Question: Hello you all, I work on plants' senses and I would like you to tell me more about pheromone that some trees release.

Jennifer Bates answered on 15 Nov 2016:

Hi,
I’m not too sure about trees particularly, but some plants do indeed send out pheromones, and unlike animal pheromones, plant pheromones are not very often studied! And plants produce hormones (phytohormones) too, though they produce and store them differently from animals as they don’t have glands or a circulation system. More simple chemicals are used by plants as phytohormones and they are more localised than the hormones in animals as plant cells don’t always respond to them, it depends on cell function and age/point in growth cycle.

A pheromone is probably best described as a chemical/mixture of chemicals that when released has an affect on the physiology or behaviour of another member of that species.

In plants these can include alarm pheromones, for example releasing a pheromone when grazed on that makes their neighbours produce tannins which are not particularly nice to eat, ideally putting off the grazer from continuing to eat their lunch.

Some algae produce pheromones as part of their reproductive strategy.

I guess you could class the phytohormone ethylene as a pheromone sometimes, if it counts when the plant’s production of ethylene affects itself…When a tree is affected by wind more ethylene is produced and this encourages the tree to grow more sturdily to withstand the wind. This phytohormone also affects fruit-ripening, as it builds up as the seed ripens, causing seed dispersal.

The same thing goes for ethene produced by a plant as a result of insect damage. This can encourage fruits to ripen or the loss of leaves (amongst other things). In producing the ethene the plant stimulates production of other chemicals that damage the insects, so a defence mechanism, but whether this affects other plants further away, making it truly a pheromone, I’m not sure.

There is also an odd one, in that it doesn’t affect members of the same species, but others: fennel! Fennel makes a ‘pheromone’ (chemical that has an impact on others) that inhibits the growth of most other plants but, oddly, makes chilli seeds grow quicker when close by! There’s always an odd one out! You could try that at home as a little experiment, plant a pot of fennel, a pot of chilli and a pot of something else, and see what happens!