What is the essence of auxin? Speed

Auxin is a class of endogenous hormones containing an unsaturated aromatic ring and an acetic acid side chain, which is referred to as IAA in English and is used internationally and is indoleacetic acid (IAA). 4-chloro-IAA, 5-hydroxy-IAA, naphthalene acetic acid (NAA), indole butyric acid, etc. are auxinoids. In 1872, the Polish horticulturist Schellensky made a study on the root apical control of the growth of the root elongation zone; Later, Darwin and his sons studied the optotropy of the coleoplasty of grass.

In 1928, Winter confirmed that the tip of the germ did produce a substance capable of controlling germ growth. In 1934, Keg et al. isolated this substance from some plants and named it indoleacetic acid, so it is customary to use indoleacetic acid as a synonym for auxin.

Auxin is synthesized in the extended young leaves and apical meristems, accumulating from top to bottom to the base through long-distance transport in the phloem. Auxin is also produced in the roots, which is transported from the bottom up. Auxin in plants is formed by tryptophan through a series of intermediates.

The main route is through indoleacetaldehyde. Indoleacetaldehyde can be formed by tryptophan first oxidative deamination to indole pyruvate and then decarboxylated, or it can be formed by tryptophan first decarboxylation to tryptophan and then oxidative deamination. Indoleacetaldehyde is then reoxidized to indoleacetic acid.

Another possible synthetic pathway is the conversion of tryptophan to indoleacetic acid via indoleacetonitrile.

Comparison of auxin concentrations and growth rates in plant roots and stems.

You're not taking an exam, are you? Indoleacetic acid. bar

If the concentration is too high, it inhibits growth.

The main parts of auxin synthesis are root tips and shoot tips, and there are also local synthesis under special conditions. The synthesis of IAA can be divided into tryptophan (TRP)-dependent synthesis pathways and non-tryptophan-dependent synthesis pathways. IaaS is mainly found in the cytoplasm and chloroplasts in plant cells.

Although tryptophan biosynthesis occurs in chloroplasts, auxin synthesis intermediates are only present in the cytoplasm, where de novo synthesis of IAA is done.

According to the curve in your textbook, high concentration within a certain range is to inhibit its growth, which means that it grows slowly, but the concentration is extremely high, and the phenomenon of "burning seedlings" will occur, that is, the plant cannot grow.

Depending on the degree to which auxin can promote the formation of another hormone, ethylene. Ethylene is a substance that promotes the maturation of plant organs, and its effect on the growth of plant cells is to inhibit elongation growth. Therefore, high concentrations of auxin will inhibit the growth of plants.

However, if the concentration is too high, it will kill the plants.

Hehe, depending on the degree, with the increase of concentration, the effect of auxin on plants is to promote inhibition to a certain extent, and it will not last long when inhibited, and some herbicides use this principle.

In addition, seedling burning refers to the loss of water in the roots due to the concentration of the external solution of the roots, which generally refers to the concentration of fertilizer.

I don't grow anymore.

When the concentration is low, it promotes the growth of plants. High concentrations of auxin will inhibit the growth of the plant and will stop the growth, and when the tip is removed, the concentration of auxin will be reduced and the plant will be promoted.

The definition of high concentration needs to be discussed, some people say that exceeding the optimal concentration is high concentration, high concentration may be slow growth, or it may not grow or die directly, otherwise auxin will not have the effect of thinning flowers and fruits; If the curve exceeds the 0 growth line, the concentration is high, and the plant will no longer grow.

Since it is inhibition, of course there will still be growth, but a little slower than normal.

Take the side buds as an example, the concentration is relatively high, in fact, it is also growing, but it is slow... The test questions are also curves, not straight lines,,, but too high will lead to the direct death of plants...