9.3 Growth in Plants

Plant hormones: Respond to changes in the environment Regulate growth Regulate reproduction and flowering Regulate water loss Regulate growth by controlling mitosis and cell division

Meristem Tissue Undifferentiated tissues that become many different types of tissues Located where plants exhibit major growth

2 types of Meristems Apical Meristems Lateral Meristems Located at the top and the root of plants Allows for growth of new leaves and flowers Allows roots to grow down into the soil Elongation of plant Lateral Meristems Responsible for secondary growth in woody plants Allows them to increase stem and root thickness

Indeterminate Growth Animal embryos have a fixed number of parts that will develop and are considered determinate growth 2 legs, 2 arms, 10 fingers/toes etc. The growth in plants is much different and is considered to be INDETERMINATE. Meaning apical meristems can continue to increase the lengths of stem and root throughout the life of a plant and can produce any number of extra branches of the stem or root. They can also produce any number of extra leaves or flowers.

Mitosis and Cell Division Occur in the shoot apex Provide cells needed for extension of the stem at that location Also important for development of leaves.

Tropisms A directional movement in plants in response to a stimulus

Type of Tropism Response Phototropism Response to light Gravitropism Response to gravity Thigmotropism Response to touch Thermotropism Response to temperature Chemotropism Response to substance Hydrotropism Response to water

Auxin (plant hormone) Responsible for phototropism Affects cells on the dark side of the plant causes the cells away from light to elongate When light shines directly down on a plant shoot auxin is equally distributed this causes the plant to grow straight This hormone is released in abundance of blue light in the shoot tip.

Auxin Auxin efflux pumps can set up concentration gradients of auxin in plant tissue. Moves Auxin from cytoplasm to cell wall Lower concentration on light side and higher concentration on dark side. Auxin influences cell growth by changing the pattern of gene expression. These genes cause secretion of H+ ions into cell walls that loosen connections in the cellulose fibers that allow cells to expand.

Micropropogation of plants The practice of rapidly multiplying stock plant material to produce a large number of plants, using modern plant tissue culture methods. Can create virus-free strains of existing plants Can propagate rare species - Orchids Uses tissue from shoot apex, nutrient agar gels and growth hormones Used in plants to increase population faster than seeding time would allow $$$$