Unformatted text preview: tion of gravity correlated with Amylopasts (starchPerception
containing type of leucoplast) settling to lowest side.
Detection of gravity in roots occurs in root cap.
Detection Thigmotropism (p. 665; 626)
• Growth response to touch.
Roots navigate around rocks.
Climbing plants wrap around supporting structures.
Activity of tendrils:
May wrap around 1+ times an hour.
Cells on touching side slightly shorten
Those on other side elongate. Circadian Rhythms (p. 665)
(p. Certain flowers open in morning, close at dusk.
Daily leaf movements.
Regular daily rhythms of photosynthesis, auxin
production, cell division.
Rhythms continue even when environment
experimentally kept constant: “biological clock”.
Also widespread in other eukaryotes (e. humans).
Entrainment: adjustment of the rhythm to fit the
environment: (Fig 28-11c, below).
environment: Photoperiodism (p. 668; 629)
Day/ night length: major determinant in flowering time.
• Flower in spring or fall.
• Bloom in Summer
Day-neutral plants: Cocklebur, a short-day plant Plants Keep Track of Daylength by
Measuring Length of Darkness (p. 669; 630)
Haner & Bonner (1938): Interruption of darkness by 1 min.
of light prevented flowering in cocklebur, (short-day
Interruption of dark period also enabled long day plant to
Wavelenth of 660nm (red) most effective in interrupting
• Far-red light (730nm) reverses the effect!
• Experiment with light-stimulated lettuce seedlings: R stimulates germinat...
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- Spring '14
- Botany, Cytokinins, Apical dominance