Phototropism (Re: How do plants turn towards light?)

Jonathan B. Marder marder at
Tue Feb 4 04:00:48 EST 1997

In article <32F6120F.7CEA at>, Fredrik Loenn <f92fl at> wrote:
>Plants turn towards the sun (or other illumination), because the cells
>not exposed to the light, split more quickly. This makes the plant bend
>against the light.

Did you know that Darwin worked on this. The response is called 
"phototropism". The version Darwin characterized was phototropism of cereal 
coleoptiles (the coleoptile is the sheath which protects the emerging first 
leaves). This bends towards the light because of unequal *elongation* of 
cells on opposite sides. Light (prinicipally blue) is perceived in the apex
and causes unequal transport of the plant "hormone" auxin down the coleoptile, 
so that more auxin reaches the non-lit side. This causes them to elongate more
rapidly. The details of this phototropic response are described in 
undergraduate Plant Physiology textbooks.

Jonathan B. Marder             ,      Department of Agricultural Botany
E-mail: MARDER at |      The Hebrew University of Jerusalem
Phone: (08 or +9728) 9481918   | /\/  Faculty of Agriculture
Fax:   (08 or +9728) 9467763   |/  \  P.O.Box 12, Rehovot 76100, ISRAEL

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