Nature on our doorsteps: Plants have hormones too …
Changing hormones govern the drop of leaves in autumn and early winter

Nature on our doorsteps: Plants have hormones too …

Just like humans and other animals, plants have hormones that control development in their lives. These hormones trigger the germination of seeds, the development of buds, the growth of leaves and stems, and the production of flowers and fruit.

There are also hormones that prevent plant growth. These slow down growth in more mature parts of the plant while allowing younger stems and leaves to grow quickly.

Hormones can also encourage a plant to become dormant in times of stress, including wintertime.

The interaction of all these plant hormones with one another is a complex story.

During the growing season, the hormone Auxin actively encourages the growth of plant cells, buds, and leaves at the plant’s growing tips.

As autumn approaches, light levels and temperatures drop.

The hormone Ethylene promotes the ripening and the fall of fruit and seeds from the tree

This causes the production of the growth-promoting Auxin to slow down. At the same time, the levels of another hormone, Abscisic Acid, begin to rise.

This hormone is a growth inhibitor. It prevents new cell growth in leaves and it sends unopened leaf buds and plant seeds into dormancy for the winter.

When Auxin levels are low, another hormone, Ethylene gas, begins to affect the cells at the point where leaves are attached to the stems. This hormone promotes the separation and drop of leaves from the stem. It also promotes the ripening and drop of fruit from the tree.

We make use of Ethylene gas in the commercial ripening of fruit.

We also dip stem cuttings into hormone rooting powder to stimulate fast root growth.

Another hormone, Salicylic acid, was the precursor to the commercial production of the pain-killer aspirin, while other plant hormones are being investigated for their potential in the treatment of tumours.

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