When a deer eats a plant it prefers to eat the fresh shoot tips of the plant. Describe what happens at the level of the plant's physiology, biochemistry, structure and health of the plant. Identify the hormones that may be utilized and other chemicals that may be involved in these changes.

 

Shoot tips are apical meristems that produce the plant hormone auxin. Auxins also induce ethylene, which is a gaseous plant hormone. In a plant, auxin maintains apical dominance, that is, they prevent lateral buds to grow.

They also promote flowering, fruit ripening and stem elongation. A high auxin to cytokinin ratio favors rooting. When the mule deer grazes on the shoot tips, it decapitates the apical meristem of the shrub.

This reduces the production and levels of auxin in the plant. This will in turn reduce ethylene and increase the cytokinin to auxin ratio.

Reduced levels of auxin will break lateral bud dormancy and cause them to grow. As a result, the plant will exhibit more branching and reduced vertical growth. Low levels of auxin will also reduce the individual shoot length.

The increased cytokinin to auxin ratio will promote formation of shoots. Therefore, the number of shoots will also increase. This will also reduce the number of lateral and adventitious roots.

A combined effect of low levels of auxins and ethylene will reduce flowering, delay fruit ripening and increase leaf abscission. When the numbers of leaves decrease, then the health of the plant will deteriorate. The shrub will appear stunted and more branched.