# Fruit respiration: putting alternative pathways into perspective

## TL;DR

This paper reviews how alternative respiratory pathways in fruits influence metabolism, ripening, and stress resilience, offering new insights for improving fruit quality.

## Contribution

The paper provides a comprehensive review of mitochondrial alternative respiratory pathways in fruits, emphasizing their regulatory roles and potential for metabolic engineering.

## Key findings

- Alternative respiratory pathways are central to metabolic flexibility and redox homeostasis in fruits.
- CO2 refixation and organic acid metabolism impose specific demands on mitochondrial electron transport.
- Interactions between respiration and ethylene signaling involve feedback loops and redox-sensitive control.

## Abstract

Over the past century, research has significantly advanced our understanding of fruit respiration, from (eco)physiological processes to molecular mechanisms. This review focuses on the functional relevance and regulatory roles of mitochondrial alternative respiratory pathways (ARPs) during fruit growth and ripening. We revisit classical distinctions between climacteric and nonclimacteric fruits, considering recent insights into the alternative oxidase, uncoupling proteins, and type II NAD(P)H dehydrogenases (NDIIs). These components are increasingly recognized as central to maintaining metabolic flexibility, energy balance, and redox homeostasis, supporting both primary and secondary metabolism. We highlight how CO2 refixation and organic acid metabolism, often displaying C4/CAM‐like features, impose specific demands on mitochondrial electron transport, and how spatial heterogeneity in metabolism and O2 availability across fruit tissues can shape respiratory activity. Interactions between fruit photosynthesis and respiration remain poorly understood, particularly under stress. The interplay between respiration, ethylene biosynthesis, and signaling is discussed, emphasizing feedback loops involving mitochondrial retrograde regulation and redox‐sensitive control of ripening. Key knowledge gaps include in vivo flux analyses, tissue‐resolved energy profiling, and functional characterization of underexplored ARP components. Finally, we outline postharvest and metabolic engineering strategies targeting ARPs as complementary to ethylene‐centered approaches to improve fruit quality, stress resilience, and nutritional value.