LIFE 103 1st Edition Lecture 19 Outline of Last Lecture I Exam topics II Ethylene III Light IV Phytochromes V Seasons Outline of Current Lecture I Seasons II Other stimuli and responses III Defenses against herbivores IV Pathogen defenses I Hypersensitive response II Current Lecture How do plants know what season it is V VI VII VIII Days are longer in summer shorter in winter I Short day plants blossom in late summer fall or winter II Long day plants blossom in late spring or early summer Plants actually cue on night length I Short day long night long day short night II Bursts of light at night can signal a short night Phytochromes signal short night if they are exposed to RED light Graph with time on x axis Pfr on y axis and over time the slope decreases 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 IX X XI There is a threshold of Pfr concentration that is a 0 slope line at the bottom and determines when to flower or not Fig 39 21 Fig 39 22 Can one part of the plant signal the whole plant to flower I II III Fig 39 23 Yes Phytochromes are in the leaves but they signal other hormones that induce flowering Clicker question long day plants can be induced to flower if they are exposed to a short night Other stimuli and responses I Read section 39 4 to learn more about plant responses to I Gravity II Mechanical stimuli III Environmental stresses i Drought ii Nutrient stresses iii Water stresses Plant defenses against herbivores I II III IV Many plants have chemical defenses that are harmful to herbivores The jackbean produces an unusual amino acid canavanine that is very simple to argenine I When an herbivore builds proteins with canavanine they don t work killing the herbivore taste bad to the herbivore Soy beans contain a protein that disables the digestive enzyme trypsin I When mammalian herbivores eat it they cannot digest the proteins contained in the soy Fig 39 28 Pathogen defenses I Gene for gene recognition I Plants recognize identity of pathogen derived molecules i Recognition is by the protein of an R resistance gene There are 100s of R genes II Recognition leads to responses II III IV Hypersensitive response death of infected cells and antibiotic production at infected site Systemic acquired resistance non specific defense genes turned on throughout plant for days after recognition Fig 39 29
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