BIOL 1030 – TOPIC 8 LECTURE NOTESTopic 8: Plant Responses (Ch. 39)I. DEVELOPMENTAL STRATEGIES VARY AMONG FUNGI, ANIMALS, AND PLANTSA. fungi grow with little specialization, except for reproductionB. animal development is usually complex but relatively inflexible (also well-studied)C. plant development1. cells within plant do not shift positions during development (unlike animals)2. plants keep growing tips and zones (meristems) – fantastic regeneration capacity3. plant bodies and structures do not have a fixed size4. hallmark is flexibility and adaptability outside of basic structural control5. adaptive development is strongly influenced by the environmentII. SEEDS AND GERMINATIONA. embryonic development1. early cell division-one cell from first division is small with dense cytoplasm; divides rapidly and repeatedly to make a ball of cells; becomes embryo-other cell from first division is larger; divides rapidly and repeatedly to make an elongated structure called suspensor; links embryo to nutrient tissue in seed-root –shoot axis determined near suspensor = future root (root meristem established) other end = future shoot (shoot meristem established)2. tissue formation from embryo ball-outermost cells – epidermal cells-middle layer – mostly ground tissue; also meristem-innermost cells – vascular tissue3. regulation of development-plant cells differentiate where they are formed-cells walls important in establishing identity (=determining development)4. mature embryo-wind up with root-shoot axis and cotyledon(s) growing out of shoot-shoot apical meristem between cotyledons (may have epicotyl)-epicotyl + young true leaves = plumule; may be encased in a protective sheath (coleoptile) – ex.: corn-hypocotyl – stem axis below cotyledons5. root – may have clear radical, or just apical meristem and root capB. review of seed formation1. food stored in endosperm and/or cotyledons2. seed coat forms from integuments of ovule-when hardened, embryo development is arrested (dormancy)-hard seed coat protects embryo, keeps water out3. seeds are quite dry – only 5-20% water4. seeds may last hundreds to thousands of years (seed bank in soil)C. role of seed dormancy1. dormancy during unfavorable conditions – suspended animation until environment is right2. environmental factors (such as temp., moisture) can influence duration of dormancy – a means to sense when things are most likely to be “right”3. seeds protect vulnerable embryos4. seeds often aid in dispersalD. mechanisms of germination1. seeds may need special treatments before germination is possible-fire (crack seed coat) – now likely in a cleared area-pass through animal guts – dispersed, and with fertilizer-scarification – term for physical and/or chemical abrasion of seed coats (like what happens with fires and passing through an animal’s gut)-stratification – periods of cold (even sub-zero) – helps ensure overwintering-variety in germination triggers within a species = better seed bank2. imbibition – intake of water that ends dormancy-dry seed rapidly takes up water when seed coat is compromised-embryo swells and ruptures seed coat1 of 4BIOL 1030 – TOPIC 8 LECTURE NOTES-metabolism renewed (O2 required)-sometimes more signals are required for complete germinationE. utilization of reserves1. reserves in cotyledons, some other places, and in endosperm if still present2. include starch grains in amyloplasts, protein bodies, sometimes fat bodiesF. early seedling growth1. root usually emerges first, directed down using gravity sensor (amyloplasts in root cap)2. cotyledons may or may not photosynthesize3. seedlings are usually very vulnerable to disease and drought4. opening of true leaves usually considered end of early seedling growthIII. REGULATION OF PLANT GROWTHA. whole plants are generally stuck where they areB. continuous development allows plants to adapt to their environmentC. many plant cells are apparently totipotentD. plants use hormones to regulate their growth and responsesE. environmental cues are also used to regulate plant growth and developmentIV. PLANT HORMONESA. even small amounts will regulate physiological processesB. control gene expressionC. transported from site of production to site of action (other cells)D. typically produced in small amountsE. five well-studied kinds of plant hormones:1. auxins (from Greek auxein, “to increase”)-basic effects increases plasticity of cell walls involved in bending of stems (promote stem elongation) promotes formation of adventitious roots inhibits leaf abscission promotes lateral bud dormancy-discovery observed by Charles and Francis Darwin over a century agoi. shoots bend toward lightii. if a shoot tip gets no light (shaded), the shoot will not bendiii. shading other parts of the plant has no effect later experiments with removed tips showed that some diffusible substance created in the tip enhances elongation (agar block experiments)-mode of action auxin causes elongation of cells by proton pumping, leading to acidic weakening of cell wall auxin is transported away from areas in the light-auxin and plant growth can cause bending within ten minutes also involved in fruit development main auxin in plants is indoleacetic acid (IAA) synthetic auxinsi. used to make unfertilized fruits developii. used as herbicides (some problems: Agent Orange; 2,4-D)-made in apical meristems, other immature areas2. cytokinins-modes of action promotes cell differentiation important component of coconut “milk” used in tissue culture works in combination with auxin to stimulate cell division promote growth of lateral buds into branches inhibit lateral root growth application to a yellowing leaf will keep that area green(promotes chloroplast development and maintenance)2 of 4BIOL 1030 – TOPIC 8 LECTURE NOTES-formation natural ones are similar to adenine most produced in root apical meristems and developing fruits3. gibberellins (gibberellic acids, or GAs)-discovery first isolated in 1920s by Kurosawa from fungus affecting rice stimulated growth of rice plants now more than 100 natural ones known; names GA1, GA2, etc.-mode of action activate production of food utilization enzymes cause shoot elongation can make many dwarf plants grow cause biennials to bolt in first year hasten seed germination (substitute for cold or light)-formation - made in apical portions of