Plant Senescence: Definition & Hormonal Regulation

Instructor: Lauren Posey

Lauren has taught intermediate reading in an English Language Institute, and she has her Master's degree in Linguistics.

In this lesson you will learn about senescence, the process of aging, in plants. In particular you'll look at the different hormones involved in the regulation of aging.

The Circle of Life

Do you remember the last time you were outside, maybe in a park with a lot of trees? If it was fall, you might have seen the leaves changing color and falling off. Actually, no matter what time of year it is, you can see this happening. It just happens all at once to many trees in the fall, which is why it is more noticeable. The next time you go outside, look around and see if you can find leaves changing color.

The reason this happens is that leaves, other parts of plants, and even entire plants are aging and dying all the time. The aging process is known as senescence. Sometimes it is a natural process of a plant as it ages that helps to recycle nutrients, and sometimes it is triggered by environmental factors, such as the seasons changing.

Leaf Senescence

Senescence of leaves is widespread, and can be the easiest aspect of senescence to see because of the sheer number of leaves all around us, especially in fall. The different colors are caused by the chlorophyll in the leaves decaying and becoming inactive. Chlorophyll is the chemical that makes leaves green and enables the plant to conduct photosynthesis.

Leaves can die and fall off from damage, such as when they are eaten by pests or get a disease. However, natural senescence is programmed into the plant even without these, and it is regulated through interactions of various hormones.

The changing colors of leaves in fall is caused by senescence
Autumn Leaves

Hormonal Regulation

There are several factors that can trigger the hormones that cause senescence in plants. Some are environmental factors, such as drought, or the changing of seasons. Senescence can also be triggered in only a small area of the plant. This might happen if the plant became infected with a disease. It could kill off only that small area and prevent the disease from spreading, thereby saving the plant as a whole.

Salicylic Acid

One of the hormones involved in regulating senescence is salicylic acid. Leaves undergoing senescence have a major increase in this hormone. It is also the hormone most involved in responding to pathogens. When a part of a plant is infected, salicylic acid is one of the main hormones responsible for shutting down only that portion of the plant. It is the hormone most responsible for partial plant senescence.

Ethylene

Another promoter of plant senescence is ethylene. This hormone mostly occurs as a gas, and as a result it is used to coordinate senescence among groups of plants.

Ethylene is particularly useful in the ripening of fruit, which is an aspect of senescence. You can even see it at work in your own kitchen! Ripe fruit gives off more ethylene than unripe fruit, and so if you store ripe and unripe fruit together, the unripe fruit will ripen more quickly than it would on its own. High levels of ethylene are one reason bananas go bad faster than other fruit.

Storing ripe bananas together causes them to go bad more quickly
Ripe bananas

Abscisic Acid

Abscisic acid, or ABA, is also a strong hormonal regulator. It is a key hormone in plant reactions to stresses in the environment. This means it is one of the main hormones involved in leaf senescence, especially if it is caused by drought, season change, or other environmental factors. In fact, ABA is such as strong senescence hormone that applying it to leaves actually causes senescence to occur, even if they were healthy previously.

Cytokinins

Just as there are hormones to begin senescence, there are also hormones that delay it. Both types of hormones work together in regulating senescence in plants. The hormones that delay senescence must decrease while the ones that speed up the aging process must increase.

Cytokinins are one group of senescence delayers. These hormones are involved in cell growth, and high levels can help prevent senescence. By the same token, lowering the levels of cytokinins can increase plant senescence.

To unlock this lesson you must be a Study.com Member.
Create your account

Register for a free trial

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Free 5-day trial

Earning College Credit

Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Create an account to start this course today
Try it free for 5 days!
Create an account
Support