Cytokinins, ethylene, and brassinosteroids are hormones that work in concert with auxin and gibberellins to mediate plant development. They have various effects on different plants, ranging from stem growth to fruit ripening. They also interact in their effects with other hormones. Ethylene is remarkable in that it is a gas.
learning outcomes
You should be able to:
Use information on the functions of cytokinins to predict how different aspects of plant growth will be affected by cytokinins and by various combinations of cytokinins and auxin.
Describe the function of ethylene in fruit ripening, and explain its importance in the cut-
Identify some effects of brassinosteroids on plant growth.
A plant has an extremely bushy growth habit. What can you say about the likely auxin-
Cytokinins stimulate axillary buds to grow into branches, which would make the plant more bushy. Auxins help maintain apical dominance, which prevents branching. Thus this plant most likely has a low ratio of auxin to cytokinin.
Supermarkets sell plastic bags that are impregnated with activated charcoal, which binds gases. The bags are designed to keep fruit fresh. How do they work?
The charcoal in the bag absorbs ethylene gas, which is released by ripening fruits. The lack of ethylene prevents over-
A plant shows rapid leaf senescence. Which hormone or hormones are most likely active in this plant? Which are most likely inactive?
Both ethylene and brassinosteroids promote leaf senescence, so either or both of these hormones are most likely active. Cytokinins delay leaf senescence, so they are most likely inactive in this plant.
A plant’s response to light—