Photoperiodism, Gravitropism, and Thigmotropism - PowerPoint PPT Presentation

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Photoperiodism, Gravitropism, and Thigmotropism

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Photoperiodism, Gravitropism, and Thigmotropism AP Biology Unit 5 Photoperiodism How a plant responds (with respect to flowering) to the relative amount of light ... – PowerPoint PPT presentation

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Title: Photoperiodism, Gravitropism, and Thigmotropism


1
Photoperiodism, Gravitropism, and Thigmotropism
AP Biology Unit 5
2
Photoperiodism
  • How a plant responds (with respect to flowering)
    to the relative amount of light (photoperiod)
  • In reality, plants are responding to the relative
    amount of night.

Slide 2 of 15
3
Photoperiodism Types of Plants
  • 3 different types of plants
  • Short Day ? flower when days are short, nights
    are long (Ex. poinsettias, chrysanthemums)
  • Long Day ? flower when days are long and
    nights are short (Ex. Spinach, Radish)
  • Day Neutral ? flowering does not depend on
    length of day or night (Ex. tomato)

Images taken without permission from
http//www.fernlea.com/xmas/pix/poinsettia.jpg,
and http//www.illinoiswildflowers.info/weeds/plan
ts/garden_radish.htm
Slide 3 of 15
4
Question
  • Poinsettias are short day plants how could
    nurseries make sure they bloom just before
    Christmas?
  • Control the amount of light and dark they
    experience

Slide 4 of 15
5
Phytochromes
  • Plants absorb light via blue-light photoreceptors
    and phytochromes (Pr and Pfr).
  • Pr and Pfr play a significant role in the
    flowering and germinating responses

Slide 5 of 15
6
Phytochromes
  • Germination and flowering occurs in response to
    red and far-red light
  • effects of both lights are reversible
  • Pr and Pfr are isomers (alternate forms)
  • red light (660 nm) activates Pr to become Pfr
  • far-red light (730 nm) activates Pfr to become Pr

Slide 6 of 15
7
Flowering
  • Pfr
  • inhibits flowering in short day plants
  • promotes flowering in long day plants
  • Sunlight consists of quite a bit of red light,
    not much far red light
  • During the day, which form of phytochrome is in?
  • Pfr

Slide 7 of 15
8
Flowering
  • At sunset, most of the phytochrome is in the Pfr
    form
  • During the night, Pfr gets converted back into Pr
    or breaks down
  • Whether a plant flowers or not depends on the
    amount of Pfr left (which relates to the amount
    of night)

Slide 8 of 15
9
Flowering Hormone?
  • There also appears to be a flowering hormone
    called florigen not fully understood yet

Slide 9 of 15
10
Flowering
  • Photoperiodism Animation

Slide 10 of 15
11
Germination
  • Red light stimulates germination
  • Far red light inhibits germination
  • What matters is the last light the seeds are
    exposed to

Slide 11 of 15
12
Gravitropism
  • Response of a plant to gravity
  • Shoots will grow against gravity (upwards)
  • Roots will grow with gravity (downwards)

Stem placed on its side
Root placed on its side
Slide 12 of 15
13
Auxin and Gravitropism
  • Auxin is responsible for gravitropism
  • inhibits cell elongation in roots
  • stimulates cell elongation in shoots

In stems
Slide 13 of 15
14
Gravitropism Starch
  • Statoliths (dense starch-containing plastids) may
    accumulate in the direction of gravity to assist
    in gravitropism

Slide 14 of 15
15
Thigmotropism
  • Response of plant to touch.
  • Ex. Tendrils of vines wrapping around things,
    venus fly traps, shy plant
  • Response is similar to nervous response in
    humans.

Slide 15 of 15
Image taken without permission from
http//images.botany.org/set-08/08-004v1.jpg
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