Question

where is auxin synthesized in plants?

Answer 1

Thanks for the question!

It is definitely a very interesting question to solve and do some brainstorming.

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Auxins are derived from plant growth regulators which are known to be small, simple molecules of diverse chemical composition, they are found to be working to regulate growth, differentiation and development by promoting or inhibiting or stopping the functions at the same time, this happens when they are found in low concentrations in the plant.

Only One type of it is going to get described here (for Auxins). Plant Hormones or phytohormones are the type of plant growth regulators in which, technically, it's a plant hormone in which a chemical substance other than its nutrient production which are natural in plants, they might get translocated to another region, this is primarily been done for regulating more than one physiological reactions involving in the presence of low concentrations.

Auxins (originated from Greek literature, auxein attributes: to grow or promotion of growth in direct manner). Auxins are weakly acidic growth Hormones which are having and unsaturated ring structure that are capable of promoting cellular elongations, especially those of shoots or the apical region (more pronounced in the means of decapitated shoots or cut-down shoots and the segments of shoots) which are present at a concentration less than that of 100 parts per million or 100 ppm that are inhibitory to the roots.

Among the plant growth regulators or growth regulators scientists (going to discuss) were the first to get it discovered in plants, by seeing other growth regulators the Auxins were the only ones to have got discovered by strenuous research and other PGR were accidentally found out in the plants.

Auxin has its history revolving around the great evolutionary scientist Charles Darwin and his son Francis Darwin (at the year of 1880) found that the sensations of unilateral illumination of light (illuminated) was picked up by a coleoptile tip of the species Phalaris canarensis or tip of Canary Grass. The same sensations does not go for a decapitated coleoptile. When the coleoptile tip is covered by a light resistant opaque foil cap this blocks the stimuli and , hence, the perception of stimulus of light is not picked up by the coleoptile tip. This happens only when the sensation is picked up by the coleoptile tip which is further transmitted to a subapical part which makes it bend to the direction of light where it receives it through a block of gelatine, but, when the medium is shifted to a mica it fails to pass through it. Paal (in 1919) did the replacement of the previously exposed excised or cut-off tip eccentrically over yhe stump of coleoptile. Observing the pact of greater growth shown by the tip even when they are placed in a dark room or room with no light. This further goes where Went (in 1928) extracted and collected the growth stimulating substance present in agar jelly. Discovering that Hormones travelled in it basipetally or, that is, starting from the tip or apex towards the Base. Agar blocks contained the chemical of it which cause the bending of an decapitated coleoptile according to its concentration prominent in it.

Went named this growth promoting substance as $\textbf{Auxin}$.

Naturally occurring or universal natural Auxin is $\textbf{Indole 3-Acetic Acid}$. Discovered by Kogl et al in 1934 and found out heteroauxin is the real plant Auxin and is filed and chemically formed Indole 3-Acetic Acid or IAA. This chemical is also found in human beings (in urine, to be specific) especially when they are suffering from pellgara, a disease which is caused by deficiency of niacin (or nicotinic acid). Heteroauxin along with Auxin a and Auxin b were named and was found out by isolating three chemicals from human urine by Karl and Haagen-Smith (in 1931).

Auxins are, therefore, synthesised in $\textbf{Shoot apices}$, $\textbf{leaf primordia}$ and $\textbf{Developing seeds}$ from the amino acid tryptophan.

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Hope it helps and solves your query!!

Answer 2

Indole Acetic Acid is the natural Auxin hormone produced in plants. It is synthesized in the stem apexes. Though other parts such roots and shoots also contain auxin but it has been studied that stem apexes contain the highest level of Auxin.

Auxin is considered to be the first phtochromes to be found in plants.

In plants, Auxin promotes stem elongation and inhibits the growth of lateral buds.