Postharvest regreening: A species- and variety-dependent process triggered by phytohormones and light.

Abstract

Background and aims: The ripening process, characterised by chlorophyll degradation and carotenoids accumulation, culminates in senescence, affecting fruit quality and shelf life. However, certain fruits can undergo regreening, a phenomenon where chlorophyll reaccumulates, opposing the typical senescence process. This study aimed to investigate the influence of phytohormones and light on postharvest regreening in grapefruit (Citrus x paradisi Macfad.) and assess its occurrence in tomatoes (Solanum lycopersicum L.).

Methods: Cherry tomatoes (red and yellow) and grapefruits were treated with phytohormones (gibberellin, cytokinin, and their combination) under fluorescent light with sunlight background to evaluate regreening potential. In yellow tomatoes, additional light conditions (fluorescent, white and blue LED light) were evaluated. Colour changes were monitored using colorimetry. Regreening in yellow tomatoes was further assessed by quantifying chlorophyll and carotenoid contents. Firmness and weight loss were measured as senescence-associated changes in regreened tomatoes.

Key results: The combination of gibberellin and cytokinin under fluorescent light with sunlight background significantly induced regreening in grapefruits. Furthermore, regreening was observed for the first time in cherry tomatoes, albeit it was exclusively observed in yellow varieties when exposed to fluorescent light with sunlight background. Regreening became apparent after 20 days of light treatment and was characterized by a 45% increase in total chlorophyll content, reversing approximately 42% of the loss of green colouration. Despite restoring green pigmentation, the regreening process did not modulate other senescence-related parameters, such as firmness or weight loss.

Conclusions: These findings highlight that regreening can occur in certain postharvest fruits, including grapefruits and yellow cherry tomatoes, under specific light and hormonal conditions. The absence of regreening in red cherry tomatoes, suggests that regreening is not only species- but also variety-dependent. Notably, this study represents the first observation of regreening in yellow tomatoes, where it results in a clear restoration of green colour through chlorophyll reaccumulation.