Abstract
Postharvest chilling injury (PCI) reduces fruit quality and shelf-life in tomato (Solanum lycopersicum L.). PCI has been traditionally studied in the pericarp, however its development is likely heterogeneous in different fruit tissues. To gain insight into PCI’s spatio-temporal development, we used postharvest biomarkers e.g. respiration and ethylene rates, ion leakage etc., to confirm the occurrence of PCI, and compared these data with molecular (gene expression), biophysical (MRI data) and biochemical parameters (Malondialdehyde (MDA) and starch content) from the pericarp or columella. Tissues were stored at control (12.5 °C) or PCI-inducing temperatures (2.5 or 5 °C) followed by rewarming at 20 °C. MRI and ion leakage revealed that cold irreversibly impairs ripening-associated membrane liquefaction; MRI also showed that the internal and external fruit tissues responded differently to cold. MDA and especially starch contents, were affected by chilling in a tissue-specific manner. The expression of the six genes studied: ACO1 and ACS2 (ripening), CBF1 (cold response), DHN, AOX1a and LoxB (stress-related) showed non-overlapping temporal and spatially-specific responses. Overall, the data highlighted the interconnectedness of fruit cold response and ripening, and showed how cold stress reconfigures the latter. They further underscored that multidimensional spatial and temporal biological studies are needed to develop effective solutions to PCI.
Highlights
Refrigeration is the most effective tool to prevent postharvest losses[1] of fruits and vegetables, its utilization is limited in cold-sensitive commodities, which typically originate from tropical and subtropical regions[2,3,4]
2.5 °C, 5 °C and 12.5 °C were used as chilling temperatures, with 2.5 °C and 5 °C expected to induce Postharvest chilling injury (PCI) while 12.5 °C should not and acts as a cold-storage control
The production of these gases was suppressed during the period of chilling and increased up to 100% relative to the control (p < 0.05) after rewarming to 20 °C (Supplementary Fig. S1a), which was proportional to the occurrence of PCI
Summary
Refrigeration is the most effective tool to prevent postharvest losses[1] of fruits and vegetables, its utilization is limited in cold-sensitive commodities, which typically originate from tropical and subtropical regions[2,3,4]. Tomato (Solanum lycopersicum L.) is the second most important vegetable crop, ranking number one in terms of gross production value in the world[8] It is a key source of antioxidants for humans[9,10] and is a model organism for the study of fleshy-fruited species[11,12,13]. If cold exposure is mild or limited, cellular homeostasis and fruit quality will be maintained through the activation of alternative oxidases, and protective proteins such as dehydrins, in part, by the regulation of upstream factors of the cold response pathways such as C-Binding Repeat transcription Factors (CBFs)[32,33] Beyond this threshold, or during rewarming of previously cold-stored fruit, progressive loss of selective membrane permeability due to lipid peroxidation may occur. This in turn, can lead to secondary metabolic and physiological dysfunction such as the leakage of water, solutes and metabolites, ROS accumulation, bursts in ethylene and respiratory rates, and later, ripening disruption, surface lesions and fungal infestation[3,14,34,35]
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