1-Methylcyclopropene differentially regulates metabolic responses in the stem-end and calyx-end flesh tissues of 'Empire' apple during long-term controlled atmosphere storage

Authors: LEE, JINWOOK - Chung-Ang University; Leisso, Rachel; Rudell, David; WATKINS, CHRISTOPHER - Cornell University

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2022
Publication Date: 6/28/2022
Citation: Lee, J., Leisso, R.S., Rudell Jr., D.R., Watkins, C.B. 2022. 1-Methylcyclopropene differentially regulates metabolic responses in the stem-end and calyx-end flesh tissues of 'Empire' apple during long-term controlled atmosphere storage. Postharvest Biology and Technology. 192. Article 112018. https://doi.org/10.1016/j.postharvbio.2022.112018.
DOI: https://doi.org/10.1016/j.postharvbio.2022.112018

Interpretive Summary: 1-Methylcyclopropene (1-MCP), a common postharvest treatment for managing aspects of fruit ripening, can provoke flesh browning in 'Empire' apples during storage, with browning beginning in the stem-end and progressing to the calyx end. This study details differences in specific primary and secondary metabolites in the stem-end versus the calyx end of 'Empire' fruit treated fruit contrasted to untreated fruit, and comments on physiological insights that this comparison offers, in terms of disorder development, ethylene action inhibition, and in-fruit spatial influence on metabolism.

Technical Abstract: Firm flesh browning, a postharvest disorder of ‘Empire’ apples, can develop during controlled atmosphere (CA) storage. The disorder is initiated in tissues at the stem-end tissue and progressively develops through the calyx-end region of fruit. The susceptibility of fruit to the disorder can be provoked by the application of 1-methylcyclopropene (1-MCP) prior to storage. To gain a better understanding of the metabolic changes associated with disorder development, we coupled metabolic profiling with measures of flesh tissue color in partial least squares-discriminant analysis (PLS-DA) to determine changes in metabolic profile occurring in stem and calyx tissues of untreated and 1-MCP treated fruit during CA storage. Flesh tissues were less light (L*) in the stem-end tissues than in the calyx-end tissues and to a greater extent in 1-MCP treated than untreated fruit. Reduction in L* in 1-MCP treated fruit corresponded to metabolic divergence between stem-end and calyx-end tissues. Furthermore, 1-MCP treatment resulted in lower levels of volatile organic compounds (VOCs), but less so in the stem-end tissue than in the calyx-end tissues. The levels of most amino acids and VOCs were higher in the stem-end tissues of 1-MCP treated fruit than in untreated fruit. Of the VOCs, methanol, acetaldehyde and ethanol concentrations were much greater in the stem-end tissue than in the calyx-end tissues. In summary, metabolic profiling indicates that 1-MCP treatment induces greater physiological changes in the stem-end tissues than in the calyx-end ones under hypoxic storage condition. While the underlying metabolic processes that result in firm flesh browning remain to be elucidated, the accumulation of small molecule compounds, such as amino acids, in the stem-end tissues suggests that 1-MCP affects ethylene related pathways in this region to a greater extent, and may be associated with higher incidence of flesh browning during long-term CA storage.