Hormonal Influences 30

Hormonal Influences : 

Hormonal Influences

Human Growth and Development : 

Human Growth and Development HORMONES are chemical messengers produced by glands and secreted into the bloodstream, where they reach a target organ. PITUITARY gland produces growth hormone and thyroid stimulating hormone (THS). Promotes growth by increasing cell division and amino acid uptake Controls thyroxine production by thyroid gland

Growth Hormone : 

Growth Hormone Overproduction: Adults- enlargement of hands, feet and jaw bones Adolescence- Increased overall growth. Underproduction: Adolescence- overall growth is reduced

TSH on thyroxine production : 

TSH on thyroxine production THYROXINE affects the rate of metabolism Overproduction Increases Thyroxine which increases the size of the thyroid gland, neck swells and eyes bulge. Underproduction Decreases Thyroxine which in CHILDREN leads to a decreased mental and skeletal development. In ADULTS it leads to lethargy and increased weight.

Auxins : 

Auxins Auxins (e.g. Indole Acetic Acid) is a plant growth substance. It is produced by active shoot and roots They promote division, elongation and differentiation of cells When compared with the growth of a control plant, the plant tissues grown in auxin solutions can be: Stimulated Inhibited High Concentration of IAA Shoot stimulated and grows taller Root inhibited grows smaller Lateral buds inhibited (apical dominance) the apical bud produces auxins and lateral buds do not grow. Fruit stimulated and fruit develops Low Concentration of IAA Lateral bud not inhibited so no apical bud forms and lateral buds grow. Leaf abscission occurs and leaves fall.

Phototropism : 

Phototropism PHOTOTROPISM is the name given to the directional movement by a plant in response to light from one direction. POSITIVE PHOTOTROPISM is when shoot tips bend towards an unidirectional source of light. This shows that an unidirectional light source cause unequal distribution of growth hormones to occur at the shoot tip. A higher concentration of auxin is produced at the non-illuminated side. Therefore more elongation will occur causing the shoot to bend towards the light.

Apical Dominance : 

Apical Dominance APICAL DOMINANCE is the ability to grow shoots to prevent lateral buds from developing.

Leaf Abscission : 

Leaf Abscission ABSCISSION is when leaves or fruit separate from the plant. Before leaf or fruit fall, auxin concentration drops and a thin abscission layer of cells is formed at the base of the leaf or fruit stalk. The walls of cells in this layer gradually become weakened until eventually the fruit or leaf stalk snaps. During the growing season auxin from the plant prevents this layer from forming and therefore prevents leaf abscission.

Applications of Plant growth substances : 

Applications of Plant growth substances Selective weed killer (herbicides): narrow leaved cereals resistant to auxin but broad leaved weeds killed Rooting Powder: growth of adventitious (arise from a plant part other than the main root or branches) roots stimulated which makes propagation easier. Parthenocarpy: This the development of fruit without fertilisation. It can be induced artificially by treating unfertilised flowers with auxin. This produces seedless fruit that is ripe for harvesting at the same time. Delaying Abscission of fruit: Fruit growers can spray auxin on plants towards the end of the growing season to delay the fall of fruit before they are fully ripe.

Gibberellic Acid : 

Gibberellic Acid Dormancy of seeds and buds is overcome by gibberellic acid. After treatment with gibberellic acid the height of plant becomes normal as the length of the internodes increases and dwarfism is demolished.

amylase induction in germinating seeds : 

amylase induction in germinating seeds Aleurone layer site of action Embryo site of production A very low GA concentration produced by embryo GA passes to aleurone layer GA induces a amylase production by the aleurone layer a amylase Starch maltose maltose (sugar) provides energy for growth Growth substance Target Action result