Perception of gravity correlated with amylopasts

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Unformatted text preview: tion of gravity correlated with Amylopasts (starchPerception containing type of leucoplast) settling to lowest side. containing Detection of gravity in roots occurs in root cap. Detection Thigmotropism (p. 665; 626) 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 Regular production, cell division. production, Rhythms continue even when environment Rhythms experimentally kept constant: “biological clock”. experimentally Also widespread in other eukaryotes (e. humans). Entrainment: adjustment of the rhythm to fit the Entrainment: environment: (Fig 28-11c, below). environment: Photoperiodism (p. 668; 629) (p. Day/ night length: major determinant in flowering time. Short-day plants: Short-day • Flower in spring or fall. Flower Long-day plants: Long-day • Bloom in Summer Day-neutral plants: Cocklebur, a short-day plant Plants Keep Track of Daylength by Measuring Length of Darkness (p. 669; 630) 630 Haner & Bonner (1938): Interruption of darkness by 1 min. Haner of light prevented flowering in cocklebur, (short-day plant). plant). Interruption of dark period also enabled long day plant to Interruption flower. flower. Wavelenth of 660nm (red) most effective in interrupting Wavelenth dark period. dark • Far-red light (730nm) reverses the effect! • Experiment with light-stimulated lettuce seedlings: R stimulates germinat...
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