Tag: auxins and gibberellins

Auxins are produced in the apical buds and they inhibit the growth of lateral buds on the stem thus leading to apical dominance. Whereas cytokinins promote the growth of lateral buds over and above the apical buds thereby antagonising the action of auxins.
So, the correct answer is, 'Apical dominance'.

Apical dominance is the condition in which an apical bud grows taller as compared to the other lateral branches. This is cause because apical bud produces IAA (Indole Acetic Acid) an auxin hormone in abundance. The presence of high concentration of auxin in the apical bud causes the lateral buds to remain dormant. It has been found that if apical bud is removed, the auxin concentration decreases which allows the lateral branches to grow. 

Auxins are present in high concentrations in the tip of apical bud and their presence inhibits the growth of lower buds and branches. Thus one shoot becomes the tallest stem and other remain lower. This type of growth shown by apical bud in herbaceous plants is known as apical dominance. 

Auxin is an important plant hormone with a wide variety of effects. Auxin produced by the apical meristems inhibits the sprouting of lateral buds, and this phenomenon is called apical dominance. Apical dominance refers to an event in which the main stem of the plant grows more dominantly than the other branches on the stems. Production of auxin strengthens the phenomenon of apical dominance. Auxin inhibits the growth of lateral bud, and thereby allow the central stem to grow more vigorously.

• Apical dominance is a phenomenon wherby, the inhibition of the growth of lateral buds occurs due to the terminal bud of a shoot.
• It is caused by the production of IAA (auxin) in abundance by the apical bud.
• This auxin is transported basipetally from the apical bud.
• The auxin causes the lateral buds to remain dormant. 
  

F. W. Went in 1928 used tip of Avena coleoptile. He removed the tip of Avena coleoptile and and placed in on the agar agar block for the definite measured amount of time. Then this agar agar block was placed asymmetrically on the stump, this showed a positive curvature. 

A tropism is a growth movement by plant part in the direction of the stimulus. According to Boysen-Jensen, the stimulus for phototropism, growth in response to light, is a diffusible chemical that passes from the tip of the coleoptile. He cut the tip of the coleoptile and the severed tip was reattached through a gelatin disc. The recapitated coleoptile showed bending of stem towards light. Paal continued with Boyse-Jensen work. He said that the tip of coleoptile produces some chemical which travels down and stimulates growth. The light causes the accumulation of that chemical on the shaded side of the coleoptile. 

Apical dominance is a phenomenon in which central stem is dominant and lateral stems are suppressed. It is due to plant hormones produced in the tip of the shoot. Auxin hormone is responsible for apical dominance and cytokinin hormone is responsible for breaking the apical dominance.