Tag: plants and animal hormones

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.