Re: Does aspirin effect a plants growth?

Aspirin can most definitely affect plants!

Aspirin another name of the chemical acetylsalicylic acid, which is very similar to salicylic acid, a plant hormone. For thousands of years, salicylic acid has been extracted from plants (although they didn’t know what it was until the 1800’s), particularly willow tree bark, and used as a pain killer. In the 1800’s chemists began synthesizing salicylic acid, which was much cheaper than extracting it from plants. In the 1890’s, the Bayer company (as in Bayer aspirin) discovered that a slightly modified version of salicylic acid had less severe side effects. This of course was acetylsalicylic acid, which we now know as aspirin. Even though it is not exactly the same as salicylic acid (the naturally occurring form), acetylsalicylic acid has much the same effect on plants.

So how does salicylic acid effect plants? There are a couple ways.

Interestingly, it is associated with disease resistance in plants. Sometimes, when a plant is exposed to a pathogen (a virus, bacteria, or fungus that can cause disease), it develops lesions, or dead spots, on the leaves that were exposed. This is called the hypersensitive response, and slows the spread of the pathogen. The rest of the plant undergoes changes that make it more resistant to a variety of pathogens, not just the one it was exposed to. For example, if a plant is exposed to a virus, the leaves that were exposed may become sick and develop dead spots, but several days later, the rest of the plant will be more resistant to disease caused by other viruses, bacteria, and fungi. This is called systemic acquired resistance.

Researchers have found that during the hypersensitive response, the plant makes salicylic acid in high amounts around the lesions. The salicylic acid then moves throughout the plant, perhaps as a signal that notifies the other leaves to turn on their defenses. They have also found that applying salicylic acid to a plant that has not been exposed to a pathogen will cause some of the same responses seen during systemic acquired resistance. In fact, spraying a small amount of aspirin on some plants can make them more resistant to diseases. There is probably a trade off though: it takes energy from the plant to have its disease defenses on all the time, so a plant treated with aspirin may benefit by being disease resistant, but pays the price by, for example, not being able to grow as fast or not being able to make as many seeds as it otherwise would. So, although the exact role of salicylic acid in this phenomenon is not understood, it is certainly involved in an important way.

Salicylic acid can also block the production of ethylene by plants. This is relevant to keeping cut flowers looking good. Even when supplied with water, cut flowers eventually die and the petals shrivel and fall off. Biologists call this senescence, and it is mediated by the plant hormone ethylene. Since salicylic acid can block the production of ethylene, adding salicylic acid (or aspirin) to the water will delay senescence, so the flowers last longer.

Alex Brands