Definition of Ethylene
Ethylene is a simple hydrocarbon gas, C₂H₄, which is an important plant hormone helping to regulate some of the physiological processes, such as fruit ripening and abscission of leaves. Chemically, it has a small molecule that contains only a double bond between two atoms of carbon; thus, it will turn out to be the simplest alkene. Probably one of the most important gases in plant biology, ethylene was discovered early in the 20th century because of its effect on hastening fruit ripening. It is for this very reason that techniques for manipulating fruit ripening have since been developed to help increase agricultural yields.
A:Plants perceive ethylene through a family of membrane-bound receptor proteins. These receptors are always active in the absence of ethylene, suppressing ethylene responses. When ethylene binds to these receptors, it inactivates them, which paradoxically activates the ethylene signaling pathway. This unique "inverse agonist" mechanism allows plants to respond rapidly to changes in ethylene levels.
A:The "ethylene burst" refers to a sudden, dramatic increase in ethylene production that occurs in response to certain stimuli, such as wounding, pathogen attack, or the onset of fruit ripening. This burst of ethylene acts as a signal, rapidly triggering various physiological responses throughout the plant. It's important because it allows plants to quickly respond to environmental changes or developmental cues, coordinating responses across different tissues.
A:Ethylene is a major promoter of plant senescence, the programmed aging and death of plant tissues. It influences senescence by:
A:The triple response is a characteristic set of changes observed in dark-grown (etiolated) seedlings exposed to ethylene. It consists of: 1) inhibition of stem and root elongation, 2) increased radial expansion of the stem (swelling), and 3) horizontal growth of the stem (exaggerated curvature of the apical hook). This response helps seedlings navigate through soil and around obstacles as they grow towards the surface.
A:In climacteric fruits, ethylene plays a central role in initiating and coordinating the ripening process. As these fruits begin to ripen, they produce a burst of ethylene, which triggers a cascade of biochemical changes including:
Functions of Ethylene in Plants
There are various functions of ethylene-
Role in Fruit Ripening
Mechanism of action in ripening
It is surmised that ethylene does so by binding to receptors in the fruit, setting off a series of reactions that ultimately alter cell-wall structure and metabolism, leading to the softening and sweetening of the fruit.
Examples of fruits affected by ethylene
Some common examples include bananas, apples, tomatoes, and avocados.
Regulation of Leaf Abscission
Process of leaf shedding
Abscission is a process of shedding leaves from the plant. Ethylene promotes it through the degradation of the cell wall in the abscission zone—a region where the petiole joins the stem.
Ethylene’s role in promoting abscission
Due to increased ethylene production, cell wall degrading enzymes are activated, which allows leaves to fall.
Flower Senescence
Ethylene's involvement in ageing and wilting of flowers
Ethylene acts to promote senescence in flowers, resulting in ageing and eventual wilting.
Examples of ethylene-sensitive flowers
It is known that some flowers, such as orchids, carnations, and petunias, are sensitive to ethylene.
Stress Responses
Ethylene’s role in response to biotic and abiotic stress
Ethylene in plants coping with stress regulates various physiological responses to such stresses.
Examples of stress responses
The stress responses include those against attack from pathogens, drought, and mechanical damage.
Seed Germination and Root Growth
Ethylene’s effect on seed dormancy and germination
Ethylene breaks seed dormancy, allowing it to germinate by stimulating the action of the enzymes responsible for the breakdown of the seed coat.
Influence on root growth and root hair development
Ethylene promotes an increase in the growth of roots and root hair and promotes increased uptake of water and nutrients from the soil.
A:Ethylene is a gaseous plant hormone that plays crucial roles in plant growth, development, and stress responses. It's important because it regulates processes like fruit ripening, leaf senescence, and plant responses to environmental stresses. Unlike other plant hormones, ethylene is unique in its gaseous nature, allowing it to diffuse easily through plant tissues and even affect neighboring plants.
A:Ethylene has a very simple structure - it's just two carbon atoms connected by a double bond, with two hydrogen atoms attached to each carbon (C2H4). This simple, small molecule can easily diffuse through cell membranes and move between cells, allowing it to rapidly spread its effects throughout plant tissues. Its gaseous nature at room temperature also enables it to act as a long-distance signaling molecule between plants.
A:Ethylene promotes leaf senescence, which is the programmed aging and death of leaves. It triggers chlorophyll breakdown, protein degradation, and the remobilization of nutrients from aging leaves to other parts of the plant. This process is important for plant survival, as it allows the plant to recycle nutrients from old leaves and prepare for dormancy or new growth.
A:When plants are submerged or their roots are waterlogged, ethylene production increases rapidly. This triggers various adaptive responses, including the formation of aerenchyma (air spaces in roots and stems that help oxygen diffusion), the elongation of stems or petioles to reach the water surface, and the initiation of adventitious roots. These responses help plants cope with the low-oxygen conditions associated with flooding.
A:Ethylene generally inhibits stem elongation and promotes radial expansion, leading to shorter, thicker stems. This is part of the plant's response to mechanical stress or wind, known as thigmomorphogenesis. In roots, ethylene can inhibit primary root growth while promoting the formation of lateral roots and root hairs, which can be beneficial for nutrient and water uptake in stressful conditions.
Ethylene in Agriculture and Horticulture
Various uses are explained below-
Commercial Uses
Ethylene in fruit ripening chambers
Ethylene in ripening chambers promotes uniform ripening of such varied fruits as bananas, tomatoes, and avocados. This controlled application makes all of them ripe simultaneously and improves the market quality. Hence, wastage is reduced and presents better market quality.
The fruit should be treated with ethylene gas under specific temperature and humidity conditions for the natural process of ripening to take place.
Applications in horticulture
Flower Preservation: Inhibitors of ethylene respiration prolong the life of cut flowers by preventing senescence and wilting. This aspect assumes great significance for ethylene-sensitive flowers such as carnations and orchids.
Stress Management: Ethylene induces stress responses in plants to strengthen defences against any undesirable incidents of drought, flood, and pathogen attacks
Case study: Use of ethylene in commercial tomato ripening
Use of Ethylene in Commercial Tomato Ripening
Process: Green harvested tomatoes are then gassed with ethylene gas in a ripening chamber to develop uniform colour and texture before the produce reaches consumers.
Benefits: This process allows tomatoes to naturally ripen off the vine and extends the period of in-transit time without spoilage, thus providing the consumer with a consistently ripe product. Ethylene Inhibitors
Ethylene Inhibitors
Chemicals used to inhibit ethylene action
1-Methylcyclopropene: This is one of the most common ethylene inhibitors, which acts by binding to ethylene receptors in plant tissues and preventing ethylene from inducing a response for ripening and senescence.
Applications: 1-MCP has very broad applications in extending the shelf life of fruits, vegetables, and flowers during storage and transport by delaying the onset of their ripening and senescence processes.
Applications and benefits in agriculture
Extended Shelf Life: 1-MCP, by inhibiting the action of ethylene, helps in maintaining the quality of produce during storage and transport. This in turn reduces losses of yield after harvesting.
Quality Preservation: It is an important Ethylene inhibitor in the flower industry, guaranteeing the outlook and extending the life of cut flowers.
A:Ethylene is called the "ripening hormone" because it plays a central role in initiating and coordinating the ripening process in many fruits. It triggers a cascade of biochemical changes that lead to fruit softening, color changes, and the development of flavor and aroma compounds. This is why placing a ripe banana near unripe fruit can speed up the ripening process - the ethylene released by the ripe banana triggers ripening in nearby fruits.
A:Climacteric fruits, such as apples, bananas, and tomatoes, show a sharp increase in respiration and ethylene production during ripening. These fruits can continue to ripen after being picked. Non-climacteric fruits, like strawberries, grapes, and citrus fruits, do not show this respiratory climb and do not continue to ripen significantly after harvest. Understanding this distinction is crucial for post-harvest handling and storage of different fruit types.
A:Plants produce ethylene through a biochemical pathway that starts with the amino acid methionine. This pathway involves several enzymatic steps, with the final step catalyzed by the enzyme ACC oxidase, which converts 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The production of ethylene can be triggered by various factors including developmental cues, environmental stresses, and even other plant hormones.
A:Ethylene promotes fruit abscission, which is the shedding of fruits from the plant. It stimulates the formation of an abscission zone at the base of the fruit stem, weakening the connection between the fruit and the plant. This process is important for seed dispersal in many species and can also be a plant's response to stress or overproduction of fruits.
A:Plants regulate ethylene production through complex feedback mechanisms. The biosynthesis of ethylene can be induced by various factors including other plant hormones, environmental stresses, and developmental cues. Ethylene can also regulate its own production through both positive and negative feedback loops. Additionally, the sensitivity of plant tissues to ethylene can be modulated, providing another level of control over ethylene responses.
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