Fichier de travail :
- ../DUMP-TEXT/Anglais/1_Direction/46.txt
Forme voulue :
- (directions?(\b)|(\b)(\w)+-ways?(\b)|(\b)ways?(\b))
Définition :
- [En parlant d'un mouvement ou d'un mobile qui se déplace] Orientation, direction.
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How does the seed know which direction to sprout?
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How does the seed know which direction to sprout?
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Post by MrMistery » Mon Sep 10, 2007 9:08 am
that is true. However, when a plant is in the ground, there is no light to sense in either direction. the signal that acts here is gravity. stems have negative gravitropism, meaning that they generally grow opposing gravity. how this is done is by the lateral movement of auxin through the stem of the cell. The uneven distribution of auxin is responsible for the growing upward of a stem in the ground.
Assume the stem has grown laterally for example. the side that is down receives more auxin which stimulates its growth. the side that is up receives less auxin, which inhibits its growth. therefore, the stem curbs upwards.
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Good question
My guess is they will grow in whatever direction they happen to begin growing unless they hit an obstacle(and ethylene directs the plant going round it) or there is a unidirectional source of light(case in which phototropism takes over: the stem grows towards the light and the root away from light.
However, something that cannot be explained by the current model of gravitropism(which is not well established, lots of things about it need to be tested) is this situation: the stem grows DIRECTLY down(without being deviated at all to neither side). in such a case, the concentration of auxin will remain the same on both sides and there will be no bending. However, this never happens. so, there is still more to be discovered.