How do seed cells know the difference between top and bottom?

Ross Koning koning at ECSUC.CTSTATEU.EDU
Mon Apr 21 07:51:59 EST 1997

At 8:48 PM -0400 4/19/97, Nanda Somarajan wrote:
>	When you place a seed on its side, it will automatically adjust
>its growth so that the shoot(stem) bends upward and the roots downward.  This
>is a response to gravity called "Gravitrophism".  It used to be called
>"Geotrophism."  Scientists are still unsure how this works.  ( I got the
>following from my Biology Text book titled "Biology"  By Neil Campbell.)



The summary of our understanding of gravitropism that
you wrote was right on target...just one tiny flaw...
it is "gravitropism" not "gravitrophism."  The root "trop"
comes from the Greek for "turning" (which is what the
plant is doing in terms of growth).  The root "troph"
also comes from Greek but means "food" or "nourishment"
which would not apply here.

By the way, the switch from geo- (earth) to gravi- (heavy)
is one of the few terminology corrections that helps
people understand the mechanism (a seed surrounded on all
sides by earth still grows downward as it is the gravity
vector to which it responds...not the proximity of earth).
There are many words that need to be fixed in plant
physiology in similar ways (photoperiodism is usually
noctoperiodism, abscisic acid should have been named dormin,
dark reactions can only operate in daylight, etc.).


Ross Koning                 | koning at
Biology Department          |
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA   | fax: 860-465-4479

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