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Re: Plant Hormones (fwd)
To: s*@eskimo.com, r*@titan.tcn.ne
Subject: Re: Plant Hormones (fwd)
From: L* H* <h*@osu.edu>
Date: Thu, 26 Mar 1998 08:18:54 -0500 (EST)
Resent-Date: Thu, 26 Mar 1998 05:21:11 -0800 (PST)
Resent-From: seeds-list@eskimo.com
Resent-Message-ID: <"2zvRF3.0.mE3.oOb6r"@mx2>
Resent-Sender: seeds-list-request@eskimo.com
>Ok, who can anwser this question?
>
>
>---------- Forwarded message ----------
>Date: Tue, 24 Mar 1998 03:03:38 -0800
>From: Ram Ramachandran <ramr@titan.tcn.net>
>To: mcalpin@eskimo.com
>Subject: Plant Hormones
>
>I am doing a project on the effects of dissorientation on plant growth.
>I am rotating the plant on its side on a rotissere skewer. What is the
>scientific proof of dissorientating the plant. Our teacher says it has
>something to do with Plant Tropisms and the hormone Auxin. Please help
>me with links or information.
>Thank you
"
"Gravitropism", like "phototropism," is a differential growth response caused by a redistribution of auxin in the translocation stream.
This is a rather complex subject that has been explained by many theories. The common theory (held by the general teaching staff here at OSU) is that starch containing membranes called "amyloplasts" will settle to the lowest side of the plant cell. The weight of the amyloplasts is great enough for gravity to draw them down through the cell cytoplasm. Here, on the lower side of the cell, the presence of the amyloplasts induces a response of auxin production which then affects growth.
The direction of growth depends on many things:
1. Type of cell: root, shoot, leaf, flower, etc.
2. Concentration of other hormones like gibberellin, cytokinin, abscisic acid, and ethylene.
3. Stage of growth: germination, vegetative, reproductive.
4. Availability of other important compounds: water, nutrients.
Some key words for gravity-related growth:
orthogravitropic: the parallel alignment of growth with the direction of the pull of gravity, roots down, stems up.
positive (ortho)gravitropism: the growth of plant tissue towards the center of the earth, primary roots for example.
negative (ortho)gravitropism: the growth of plant tissue away from the center of the earth, is in the principle shoot axis (top of the plant).
diagravitropism: the growth of plant tissue at right angles to the pull of gravity. These would be stolons, rhizomes, and some lateral branches.
plagiogravitropism: the growth of plant tissue at angles between 0 and 90 degrees to the pull of gravity. These would be lateral stems and lateral roots.
agravitropic: plants which show little or no sensitivity to gravity.
HOPE THIS HELPS!
Lance Herron * Extension Associate
Department of Horticulture and Crop Science
The Ohio State University * www.hcs.ohio-state.edu
614.292.8373 * herron.42@osu.edu