Plant Tissues and Meristems All derived from meristematic

Plant Tissues and Meristems All derived from meristematic tissue • Meristematic tissue is composed of aggregates of small cells, which have the ability to divide. When the cells divides: 1 stem cell (initials)/1 differentiated cell (derivatives) Continually renewed Most plants have 3 basic types of tissues: • Dermal • Ground • Vascular Outer covering which protects against physical agents and organisms. It also prevents water loss Thin walled cells Functions: storage, photosynthesis, support, secretion Xylem/phloem: carryout long distance conduction (water, minerals, nutrients), provide support

Plant Growth Plants Continual pattern of growth Animals/leaves Growth ceases at a point Death: Annuals (die yearly) Biennials (2 yr cycle) Perennials (die due to infection, environmental factors)

Apical Meristems- often are differentiated based on location within the plant. 1⁰ meristem -produces new tissues and causes primary growth through mitosis and cell division Grow tall to increase exposure to light, CO 2 Results in: Herbaceous, nonwoody plants Extends into soil 2⁰ meristem: increase thickness of stem/root Results in: Woody plants Produces cork cells of outer bark Produces 2⁰ vascular tissue - lies between xylem and phloem

Plant Hormones Means of communication within plant Affect development and growth: Environmental stimulus (day length/water) Receptor types (detection of factors) Genetic makeup Hormones

Process of Hormone signaling Specific cells have specific receptors Receive environmental stimulus Protein receptor activated Initiates metabolic pathway Plant hormones differ from animal hormones. -Plant hormones have varying effects depending on the receptor's location. -Animals ususally have a specialized gland to produce the hormone. -Plant hormones may be produced throughout the plant. Produces hormone (produced throughout plant) Travel via phloem Target cell affects specific area of plant

Auxin and Phototropism Tropisms: growth/movement to directional external stimuli Positive – towards Negative - away Phototropism: response to light Stems (+) Roots (-) Hormone Increases flexibility of cell walls in young plants Auxin found in embryo of seed, the meristems of apical buds and young leaves. Redistributed to shaded side Auxin only works on plants cells that have auxin receptors. -increase plants flexibility, allowing cells to elongate during growth Creates curvature towards light Auxin repositions closer to light.

Auxin and Phototropism 1. Auxin produced in all cells in stem on light side (auxin efflux) 2. Auxin moves by efflux pump action into the cell on the “dark” side of the cell. 3. Auxin and receptor form complex which activates H+ pump 4. The proton pumps H+ into cell wall 5. Causes p. H drop; resulting in H-bonds between cellulose fibers – breaking cell wall 6. This results in the elongation of the cells on the side away from the light.

Auxin involved with: – Stimulation of cell division in meristematic tissue – Xylem/phloem differentiation – Development of lateral roots – Suppress lateral bud growth when found in apical bud – Stimulate growth of flower parts – Fruit production without pollination Changes in gene expression

Micropropogation -is used to stimulate existing plant material to produce large numbers of progeny (offspring). Culture cells from shoot apex Nutrient agar with growth hormones Uses: • Rare/endangered plants maintained • Develop virus-free strains • Alter genome to create beneficial plants Problems: • Extremely expensive • Difficult to maintain pathogen free environment