinting or liquid chromatography-mass spectrometry sequencing and expressed sequence tag database searching. Clustered correlation analysis results pointed out groups of proteins with similar expression profiles during fruit development. In young fruit, spots linked to amino acid metabolism or protein synthesis were mainly expressed during the cell division stage and down-regulated later. Some spots linked to cell division processes could be identified. During the cell expansion phase, spots linked to photosynthesis and proteins linked to cell wall formation transiently increased. In contrast, the major part of the spots related to C compounds and carbohydrate metabolism or oxidative processes were up-regulated during fruit development, showing an increase in spot intensity during development and maximal abundance in mature fruit. This was also the case for spots linked to stress responses and fruit senescence. We discuss protein variations, taking into account their potential role during fruit growth and comparing our results with already known variations at mRNA and metabolite-profiling levels.

Seasonal and diurnal patterns of monoterpene emissions from Pinus pinea (L.) under field conditions

Abstract Within the activity of the BEMA project (Biogenic Emission in the Mediterranean Area), the emission of volatile organic compounds from Pinus pinea L. was studied in a nature reservation close to Rome (Italy). Measurements were carried out during five campaigns from June 1993 to October 1994 using a dynamic branch enclosure technique. Investigations principally focused on studying diurnal and seasonal variability. P. pinea emitted mainly monoterpenes of which limonene, trans -β-ocimene, linalool, α-pinene, myrcene and 1,8-cineole were the most abundant. At a temperature of 30°C and PAR > 600 μmol photons m -2 s −1 the sum of emissions was about 2–3.5 μg g −1 leaf dry weight h −1 in spring and autumn, and about 7 to 15 μg g −1 h −1 in summer. Absolute daytime emission rates were very high in summer (35 μg g −1 h −1 ) leading to a carbon loss of up to 8% of the 24 h photosynthetic carbon gain. α-pinene and limonene emissions were found in all campaigns and were emitted during day and night. Other compounds like trans -β-ocimene, linalool and 1,8-cineole occurred seasonally and were not or hardly emitted in the night. The lack of emissions during night point to a strong influence of light as confirmed by an artificial darkening experiment. Diurnal emissions of limonene and trans -β-ocimene were simulated by the monoterpene model. of Tingey et al. (1980, Plant Physiology 65 , 797–801) and the isoprene model of Guenther et al . (1991, J. geophys. Res. , 96 , 10,799–10,808), using parameters suggested by Guenther et al. (1993, J. geophys. Res. , 96 ,10,799–10,808) and parameters adjusted to data by best-fit regression analysis. Model predictions were fairly good with the adjusted parameters ( R 2 = 0.71 and 0.77, n = 139 and 72). Trans -β-ocimene data clearly fitted better with the isoprene model while Tingeys monoterpene model was more appropriate for limonene data. The pronounced seasonality in amount and composition of the emissions demonstrate that the existing models describing the short-term response of emissions to temperature and light cannot always be used alone to estimate the annual monoterpene release from vegetation.

Diurnal and seasonal course of monoterpene emissions from Quercus ilex (L.) under natural conditions application of light and temperature algorithms

Abstract Quercus ilex is a common oak species in the Mediterranean vegetation and a strong emitter of monoterpenes. Since the short-term control of monoterpene emissions from this species involved both temperature and light, the usual exponential function of temperature may not be sufficient to model the diurnal and seasonal emission course. In the frame of the BEMA-project (Biogenic Emissions in the Mediterranean Area), we investigated the tree-to-tree, branch-to-branch, diurnal, and seasonal variability of monoterpene emissions from Q. ilex over one and a half years at Castelporziano (Rome, Italy). In addition, we checked the suitability of the model developed for isoprene by Guenther et al. (1991, 1993) to simulate the short- and long-term variations of monoterpene emissions from this particular species. We found that the tree-to-tree variability was rather small compared to the experimental error during air sampling acid analysis by diverse laboratories. The branch-to-branch variability was noticeable between sun- and shade-adapted branches only. 80% of total emissions were represented by α-pinene, β-pinene and sabinene, whose proportions were stable over the year and independent of light exposure. The emission factor (emission rate at 30°C and 1000 μmol photon m −2 s −1 ) estimated by the isoprene model or extrapolated from measurements was similar: it was about 22 μg g dw −1 h −1 for sun-exposed branches and 2.3 μg g dw −1 h −1 for shade-adapted branches. It was rather stable over the seasons except during leaf development. The diurnal and seasonal emission patterns from Q. ilex were simulated in a satisfying way by Guenthers algorithms especially if we excluded the laboratory variability. For shade-adapted branches, an emission factor 17 times lower had to be applied, but temperature and light responses were unchanged.

Genetic and physiological analysis of tomato fruit weight and composition: influence of carbon availability on QTL detection

Throughout tomato domestication, a large increase in fruit size was associated with a loss of dry matter and sugar contents. This study aims to dissect the contributions of genetic variation and the physiological processes underlying the relationships between fruit growth and the accumulation of dry matter and sugars. Fruit quality traits and physiological parameters were measured on 20 introgression lines derived from the introgression of Solanum chmielewskii into S. lycopersicum, under high (HL, unpruned trusses) and low (LL, trusses pruned to one fruit) fruit load conditions. Inter- and intra-genotypic correlations among traits were estimated and quantitative trait loci (QTL) for size, composition, and physiological traits were mapped. LL increased almost all traits, but the response of sugar content was genotype-dependent, involving either dilution effects or differences in carbon allocation to sugars. Genotype×fruit load interactions were significant for most traits and only 30% of the QTL were stable under both fruit loads. Many QTL for fresh weight and cell or seed numbers co-localized. Eleven clusters of QTL for fresh weight and dry matter or sugar content were detected, eight with opposite allele effects and three with negative effects. Two genotypic antagonistic relationships, between fresh weight and dry matter content and between cell number and cell size, were significant only under HL; the second could be interpreted as a competition for carbohydrates among cells. The role of cuticular conductance, fruit transpiration or cracking in the relationship between fruit fresh weight and composition was also emphasized at the genetic and physiological levels.

Fluxes of biogenic VOC from Mediterranean vegetation by trap enrichment relaxed eddy accumulation

Abstract Results are presented for the application of a modified relaxed eddy accumulation system for the determination of VOC fluxes in the atmosphere (TREA). First, system design, performances and testing against eddy covariance carbon dioxide fluxes are presented. Subsequently, the capability of TREA to discriminate between biogenic and anthropogenic VOC fluxes is discussed with some examples. TREA fluxes are also compared with the major biogenic VOC fluxes calculated with the gradient method and the relative merits and problems of the two techniques are discussed. TREA fluxes for two consecutive days are presented for 18 biogenic compounds. Compounds mostly emitted from the canopy were α-pinene, β-pinene, limonene and trans -β ocimene. The parallel analysis of fluxes determined by TREA and bag enclosures is carried out and discrepancies are discussed in terms of the removal processes of VOC in the atmosphere.

Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load

The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.

Under what circumstances can process-based simulation models link genotype to phenotype for complex traits? Case-study of fruit and grain quality traits

Detailed information has arisen from research at gene and cell levels, but it is still incomplete in the context of a quantitative understanding of whole plant physiology. Because of their integrative nature, process-based simulation models can help to bridge the gap between genotype and phenotype and assist in deconvoluting genotype-by-environment (GxE) interactions for complex traits. Indeed, GxE interactions are emergent properties of simulation models, i.e. unexpected properties generated by complex interconnections between subsystem components and biological processes. They co-occur in the system with synergistic or antagonistic effects. In this work, different kinds of GxE interactions are illustrated. Approaches to link model parameters to genes or quantitative trait loci (QTL) are briefly reviewed. Then the analysis of GxE interactions through simulation models is illustrated with an integrated model simulation of peach (Prunus persica (L.) Batsch) fruit mass and sweetness, and with a model of wheat (Triticum aestivum L.) grain yield and protein concentration. This paper suggests that the management of complex traits such as fruit and grain quality may become possible, thanks to the increasing knowledge concerning the genetic and environmental regulation of organ size and composition and to the development of models simulating the complex aspects of metabolism and biophysical behaviours at the plant and organ levels.

Number of cells in tomato fruit depending on fruit position and source-sink balance during plant development

Fruit sink strength or its ability to attract assimilates depends bothon sink activity and size. This study investigated one main component of sinksize, that is the number of fruit cells during tomato plant development. Plantswere grown in a controlled climate chamber under a limiting (LS, six fruits pertruss) and non-limiting (NLS, two fruits per truss and CO2enrichment) supply of carbon assimilates. Under NLS conditions, fruit cellnumber was homogeneous among successive trusses, and fruits contained onaverage1.2 × 106 more cells than under LS conditions,though differences were not significant on the first truss which underwent thelowest competition. Under LS conditions, an ontogenetic increase in cell numberwas observed in proximal fruits of the upper trusses attributed to theenlargement of the apical meristem during plant development. The decrease ofcell number from proximal to distal fruits within a truss, that was expectedfrom the literature, was generally observed in the LS experiment, with anaverage significant difference of about1.6 × 106cells between the first and fifth fruits. Nevertheless, whereas the gradient incell number from proximal to distal fruits was steep in the upper trusses, itwas not significant on the lower trusses indicating that this gradient largelydepended on the level of competition during floral development. Thus, under lowassimilate supply, cell division is a main limiting factor for fruit growth,although cell enlargement during further fruit development is also affected,butwas not measured in this work.

Biogenic emissions and CO2 gas exchange investigated on four Mediterranean shrubs

Abstract In order to investigate the impact of plant physiology on emissions of biogenic volatile organic compounds monoterpene emission rates from Rosmarinus officinalis (L.) and Pistacia lentiscus (L.) and isoprene emission rates from Erica arborea (L.) and Myrtus communis (L.) were determined. The study, an activity in the framework of BEMA (Biogenic Emissions in the Mediterranean Area), was carried out in May 1994 at Castelporziano near Rome in Italy, using a dynamic enclosure technique combined with recording CO2 gas exchange, temperature and irradiance data. The monoterpenes dominating the emission pattern were 1,8-cineol, α-pinene and β-pinene for rosemary and α-pinene, linalool and β-pinene + sabinene for pistachio. Total monoterpene emission rates standardized to 30°C of 1.84 ± 0.24 and 0.35 ± 0.04 μg Cg−1 dw h−1 were found for rosemary and pistachio, respectively (on a leaf dry weight basis). Myrtle emitted 22.2 ± 4.9 μg C g−1 dw h−1 at standard conditions (30°C, PAR 1000 μmol photons m−2 s−1 as isoprene and erica 5.61 μg C g−1 dw h−1 The carbon loss due to terpenoid emissions per photosynthetically carbon uptake was about 0.01–0.1% for the monoterpene emitters. The isoprene emitting shrubs lost 0–0.9% of the assimilated carbon. The rapid induction of emissions in the sun after temporary shading indicates that isoprene emissions were closely linked to photosynthesis. A higher proportion of the assimilated carbon was lost as isoprene under conditions of high light and temperature compared to the morning and evening hours.

Identification of growth processes involved in QTLs for tomato fruit size and composition

Many quantitative trait loci (QTLs) for quality traits have been located on the tomato genetic map, but introgression of favourable wild alleles into large fruited species is hampered by co-localizations of QTLs with antagonist effects. The aim of this study was to assess the growth processes controlled by the main QTLs for fruit size and composition. Four nearly isogenic lines (NILs) derived from an intraspecific cross between a tasty cherry tomato (Cervil) and a normal-tasting large fruit tomato (Levovil) were studied. The lines carried one (L2, L4, and L9) or five (Lx) introgressions from Cervil on chromosomes 1, 2, 4, and 9. QTLs for fruit size could be mainly associated with cell division processes in L2 and L9, whereas cell expansion was rather homogeneous among the genotypes, except Cervil for which the low expansion rate was attributed to low cell plasticity. The link between endoreduplication and fruit size remained unclear, as cell or fruit sizes were positively correlated with the cell DNA content, but not with the endoreduplication factor. QTLs for fruit composition reflected differences in water accumulation rather than in sugar accumulation, except in L9 for which the up-regulation of sucrose unloading and hexose transport and/or starch synthesis was suggested. This may explain the increased amount of carbon allocated to cell structures in L9, which could be related to a QTL for fruit texture. In Lx, these effects were attenuated, except on fruit size and cell division. Finally, the region on top of chromosome 9 may control size and composition attributes in tomato, by a combination of QTL effects on cell division, cell wall synthesis, and carbon import and metabolism.