Author's manuscript for published article. See Additional Links field for link to published version. / Ethylene production by different needle age classes was characterized using a mercuric perchlorate traps in natural populations of two ponderosa pine varieties (Pinus ponderosa var. arizonica [Engelm] Shaw and var. ponderosa Dougl. ex Laws.) and Jeffery pine (Pinus leffrevi Grev. and Balf.). All ozone -exposed populations contained individuals which were symptomatic and asymptomatic with respect to visible ozone injury. Ethylene production of different needle age classes was also characterized in Pinus ponderosa var. ponderosa seedlings grown in open top ozone fumigation chambers. Older age class needles produce more ethylene than younger age class needles. Needles of both P. ponderosa var. ponderosa and P. jeffreyi exhibiting ozone injury in the field produced significantly (p >0.05) higher levels of ethylene than asymptomatic conspecifics. Seedlings exposed to highest treatment level of ozone in the fumigation study produced the highest levels of ethylene followed by fumigation with medium and low ozone concentrations and carbon filtered air. These data indicate that measurement of ethylene in conifer needles as a measure of stress needs to be calibrated for needle age class. It also suggests that the sensitivity of a tree to ozone injury may be regulated by the inherent ability of the individual to produce ethylene.

Peptídeos de sinalização ou hormonais desempenham papéis importantes nas plantas por serem determinantes no crescimento, desenvolvimento e defesa. RALF é um peptídeo ubíquo no reino vegetal e na planta modelo Arabidopsis thaliana os peptídeos RALF formam uma família multigênica de 37 membros alguns com expressão gênica tecido-específica e outros com expressão em toda a planta. A isoforma AtRALF1 é a mais estudada e é expressa principalmente na raiz e no hipocótilo. Uma das funções deste peptídeo é a regulação da expansão celular, um processo que também envolve auxina, giberelina, etileno, brassinosteróides e citocininas. O objetivo deste trabalho foi estudar a relação entre o AtRALF1 e o hormônio etileno, principalmente na expansão celular e alcalinização celular que são efeitos característicos do peptídeo. AtRALF1 inibe o crescimento da raiz primária porém plantas de arabidopsis tratadas simultaneamente com o peptídeo e inibidores da biossíntese ou percepção de etileno não tiveram o crescimento de suas raízes inibido. Etileno induz a deposição de calose e plantas selvagens expostas ao AtRALF1 e plantas que super-expressam AtRALF1 exibiram depósito de calose nas células da ponta da raiz. Curiosamente, quando a alcalinização do meio de células em suspensão induzida por AtRALF1 foi avaliada perante o aumento da produção de etileno ou perante o bloqueio de sua síntese ou percepção, não foi observada alteração na resposta. Os resultados aqui apresentados demonstram que a resposta de inibição da expansão celular ocasionada por AtRALF1 é dependente de etileno e sugere que os efeitos de alcalinização do meio extracelular e da inibição do crescimento da raiz primária estão dissociados. / Peptide hormones or signaling peptides play important roles that determine growth, development and defense in plants. RALF is a ubiquitous peptide in the plant kingdom and in model plant Arabidopsis thaliana comprises a multigene family of 37 members, some of them with tissue-specific gene expression and others that are expressed throughout the plant. AtRALF1 isoform is the most studied and is expressed in roots and hypocotyls. One of the peptide functions is the negative regulation of cell expansion, a process also controled by auxin, gibberelin, ethylene, brassinosteroids, cytokinin. The aim of this work was to study ethylene and AtRALF1 peptide relation, mainly in the cell alkalinization and inhibition of cell expansion responses that characteristic of the peptide. AtRALF1 inhibits root growth but simultaneous treatment with both AtRALF1 and inhibitors of the ethylene perception or biosynthesis show no inhibition on root growth. Ethylene increases callose deposition and wild-type plants treated with AtRALF1 or plants overexpressing the AtRALF1 gene show increased callose plate formation on root tips. Curiously, when the extracellular alkalinization induced by AtRALF1 was evaluated against ethylene production or against ethylene inhibitors, no alteration was observed. The data presented here reveal that the cell expansion inhibition caused by AtRALF1 is ethylene dependent and suggest that the extracellular alkalinization response and root growth inhibition are dissociated.

Plants are exposed to a variety of environmental stresses, ranging from insects and phytopathogens known as biotic stressors, to edaphic stressors including drought and salinity - clustered under the group of abiotic stresses. Facing these pernicious risks, plants have adopted several strategies to survive in stressful environments. With contemporary advances in technology and scientific research, it is possible to insert a specific gene or trait into a plant in order to confer salt tolerance. For example, a thiol methyltransferase enzyme in cabbage converts Cl¯ and other halide ions into their corresponding methyl halides, which are released directly into the air. Cloning the TMT1 gene and functionally expressing this gene into tobacco plants conferred salt tolerance on these plants. Although increased salt tolerance is a favourable and beneficial trait for plant productivity, the emission of methyl halides into the atmosphere can be noxious for the environment. Indeed, methyl halides are some of the factors contributing to climate change, widely believed to be the foremost environmental problem of the twenty-first century. Climate change is affecting all forms of life on earth and its impacts are often severe and irreversible. For that reason, it has been placed at the forefront of the international political agenda. The present study focused on two main physiological traits of stress resistance in tobacco plants which have been genetically engineered with the cabbage TMT1 gene: The production of methyl halides, particularly methyl chloride, as a way to confer salt tolerance; and synthesis of the stress hormone, ethylene. Both pathways share a common metabolite, S-adenosyl-L-methionine (SAM), for the synthesis of the final products. SAM, derived from the amino acid methionine (Met), is a universal methyl group donor. It plays essential roles in plant metabolism, by acting as a precursor for ethylene, polyamines, and vitamin B1 synthesis, and as a source of atmospheric dimethylsulphides. Therefore, it is important that the plant maintains the SAM pool at a level sufficient to serve all the different metabolic pathways. The present work set out to determine whether addition of another SAM-dependent pathway through TMT insertion in tobacco plants would negatively affect ethylene synthesis by lessening the amount of SAM available for ethylene biosynthesis. Detailed experimental studies were conducted, including in vitro and in vivo experiments, to examine the potential effect of TMT gene insertion on SAM availability for ethylene synthesis in tobacco plants. Three series of in vitro tests, differing by the number of leaf discs used, the final headspace volume in each flask, the incubation period in the different solutions and the time of introducing salt solutions, were carried out. Data obtained from two series of in vitro experiments revealed a decrease in ethylene emission when salt solutions were added at the beginning of the experiment and when leaves where incubated overnight in the presence of 0.1 M NaBr, coupled with the production of methyl halides, whereas the other series of in vitro tests as well as the in vivo results showed no alteration in ethylene accumulation because of TMT insertion when tobacco leaves were exposed to salt treatments. According to the results presented in this study, the amounts of available SAM in transformed tobacco are likely sufficient to serve both ethylene and methyl halides biosynthetic pathways. Besides, in vivo results indicate that inserting the TMT1 gene that improves salt stress resistance in tobacco should not dramatically alter ethylene synthesis, and therefore, would be unlikely to affect any physiological trait associated with ethylene production if this gene is used to engineer salt tolerance in high-value crops. Although TMT insertion does not alter ethylene emission in transgenic plants and tends to be an efficient tool to confer salt tolerance in halo-intolerant crops, its environmental cost is of great concern and, therefore, should be taken into consideration to mitigate the amounts of methyl halides emitted into the atmosphere because of this insertion.

Plants are exposed to a variety of environmental stresses, ranging from insects and phytopathogens known as biotic stressors, to edaphic stressors including drought and salinity - clustered under the group of abiotic stresses. Facing these pernicious risks, plants have adopted several strategies to survive in stressful environments. With contemporary advances in technology and scientific research, it is possible to insert a specific gene or trait into a plant in order to confer salt tolerance. For example, a thiol methyltransferase enzyme in cabbage converts Cl¯ and other halide ions into their corresponding methyl halides, which are released directly into the air. Cloning the TMT1 gene and functionally expressing this gene into tobacco plants conferred salt tolerance on these plants. Although increased salt tolerance is a favourable and beneficial trait for plant productivity, the emission of methyl halides into the atmosphere can be noxious for the environment. Indeed, methyl halides are some of the factors contributing to climate change, widely believed to be the foremost environmental problem of the twenty-first century. Climate change is affecting all forms of life on earth and its impacts are often severe and irreversible. For that reason, it has been placed at the forefront of the international political agenda. The present study focused on two main physiological traits of stress resistance in tobacco plants which have been genetically engineered with the cabbage TMT1 gene: The production of methyl halides, particularly methyl chloride, as a way to confer salt tolerance; and synthesis of the stress hormone, ethylene. Both pathways share a common metabolite, S-adenosyl-L-methionine (SAM), for the synthesis of the final products. SAM, derived from the amino acid methionine (Met), is a universal methyl group donor. It plays essential roles in plant metabolism, by acting as a precursor for ethylene, polyamines, and vitamin B1 synthesis, and as a source of atmospheric dimethylsulphides. Therefore, it is important that the plant maintains the SAM pool at a level sufficient to serve all the different metabolic pathways. The present work set out to determine whether addition of another SAM-dependent pathway through TMT insertion in tobacco plants would negatively affect ethylene synthesis by lessening the amount of SAM available for ethylene biosynthesis. Detailed experimental studies were conducted, including in vitro and in vivo experiments, to examine the potential effect of TMT gene insertion on SAM availability for ethylene synthesis in tobacco plants. Three series of in vitro tests, differing by the number of leaf discs used, the final headspace volume in each flask, the incubation period in the different solutions and the time of introducing salt solutions, were carried out. Data obtained from two series of in vitro experiments revealed a decrease in ethylene emission when salt solutions were added at the beginning of the experiment and when leaves where incubated overnight in the presence of 0.1 M NaBr, coupled with the production of methyl halides, whereas the other series of in vitro tests as well as the in vivo results showed no alteration in ethylene accumulation because of TMT insertion when tobacco leaves were exposed to salt treatments. According to the results presented in this study, the amounts of available SAM in transformed tobacco are likely sufficient to serve both ethylene and methyl halides biosynthetic pathways. Besides, in vivo results indicate that inserting the TMT1 gene that improves salt stress resistance in tobacco should not dramatically alter ethylene synthesis, and therefore, would be unlikely to affect any physiological trait associated with ethylene production if this gene is used to engineer salt tolerance in high-value crops. Although TMT insertion does not alter ethylene emission in transgenic plants and tends to be an efficient tool to confer salt tolerance in halo-intolerant crops, its environmental cost is of great concern and, therefore, should be taken into consideration to mitigate the amounts of methyl halides emitted into the atmosphere because of this insertion.

Peptídeos de sinalização ou hormonais desempenham papéis importantes nas plantas por serem determinantes no crescimento, desenvolvimento e defesa. RALF é um peptídeo ubíquo no reino vegetal e na planta modelo Arabidopsis thaliana os peptídeos RALF formam uma família multigênica de 37 membros alguns com expressão gênica tecido-específica e outros com expressão em toda a planta. A isoforma AtRALF1 é a mais estudada e é expressa principalmente na raiz e no hipocótilo. Uma das funções deste peptídeo é a regulação da expansão celular, um processo que também envolve auxina, giberelina, etileno, brassinosteróides e citocininas. O objetivo deste trabalho foi estudar a relação entre o AtRALF1 e o hormônio etileno, principalmente na expansão celular e alcalinização celular que são efeitos característicos do peptídeo. AtRALF1 inibe o crescimento da raiz primária porém plantas de arabidopsis tratadas simultaneamente com o peptídeo e inibidores da biossíntese ou percepção de etileno não tiveram o crescimento de suas raízes inibido. Etileno induz a deposição de calose e plantas selvagens expostas ao AtRALF1 e plantas que super-expressam AtRALF1 exibiram depósito de calose nas células da ponta da raiz. Curiosamente, quando a alcalinização do meio de células em suspensão induzida por AtRALF1 foi avaliada perante o aumento da produção de etileno ou perante o bloqueio de sua síntese ou percepção, não foi observada alteração na resposta. Os resultados aqui apresentados demonstram que a resposta de inibição da expansão celular ocasionada por AtRALF1 é dependente de etileno e sugere que os efeitos de alcalinização do meio extracelular e da inibição do crescimento da raiz primária estão dissociados. / Peptide hormones or signaling peptides play important roles that determine growth, development and defense in plants. RALF is a ubiquitous peptide in the plant kingdom and in model plant Arabidopsis thaliana comprises a multigene family of 37 members, some of them with tissue-specific gene expression and others that are expressed throughout the plant. AtRALF1 isoform is the most studied and is expressed in roots and hypocotyls. One of the peptide functions is the negative regulation of cell expansion, a process also controled by auxin, gibberelin, ethylene, brassinosteroids, cytokinin. The aim of this work was to study ethylene and AtRALF1 peptide relation, mainly in the cell alkalinization and inhibition of cell expansion responses that characteristic of the peptide. AtRALF1 inhibits root growth but simultaneous treatment with both AtRALF1 and inhibitors of the ethylene perception or biosynthesis show no inhibition on root growth. Ethylene increases callose deposition and wild-type plants treated with AtRALF1 or plants overexpressing the AtRALF1 gene show increased callose plate formation on root tips. Curiously, when the extracellular alkalinization induced by AtRALF1 was evaluated against ethylene production or against ethylene inhibitors, no alteration was observed. The data presented here reveal that the cell expansion inhibition caused by AtRALF1 is ethylene dependent and suggest that the extracellular alkalinization response and root growth inhibition are dissociated.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Polyamines and ethylene have been cited as important regulators of plant growth and development, and may be involved in plant defense against several abiotic stresses, such as salinity. To withstand with salt harmful effects, plants respond through a coordinated set of physiological and molecular responses to improve their performance under salinity. In order to test the hypothesis that salt tolerance degree in maize genotypes is related to changes in polyamine metabolism associated with ethylene production, two experiments were performed. In the first one, BR5033 (salt-tolerant) and BR5011 (salt-sensitive) maize genotypes were subjected to 80 mM NaCl stress to identify the pattern of ethylene production in leaves and roots. Two peaks of ethylene production at 5.5 h (phase I) and 12.5 h (phase II) after onset the salinity treatment were registered in salt-sensitive leaves; whereas only the first peak of ethylene synthesis was detected in salt-tolerant leaves. Surprisingly, the biphasic ethylene production in roots was much less pronounced than in leaves. In the second experiment, we sought to investigate whether the phases I and II of ethylene production alter the polyamine metabolism in the leaves of maize genotypes. In salt-tolerant genotype, the phase I of ethylene synthesis was associated with signaling events, as evidenced by increased H2O2 levels, which were generated by putrescine (Put) catabolism. An early signaling (at 5.5 h) in the salt-tolerant genotype seemed to be effective to suppress the second peak of ethylene production, known as âstress ethyleneâ. Yet, in the salt-sensitive genotype, the decreased H2O2 concentration during the phase I was associated with a marked increase in ethylene production, which was resulted from upregulation of acid 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) activity and ZmACO5 gene expression. At the phase I, the total polyamine content was increased by salinity in the salt-tolerant, whereas it was decreased in the salt-sensitive one. In the salt-tolerant genotype, the increased total polyamine was sustained by high spermine (Spm) and spermidine (Spd) contents, while the decay in the salt-sensitive genotype was due to the reductions of Put and Spd forms. Otherwise, in the phase II, no significant changes in the total polyamines in salt-tolerant genotype (it was likely due to conversion of Put to Spm/Spd), and decreases in salt-sensitive genotype were registered. Under stress conditions, the salinity-induced improvement of Spd and Spm (free and soluble conjugated forms) in salt-tolerant genotype was bigger than in salt-sensitive one, thus suggesting a key role of polyamines in the maize salt stress acclimation processes. Finally, we investigated if the lack of ethylene production during phase II in salt-tolerant genotype was correlated to improved antioxidant capacity. Salt stress dramatically increased the superoxide levels, the electrolyte leakage and lipid peroxidation, it being more pronounced in both leaves and roots of salt-sensitive genotype. On the other hand, under salinity, salt-tolerant genotype displayed a better performance of enzymatic and non-enzymatic antioxidant system, evidenced by a higher ascorbate and glutathione content and upregulation of superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase activity. In conclusion, our results suggest that the ethylene is intimately involved in salt stress acclimation through activation of intricate signaling pathways mediated by H2O2 that is originated from polyamine catabolism. An efficient signal network raises the polyamine content and antioxidant capacity and is responsible, at least in part, for greater tolerance to salinity of BR5033 maize genotype. / Poliaminas e etileno sÃo reguladores do crescimento e desenvolvimento vegetal, que tambÃm estÃo envolvidos nas respostas de defesa das plantas contra estresses abiÃticos, dentre eles a salinidade. Para lidar com o estresse salino, as plantas realizam ajustes fisiolÃgicos, bioquÃmicos e moleculares, que podem resultar em sua aclimataÃÃo diante dessa condiÃÃo adversa, tornando o indivÃduo mais tolerante ao estresse, em comparaÃÃo Ãqueles que nÃo se encontram aclimatados. Essa pesquisa foi desenvolvida para testar à hipÃtese de que o grau de tolerÃncia à salinidade entre genÃtipos de milho envolve alteraÃÃes no metabolismo das poliaminas associadas à produÃÃo de etileno. Para isso, foram realizados dois experimentos. No primeiro, plantas de milho dos genÃtipos BR5011 (sensÃvel) e BR5033 (tolerante) foram submetidas ao estresse salino (NaCl a 80 mM) para identificar o padrÃo de produÃÃo de etileno em folhas e raÃzes. Nas folhas do genÃtipo sensÃvel, a salinidade intensificou a produÃÃo de etileno apÃs 5,5 h (fase I) e 12,5 h (fase II) apÃs o inÃcio do estresse, enquanto no tolerante isso aconteceu somente com 5,5 h. Nas raÃzes, embora tenha sido observada a produÃÃo bifÃsica de etileno no genÃtipo sensÃvel, esse processo foi muito menos intenso que nas folhas. O segundo experimento teve como objetivo principal investigar se a produÃÃo de etileno pela salinidade nas fases I e II resultava em alteraÃÃes no metabolismo das poliaminas nas folhas dos genÃtipos de milho. No genÃtipo tolerante, a fase I de produÃÃo de etileno foi associada à eventos de sinalizaÃÃo, dado o aumento dos teores de H2O2, mediado pelo catabolismo da putrescina (Put). Essa sinalizaÃÃo pareceu ser eficiente para suprimir a produÃÃo do etileno em condiÃÃes de estresse (fase II ou âetileno do estresseâ) nesse genÃtipo. Jà no sensÃvel, a diminuiÃÃo dos teores de H2O2 na fase I foi acompanhada por um aumento acentuado na produÃÃo do etileno, decorrente de acrÃscimos na atividade da enzima oxidase do Ãcido 1-carboxÃlico-1-aminociclopropano (ACO) e na expressÃo de transcritos do gene ZmACO5 (principal membro expresso). Em geral, a salinidade aumentou os teores de poliaminas totais no genÃtipo tolerante, enquanto reduziu no sensÃvel. Na fase I, na condiÃÃo salina quando comparada com o controle, os teores de poliaminas totais foram aumentados no genÃtipo tolerante enquanto no sensÃvel esses teores foram reduzidos. No genÃtipo tolerante, o aumento nos teores de poliaminas totais foi sustentado principalmente pelo aumento nos teores de espermina (Spm) e espermidina (Spd), enquanto a diminuiÃÃo observada no genÃtipo sensÃvel foi devida, sobretudo, Ãs reduÃÃes nas formas de Put e Spd. Jà na fase II, no genÃtipo tolerante nÃo houve alteraÃÃes nos teores totais de poliaminas (provavelmente, devido a utilizaÃÃo de Put para a sÃntese de Spm e Spd), enquanto no sensÃvel esses teores foram reduzidos. Sob condiÃÃes de salinidade, o aumento nas formas livre e conjugada solÃvel de Spm e Spd foi mais pronunciado no genÃtipo tolerante do que no sensÃvel, sugerindo assim importante papel para essas duas poliaminas nos processos de aclimataÃÃo ao estresse salino em plantas de milho. Por fim, foi investigado se a ausÃncia de produÃÃo do etileno na fase II, causado pela salinidade no genÃtipo tolerante, foi relacionada com uma melhor capacidade antioxidante. O estresse salino aumentou drasticamente os teores do radical superÃxido, o vazamento de eletrÃlitos e a peroxidaÃÃo lipÃdica, sendo isso mais pronunciado nas folhas e raÃzes do genÃtipo sensÃvel. De modo geral, o genÃtipo tolerante teve melhor desempenho do sistema antioxidante enzimÃtico e nÃo enzimÃtico, sob condiÃÃes de estresse salino, evidenciado pelos maiores incrementos nos teores de ascorbato e glutationa e na atividade das enzimas dismutase do superÃxido, peroxidase do ascorbato e peroxidase do guaiacol. Em conclusÃo, os resultados aqui apresentados sugerem que o etileno està intimamente envolvido na aclimataÃÃo ao estresse salino, por meio da ativaÃÃo de vias de sinalizaÃÃo mediadas pelo H2O2 produzido a partir do catabolismo de poliaminas. AlÃm disso, sugere-se que essa sinalizaÃÃo induz o aumento nos teores de poliaminas e melhor capacidade antioxidante no genÃtipo BR5033, sendo isto, pelo menos em parte, responsÃvel por sua maior tolerÃncia ao estresse salino, quando comparado ao BR5011.

Although concentrated solar power can be used to produce power using traditional electricity generation, energy storage has become a problem due to the intermittent supply of solar energy. By using solar energy in chemical production processes, the solar energy can be stored in a useful chemical product. The purpose of this thesis will be to examine the possibilities of a new solar chemical cycle the produces iron and ethylene from hematite (a form of iron oxide) and ethane using concentrated solar power. These two products are important stepping stones in the production of steel and polymers. This process could allow for the current process of steel production to move away from processes using coal and towards a more sustainable process using the hydrogen formed from the ethane cracking process and solar energy. The thesis will include: (1) the development of a new solar powered iron and ethylene combined cycle, (2) a feasibility study of a Concentrated Solar Heat Supply System (CSHSS) being developed at Georgia Tech, and (3) an assessment of the proposed cycle. The assessment will include an estimate of production including a thermodynamic ASPEN model, assessment of research to realize actualization of the theoretical cycle, an exergy analysis, and a heat exchanger analysis for the exchange of heat between the CSHSS and the chemical process.

Doctor of Philosophy (PhD) / The goal of this research was to investigate changes in the physiological properties including firmness, stiffness, weight, background colour, ethylene production and respiration of ‘Cripps Pink’ apple stored under different temperature and atmosphere conditions,. This research also seeks to establish mathematical models for the prediction of changes in firmness and stiffness of the apple during normal atmosphere (NA) storage. Experiments were conducted to determine the quality changes in ‘Cripps Pink’ apple under three sets of storage conditions. The first set of storage conditions consisted of NA storage at 0oC, 2.5oC, 5oC, 10oC, 20oC and 30oC. In the second set of conditions the apples were placed in NA cold storage at 0oC for 61 days, followed by NA storage at the aforementioned six temperatures. The third set of conditions consisted of controlled atmosphere (CA) (2 kPa O2 : 1 kPa CO2) at 0oC storage for 102 days followed by NA storage at the six temperatures mentioned previously. The firmness, stiffness, weight loss, skin colour, ethylene and carbon dioxide production of the apples were monitored at specific time intervals during storage. Firmness was measured using a HortPlus Quick Measure Penetrometer (HortPlus Ltd, Hawke Bat, New Zealand); stiffness was measured using a commercial acoustic firmness sensor-AFS (AWETA, Nootdorp, The Netherlands). Experimental data analysis was performed using the GraphPad Prism 4.03, 2005 software package. The Least-Squares method and iterative non-linear regression were used to model and simulate changes in firmness and stiffness in GraphPad Prism 4.03, 2005 and DataFit 8.1, 2005 softwares. The experimental results indicated that the firmness and stiffness of ‘Cripps Pink’ apple stored in NA decreased with increases in temperature and time. Under NA, the softening pattern was tri-phasic for apples stored at 0oC, 2.5oC and 5oC for firmness, and at 0oC and 2.5oC for stiffness. However, there were only two softening phases for apples stored at higher temperatures. NA at 0oC, 2.5oC and 5oC improved skin background colour and extended the storage ability of apples compared to higher temperatures. CA during the first stage of storage better maintained the firmness and stiffness of the apples. However, it reduced subsequent ethylene and carbon dioxide (CO2) production after removal from storage. Steep increases in ethylene and CO2 production coincided with rapid softening in the fruit flesh and yellowing of the skin background colour, under NA conditions. The exponential decay model was the best model for predicting changes in the firmness, stiffness and keeping quality of the apples. The exponential decay model satisfied the biochemical theory of softening in the apple, and had the highest fitness to the experimental data collected over the wide range of temperatures. The softening rate increased exponentially with storage temperature complying with the Arrhenius equation. Therefore a combination of the exponential decay model with the Arrhenius equation was found to best characterise the softening process and to predict changes in the firmness and stiffness of apples stored at different temperatures in NA conditions.

El presente trabajo está justificado por la necesidad real constatada por las empresas hortofrutícolas de mejorar la calidad de la lechuga Iceberg en vistas a su exportación a los países de la Unión Europea y, también, con el propósito de conocer el comportamiento fisiológico de esta hortaliza cultivada en la comarca del Campo de Cartagena de la Región de Murcia (España). La mejora de la calidad hace referencia a conseguir mantenerla desde la cosecha hasta el lugar de consumo, ya que la calidad del producto cosechado suele ser bastante buena. Respecto al comportamiento fisiológico, se ha pretendido conocer el potencial de conservación de la lechuga y el efecto del preenfriamiento y uso de las atmósferas modificadas en el mantenimiento de la calidad. También se han estudiado las alteraciones fisiológicas y microbianas que aparecen en las lechugas del Campo de Cartagena y el efecto de la refrigeración y coadyuvantes durante su almacenamiento. Como un complemento necesa rio al estudio de la calidad, se han determinado las características de permeación a los gases metabólicos de los envases plásticos destinados a la conservación de los productos vegetales en atmósferas modificadas y el comportamiento respiratorio de la lechuga con el fin de obtener una estrategia de diseño de envase que permita conocer las exigencias de este producto en relación al tipo de envasado que requiere. Los resultados han puesto de manifiesto que la lechuga Iceberg cultivada en el Campo de Cartagena es muy sensible a las alteraciones fisiológicas de nervaduras rosáceas y mancha canela sin mediación del etileno, que constituyen los principales problemas en su exportación. La solución planteada pasa por sustituir el envase actual, polipropileno macroperforado, por polipropilenos no perforados, biorientados o de tipo estándar, que han permitido reducir de forma drástica la incidencia de estas dos alteraciones y mantener un mejor aspecto visual incluso tras dos semanas de almacenamiento refrigerado. Si embargo, se debe controlar correctamente la temperatura y mantener la cadena de frío, ya que el envasado de la lechuga en estos polímeros no perforados presenta riesgos de incidencia de otras alteraciones fisiológicas como la mancha parda y el daño del cogollo interior. La reducción de las alteraciones en atmósfera modificada se ha atribuido a los niveles favorables de O2 (no menos del 10% y no más del 15%) y de CO2 (entre el 1 y el 4%) y su efecto beneficioso para frenar el metabolismo combinado con la reducción de la temperatura de refrigeración. / This study was accomplished because of horticultural Spanish companies needed to improve Iceberg lettuce quality to be exported towards the European Community countries and, at the same time, to know the physiological behaviour of this vegetable grown in the Campo de Cartagena area of the Murcia Region (Spain). The quality improvement consists of maintaining the lettuce quality from harvest to consumption, since the lettuce quality was usually quite good at harvest. Regarding to physiological behaviour, in this work it was searched both the lettuce shelf life and the effect of cooling and modified atmosphere packaging on maintaining quality. In the same way, the physiological and microbiological disorders which appeared in the lettuces grown in the Campo de Cartagena and the effect of chilling storage and other techniques were studied. In addition to this quality study, lettuce respiration and metabolic gas permeation throughout polymeric packages for using in modifi ed atmosphere packaging were studied. The data obtained permit to know the film requirements and to design an optimum modified atmosphere packaging for Iceberg lettuce. The results demonstrated that Iceberg lettuce grown in Campo de Cartagena is very sensitive to physiological disorders ‘pink rib’ and ‘russet spotting’ this last one without ethylene releasing. These are the main problems when lettuces are exported. Both non-perforated bioriented polypropylene and standard polypropylene were proposed as alternatives to substitute the conventional macroperforated polypropylene. The gas composition reached within packages with these films permitted to reduce drastically the above mentioned disorders and to maintain the overall quality for periods longer than two weeks under chilling. Both temperature and cold chain must be correctly kept so that no risks of either ‘brown stain’ or ‘heart-leaf injury’ can appear due to an inadequate use of non-perforated films. The disorders red uction was attributed to levels of O2 (between 10 to 15%) and CO2 (between 1 and 4%) within the packages and the favourable effects of those atmospheres combined with the use of chilling storage temperatures on restraining lettuce metabolism.

Doctor of Philosophy (PhD) / The goal of this research was to investigate changes in the physiological properties including firmness, stiffness, weight, background colour, ethylene production and respiration of ‘Cripps Pink’ apple stored under different temperature and atmosphere conditions,. This research also seeks to establish mathematical models for the prediction of changes in firmness and stiffness of the apple during normal atmosphere (NA) storage. Experiments were conducted to determine the quality changes in ‘Cripps Pink’ apple under three sets of storage conditions. The first set of storage conditions consisted of NA storage at 0oC, 2.5oC, 5oC, 10oC, 20oC and 30oC. In the second set of conditions the apples were placed in NA cold storage at 0oC for 61 days, followed by NA storage at the aforementioned six temperatures. The third set of conditions consisted of controlled atmosphere (CA) (2 kPa O2 : 1 kPa CO2) at 0oC storage for 102 days followed by NA storage at the six temperatures mentioned previously. The firmness, stiffness, weight loss, skin colour, ethylene and carbon dioxide production of the apples were monitored at specific time intervals during storage. Firmness was measured using a HortPlus Quick Measure Penetrometer (HortPlus Ltd, Hawke Bat, New Zealand); stiffness was measured using a commercial acoustic firmness sensor-AFS (AWETA, Nootdorp, The Netherlands). Experimental data analysis was performed using the GraphPad Prism 4.03, 2005 software package. The Least-Squares method and iterative non-linear regression were used to model and simulate changes in firmness and stiffness in GraphPad Prism 4.03, 2005 and DataFit 8.1, 2005 softwares. The experimental results indicated that the firmness and stiffness of ‘Cripps Pink’ apple stored in NA decreased with increases in temperature and time. Under NA, the softening pattern was tri-phasic for apples stored at 0oC, 2.5oC and 5oC for firmness, and at 0oC and 2.5oC for stiffness. However, there were only two softening phases for apples stored at higher temperatures. NA at 0oC, 2.5oC and 5oC improved skin background colour and extended the storage ability of apples compared to higher temperatures. CA during the first stage of storage better maintained the firmness and stiffness of the apples. However, it reduced subsequent ethylene and carbon dioxide (CO2) production after removal from storage. Steep increases in ethylene and CO2 production coincided with rapid softening in the fruit flesh and yellowing of the skin background colour, under NA conditions. The exponential decay model was the best model for predicting changes in the firmness, stiffness and keeping quality of the apples. The exponential decay model satisfied the biochemical theory of softening in the apple, and had the highest fitness to the experimental data collected over the wide range of temperatures. The softening rate increased exponentially with storage temperature complying with the Arrhenius equation. Therefore a combination of the exponential decay model with the Arrhenius equation was found to best characterise the softening process and to predict changes in the firmness and stiffness of apples stored at different temperatures in NA conditions.