- Fruit ripening is a complex process that involves physical, chemical, and biological changes.
- One of the key factors regulating this process is ethylene (IUPAC name: ethene), a simple gas that acts as a phytohormone.
- Ethylene plays a central role in triggering ripening in many fruits, and it is a prime example of a positive feedback mechanism.
Positive feedback
Positive feedback is a process where the end product of a reaction amplifies or enhances the initial stimulus, creating a self-reinforcing cycle.
IUPAC name
An IUPAC name is a name given to a chemical compound by the International Union of Pure and Applied Chemistry (IUPAC). IUPAC is an international organization that develops and maintains a standardized system for naming chemical compounds.
Ethylene: The Ripening Hormone
- Ethylene is a phytohormone (plant hormone) that plays a key role in fruit ripening.
- It is a simple gaseous molecule with the chemical formula $C_2H_4$.
Ethylene is produced in small amounts by nearly all parts of a plant, but its production increases dramatically during fruit ripening.
How Ethylene Works
Ethylene triggers several changes in fruits:
- Color Change: Chlorophyll breaks down, revealing pigments like carotenoids (orange) or anthocyanins (red).
- Softening: Enzymes break down cell wall components, making the fruit softer.
- Sweetening: Starches and acids are converted into sugars, enhancing sweetness.
- Aroma Production: Volatile compounds are synthesized, giving the fruit its characteristic smell.
A ripe banana emits ethylene, which can speed up the ripening of nearby fruits. This is why placing a banana in a bag with unripe tomatoes helps them ripen faster.
Positive Feedback in Ethylene Production
Initial Ethylene Production
- Fruits such as apples, bananas, and tomatoes start producing small amounts of ethylene as they approach ripening.
- Ethylene triggers the enzymatic breakdown of starches and acids in the fruit, causing the softening and sweetening of the fruit.
Ripening Triggers Increased Ethylene Production
- As the fruit ripens, it releases more ethylene, which stimulates neighboring fruits to also begin ripening.
- This increase in ethylene production is part of the positive feedback loop, causing a synchronized ripening process among all fruits in the vicinity.
