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Chptr 30 BI 111

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Tristan Long

Chapter 30 13-03-03 1:59 PM Hormone: a signaling molecule secreted by a cell that can alter the activity of any cell with receptor for it. Dormancy: a period in the lifecycle in which biological activity is suspended Photoperiodism: the response of plants to changes in the relative lengths of light and dark periods in their environment during each 24-hour period • There must be a certain period of darkness… if this period is interrupted, the plant will cease to grow and will die Circadian Rhythm: any biological activity that is repeated in cycles, each about 24 hours long, independently of any shifts in environmental changes. Thigmotropism: growth in response to contact with a solid object. Nadistic Movement: in plants, a reversible response to non-directional stimuli, such as mechanical pressure or humidity. Phototropism: Growth in response to light. Gravitropism: a directional growth response to earth’s gravitational pull that is induced by mechanical or hormonal influences. Statolith: a moveable starch- or carbonate-containing stone-like body involved in sensing gravitational pull. Second-Messenger system: in particular , signal transduction pathway, an internal, nonprotein signal molecule that directly or indirectly activates protein kinases, which elicit cellular response. Abscission: in plants, the dropping of flowers, fruits, and leaves in response to environmental signals. Acid-Growth Hypothesis: ⋅ plant cell walls grow much faster in an acid environment ⋅ this hypothesis suggests that that auxin causes cells to secrete acid (H+) into the cell wall by stimulating the plasma membrane H+ pumps to move hydrogen ions from the cell interior into the cell wall 30.1 Plant Hormones - hormones in plants are less complex and fewer in number than animal hormones. - in animals, hormones travel around via circulatory and nervous system but plants don’t have that.. • hormones in plants can move via the vascular system, from cell to cell, or through intercellular spaces. In plants, a hormone is a signaling molecule that regulates or helps coordinate some aspect of the plant’s growth, metabolism, or development. Plant hormones act in response to two types of cues: 1. Internal chemical conditions related to growth and development 2. Conditions in the external environment that affect plant growth, such as light or water availability. Some hormones exert their effects where they are while others must be transported to other parts of the plant. • They are very small organic molecules and act in extremely low concentrations • Hormone have specificity: each one effects a particular tissue in a certain way. Hormone Where Tissues Effected Effects Synthesized Auxins Apical meristems, Growing tissues, Promote growth developing leaves buds, roots, and elongation of and embryos leaves, fruits, stems, formation of vascular tissues lateral roots and dormancy in lateral buds; promote fruit development; inhibit leaf abscission; orient plants with respect to light, gravity Gibberellins Root and shoot Stems and Promote cell tips, young leaves developing divisions and and developing seeds growth and embryos elongation of stems promote seed germination Cytokinins Mainly in root tips Shoot apical Promote cell meristems, division; inhibit leaves, buds senescence of leaves; coordinate growth of roots and shoots (with auxin) Ethylene Shoot tips, roots, Seeds, buds, Regulates leaf nodes, seedlings, elongation and flowers, fruits mature leaves, division of cells in fruits, flowers seedling stems, roots; in mature plants, regulate senescence and abscission of leaves flowers and fruits Brassinosteroids Young seeds, Mainly shoot Stimulate cell shoots and tips, developing division and leaves, pollen embryos elongation, differentiation of vascular tissue Abscisic Acid Leaves, roots Buds, seeds Promotes responses stomata to environmental stress, including inhibiting growth/ promoting dormancy; stimulates stomata to close in water- stressed plants Jasmonates Roots, seed, Various tissues, In defense probably other including responses, promote tissues damaged ones transcription of genes encoding protease inhibitors; possible role in plant response to nutrient deficiencies Oligosaccharins Cell walls Damages Promote synthesis tissues, most of phytoalexins in plant cells injured plants; may also regulate growth Systemin Damaged tissues Damaged In tomatoes and tissues closely related species; roles in defense
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