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Geotropism?
In article ,
"Don H" wrote: Tropism ("turning") in plants is their orientation when growing: upwards for stems, and downwards for roots. The upwards trend can be attributed to an attraction to light (phototropism), but downwards - due to gravity? Plant shoots also respond to gravity. They grow "up" in the dark when seeds germinate buried in soil. I also have a vague recollection of experiments done decades ago where plants growing in rotating chambers lost the effect of geotropism and grew in "random" directions. Maybe someone in sci.bio.botany will put me straight on this. Cheers, Phred. -- LID |
#2
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Geotropism?
I also have a vague recollection of experiments done decades ago where
plants growing in rotating chambers lost the effect of geotropism and grew in "random" directions. We did this in high school. They don't grow in random directions (if I remember correctly). They grow sideways. Iris, Central NY, Zone 5a, Sunset Zone 40 "If we see light at the end of the tunnel, It's the light of the oncoming train." Robert Lowell (1917-1977) |
#3
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Geotropism?
In article ,
Phred wrote: In article , "Don H" wrote: Tropism ("turning") in plants is their orientation when growing: upwards for stems, and downwards for roots. The upwards trend can be attributed to an attraction to light (phototropism), but downwards - due to gravity? Plant shoots also respond to gravity. They grow "up" in the dark when seeds germinate buried in soil. I also have a vague recollection of experiments done decades ago where plants growing in rotating chambers lost the effect of geotropism and grew in "random" directions. Maybe someone in sci.bio.botany will put me straight on this. Wow, what a blast from the past! In 1968, I was at Argonne National Labs near Chicago as an undergrad summer student. On a tour, we were shown the place where some of these experiments were in progress. It was a concrete blockhouse, and you had to go through a series of doors to make sure no light got in. There was an extremely faint green safelight to turn on, and once your eyes adapted to the very near total darkness, you could see the three "gravitational compensators" going through a slow synchronized dance controlled by IIRC a PDP-6 minicomputer. The seeds were placed in containers of vermiculite which were moved in three dimensions in a pattern that ensured that the gravitational vector was never constant long enough for the plants to "perceive" it. They did, indeed, send their shoots and roots in random directions. I remember that there was a problem in that seeds which rooted up into the air portion of the chambers tended to dry out and die, skewing the results, and they'd had to go to some trouble to deal with this. IIRC, the mechanism of geotropism as understood at the time had to do with starch granules settling towards the bottom of the cells. I don't know what the current belief is. It's an old problem - Darwin wrote about it. The research at Argonne was funded by NASA. In those days before the Vietnam War clobbered so much research funding, it looked like the growth of plants in microgravity might become of considerable practical interest in the not-too-distant future. So it goes. |
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