Search

Author(s): Albornoz, K; Chen, B; McCarthy, M; Zhang, L; Cantwell, M; Beckles, DM | Abstract: Tomato, like most species from tropical and subtropical regions, exhibits postharvest chilling injury (PCI) when stored at low temperatures. Because of its economic importance and the functional genomics tools available, we used tomato to investigate aspects of fruit PCI development. We asked two questions: First, are there spatial-temporal differences in the development of PCI that can be detected by magnetic resonance imaging (MRI)? Here, the aim was to use a non-invasive method to study PCI progression in vivo. At mature green and breaker, the pericarp, locular tissue and columella produced distinct D-values while in contrast, there was no such differentiation in riper fruit. Although the pericarp is where most PCI symptoms are visible, this tissue showed less dynamism upon cold exposure, compared to the inner tissues as detected by MRI. This suggests the occurrence of distinct, independently modulated mechanisms contributing to the development of PCI-symptomatology. Collectively our data showed that the MRI could detect fruit ripening, its attenuation by cold, and fruit tissue-specific responses to chilling stress. The second question we asked was if epigenetic modification of the tomato genome or transcriptome influences PCI response. We examined PCI severity in fruit injected with a demethylating agent, 5- azacytidine (AZA). Two tomato genotypes exposed to varying severities of cold-stress were studied. Results suggested that AZA was able to moderate PCI in 'Micro-Tom' after 3 weeks at 2.5°C, while different patterns were observed in 'Sun Cherry' across various cold treatments. The effects of AZA on PCI were complex, multilayered and highly context-dependent.

Fruit ripening is a genetically programmed process which leads to an assortment of physiological and metabolic changes that irreversibly alter its characteristics. Depending on the species, fruit maturation can be either climacteric or non-climacteric. In both cases there is a metabolic shift from normal development conditions toward the fully mature state, but climacteric fruit is characterized by a sharp increase in respiration. In non-climacteric fruit, that generally does not display this feature, respiration changes can be affected by processes related to postharvest storage. This review describes some of the many ways in which mitochondrial metabolism is implicated in this crucial reproductive stage, such as the connection between ethylene production and respiration rate, the involvement of alternative oxidase (AOX) and plant uncoupling mitochondrial protein (PUMP) during the ripening and the common alterations of this organelle in fruits affected by different stress conditions Fil: Perotti, Valeria Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Centro de Estudios Fotosinteticos y Bioquimicos. Universidad Nacional de Rosario. Facultad de Cs.bioquímicas y Farmaceuticas. Centro de Estudios Fotosinteticos y Bioquimicos; Argentina Fil: Moreno Blando, Alejandra Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Centro de Estudios Fotosinteticos y Bioquimicos. Universidad Nacional de Rosario. Facultad de Cs.bioquímicas y Farmaceuticas. Centro de Estudios Fotosinteticos y Bioquimicos; Argentina Fil: Podesta, Florencio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Centro de Estudios Fotosinteticos y Bioquimicos. Universidad Nacional de Rosario. Facultad de Cs.bioquímicas y Farmaceuticas. Centro de Estudios Fotosinteticos y Bioquimicos; Argentina

Temperature effect on postphloem transport in tomato fruits was analyzed by measuring fruit growth rate, pedicel sugar flux and fruit respiratory CO_2 efflux under changes in air temperature around fruits. Dynamic responses of fruit growth rate and pedicel sugar flux to temperature change around fruits were clearly found to be associated with change in fruit respiration. Fruit growth rate and pedicel sugar flux were remarkably enhanced with fruit respiration by temperature rise around fruits, where those Q_ values between 20℃ and 30℃ distributed around 2.3. These enhancements in fruit growth and sugar translocation by the temperature rise were not found in the truss with the respiration-inhibited fruits. From these results, it can be suggested that respiration in tomato fruits contributes to the temperature effects on the expansive growth and the sugar accumulation through regulation of the energy-dependent process of the postphloem sugar transport in the fruits.

A multiple chamber system was developed for on-line measurements of gas (CO_2 and H_2O) fluxes in intact fruits and leaflets of tomato plants, where fruit growth rate and pedicel sap flux can be also measured. By using the system for the simultaneous measurements with six plants, effect of water deficit on fruit growth was analyzed in relation to water balance and respiration in the fruits and to photosynthesis and transpiration in the leaflets. The water deficit caused drastic depression in fruit growth in the daytime, which was considered to be associated with depressions in pedicel sap flux, fruit respiration and leaf photosynthesis. Furthermore, sap back flow and fruit shrinkage corresponding to about 2% of the fruit volume were induced by rise in evaporative demand under the water deficit. These results suggest that the multiple chamber system developed can be applied to quantitative analyses of environmental effects on fruit growth, translocation and sink-source relationship in tomato plants.

A system for on-line measurements of CO_2 and H_2O gas fluxes, pedicel sap flux and expansive growth in an intact tomato fruit was newly developed, where the gas fluxes in leaflets also can be measured. The system was composed of a fruit chamber, a leaf chamber, CO_2 and H_2O gas analyzing unit and an on-line computer. Furthermore a laser displacement sensors system was equipped in the fruit chamber for evaluating fruit expansive growth, and the pedicel sap flux was evaluated as sum of the H_2O gas flux and the growth rate in the fruit. Diurnal dynamics as affected by light condition were observed in respiration, transpiration, pedicel sap flux and expansive growth in the immature intact fruit, which were clearly enhanced in the light. In fruit water balance, about 30% of the sap flux imported through the pedicel was lost by transpiration from the calyx and the berry, and the residual 70% contributed to fruit expansive growth. These results suggest that the on-line system developed is applicable to quantitative analyses of respiration, sap flux and water balance of an intact tamato fruit in environmental studies on fruit expansive growth and photoassimilate translocation.

International audience; Based on the citrate model of Lobit and colleagues and measured data, a new model, which is able to reproduce the variation over time of citrate concentration in two peach cultivars, has been proposed. As in the original one, the new model calculates the rate of citrate synthesis or degradation as the product of a 'synthesis potential' and an 'efficiency level'. While in the old model the 'efficiency level' was a simple linear function of temperature and respiration, in the new one its relationship with respiration is accounted for by a coefficient that decreases throughout fruit development. The differences in model parameters between the two cultivars were investigated: late-maturing cv. Suncrest had significantly lower citrate synthesis potential than mid-maturing cv. Fidelia. The responses of citrate concentration to model parameters, temperature, fruit respiration, and growth curves were studied. The most important parameter in the new model, k(4,2), represented the date when the relationship between respiration and 'efficiency level' changed from positive to negative. Raising mean temperature increased the citrate concentration at the beginning and decreased it near maturity for cv. Suncrest, while citrate concentration increased throughout fruit development and more strongly for cv. Fidelia. An increase in the mesocarp dry weight increased both fruit respiration and citrate concentration at the beginning of fruit development, while near maturity it increased fruit respiration but decreased citrate concentration. The model was also able to reproduce the effect of assimilate supply (leaf:fruit ratio). Further potential uses of the model were discussed

The rates of dry weight increase and respiration of fruits were measured throughout fruit ontogeny at 20, 25 and 30°C in cucumber (Cucumis sativus L. cv. Corona). By maintaining one or five fruits per plant, which strongly affected fruit dry weight but not ontogeny, the effects of fruit size and ontogeny on respiration could be studied separately. The respiration rate per fruit followed a sigmoid curve during fruit ontogeny, while the specific respiration rate (respiration rate per unit dry weight) declined with time after anthesis. The specific respiration rate was almost linearly related to the relative growth rate. The specific respiratory costs for both growth and maintenance were highest in young fruits, but were not affected by fruit size. The average specific respiratory costs for growth and maintenance at 25°C were 3.3-3.9 mmol CO 2 g −1 and 4.0 nmol CO 2 g −1 s −1 , respectively. An increase in temperature had no effect on the specific respiratory costs for growth, while the costs for maintenance increased with a Q 10 of about 2. The costs for growth agreed reasonably well with theoretical estimates based on the chemical composition of the fruits but not with estimates based on only the carbon and ash content. The respiratory losses as a fraction of the total carbon requirement of a fruit changed during fruit ontogeny, but were independent of temperature and were similar for slow- and fast-growing fruits. The cumulative respiratory losses accounted for 13-15% of the total carbon requirement