Different Preclimacteric Events in Apple Cultivars with Modified Ripening Physiology

Area of Science:

• Plant Physiology
• Fruit Ripening Science
• Molecular Biology

Background:

• Apple (Malus domestica) cultivars exhibit varied storage potential, with early-season varieties like 'Anna' often showing faster deterioration compared to mid-late season types ('Galaxy', 'GD').
• Poor storage is linked to physiological factors such as respiration rate, ethylene production, and lipid oxidation, which are influenced by gene expression.
• Understanding pre-harvest physiological events is crucial for predicting and potentially mitigating post-harvest storage issues in apples.

Purpose of the Study:

• To investigate the pre-climacteric physiological and molecular factors contributing to the poor storage capacity of the 'Anna' apple cultivar.
• To compare ethylene biosynthesis, respiration, and gene expression patterns during fruit development in 'Anna' versus better-storing cultivars 'Galaxy' and 'GD'.
• To elucidate the role of ethylene signaling and ripening regulatory genes in the differential storage performance of apple cultivars.

Main Methods:

• Comparative analysis of respiration rates and ethylene production throughout fruit development in 'Anna', 'Galaxy', and 'GD' apples.
• Assessment of cultivar response to exogenous ethylene application to determine ethylene production systems (System I vs. System II).
• Quantitative real-time PCR (qRT-PCR) to measure the expression levels of key genes involved in ethylene biosynthesis (e.g., MdACS, MdACO), ethylene response (e.g., MdETR, MdCTR), and ripening regulation (e.g., AP2/ERF, SBP-box, MdFUL).

Main Results:

• 'Anna' apples exhibited significantly higher respiration and ethylene production rates during fruit development compared to 'Galaxy' and 'GD'.
• 'Anna' showed a System II-like auto-stimulatory ethylene production in response to exogenous ethylene, even during pre-climacteric stages.
• Elevated expression of ethylene biosynthesis genes (MdACS3a, MdACO2, 4, 7) and lower expression of ripening repressors (AP2/ERF) and ethylene response regulators (MdETR1,2, MdCTR1) were observed in 'Anna' throughout development.

Conclusions:

• Pre-harvest physiological and molecular characteristics, including elevated ethylene production and altered gene expression profiles, contribute to the poor storage capacity of 'Anna' apples.
• The early activation of ethylene biosynthesis and a heightened sensitivity to ethylene during fruit development in 'Anna' predispose it to rapid ripening and quality loss.
• These findings provide insights into the genetic and physiological basis of storage potential in apples, offering targets for breeding and management strategies.