BOT3015 - Hormones and Growth

Internal Conditions

Conditions that control the development of growth

Heredity, age and position. For example, the shape of leaves tends is an inherited trait common across members of a

species

External Environment

Environment that involves light, wind, temperature, etc. For example, wind-blown trees in sub-alpine areas form what is known as krummholz

Development: Growth

Cell division and enlargement

Development: Differentiation

Specialization of cells (via expression of genes)

Induced Changes

Modifications to cells through the life of the plant (e.g. preparation for winter)

Totipotency

Also known as cell potency. It is the ability of a cell to

differentiate into other cell types. Animal cells are only totipotent early in the development of the zygote (the become determined)

Reversible Cells

Adventitious shoots and roots. Protoderm might divide and become part of the ground tissue. Tissue culturing

Plant Hormones

Substances that provide long-range signaling to

coordinate growth, development and response to

environmental stimuli.

Target Cells

(Those affected by the hormone) have

receptor proteins with binding sites. Higher calcium activates enzymes

Target Cells - Enzymes

Can play several roles in target cells including: the activation of transcription factors that regulate

gene expression

Auxins

A class of hormones that play an essential role in

regulating growth (e.g. lateral root growth) and

responses to the environment (e.g. gravitropism). These hormones are produced in the shoot apical meristems and in young leaves. This hormone initiates lateral roots. Promotes xylem differentiation

Apical Dominance - Auxins

Inhibits growth of axillary buds. High levels of auxin near the apical meristem prevent branching. Levels decrease further down - releasing axillary buds. Pruning also releases apical dominance.

Phototropism

Moment with respect to light sources

Gravitropism

Movement with respect to direction of gravitational force

Gibberellin

Hormone that plays a key role in the division and elongation of cell in the internode areas. In addition, this hormone promotes germination of dormant seeds. This hormone promotes phloem differentiation

Cytokinin

A class of plant hormones that often play a complementary role to auxins - e.g. growth of axillary buds depends on the ration of auxin to cytokinin. This hormone is produced in the root apical meristem, and developing fruits. Its main function is to promote cell division (cytokinesis) - additionally, it diverts nutrients towards areas with high concentrations

Abscisic Acid

This hormone plays a key role in preventing seed germination and promoting dormancy. Higher ABA levels in the seeds: Allows them to survive low water conditions & prevents premature germination. This hormone is produced in leaves and ovules

Ethylene

An unusual hormone which exists as a gas in normal conditions. Produced in damaged (wounded or aged) tissue! One of its main roles is to induce fruit ripening. Another key function of ethylene is to signal for leaf and flower senescence. It is also involved in the formation of root hairs

Tissue Culturing

Allows seedlings to be produced from individual plant cells grown in the laboratory

Rosettes

Plants with internodes so short, leaves seem to grow from the same point.

Bolting

When the flower-bearing stems (scapes) elongate quickly. Bolting can be induced by spraying a plant with Gibberellin

Abscisic Acid - Seed Development

This acid plays a key role in the formation of viable seeds:. It induces the production of hormones that will provide nitrogen and energy to the growing embryo. It accumulates in the seed coat, preventing the seed from germinating (dormancy)

Gibberellin - Seed Development

This hormone promotes germination by stimulating cell

division and elongation in the embryo. Other mechanisms might include: promoting breakdown of storage materials

Ethylene - Senescence (Aging)

Upregulates genes leading to an the synthesis of chlorophyllase and protease - enzymes that breakdown chlorophyll and proteins respectively.