9.3 Growth in Plants Understanding: Undifferentiated cells in the meristems of plants allows indeterminate growth Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves Plant hormones control growth in the shoot apex Plants respond to the environment by tropisms Auxin influences cell growth rates by changing the pattern of gene expression Auxin efflux pumps can set up concentration gradients of auxin in plant tissues Applications: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species Nature of science: Developments in scientific research follow improvements in analysis and deduction: improvements in analytical techniques allowing the detection of trace amounts of substances have led to advances in the understanding of plant hormones and their effect on gene expression

Growth Determinate growth: Growth stops when a certain size is reached (animals and some plants) Indeterminate growth: Growth continues (some plants) Understanding: Undifferentiated cells in the meristems of plants allows indeterminate growth

Regions of plant that grow Undifferentiated cells Active cell division Meristems Regions of plant that grow Undifferentiated cells Active cell division Understanding: Undifferentiated cells in the meristems of plants allows indeterminate growth

Primary growth Plant grows longer Tips of stem and roots Apical Meristems Primary growth Plant grows longer Tips of stem and roots Understanding: Undifferentiated cells in the meristems of plants allows indeterminate growth

Secondary growth Plant grows wider Responsible for thickness of stems Lateral Meristems Secondary growth Plant grows wider Responsible for thickness of stems Understanding: Undifferentiated cells in the meristems of plants allows indeterminate growth

Mitosis Cells go through cell cycle repeatedly New cells absorb water and nutrients Increase in volume and mass After mitosis, one cell continues on into the cell cycle, one cell is used for growth Understanding: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves

Shoot apical meristems produce cells for: Mitosis Shoot apical meristems produce cells for: Continual stem growth Flower production Leaf production Understanding: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves

Protoderm Procambium Ground meristem Meristems Apical meristems can create additional meristems What do these additional meristems create? Protoderm Procambium Ground meristem Understanding: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves

Meristems Apical meristems can create additional meristems Protoderm: Creates epidermis Procambium: Produces cambium and vascular tissue Ground meristem: Produces pith and cortex Understanding: Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves

Hormones Auxins Cytokinins Gibberellins Understanding: Plant hormones control growth in the shoot apex

Hormones Auxins Growth of roots Growth of shoots Development of fruits Leaf development Too high concentrations = inhibits growth Cytokinins Produced in the root Promote bud growth Gibberellins Contribute to stem elongation Understanding: Plant hormones control growth in the shoot apex

Tropisms Hormones control rate and direction of growth Also influenced by external factors Gravity Light Understanding: Plants respond to the environment by tropisms

Tropisms Tropism Phototropism Geo/gravitropism Positive Negative Growth away from the stimulus Stimulus for growth is light Stimulus for growth is gravity Directional growth Growth towards the stimulus Understanding: Plants respond to the environment by tropisms

Tropisms Directional growth = Tropism Light = phototropism Gravity = geo/gravitropism Positive = towards stimulus Negative = away from stimulus Understanding: Plants respond to the environment by tropisms

Tropisms Stems have positive phototropism (towards strongest light source) Stems have negative gravitropism (against gravity) Roots have positive gravitropism (with gravity) Understanding: Plants respond to the environment by tropisms

Micropropagation What is micropropagation? What is totipotency? Describe the procedure of micropropagation What are some of the uses of micropropagation? Applications: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species

Proteins transcribed to move auxin Understanding: Auxin influences cell growth rates by changing the pattern of gene expression Proteins transcribed to move auxin Photoreceptors (made from proteins) absorb light These proteins bind to receptors on cells Causes certain genes to be transcribed Specific proteins made (PIN3) Proteins transport auxin from cell to cell

Phototropism Auxin produced at the stem tip PIN 3 proteins move auxin to side of the stem with least light Causes cells on dark side to elongate or grow faster Gene expression in those cells altered to promote cell growth Understanding: Auxin influences cell growth rates by changing the pattern of gene expression

Phototropism Auxin causes transport of protons from cytoplasm to cell wall (Active process – requires a proton pump) Breaks bonds in cell walls Cell walls become more flexible Cells can increase in size easily (water into vacuole) Understanding: Auxin efflux pumps can set up concentration gradients of auxin in plant tissues

Micropropagation What is micropropagation? What is totipotency? Describe the procedure of micropropagation What are some of the uses of micropropagation? Applications: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species