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Life 103 Week 8 Notes

by: Addy Carroll

Life 103 Week 8 Notes Life 103

Addy Carroll
GPA 3.65

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These notes cover part of Plant Reproduction and Biotechnology, Plant Responses to Stimuli, and Light.
Biology of organisms-animals and plants
Dr. Dale Lockwood and Dr. Tanya Dewey
Class Notes
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This 5 page Class Notes was uploaded by Addy Carroll on Friday March 11, 2016. The Class Notes belongs to Life 103 at Colorado State University taught by Dr. Dale Lockwood and Dr. Tanya Dewey in Winter 2016. Since its upload, it has received 11 views. For similar materials see Biology of organisms-animals and plants in Biology at Colorado State University.


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Date Created: 03/11/16
Life 103 Notes *adapted from the lecture notes of Dr. Dale Lockwood* Plant Reproduction and Biotechnology ctn. • Vegetative Propagation and Agriculture -Humans have devised methods for asexual propagation of angiosperms -Most methods are based on the ability of plants to form adventitious roots or shoots • Clones from Cuttings -Many kinds of plants are asexually reproduced from plant fragments called cuttings -A callus is a mass of dividing undifferentiated cells that forms where a stem is cut and produces adventitious roots • Grafting -A twig or bud can be grafted onto a plant of a closely related species or variety -The stock provides the root system -The scion is grafted onto the stock • Biotechnology -Plant biologists have adopted in vitro methods to create and clone novel plant varieties -Transgenic plants are genetically modified (GM) to express a gene from another organism ~Take a gene from one organism and move it to another organism -Humans have intervened in the reproduction and genetic makeup of plants for thousands of years -Hybridization is common in nature and has been used by breeders to introduce new genes • Plant Biotechnology and Genetic Engineering -Plant biotechnology has two meanings: ~In a general sense, it refers to innovations in the use of plants to make useful products ~In a specific sense, it refers to use of GM organisms in agriculture and industry -Modern plant biotechnology is not limited to transfer of genes between closely related species or varieties of the same species • Genetically Modified Organisms (GMOs) -Organisms that contain genes from an unrelated species ~Used for research, gene therapy, agriculture, and medicine production • The potential to reduce hunger -Genetically modified plants may increase the quality and quantity of food worldwide -Transgenic crops have been developed that: ~Produce proteins to defend them against insect pests -Insects try to eat the plant and then they die ~Tolerate herbicides -The plants have grown resistant to certain herbicides so, when applied, they can kill the weeds without killing the plant ~Resist specific diseases -However, farmers are prevented from storing seeds of transgenic crops -Nutritional quality of plants is being improved • Bt Genes -Bacillus thuringiensis ~Bacteria that contain proteins that kill insects ~Bacteria can be used as a pesticide or larvacide -Endospores -Crystalline form of endotoxins -The cry gene has been inserted into plants because the sprayed form killed all insects (which was bad for the ecosystem), while the injected form doesn’t ~Cotton, corn, potato (potato was discontinued) • Bt Benefits -Toxin is specific to two insect orders -Does not affect non-target species unlike sprayed form -Safe for humans -Dramatic reduction in pesticide usage • Bt Costs -Farmers beholden to corporate products -Non-target species can be affected (relatives of pest species) • Biofuels -Energy sources derived from living sources ~Bio alcohols -Ethanol, Sugar Cane, Corn, Switchgrass ~Biodiesel -Recycled cooking oils, Animal fats, Plant based oils • Algal Biofuels -Algae used to produce oil, gasoline (with refining), alcohol, hydrogen • Biofuels Benefits -Can be more carbon neutral -Can remove dependence on foreign sources of energy -Can produce less pollutants • Biofuels Costs -Removes agricultural lands from food production, thereby increasing the price of food -Can use more fossil fuels to produce than is saved Plant Responses to Stimuli • Mechanism of Signaling (see textbook figure 39.3) -Reception ~Internal and external signals are detected by receptors, proteins that change in response to specific stimuli -Transduction (see textbook figure 39.4) ~Second messengers transfer and amplify signals from receptors to proteins that cause responses -Response ~A signal transduction pathway leads to regulation of one or more cellular activities ~In most cases, these responses to stimulation involve increased activity of enzymes ~This can occur by transcriptional regulation or post-translational modification • Transcriptional Regulation -Specific transcription factors bind directly to specific regions of DNA and control transcription of genes -Positive transcription factors are proteins that increase the transcription of specific genes, while negative transcription factors are proteins that decrease the transcription of specific genes • Post-Translational Modification of Proteins -Post-translational modification involves modification of existing proteins in the signal response -Modification often involves the phosphorylation of specific amino acids • Hormones (see textbook table 39.1) -Chemical signals that coordinate different parts of an organism -In the late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism, a plant’s response to lights (see textbook figure 39.5) -They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present -They postulated that a signal was transmitted from the tip to the elongating region • Auxin -The term auxin refers to any chemical that promotes elongation of coleoptiles -Indoleacetic acid (IAA) is a common auxin in plants -Auxin transporter proteins move the hormone from the basal end of one cell into the apical end of the neighboring cell • The Role of Auxin in Cell Elongation (see textbook figure 39.7) -According to the acid growth hypothesis, auxin stimulates proton pumps in the plasma membrane -The proton pumps lower the pH in the cell wall, activating expansins, enzymes that loosen the wall’s fabric -With the cellulose loosened, the cell can elongate • Auxins stimulate other growth -Auxin affects secondary growth by inducing cell division in the vascular cambium and influencing differentiation of secondary xylem • Cytokinins -Named because they stimulate cytokinesis (cell division) -Produced in actively growing tissues such as roots, embryos, and fruits -Work together with auxin to control cell division and differentiation -Retard the aging of some plant organs by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues • Control of Apical Dominance (see textbook figure 39.8) -Cytokinins, auxin, and other factors interact in the control of apical dominance, a terminal bud’s ability to suppress development of axillary buds -If the terminal bud is removed or damaged, plants become bushier • Gibberellins -Stem Elongation ~Gibberellins stimulate growth of leaves and stems ~In stems, they stimulate cell elongation and cell division -Fruit Growth ~In many plants, both auxin and gibberellins must be present for fruit to set ~Gibberellins are used in spraying of Thompson seedless grapes (see textbook figure 39.9) -Germination ~After water is imbibed, release of gibberellins from the embryo signals seeds to germinate • Brassinosteroids -Chemically similar to the sex hormones of animals -They induce cell elongation and division in stem segments • Abscisic Acid (ABA) -Slows growth -Seed dormancy ~Ensures that the seed will germinate only in optimal conditions ~In some seeds, dormancy is broken when ABA is removed by heavy rain, light, or prolonged cold ~Precocious germination is observed in maize mutants that lack a transcription factor required for ABA to induce expression of certain genes (see textbook figure 39.11) -Primary internal signal that enables plants to withstand drought • Ethylene -Produced in response to stresses such as drought, flooding, mechanical pressure, injury, and infection -The effects include ~Response to mechanical stress ~Senescence ~Leaf abscission ~Fruit ripening • The Triple Responses to Mechanical Stress (see textbook figure 39.12) -Ethylene induces the triple response, which allows a growing shoot to avoid obstacles -The triple response consists of ~Slowing of stem elongation ~Thickening of the stem ~Horizontal growth • Effects of Ethylene -Senescence ~The programmed death of plant cells or organs ~A burst of ethylene is associated with apoptosis, the programmed destruction of cells, organs, or whole plants -Leaf Abscission ~A change in the balance of auxin and ethylene controls leaf abscission -Fruit Ripening ~Triggered by a burst of ethylene production (one bad apple spoils the bunch) Light • Light and Plants -Light cues many key events in plant growth and development -Effects of light on plant morphology are called photomorphogenesis -Plants detect light direction, intensity, and wavelength -Action spectrum depicts relative response of a process to different wavelengths • Classes of Light Receptors -Blue-light photoreceptors ~Control hypocotyl elongation ~Control stomatal opening ~Control phototropism -Phytochromes ~Pigments that regulate many of a plant’s response to light throughout its life ~Seed germination ~Shade avoidance


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