A Continuum Model for Metabolic Gas Exchange in Pear Fruit

Exchange of O2 and CO2 of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O2 and increased CO2 levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres

Spatial development of transport structures in apple (Malus x domestica Borkh.) fruit

The void network and vascular system are important pathways for the transport of gases, water and solutes in apple fruit (Malus x domestica Borkh). Here we used X-ray micro-tomography at various spatial resolutions to investigate the growth of these transport structures in 3D during fruit development of ‘Jonagold’ apple. The size of the void space and porosity in the cortex tissue increased considerably. In the core tissue, the porosity was consistently lower, and seemed to decrease towards the end of the maturation period. The voids in the core were more narrow and fragmented than the voids in the cortex. Both the void network in the core and in the cortex changed significantly in terms of void morphology. An automated segmentation protocol underestimated the total vasculature length by 9 to 12% in comparison to manually processed images. Vascular networks increased in length from a total of 5 meter at 9 weeks after full bloom, to more than 20 meter corresponding to 5 cm of vascular tissue per cubic centimeter of apple tissue. A high degree of branching in both the void network and vascular system and a complex three-dimensional pattern was observed across the whole fruit. The 3D visualisations of the transport structures may be useful for numerical modeling of organ growth and transport processes in fruit

Internal browning disorders of 'Rocha' pear during long-term storage

A pera 'Rocha' (Pyrus communis L.) é uma cultivar Portuguesa que pode ser armazenada em atmosfera controlada (AC) durante 10 meses. No entanto, sabe-se que é suscetível ao acastanhamento interno (AI), uma das principais causas de perdas económicas durante o armazenamento prolongado. Embora muitos estudos tenham sido realizados para melhor compreender o AI em peras, os mecanismos subjacentes não permanecem por elucidar. O objetivo desta tese é investigar os mecanismos fisiológicos, bioquímicos e moleculares envolvidos no desenvolvimento do AI em pera 'Rocha', estabelecendo a base científica para o desenvolvimento de modelos preditivos para o AI e recomendações de manuseio pós-colheita, visando reduzir a incidência de AI em um ambiente regulatório em que as ferramentas químicas convencionais já não se encontram disponíveis. O AI em pera pode ter vários sintomas e foi demostrado que a suscetibilidade da pera para desenvolver este acidente fisiológico é afetada pela maturação dos frutos à colheita. Neste trabalho, os AIs em pera 'Rocha' foram classificados em duas categorias: decomposição necrótica húmida e cavidades secas, que podem coexistir no mesmo fruto. A ocorrência de cavidades foi associada a períodos de armazenamento mais prolongados e à exposição dos frutos a alto CO2. Os resultados mostraram claramente que as peras colhidas tardiamente eram mais suscetíveis ao AI do que as colhidas num estado de maturação precoce ou ótimo. Para o estudo da base bioquímica do AI foram conduzidos três ensaios em três anos consecutivos. Na nossa primeira avaliação, realizada numa base de longo prazo, a fermentação desempenhou um papel importante no AI, mas o sistema antioxidante não. No entanto, no segundo ensaio, realizado numa base de curto prazo, os resultados sugeriram que o AI em pera 'Rocha' era desencadeado por stress oxidativo. Finalmente, no terceiro ensaio, a base bioquímica do AI relacionado com o CO2 em pera 'Rocha' foi estabelecida. Os resultados mostraram que o mecanismo subjacente ao AI em pera 'Rocha' envolve a conjugação de ambos os metabolismos, antioxidante e fermentativo. A partir dos resultados obtidos um mecanismo o para o desenvolvimento do AI relacionada com o CO2 foi proposto. Neste estudo também se analisou pela primeira vez a regulação molecular de genes que codificam enzimas antioxidantes e fermentativas. As diferenças encontradas na regulação da transcrição destes genes apoiaram os dados bioquímicos. Os resultados também mostraram que o armazenamento dos frutos em alto CO2 leva a uma disfunção do sistema antioxidante e que, quando o alto CO2 é combinado com níveis muito baixos de O2 a fermentação é altamente induzida, com ambos os fatores a atuar sinergicamente no desenvolvimento de IBD. Também trabalhamos para identificar marcadores de predisposição dos frutos para desenvolver AI, o que poderá ser útil para uma avaliação precoce do risco de desenvolvimento de AI. Entre os marcadores bioquímicos, os resultados evidenciaram o acetaldeído, o etanol e o ácido ascórbico como os mais promissores, ao passo que, entre os minerais, o cobre (Cu) era o melhor candidato. Em geral, modelos de previsão do AI em pera 'Rocha' foram desenvolvidos e validados neste trabalho, representando um importante passo na previsão do AI em pera 'Rocha'. De forma a encontrar estratégias de controlo eficazes para prevenir o AI em pera 'Rocha' foram realizados três ensaios em dois anos consecutivos. Dois dos ensaios foram realizados no primeiro ano e o outro no ano seguinte. No primeiro ensaio, atmosferas controladas dinâmicas monitorizadas por fluorescência da clorofila (ACD-FC) e etanol (ACD-EtOH) foram avaliadas para a prevenção do AI. Pela primeira vez mostramos que o armazenamento dos frutos em ACD-FC conduz a uma incidência reduzida de AI, sendo esta uma metodologia promissora para o armazenamento prolongado de pera 'Rocha'. Pelo contrário, mostramos também que o armazenamento em ACD-EtOH poderá não ser adequado para prevenir o AI. No segundo e terceiro ensaios, a eficácia do tratamento com 1-metilciclopropeno (1-MCP) e do armazenamento em atmosfera controlada diferida na prevenção do AI foi avaliada. Pela primeira vez, mostrámos que a eficácia do 1-MCP depende da maturidade dos frutos à colheita e que, quando aplicado em frutos tardios, induz uma maior incidência de AI. Os resultados também mostraram que o armazenamento de frutas atmosfera controlada diferida, em contraste com o observado para outras cultivares de pera, não foi eficaz na prevenção do AI em pera 'Rocha', podendo mesmo induzir a sua incidência. Em geral, os resultados obtidos no decorrer desta tese proporcionaram novo conhecimento e uma melhor compreensão do AI em pera 'Rocha'. Os mecanismos bioquímicos subjacentes foram estabelecidos e pistas moleculares foram desvendadas; novas perspetivas para a modelação preditiva do AI foram dadas; uma nova e promissora metodologia para a prevenção do AI foi revelada e as limitações das estratégias de controlo atualmente usadas, quando aplicadas à pera 'Rocha', foram evidenciadas.‘Rocha’ pear (Pyrus communis L.) is a Portuguese native cultivar which can be stored under controlled atmosphere (CA) for up to ten months. However, it is known to be susceptible to internal browning disorders (IBD), one of the major causes of economic losses during long-term storage. Although many studies have been conducted to better understand IBDs in pears, the underlying mechanisms of this disorder remains to be elucidated. The aim of this thesis is to investigate the physiological, biochemical and molecular mechanisms involved on IBD development in ‘Rocha’ pear, establishing the scientific basis for the development of IBD predictive models and postharvest handling recommendations aiming at reducing the incidence of IBD in a regulatory environment where conventional chemical tools are no longer available. IBDs in pear can have various symptoms and pear susceptibility to develop this disorder has been shown to be affected by fruit maturity at harvest. In the current work IBDs in ‘Rocha’ pear were classified into two categories: wet necrotic breakdown and dry cavities, which may coexist in the same fruit. The occurrence of cavities was associated to longer storage durations and fruit exposure to high CO2. The results clearly showed that late harvested pears were more susceptible to IBD than early and optimally harvested. For the study of the biochemical basis of IBD three trials were conducted in three consecutive years. In our first assessment, conducted on a long-term basis, fermentation played a major role on IBD whereas the antioxidant system did not. However, in the second trial, conducted on a short-term basis, the results suggested that IBD in ‘Rocha’ pear was triggered by oxidative stress. Finally, in the third trial, the biochemical basis of CO2-related IBD in ‘Rocha’ pear was established. The results showed that the underlying mechanism of IBD in ‘Rocha’ pear involves the conjugation of both, the antioxidant and fermentative metabolisms. From the results obtained a mechanism of CO2-related IBD development was proposed. In this study we also looked for the first time to the molecular regulation of genes codifying antioxidant and fermentative enzymes. The differences found in the transcriptional regulation of these genes supported the biochemical findings. The results also showed that fruit storage under high CO2 leads to an impairment of the antioxidant system and that, when high CO2 is combined with very low O2 levels, there is a highly induction of fermentation with both factors acting synergistically on IBD development. We also worked to identify markers of fruit predisposition to develop IBD, which could be useful for an early assessment of the risk of IBD development. Among the biochemical markers, the results evidenced acetaldehyde (AcDH), ethanol (EtOH) and ascorbic acid (AA) as the most promising ones, whereas, among the minerals, copper (Cu) was the best candidate. Overall, IBD prediction models for ‘Rocha’ pear have been developed and validated in this work, representing a major step forward in the prediction of IBD in ‘Rocha’ pear. In order to find effective control strategies to prevent IBD in ‘Rocha’ pear three trials were conducted in two consecutive years. Two trials were conducted in the first year and the other in the following year. In the first trial, dynamic controlled atmospheres monitored by chlorophyll fluorescence (DCA-CF) and ethanol (DCA-EtOH) were evaluated for IBD prevention. For the first time, we showed that fruit storage under DCA-CF leads to a reduced IBD incidence, making it a promising methodology for ‘Rocha’ pear long-term storage. On the contrary, we also showed that storage under DCA-EtOH may not be suitable to prevent IBD. In the second and third trials, the efficacy of 1-MCP treatment and storage under delayed CA, in preventing IBD was assessed. For the first time, we showed that 1-MCP efficacy is dependent on fruit maturity at harvest and that, when applied to late harvested fruits, induces higher IBD incidence. The results also showed that fruit storage under delayed CA, in contrast to the observed for other pear cultivars, was not effective in preventing IBD in ‘Rocha’ pear, and may even induce its incidence. Overall the results obtained in the course of this thesis provided novel knowledge and a better understanding of IBDs in ‘Rocha’ pear. The underlying biochemical mechanisms were established and molecular clues were unraveled; new perspectives for IBD predictive modelling were provided; a new promising methodology for IBD prevention was revealed and the limitations of currently used control strategies, when applied to ‘Rocha’ pears, were evidenced

Determination of Evapotranspiration and Annual Biomass Productivity of a Cactus Pear [Opuntia ficus-indica L. (Mill.)] Orchard in a Semiarid Environment

A micrometeorological approach based on the surface energy balance was adopted to estimate evapotranspiration fluxes and crop coefficient data from an irrigated cactus pear [Opuntia ficus-indica L. (Mill.)] orchard under Mediterranean climatic conditions. Highfrequency temperature readings were taken above the canopy top to get sensible heat flux values (HSR) using the surface renewal technique. These values were compared against eddy covariance sensible heat fluxes (HEC) for calibration. Latent heat flux (or evapotranspiration, ET) was obtained by solving the daily energy balance equation. Measurements of soil hydraulic components were integrated with the analysis of the surface energy fluxes and crop development in terms of phenology and aboveground biomass accumulation. Microlysimeters were used to compute evaporation rates, allowing the separation of daily transpiration from ET data. Ecophysiological measurements were carried to estimate dry weight accumulation and partitioning. Cactus pear evapotranspired a total of approximately 286 and 252 mm of water during the two monitored growing seasons, respectively. Average daily values of crop (ETc) and reference (ET0) evapotranspiration were in the order of 2.5 and 5.0 mm, respectively, with a corresponding value of the mean crop coefficient of approximately 0.40. The annual dry mass fixed per single tree was 38.8 1.3 kg, with a total production of 12.9 t ha 121, which is comparable to many C3 and C4 plants and resulted in a water use efficiency (WUE) of 4.6 and 4.4 gDMkgH2O 121 in 2009 and 2010, respectively. The stem area index (SAI) was 3.5

Applying Membrane Systems in Food Engineering

Food engineering deals with manufacturing, packaging and distributing systems for drug and food products. In this work, we discuss about the applicability of membrane systems to model environmental conditions and their e ects on the produces during storage of fresh fruits and vegetables. In particular, we are interested in abstract molecular interactions that occur between produce, lm and surrounding atmosphere factors involved in fresh fruit and vegetable package designs. We present a basic implementation to simulate the dynamical behaviour of these systems, due to gas exchanges and temperature uctuations. Additionally, we reveal the bene ts of this modelling approach and suggest some extensions as future directions to be considered

Developmental physiology, nitrogen preference, and estimated biofuel production of Opuntia ficus-indica (prickly pear cactus) in the United States

Opuntia ficus-indica (Prickly pear cactus) is a large succulent cactus species that has a long history of agricultural production for carmine dye, fruits, and edible young cladodes. As a CAM plant O. ficus-indica uses crassulacean acid metabolism (CAM) which is characterized by assimilation of CO2 at night, which greatly increases water use efficiency. More recently, O. ficus-indica has been recognized as having high biomass and biogas (CH4) production values comparable to other large CAM species. Opuntia eliator, a closely related tropical epiphyte species, has been shown to predominantly use C3 photosynthesis in seedlings before switching to CAM photosynthesis. Similarly, young cladodes in Opuntia ficus-indica have been shown to predominantly fix CO2 during the day until they mature. Some plants can also switch to CAM photosynthesis when preferred nitrogen sources (nitrate or ammonium) become limiting and O. ficus-indica has been shown to have a slight increase in nitrogen uptake in ammonium vs.. nitrate. A field trial, and life cycle assessment has been conducted on biogas production from O. ficus-indica in Mexico, but biogas production values in the United States are unknown. Here, measured carbon isotope ratios, 24-hour gas exchange, and tissue acidity in O. ficus-indica seedlings and daughter cladodes to determine the occurrence of CAM vs. C3 photosynthesis. Results demonstrated that O. ficus-indica seedlings used predominantly CAM photosynthesis to assimilated CO2 even under well-watered conditions, while developing cladodes were shown to be sink tissues that switched directly from C3 photosynthesis to CAM photosynthesis in greenhouse conditions. Here, N preference was investigated by placing O. ficus-indica cladodes in sand culture and providing nutrient solutions with varying amounts of nitrate and ammonium for one month, and measuring differences in growth, biochemistry, and CAM and N-related gene expression. Statistical differences in O. ficus-indica growth, chlorophyll content, tissue acidity, soluble sugars, nitrate reductase activity, nitrate and ammonium content, glyoxylic acid content, N:C ratio and relative expression of genes involved N metabolism, and CAM activity were all detected when nitrate and ammonium were varied in sand culture. A life cycle inventory of biogas production from O. ficus-indica was built using results from an irrigation field trial that took place in Logandale, NV. Estimated biogas production from O. ficus-indica in the United States was 13,004.29-26,877.85 Nm3 ha-1 yr-1 produced from plants receiving 716 mm year−1 which is comparable to that of actual production values in Mexico

Réponses morphologiques, physiologiques et biochimiques au déficit en eau chez les jeunes plants de trois populations de poiriers sauvages (Pyrus boisseriana)

Water shortage limits production of fruit orchards, like pear, in arid and semi-arid regions. The identification of wild pear germplasm for potential use as rootstock would be valuable for pear cultivation in semi-arid regions. Relative drought tolerance of wild pear germplasm (Pyrus boisseriana) from three different populations distributed along an elevational gradient (semi-arid 1000, semi-wet 1350 and semi-wet 1600 populations) was evaluated in a greenhouse trial. Established container-grown seedlings were exposed to 18 days of simulated drought, or not, followed by a seven day recovery. Biomass allocation and accumulation, physiological (stomatal conductance, photosynthesis, transpiration, xylem water potential) and biochemical parameters (leaf pigments, free proline, malondialdehyde and hydrogen peroxide production) were evaluated. Although all populations were able to recover from water shortage, thereby being relatively drought tolerant, some differences among populations were detected for gas exchange parameters, biomass accumulation and proline concentration in favor of the semi-arid 1000 elevation population, which was more drought tolerant; it had the most rapid and complete recovery of physiological activity (stomatal conductance and carbon fixation). In addition, all populations increased carotenoids in leaves. Overall, we showed that plants from semi-arid 1000 elevation greater tolerance to drought than those from higher elevations. Although the initial drought resistance response of the 1000 elevation source was promising, additional field studies are needed to confirm the greenhouse results and the benefit of a more drought resistant rootstock to commercial scions.En régions arides et semi-arides, la disponibilité en eau est le facteur limitant des vergers de production, comme en culture de poirier, par exemple. À cet égard, l’évaluation d’une collection de poiriers sauvages pourrait mettre en évidence du matériel potentiellement utilisable comme porte-greffe et tolérant à la sécheresse dans ces régions. Des poiriers sauvages (Pyrus boisseriana) originaires de trois populations différentes selon leur répartition en altitude (populations « semi-aride 1 000 m », « semi-humide 1350 m » et « semi-humide 1 600 m ») ont été évalués pour leur tolérance à la sécheresse dans un essai en serre. Des semis cultivés en pots ont été soumis à 18 jours de sécheresse, puis à une reprise de sept jours de croissance en conditions normales d’irrigation. La répartition et l’accumulation de la biomasse, les paramètres physiologiques (conductance stomatique, photosynthèse, transpiration, potentiel hydrique du xylème) et biochimiques (teneurs en pigments des feuilles, proline libre et malondialdéhyde ; production de peroxyde d’hydrogène) ont été évalués par rapport à des témoins non soumis au stress hydrique. Bien que toutes les populations de poirier aient pu se rétablir après la période sans irrigation et présentent de ce fait une certaine tolérance à la sécheresse, certaines différences de comportement entre celles-ci ont été détectées pour ce qui concerne les échanges gazeux, l’accumulation de la biomasse et la concentration de la proline dont les valeurs étaient en faveur de la population établie en zone semi-aride à une altitude de 1000 m. Celle-ci a d’ailleurs montré une reprise plus rapide et plus complète de son activité physiologique (conductance stomatique et fixation du carbone). À noter que le taux de caroténoïdes dans les feuilles a augmenté dans toutes les populations soumises au stress hydrique. De manière générale, nous avons montré que les plantes appartenant à la population établie en zone semi-aride à 1 000 m d’altitude présentaient une plus grande tolérance à la sécheresse que celles appartenant aux populations des altitudes plus élevées (populations semi-humides). Ces plantes constituent donc un matériel prometteur comme candidats porte-greffe pour les greffons commerciaux de poiriers destinés à la culture dans les régions soumises fréquemment à des déficits hydriques.Fil: Zarafshar, Mehrdad. Tarbiat Modares University. Faculty of Natural Resources and Marine Sciences. Department of Forestry; IránFil: Akbarinia, Moslem. Tarbiat Modares University. Faculty of Natural Resources and Marine Sciences. Department of Forestry; IránFil: Askari, Hossein. Shahid Beheshti University, G.C. Faculty of New Technologies and Energy Engineering. Biotechnology Department; IránFil: Hosseini, Seyed Mohsen. Tarbiat Modares University. Faculty of Natural Resources and Marine Sciences. Department of Forestry; IránFil: Rahaie, Mehdi. University of Tehran. Faculty of New Science and Technology. Department of Life Science Engineering; IránFil: Struve, Daniel. Ohio State University. Department of Horticulture and Crop Science.; Estados UnidosFil: Striker, Gustavo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin