Ethylene is a naturally occurring chemical signal in plants, unique as a gaseous plant hormone. This simple, unsaturated hydrocarbon influences various physiological processes throughout a plant’s life cycle. Ethylene acts at very low concentrations to stimulate or regulate numerous plant functions. Its gaseous nature allows it to diffuse easily, making it an efficient messenger within the plant and even between plants.
How Ethylene Shapes Plant Life
Ethylene plays a significant role in various stages of a plant’s development, orchestrating changes necessary for its life cycle and reproduction. One of its most recognized functions is in fruit ripening, particularly for climacteric fruits such as bananas, apples, and tomatoes. Ethylene triggers a burst of respiration and its own production, a process known as autocatalysis, which accelerates changes in color, texture, flavor, and aroma, making the fruit palatable.
The hormone also promotes senescence, the aging and death of plant parts. This is evident in the yellowing of leaves in autumn as chlorophyll breaks down or the wilting of flowers after pollination. Ethylene production is associated with the onset and progression of leaf senescence, and its application can stimulate this process, while inhibitors can delay it.
Beyond ripening and aging, ethylene is involved in abscission, the controlled shedding of leaves, flowers, and fruits. This process occurs in response to environmental cues or as a natural part of the plant’s life cycle. Ethylene triggers programmed cell death at a specialized abscission layer, allowing the organ to detach without harming the rest of the plant.
Ethylene’s Role in Plant Survival
Ethylene also functions as a stress hormone, increasing its production when plants face environmental challenges. This heightened ethylene production can be triggered by various abiotic stresses, including drought, flooding, wounding, and even pathogen attacks. This increased output signals the plant to initiate protective responses.
In response to stress, ethylene can activate defense mechanisms within the plant. It enhances the emission of volatile organic compounds and the accumulation of phenolic compounds, which protect against herbivores and pathogens. Ethylene also plays a role in immunity by regulating genes responsible for defense responses, including those related to pathogenesis-related proteins.
Furthermore, ethylene assists plants in adapting to challenging conditions. For example, during flooding, oxygen diffusion is restricted within plant tissues, leading to low-oxygen (hypoxic) conditions. Ethylene accumulates rapidly in submerged tissues, initiating adaptive growth responses such as the formation of adventitious roots and aerenchyma, which are air-filled tissues that improve oxygen transport.
Putting Ethylene to Work
Understanding ethylene’s functions has led to its widespread application in agriculture and horticulture. Commercially, ethylene gas is used to artificially ripen climacteric fruits post-harvest. Bananas, mangoes, and tomatoes, often picked green for transport, are exposed to controlled concentrations of ethylene to achieve uniform ripeness before reaching consumers.
In the cut flower industry, ethylene can cause premature wilting and decay, leading to significant post-harvest losses. Florists use strategies to mitigate ethylene damage, such as maintaining optimal storage temperatures and ensuring good air exchange in coolers. They also employ ethylene inhibitors, which bind to ethylene receptors and prevent its detrimental effects, extending the vase life of sensitive flowers.
For consumers at home, knowledge of ethylene can help manage produce and flowers more effectively. Since ripe fruits release ethylene, storing them separately from ethylene-sensitive produce can prevent premature spoilage. To speed up ripening of an unripe fruit, placing it in a paper bag with a ripe fruit can concentrate the ethylene and accelerate the process.