BIOL 240W 1st Edition Lecture 16Outline of Last Lecture I. Signal TransductionII. Plant HormonesOutline of Current Lecture I. Hormones (continued)II. Plant Responses to LightIII. PhotoperiodismIV. Plant Responses to GravityV. Other ResponsesCurrent LectureI. Hormones (continued)a. Ethylenei. Triple response to mechanical stress involves stem elongation, thickening of the stem, and horizontal growthii. Important in the food ripening process, their bursts control senescence and apoptosis of cells or organsiii. Ethylene + auxin ration controls leaf abscissionb. Brassinosteroidsi. Chemically similar to sex hormones of animalsii. Responsible for inducing cell elongation and division, promote xylem differentiationiii. Slow leaf abscissionc. Jasmonatesi. Jasmonates and methyl jasmonates are important for plant defense, development, and response to woundingd. Strigolactonesi. Present in xylemii. Named for parasitic Striga, which germinate when host plants exude strigolactones through their rootsiii. Important for seed germination, suppress adventitious root formation, aid in mycorrhizal associations, help to control apical dominanceII. Plant Responses to Lighta. Phototropism These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Plants tend to move toward light more responsive to blue light because of its wavelength (below 500 nm)b. Germination of many seeds is controlled by lightc. Early experiments with lettuce seed: red light (660 nm) encourages seed germination while far-red light (730 nm) prevents seed germinationi. These effects are reversible depending on the final light exposured. Phytochromes receive the red and far-red light and are important in regulating plant responses (ex: seed germination, shade avoidance) to lighti. Red light triggers conversion of Pr to Pfr (fast, dominates)ii. Far red triggers conversion of Pfr to Pr (slower)iii. Sunlight increases ration of Pfr to Pr, which triggers germinationiv. Shade avoidance1. Pfr dominates in unfiltered light2. Pr dominates when light is filtered through leaves because chlorophyll absorbs most red light, but allows far red to pass through. This induces verticle growthe. Circadian Rhythmsi. 24 hour cycles which regulate processes such as transpirationii. These are controlled by light perceptions via phytochromesiii. Reset at dawn when a rapid conversion to Pfr occursiv. Phytochrome conversion marked by sunrise and sunsetv. Photoperiodism is a physiological response to a photoperiod, or relative lengths of night and dayIII. Photoperiodisma. Photoperiods controls floweringb. Short-day plants (long night plants) flower when the light period is shorter than a critical lengthi. Adapted for autumnal or winter floweringii. One flash of light interrupting the night will prevent this responsec. Long-day plants (short night plants) flower when a light period is longer than a critical lengthi. Adapted for spring or early summer floweringii. One flash of light interrupting the night stimulates this responsed. Day-neutral plants flower depending on plant maturity, not photoperiodIV. Plant Responses to Gravitya. Gravitopism occurs during the moment of seed germinationb. Roots- positive gravitropismc. Shoots- negative gravitropismd. May be stronger than phototropism in relation to positioning the shoot upwardV. Other Responsesa. Thigmotropism: Growth patterns changed by physical forcesb. Envrinomental stresses such as drought, flooding, heat, cold, and saltc. Plant defenses against pathogens and
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