The conundrum for the researchers was that many of the angles in branch and root architectures are at an angle to gravity, rather than being completely upright. Scientists did not understand how plants were able to set, relative to gravity, the particular non-vertical angle of growth for their branchesknown as their "gravitropic set-point angle"that determines their architecture.
Dr Kepinski said: "We have found that another growth componentthe 'anti-gravitropic offset'counteracts the normal gravitropic growth in these lateral branches. This offset mechanism sustains growth on the other side of a branch from the gravity-sensitive growth and prevents the branch from being moved beyond a set angle to the vertical. It turns out that this countervailing growth is also driven by auxin, the same hormone that causes gravity responsive growth on the lower side of the branch."
Branches that are growing close to the vertical have a weak anti-gravitropic offset, while in branches that are growing out at shallow angles away from the vertical the anti-gravitropic offset is relatively strong.
Dr Kepinski added: "You can compare it to the way a tank or paddle steamer is steered. If you want to go one direction, you speed up the track or paddle on the other side. If you want to straighten up, you balance the speedsor in our case the 'speed' of growth on either side of the branch. In a given non-vertical branch, the anti-gravitropic offset is constant, while gravity responsive growth increases in magnitude according to how far the branch is away from the vertical, generating a robust system for maintaining a who
|Contact: Chris Bunting|
University of Leeds