(Higher tier) How does ethene influence cell division and fruit ripening in plants?

SouravNovember 12, 2024

Answer

Ethylene is a gaseous plant hormone that plays a pivotal role in regulating various aspects of plant growth and development, particularly in cell division and fruit ripening. Here’s a detailed examination of how ethylene influences these processes:

1. Ethylene and Cell Division

• Promotion of Cell Division: Ethylene is known to stimulate cell division in certain tissues, particularly in the context of fruit development and ripening. It acts by promoting the expression of genes involved in the cell cycle, thereby facilitating the transition from the G1 phase to the S phase, where DNA replication occurs.
• Interaction with Other Hormones: Ethylene interacts with other plant hormones such as auxins and cytokinins to coordinate growth responses. For instance, while auxins promote cell elongation, ethylene can enhance the proliferation of cells in specific tissues, contributing to overall growth.
• Response to Stress: Ethylene also plays a role in plant responses to biotic and abiotic stresses, which can involve changes in cell division patterns. For example, during flooding or pathogen attack, ethylene can induce aerenchyma formation (air-filled cavities) to enhance oxygen availability, thereby promoting survival through increased cell division and tissue adaptation.

2. Ethylene and Fruit Ripening

• Initiation of Ripening: Ethylene is often referred to as the “ripening hormone” because it triggers the ripening process in climacteric fruits (e.g., bananas, tomatoes, apples). The production of ethylene increases significantly as fruits begin to ripen, initiating a cascade of physiological changes.
• Biochemical Changes: Ethylene regulates several biochemical pathways involved in fruit ripening:
  • Starch to Sugar Conversion: Ethylene promotes the breakdown of starches into sugars, enhancing sweetness.
  • Cell Wall Modification: It stimulates the production of enzymes such as pectinase and cellulase, which soften the fruit by breaking down cell wall components. This softening is essential for making fruits more palatable.
  • Color Changes: Ethylene influences pigment synthesis, leading to color changes associated with ripening (e.g., green chlorophyll breaks down while carotenoids and anthocyanins accumulate).
  • Flavor Development: Ethylene also regulates the synthesis of volatile compounds that contribute to fruit aroma and flavor.

3. Mechanism of Action

• Signal Transduction Pathway: Ethylene signaling involves a well-characterized pathway:
  • Ethylene binds to specific receptors located in the endoplasmic reticulum (ER), which leads to a cascade of events that ultimately activates transcription factors known as ethylene response factors (ERFs).
  • These ERFs regulate the expression of genes responsible for various ripening processes, including those involved in softening, color change, and flavor development .
• Feedback Mechanisms: The production of ethylene can also be influenced by feedback mechanisms where ripened fruits emit ethylene gas that accelerates ripening in neighboring fruits—a phenomenon often observed in postharvest handling (e.g., placing ripe bananas with unripe avocados).

4. Practical Applications

• Agricultural Practices: Understanding ethylene’s role has significant implications for agriculture and food storage. Farmers can manipulate ethylene levels through controlled atmospheres or by applying inhibitors (like 1-methylcyclopropene) to delay ripening during transport and storage.
• Postharvest Management: Managing ethylene production is crucial for maintaining fruit quality during storage. Monitoring ethylene levels can help prevent premature ripening and spoilage.