Auxin And Gibberellin Growth Hormone Of The Plant

The activity of growing and developing is also regulated by chemical substance, namely growth hormone. There are six types of growth hormones, auxin, gibberellin, cytokinins, ethylene, abscisic acid, and caline.

Auxin

Frits W. Went (1928), a Dutch expert in plant anatomy, had succeeded proofing that auxin can influence shoot growth. Auxin produced on the shoot and young leaves will be distributed to the lower parts.

Experiment plant of Frits W.went. Gelatin block is put

a. throughly on the surface of shoot tip drives the cell to grow evenly

b. only on some part of shoot tip surface causes unbalance cell growth so that the plant bend 

The followings are several functions of auxin. 

1. Affecting apical growth (tip of stem). As long as auxin is still produced, apical bud continues growing but lateral bud does not. That condition is known as apical dominance. 
2. Affecting fruit development. As the seed develops, it releases auxin which is distributed to flower in order to stimulate fruit growth. 
3. Inhibiting the growth of lateral branch. The growth of lateral branch is inhibited because auxin is distributed from the tip of the stem to the lower part and not spread out to side part. As the consequence, that lateral branch growth becomes slow. 
4. Affecting the fall of leaves and fruits. The production of auxin on mature leaves and fruits is restrained. It is caused by the forming of abscission layer on leaf and fruit stalk, so leaves and fruits cannot attach to the stem and falls to the ground. 
5. Stimulating the formation of adventitious root. It can be proven by cutting leaf or stem and treating the cuttings with solution containing synthetic auxin.

Apical Dominance

a. Auxin on apical bud hampers the growth of lateral bud.

b. lateral bud grows after apical bud is cut

Gibberellin

It began when E. Kurosawa, a researcher from Tokyo University, Japan found that rice, the object of his research, was infected by fungus Gibberella fujikuroi. The stem of infected plants was longer than that of the uninfected plants. Finally, it was recognized that the cause of the abnormal growth on the infected rice was gibberellin, a chemical compound obtained from the extraction of fungus Gibberetta

.

Effect of gibberellin

a. Cabbage growth without gibberellin

b. cabbage with gibberellin grow longer 

Gibberellin is mostly found on leaf tip, bud, seed, and root tip. 

The following are several functions of gibberellin.

1. Simulating the growth of stem, leaf, and root. 
2. Simulating anther maturation and filament development. 
3. Simulating flower development (on particular plant). 
4. Simulating budding. 
5. Sopping seed dormancy. 
6. Promoting seed germination.

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