Abstract
Cuticle composition is an important economic trait in agriculture, as it is the first protective barrier of the plant against environmental conditions. The main goal of this work was to study the role of the cuticular wax in maintaining the postharvest quality of zucchini fruit, by comparing two commercial varieties with contrasting behavior against low temperatures; the cold-tolerant variety ‘Natura’, and the cold-sensitive ‘Sinatra’, as well as ‘Sinatra’ fruit with induced-chilling tolerance through a preconditioning treatment (15°C for 48 h). The freshly-harvested ‘Natura’ fruit had a well-detectable cuticle with a significant lower permeability and a subset of 15 up-regulated cuticle-related genes. SEM showed that zucchini epicuticular waxes mainly consisted of round-shaped crystals and clusters of them, and areas with more dense crystal deposition were found in fruit of ‘Natura’ and of preconditioned ‘Sinatra’. The cuticular wax load per surface was higher in ‘Natura’ than in ‘Sinatra’ fruit at harvest and after 14 days at 4°C. In addition, total cuticular wax load only increased in ‘Natura’ and preconditioned ‘Sinatra’ fruit with cold storage. With respect to the chemical composition of the waxes, the most abundant components were alkanes, in both ‘Natura’ and ‘Sinatra’, with similar values at harvest. The total alkane content only increased in ‘Natura’ fruit and in the preconditioned ‘Sinatra’ fruit after cold storage, whereas the amount of total acids decreased, with the lowest values observed in the fruit that showed less chilling injury (CI) and weight loss. Two esters were detected, and their content also decreased with the storage in both varieties, with a greater reduction observed in the cold-tolerant variety in response to low temperature. Gene expression analysis showed significant differences between varieties, especially in CpCER1-like and CpCER3-like genes, involved in alkane production, as well as in the transcription factors CpWIN1-like and CpFUL1-like, associated with cuticle development and epidermal wax accumulation in other species. These results suggest an important role of the alkane biosynthetic pathway and cuticle morphology in maintaining the postharvest quality of zucchini fruit during the storage at low temperatures.
Highlights
The cuticle is a barrier that was first developed in plants during their colonization to dry land
Cuticular waxes consist of a mixture of very-long chain fatty acids (VLCFAs) and its derivatives, which are synthesized by two pathways: the alcohol-forming pathway, which generates primary alcohols and esters, and the alkane-forming pathway, which produces aldehydes, alkanes, secondary alcohols, and ketones (Yeats and Rose, 2013)
The implication of the cuticular waxes in the resistance to cold stress during postharvest storage of zucchini was investigated in the present study
Summary
The cuticle is a barrier that was first developed in plants during their colonization to dry land. The cuticle is synthesized by the epidermal cell layer and is composed of a cutin matrix, in contact with the cell wall, and a complex group of different cuticular waxes that embed and cover the cutin matrix, constituting intracuticular and epicuticular waxes, respectively, (Ensikat et al, 2006; Koch and Ensikat, 2008; Buschhaus and Jetter, 2011). Cuticular waxes consist of a mixture of very-long chain fatty acids (VLCFAs) and its derivatives, which are synthesized by two pathways: the alcohol-forming pathway, which generates primary alcohols and esters, and the alkane-forming pathway, which produces aldehydes, alkanes, secondary alcohols, and ketones (Yeats and Rose, 2013). Fatty acid alcohols, aldehydes, ketones, and triterpenoids have been detected (Bauer et al, 2004; Parsons et al, 2012; Wang et al, 2015a; Wu et al, 2018)
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