door Hesi Plantenvoeding

By Siglinde from Hesi

Hormones of human beings and plants have some things in common: hormones are produced and regulate the metabolism in low concentrations. Differences are: hormones of plants can be made in different places (they don't need a gland), use all kinds of transport paths and the effect of hormones depends on the concentration.

In last Highlife we got to know one of the plant active hormones, the auxines. These are know best by the synthetic cutting powder and take especially effect on the making of the roots but also on many other parts of the plant.

Besides auxines, other plant hormones are:

gibberellene

cytoquinine

abscising acid

ethylene

These are less popular but also very important for the plant.

The next we've already heard. The auxines influence mainly the growth of the roots an are produced in the young and green parts of the plant. The auxines have a spectacular way of moving. The go straight across the cells, and stream in one unchanging way only. Each cell has the information where the leaves and the roots are, so that is why the plants indicate the direction of the roots, even when the plant is upside down.

In this article I will not go further than the main actors of the web of hormones and will introduce abscising acid and tell something about it. The list of hormones begins with 'others'. These are short sugars, like CALCIUM.

The gibberellenes

In 1926 the Japanese Kurosawa tested an in Asia well know disease of rice plants, that was called 'crazy rice-sprout disease'. This disease caused en extreme fast growth of the rice sprouts, so they got too thin and unstable for wind and rain. The yield was minimal. The Japanese researcher found a fungus that was responsible for this fast growth of the rice. Later on in the thirties the working matters in the fungus gibberella were isolated, so gave it the name gibberellene and forgot about it. Only in 1956 one began to experiment with gibberellene again.

Today the fungus gibberella fujikuroi is classified like fusarium moniliforme (variants of this fusarium fungi do not only exist in Japan but also in the 'Low Lands').

Until today over 110 different kinds of gibberellenes is known. 30% of it is biologically active, the others are non-active kinds, that can be turned into active ones by little changes. In spite of the very little differences in the structure, all these hormones of the gibberella kind have all different functions. Like all hormones of plants it the job of the gibberellene are not to describe in ONE function.One function of the gibberellene is very spectacular: of different plants stunting is known, for instance of corn or beans. These stunting are mutants of a normal growing plant and have a genetic defect. By adding gibberellene these plants can be brought to a normal height. All other hormones of the plant do no influence stunting.

This experiment indicates that stunting is caused by an error in the production of gibberellene, but proves particularly that gibberellene takes care for stretching.The reaction of gibberellene is that specific, that the growth of small corn a sensible biotest is for the amount of these hormones.

Gibberellene is often referred to as blooming hormone, but is also responsible for sprouting of seed, cell division, stretching and the development of fruits.

In quickly growing parts of the plants like the sprouts, young leaves and roots are they in amounts of µg to mg per kilo material of the plant, these are high concentrations for plants.

Together with other matters, gibberellene can be restraining as well as stimulating. When you have an overdose we get symptoms that look like the crazy rice sprout disease, excessive growth (so a less stable plant construction) which is at the expense of the yield. Like all hormones (also the ones of the human beings) applies: a little is good, but too much can mean the opposite effect.Like the auxines, the gibberellenes (except for the hemp plant) are used in industry: barley that is used with gibberellene is sprouting sooner than not treated barley. Brewing beer the enzymes are working faster and beer would get a better taste of it. If this beer gives you more headaches, was nowhere to be found

Gibberellene is made in the young parts of the plant and the transport is mainly via the sugar piping to the growing points. But it is also partly produced in the roots and brought via the central cylinder to the top, depending on their tasks.

Cytoquinine

The important function of cytoquinine is cleared with the following experiment:

A cutting without roots, with water and nutrition, is only growing when the first roots are made. In the roots something is produced that activates the building of protein and leaf green. If we give the rootless cuttings cytoquinine in the water, the cuttings will grow without making roots. These reaction is only caused by cytoquinine and not with other hormones

Cytoquinine is made in the root and transported upwards via the central cylinder in the stem, to stimulate growth That is why cytoquinine is mainly found in young organs like seeds, fruits, leaves and the grow points of the roots.

Another experiment shows the second function

The roots of young hemp plants are removed over and over again. The result: 80% of the plants were male instead of 50%. Adding cytoquinine could make the plants female.Cytoquinine has a certain but not very specific effect on the sex determination. In combination with gibberellene (benefits the female plants) or auxine (benefits the male plants) you can manipulate the sex of the plants. Other factors are also important, like the influence of light, temperature and air humidity on the seeds and the amount of minerals and the pH value of the ground. All these factors can be combined in such way that a maximum percentage of female seed is produced. This knowledge is also used in growing cucumbers, to enlarge the percentage on female flowers.

Another experiment with cytoquinine: a leaf that is treated with cytoquinine has a lager concentration of amino acids than other leaves.Cytoquinine is bait for sugar and protein. There where cytoquinine is (at the growing points) sugar (nutrition) and amino acids are brought, because a lot of growing energy and material is needed there.

Abscising acid

The abscising acid is a hormone that has mainly restraining qualities. The strange name comes from the abscission - loss of a part of the plants - most of the time fruit or leaves.

The abscising acid has a very specific task for the leaf pores. The leaf pores at the bottom of the leaves are the only direct connection to the outside. Here vaporizes the water and the carbon dioxide goes in. Is a well-watered plant suddenly brought into a water stress, in a few minutes an increase of the abscising acid can be measured. This time is much too short for a transport of the roots to the leaves. That is why (probably) the carotene (red color) is degraded, until abscising acid is made.

We used to call abscising acid dormine (sleeping) because dormine is responsible for the resting periods of trees and other plants. Buds are made to winter sleep and seeds rest as long as necessary.

to be continued

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