Integrated Oxidative Stress, Cell Wall Modification, and Transcriptomic Responses Associated with Postharvest Quality Deterioration in ‘Sapphire’ Blueberry

The transition of blueberry fruits from the ripening stage to the post-harvest senescence stage is rapid. However, the internal physiological, biochemical, and molecular mechanisms underlying this process have not been elucidated. This study analyzed changes during blueberry fruit development and post-harvest storage senescence to examine processes associated with quality loss. Post-harvest senescence was associated with a marked metabolic transition, which coincided with a transient ethylene peak at maturity and the accumulation of sugars and anthocyanins. This ripening phase was followed by increased oxidative stress, reflected in higher membrane damage, elevated malondialdehyde (MDA) levels, and shifts in conductivity and antioxidant activities, including reduced superoxide dismutase (SOD) levels and increased catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO) activities. The oxidative conditions were associated with higher rotting rates and coincided with fruit softening and increased polygalacturonase (PG) and β-galactosidase (β-Gal) activities. Correlation analysis identified a “ripening stress-activation cluster” (ethylene, sugars, anthocyanin, CAT/POD/PPO, MDA, PG/β-Gal, and RR) and a “textural integrity cluster” (hardness, chewiness, titratable acidity (TA), and ascorbic acid); these clusters represent correlation-based groupings of variables rather than experimentally validated functional modules. Transcriptomic profiling further showed extensive gene expression changes during storage. Functional enrichment analysis supported a shift from developmental metabolism toward senescence-associated pathways, including starch and sucrose metabolism, phenylpropanoid biosynthesis, flavonoid biosynthesis, mitogen activated protein kinase (MAPK) signaling, and cell wall modification. Overall, the results support a model in which ethylene signaling, oxidative stress, and cell wall disassembly are associated with the transition from ripening to senescence, offering insights for improving blueberry post-harvest quality and extending shelf life.