BIOL 240W 1st Edition Lecture 17Outline of Last Lecture I. Hormones (continued)II. Plant Responses to LightIII. PhotoperiodismIV. Plant Responses to GravityV. Other ResponsesOutline of Current Lecture I. PhytochromeII. Circadian RhythmIII. Plant Responses to Gene ExpressionCurrent LectureI. Phytochromea. Two different versions of phytochrome: absorb at red wavelength and far red wavelength i. Red version is inactive. It converts into far red form which is active (occurs when sun comes up)ii. When the sun sets, far red converts back to redb. Shining red light on plants to convert to far red and increase seed germinationc. Shining far-red light inhibits germinationd. Chlorophyll absorbs most red, but far-red passes through. Thus, red dominatese. Pr (red, inactive form) absorbs red light and is converted to Pfr (far red, active form)f. Pfr absorbs far-red light and is converted to Pr (inactive form)II. Circadian Rhythma. Phytochrome conversion creates biological clock with cues such as sunrise and sunsetb. A photoperiod is the relative length of night and dayc. Short-day plantsi. “long night plants” plants that flower when a light period is shorter than a critical lengthii. Adapated for autumnal or winter flowering d. Long-day plantsi. “short-night plants”ii. adapted for spring or early summerThese 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.iii. Too much darkness leads to no flowering e. Seasonal changesi. As days get longer (spring into summer), more light is available over course of day and Pfr becomes predominantii. As Pfr becomes predominant on a daily basis, a critical compound is produced that causes the plant to flowerIII. Plant Responses and Gene Expressiona. Plants respond to environment to activate or silence gene expressionb. Pfr unduces flower in long-day (summer-flowering) plant speciesi. Turns on gene flowering “hormone”c. Pfr inhibits flowering on a short day (winter-flowering) plant speciesi. Turns off a gene “hormone”ii. As nights get longer, less Pfr is available, so gene is switched on and hormone is producedd. Gene regulation only depends on far red.e. Long day, short night, summer flowering has a lot of far red. In certain plants, the gene isactivated so it flowers.f. In short day, long night, uses Pfr to inhibit gene and hormone is not
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