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Harvested fruit undergo carbon and energy deprivation. However, the events underlying this energy-related stress in detached fruit and their involvement in cell damage have not yet been elucidated. We showed that supplementing detached sweet oranges with additional carbon or energy sources reduced peel damage, while inhibitors of energy metabolism increased it. We investigated the effect of an exogenous source of carbon (glycerol), energy (ATP), and an inhibitor of energy metabolism 2-deoxy-D-glucose (DeOGlc) + sodium iodoacetate (IAc), on the transcriptome of harvested fruit flavedo (outer peel part). ATP and Gly induced common, but also specific, alternative modes of energy metabolism by reducing the stress caused by energy shortage. They also induced shifts in energy metabolism that led to the production of the intermediates required for plant defense secondary metabolites to form. ATP and Gly triggered changes in the expression of the genes involved in cell lesion containment through a defined pathway involving hormones and redox-mediated signaling. DeOGlc + IAc had a contrasting effect on some of these mechanisms. These chemicals altered the biological processes related to membrane integrity and molecular mechanisms involving reactive oxygen species (ROS) production, and lipid and protein degradation.

Low non-freezing temperature may cause chilling injury (CI), which is responsible for external quality deterioration in many chilling-sensitive horticultural crops. Exposure of chilling-sensitive citrus cultivars to non-lethal high-temperature conditioning may increase their chilling tolerance. Very little information is available about the molecular events involved in such tolerance. In this work, the molecular events associated with the low temperature tolerance induced by heating Fortune mandarin, which is very sensitive to chilling, for 3 days at 37°C prior to cold storage is presented. A transcriptomic analysis reveals that heat-conditioning has an important impact favoring the repression of genes in cold-stored fruit, and that long-term heat-induced chilling tolerance is an active process that requires activation of transcription factors involved in transcription initiation and of the WRKY family. The analysis also shows that chilling favors degradation processes, which affect lipids and proteins, and that the protective effect of the heat-conditioning treatment is more likely to be related to the repression of the genes involved in lipid degradation than to the modification of fatty acids unsaturation, which affects membrane permeability. Another major factor associated with the beneficial effect of the heat treatment on reducing CI is the regulation of stress-related proteins. Many of the genes that encoded such proteins are involved in secondary metabolism and in oxidative stress-related processes.

The ethylene perception inhibitor 1-methylcyclopropene (1-MCP) has been critical in understanding the hormone's mode of action. However, 1-MCP may trigger other processes that could vary the interpretation of results related until now to ethylene, which we aim to understand by using transcriptomic analysis. Transcriptomic changes in ethylene and 1-MCP-treated ‘Navelate’ (Citrus sinensis L. Osbeck) oranges were studied in parallel with changes in ethylene production, respiration and peel damage. The effects of compounds modifying the levels of the ethylene co-product cyanide and nitric oxide (NO) on fruit physiology were also studied. Results suggested that: 1) The ethylene treatment caused sub-lethal stress since it induced stress-related responses and reduced peel damage; 2) 1-MCP induced ethylenedependent and ethylene-independent responsive networks; 3) 1-MCP triggered ethylene overproduction, stress-related responses and metabolic shifts aimed to cope with cell toxicity, which mostly affected to the inner part of the peel (albedo); 4) 1-MCP increased respiration and drove metabolism reconfiguration for favoring energy conservation but up-regulated genes related to lipid and protein degradation and triggered the over-expression of genes associated with the plasma membrane cellular component; 5) Xenobiotics and/or reactive oxygen species (ROS) might act as signals for defense responses in the ethylene-treated fruit, while their uncontrolled generation would induce processes mimicking cell death and damage in 1-MCP-treated fruit; 6) ROS, the ethylene co-product cyanide and NO may converge in the toxic effects of 1-MCP.

Muchos productos hortofrutícolas desarrollan 'daños de frío' durante la conservación a temperaturas inferiores a 12-15 ºC. El tratamiento de 'curado' (3 días 37 ºC) previene la aparición de esta alteración en los frutos cítricos cuando se conservan a 2 ºC. En la mandarina 'Fortune', muy susceptible al frío, los daños se manifiestan como un picado y áreas de color pardo en la parte más externa de la corteza (flavedo). Otra de las alteraciones frecuentes en la postcosecha de los frutos cítricos es el 'colapso de la corteza', que se produce a temperaturas superiores a las que causan 'daños de frío' y cuyos síntomas se caracterizan por la aparición de depresiones en la piel. El acondicionamiento de frutos de 'Navelate' durante 4 días con 10 ?L L-1 de etileno a 22 ºC y 90-95% de humedad relativa (HR) redujo notablemente la incidencia de esta alteración, mientras que la aplicación de 1 ?L L-1 de 1-metilciclopropeno (1-MCP), un inhibidor de la percepción de etileno, la potenció. Para entender los mecanismos asociados al efecto beneficioso del curado reduciendo el 'daño de frío' y del etileno frente al 'colapso de la corteza', se han evaluado cambios globales en la expresión génica en el flavedo de frutos de mandarina 'Fortune' almacenados a 2 ºC, directamente o después del curado, y en el flavedo y albedo de frutos de naranja 'Navelate' almacenados a 22 ºC y 90-95% de HR después de ser tratados con etileno o 1-MCP. Para ello se han empleado dos micromatrices de cDNA generadas en el Consorcio de Genómica Funcional de Cítricos (CFGP). La eficacia del curado reduciendo la incidencia de 'daños de frío' parece estar más relacionada con su efecto evitando la inducción de genes implicados en la degradación de lípidos durante el almacenamiento en frío, que con cambios en la expresión de genes del metabolismo de ácidos grasos que afectan al grado de insaturación de los mismos o a la síntesis de ceras. Además, la expresión de genes del metabolismo de fenilpropanoides, y de otros que