Ethylene is an important natural plant hormone, used in agriculture to force the ripening of fruits. Binding of ethylene to the receptors unleashes a signaling cascade that leads to activation of transcription factors and the turning on of gene expression. The climacteric is a stage of fruit ripening associated with increased ethylene production and a rise in cellular respiration.

Ethylene is a plant hormone which is present in gaseous form. It is formed by the breakdown of methionine, which is in all cells. Thus, methionine is called as the precursor of ethylene hormone. Ethylene hormones helps in the ripening of fruits when sprayed onto it. Ethylene hormone is present mainly in rapidly dividing cells, which is usually in darkness due to the action of methionine, which is the precursor molecule.

Ethylene is a gas that forms through the breakdown of methionine, which is in all cells. Ethylene has very limited solubility in water and does not accumulate within the cell but diffuses out of the cell and escapes out of the plant. Its effectiveness as a plant hormone is dependent on its rate of production versus its rate of escaping into the atmosphere. Ethylene is produced at a faster rate in rapidly growing and dividing cells, especially in darkness.

Ethylene is a simple gaseous PGR. It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Ethylene is used to initiate flowering and for synchronising fruit-set in pineapples. It also induces flowering in mango. Since ethylene regulates so many physiological processes, it is one of the most widely used PGR in agriculture. The most widely used compound as source of ethylene is ethephon. Ethephon in an aqueous solution is readily absorbed and transported within the plant and releases ethylene slowly. Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton, cherry, walnut). It promotes female flowers in cucumbers there by increasing the yield.

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climactic.

Ethylene is a simple gaseous plant growth regulator. It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climactic.

Ethylene is a simple gaseous plant growth regulator. It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climactic.

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climacteric.

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climactic.

During the early 20th century, scientists observed that the gas ethylene (C$ _2$H$ _4$) has several effects on plant growth, but not until 1934 did they demonstrate that plants produce ethylene. This natural hormone influences many plant processes. Ethylene inhibits cell elongation, promotes seed germination, promotes apical dominance and is involved in plant responses to wounding or invasion by disease causing microorganisms. Ethylene also has a major role in many aspects of senescence, including fruit ripening. As a fruit ripens, it produces ethylene, which triggers an acceleration of the ripening process. This induces the fruit to produce more ethylene, which further accelerates ripening.

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climacteric.

Ethylene is also known as ripening hormone.It is responsible for the changes in texture, softening, colour and other processes required for ripening. Thus the correct answer is option A. 

Hormones are the biochemicals which target the cells/organs away from the site of their secretion. Enzymes are the biocatalysts which accelerate the bioreactions by lowering the activation energy of the reaction. Ethylene is a gaseous hormone which is involved in germination, growth, abscission, ripening and stress responses. Thus, option A is correct. 

Ethylene is a volatile compound and the only gaseous plant growth hormone which is mainly found in ripening fruits, flowers and leaves. Its unsaturated nature and small structure make it a volatile compound. It is responsible for fruit ripening and induction of leaf senescence. This makes option B correct. Auxins are growth hormones that stimulate growth by cell division and cell elongation. They are synthesized in shoot and root tip and are also used as weedicide that selectively acts against certain weeds. Auxins includes IAA, IBA and 2,4-D which are complex compounds and are not gaseous. Cytokinins stimulate cell division, even in non-meristematic cells, in presence of auxin. They are most abundant in the growing tissues which are active site of cell division, for example: root, embryos, fruits etc. They are substituted adenosine compounds and are not gaseous. Gibberellins are hormones of bolting (stem elongation) and reversal dwarfism by increasing the internodal length. They are tetra carbocyclic compounds with characteristic gibbane skeleton having four rings of carbon and hence are not gaseous hormones. Thus, the correct answer is option B.

Fruit ripening is controlled by hormone, ethylene. Ethylene is a gaseous hormone. It affects the growth, development, ripening and senescence (aging) of all plants.

Two pathways for biosynthesis of ethylene in higher plants have been postulated. One is associated with the breakdown of peroxidized linolenic acid and the other involves degradation of methionine. 
A chemical mechanism accounting for such enzymatic formation of ethylene has been described. On the basis of this information, scientist has proposed the following scheme for the biosynthesis of ethylene in plants:
methionine -> alpha-keto-gamma-methylthiobutyric acid -+ methional--> ethylene.
In order to test the proposed pathways, radioactive linolenic acid and the appropriate radioactive methionine analogs were fed to apple tissue. None of these suggested precursors of ethylene was converted to ethylene as effectively as was methionine.

Ethylene gas acts to retard flowering in most of the plants. Whereas, in the case of pineapple, it increases the flowering in off season. Ethylene gas is also found useful in ripening fruits, when sprayed on to it.

Ethylene gas is a gaseous hormone which stimulates the transverse or isodiametric growth but retards the longitudinal. It is having a prominent ability to promote early ripening of fruits when sprayed on to it.

Ethylene is a gaseous plant hormone. It is also called as ripening hormone as it plays the important role in controlling the fruit ripening. During fruits ripening, the respiration rate in fruits is increased by ethylene. Due to increased respiration, complex carbohydrates are broken down into simpler sugars and cell wall becomes soft.

Cytokinin is synthesized in the root and is translocated from roots to shoots via xylem. Auxin is synthesized in the stem tip and is translocated via parenchyma cells to different sites. Gibberellin is translocated via phloem and xylem. Abscisic acid is translocated through vascular tissue and activated diffusion. Ethylene is diffused through intracellular spaces throughout the plant as it is gaseous in nature.

Ethylene induces seed germination. It breaks seed and bud dormancy. So 1 is the right answer.

Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. 

Ethylene is a small hydrocarbon gas. Ethylene is responsible for the changes in texture, softening, colour, and other processes involved in ripening. 

Artificial ripening of fruits is caused by the treatment of ethylene. This process is achieved by spraying a commercial product Ethephon, that releases ethylene gradually on aerobic degradation. It is generally used for the faster ripening of cotton, wheat, coffee, tobacco, rice etc

Ethylene is a fruit ripening hormone. It stimulates the biochemical changes which take place upon fruit ripening.

Ethephon, 2-chloroethyl phosphonic acid (Ethrel) is a source of ethylene used commercially. It is used in aqueous solution and releases ethylene slowly.

Ethylene has a feminising effect on sex expression. The genetically male plants of cucumber can be induced to produce female flower in the presence of ethylene. The number of female flowers and hence fruit is enhanced in these plants.

Ethylene production by plants is autocalalytic, i.e., a small amount of ethylene will stimulate production of its larger amounts. Thus, a few ripe fruits will initiate ripening of nearby fruits. It is, therefore, a common practice to keep few ripe bananas with unripe bananas to hasten ripening.

Ethylene is a small hydrocarbon gas as well as a phytohormone. Some fruit will produce ethylene as ripening begins. Apples and pears are examples of fruit that produce ethylene with ripening. Ethylene is responsible for the changes in texture, softening, color, and other processes involved in ripening. Ethylene gas is used commercially to ripen tomatoes, bananas, pears, and a few other fruits postharvest. 

Ehtylene is a simple gaseous plant growth regulator. It is synthesized in large amounts by tissues undergoing senescence and ripening of fruits. It enhances the respiration rate during ripening of fruit. This rise in rate of respiration is called as respiratory climacteric. 
Exposure of plants to ethylene causes drooping of leaves and flowers, a phenomenon known as epinasty.

Flowering in pineapple is not only based on external factors like temperature, daylength but also is based on internal factors like phytohormones. Pineapple flowering can be artificially induced by activity of the ethylene and IAA (indoleacetic acid). During flowering of pineapple, low temperature stimulates ethylene biosynthesis. Other hormones which are involved in initiating pineapple flowering are a-naphthalene acetic acid (NAA), indolbutiric acid (IBA), 2,4-dichlorofenoxiacetic acid (2,4-D). 

Ethylene is a plant hormone. It is also called as ripening hormone as it is responsible for ripening of fruits. Fruit ripening is accompanied by increase rate of respiration. The climacteric respiration occurs during fruit ripening which is associated with increased ethylene production. Due to increased respiration, complex carbohydrates are broken down into simpler sugars and cell wall becomes soft. 

Ethylene is a metabolic product of methionine. It is synthesized from methionine amino acid by methionine cycle or yang cycle. Methionine is first converted to adenosylmethionine. It is then converted to Aminocyclopropane carboxylic acid. It is then oxidized to form ethylene. It is a gaseous plant hormone which stimulates ripening of fruits in plants.

Ethylene is a gaseous hormone that promotes transverse growth but inhibits lateral growth. They are produced by the amino acid methionine. It was found that ripened fruits produce this hormone, so when the ripened fruits are placed together with unripe fruits, the unripe fruits will get ripened due to the release of this gas. Ethylene evolution is highest at the time of ripening but it diminishes when the fruit matures and the evolution of gas got reduced.

• Ethylene is a simple gaseous PGR. 
• It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. 
• Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. 
• Ethylene promotes senescence and abscission of plant organs, especially of leaves and flowers. 
• Ethylene is highly effective in fruit ripening
  
• So, the correct option is 'Ethylene'.