Updated May, 2006Created by C. Ippolito May, 2006 Chapter 15 Plant Growth and Development

Updated May, 2006Created by C. Ippolito May, 2006 The Embryo and the Seed Seed is a mature ovule Two Types: Monocotyledonous (monocot) one seed leaf (cotyledon) embryo plant endosperm Dicotyledonous (dicot) two seed leaves embryo plant endosperm not obvious

Updated May, 2006Created by C. Ippolito May, 2006 Monocotyledonous Seed one seed leaf (cotyledon) stored food to start growth embryo plant – coleoptile epicotyl forms stem and upper leaves hypocotyl forms lower stem root radicle forms roots endosperm additional food store seed coat protection seed coat endosperm cotyledon epicotyl hypocotyl root radicle

Updated May, 2006Created by C. Ippolito May, 2006 Dicotyledonous Seed two seed leaves (cotyledon) stored food to start growth embryo plant epicotyl forms stem and upper leaves hypocotyl forms lower stem root radicle forms roots hilum attachment to fruit micropyle opening into ovule seed coat protection seed coat micropyle cotyledons epicotylhypocotyl seed coat root radicle

Updated May, 2006Created by C. Ippolito May, 2006 Monocot Seed Germination sprouting of seed moisture, warmth, light

Updated May, 2006Created by C. Ippolito May, 2006 Dicot Seed Germination sprouting of seed moisture, warmth, light

Updated May, 2006Created by C. Ippolito May, 2006 Primary and Secondary Growth Meristem growth areas in plants mitotic regions Primary Growth up/down from zones of cell division apical meristem in roots (  ) and shoots (  ) Secondary Growth growth in width cambium meristem – growth tissue between xylem and phloem

Updated May, 2006Created by C. Ippolito May, 2006 Factors Affecting Plant Growth Plant hormones influence growth Controlled by genes May be made in different area from tissue they affect Five Types: Auxins Gibberellins Cytokinins Abscisic Acid Ethylene

Updated May, 2006Created by C. Ippolito May, 2006 Auxins Promote cell growth Made in apical buds Auxin concentration varies affect Low concentration – root elongation Apical bud auxin stops lateral growth Auxin can stimulate fruit growth w/o flower fertilization to form seedless fruit Synthetic auxins 2,4 D kills dicot weeds making them grow faster than they can make food (no affect on monocots) 2,4 T kills small woody plants and seed Component of “agent orange”- defoliant

Updated May, 2006Created by C. Ippolito May, 2006 Gibberellins Discovered in 1920’s in Japan Fungus Gibberella caused tall weak plants Speeds up growth in both monocots and dicots Treatment with hormone Larger fruit Seedless fruit Normal growth in dwarf species

Updated May, 2006Created by C. Ippolito May, 2006 Cytokinins Promote cell division and growth in lateral buds Made in roots and seeds

Updated May, 2006Created by C. Ippolito May, 2006 Abscisic Acid Made in mature leaves, root caps, fruit Promotes dormancy Affects stomate closing May protect plants in times of stress

Updated May, 2006Created by C. Ippolito May, 2006 Ethylene Gas Produced by mature fruit Promotes ripening

Updated May, 2006Created by C. Ippolito May, 2006 Plant Movement Tropisms Directional growth or plant movement in response to an environmental stimulus Controlled by auxin concentrations Phototropism – in relation to light Classical experiments by Francis Darwin Gravitotropism – in relation to gravity Chemotropism – in relation to chemicals Positive – towards stimulus Negative – away from stimulus

Updated May, 2006Created by C. Ippolito May, 2006 Photoperiodism Responses related to the relative amount of light and dark experience in a 24 hour period Long Day Plants spring/summer flowers Flower when nights are shorter Short Day Plants fall flowers Flower when nights are longer Phytochrome – pigment has 2 forms Pr absorbs red light (made first – changed back in dark) Pfr absorbs “far” red light at end of spectrum (changed to in light)