BendToLight

BendToLight - iClicker experimental design What experiment...

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Charles and Francis Darwin, 1880: (Triggered by blue light) Cut tip Add cap Add shield Add transparen cap Light-sensing in tip; signal moves down into shoot.
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Peter Boysen-Jensen, 1913 Separate by permeable agar block Separate by NON-permeable mica strip Water-based = Water-soluble chemical that diffuses through shoot.
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Peter Boysen-Jensen, 1913 Also tried butter! iClicker Given what you now know about this chemical, did the butter experiment lead to a bent coleoptile, or a straight coleoptile? A) BENT B) STRAIGHT ?
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Fritz Went, 1920’s (In the dark) Add “control” agar block Add agar block with tip extract Tip-less shoot Add agar on side
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A chemical transferred to the agar causes the bending response. (First isolation of chemical.) Fritz Went, 1920’s AUXIN (Greek: “to grow”) Bending occurs because cells on one side elongate. But why do they elongate on one side? -> Asymmetric distribution of auxin. Redistribution hypothesis? or Auxin destruction hypothesis?
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Unformatted text preview: iClicker experimental design: What experiment could you do to distinguish between the auxin redistribution H and the auxin destruction H? a) Put tips on agar, then put the agar in sunlight. See if you can make a tipless shoot bend with that agar. b) Put a barrier between the two halves of a shoot tip, see if bending still occurs. c) either a) or b) But why do they elongate on one side? Redistribution hypothesis? or Auxin destruction hypothesis? Test ( Winslow Briggs ): Will light cause breakdown of auxin?) Agar containing auxin Still elicits bending --> no breakdown. Test 2 ( Winslow Briggs ) Isolate the two halves from each other. Both halves elicit equal bending. If two halves NOT isolated, Half away from light elicits stronger bending. Support for auxin redistribution hypothesis Redistribution H? or Destruction H? 1 < < 4 2 = 3 2 3 1 4...
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BendToLight - iClicker experimental design What experiment...

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