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Home Q & A Board Biology-Related Homework Help Zoology and Botany (Moderator: ehd123)
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Bisquit Bisquit
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A month ago Edited: A month ago, Bisquit
Hi,

It is well known that climbing roses with their stems orientated more horizontally stimulates more lateral bud growth as opposed to a vertical stem that only flowers at the end. Tried to find some stuff online and think it may be to do with apical dominance. Wondered if anyone had a good explanation of why making the stems more horizontal stimulates lateral bud growth along the entire stem?

Thanks for any insights offered.
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duddyduddy
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Growth of lateral buds is directed by the terminal bud, which produces a hormone called auxin. Auxin moves downward in the shoot (toward the Earth's center) from the shoot apex and inhibits the growth and development of lateral buds. This phenomenon is called apical dominance (see first attachment).

The orientation of a limb or shoot along the main branch has a major influence on growth by its effect on apical dominance. Because auxin moves downward in the shoot toward the Earth's center, apical dominance is strongest in vertical or upright shoots or limbs. In vertical limbs, vigorous shoot growth occurs near the terminal bud with lateral shoots becoming more sparse with increasing distance from the apex.

On the other hand, orientation of lateral branches at 45° to 60° angles from the vertical or main shoot reduces the vigor of shoot growth near the apex and increases the number and length of laterals along the limb further from the apex (see second attachment). On horizontal limbs, apical dominance is totally lost. Without apical dominance to control their growth, lateral buds on the upper side of horizontal limbs develop into vigorous, upright shoots, called water sprouts. As they develop, water sprouts show very strong apical dominance. Water sprouts are a common problem on the upper surface of flat limbs in fruit trees and are removed by pruning.
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