Why do flowers wilt? We’ve finally found out

We have long known why plants grow flowers – to encourage pollination. But what prompts a flower to shrivel up, once it’s done its job?

While there have been plenty of theories, the reason has not – until now – ever been directly tested.

But some experiments on colourful Christmas bells (Blandfordia grandiflora) have finally yielded evidence.

The study is published in Plant Biology.

Lead author Professor Graham Pyke, a researcher at Macquarie University, tells Cosmos he took an interest in wilting while studying resource conservation in Christmas bells.

“I decided to think: Okay, what’s the advantage to a plant having flowers wilt? The obvious answer, when you think about it, is it enables a plant to salvage some of those resources it has put into petals and reuse those resources at some other place, at some other time.”

There are several different hypotheses on why flowers wilt, suggesting different ways the energy and nutrients might be redistributed.

“We set up 3 experiments aimed at preventing or allowing reallocation of resources from  flowers, one way or another,” says Pyke.

In the first experiment, the team removed the petals from some Christmas bell flowers with tiny scissors, preventing the plant from salvaging the petals’ resources. Then, they artificially pollinated each flower, so that they could still germinate without petals. They left other flowers on each plant intact, to see if the wilted flowers produced more seeds than the non-wilted flowers.

“We found no difference between plants with wilting flowers and plants with normal flowers,” says Pyke.

In the second experiment, they removed petals and stigma (the part of a flower which germinates pollen), so those flowers couldn’t wilt or produce seeds.

“We arranged, at the end, to have counselling for all our plants,” jokes Pyke, saying that this was probably a stressful experience for the flowers.

They again left other flowers on the plant intact, to see if the plants redistributed their resources to make seeds elsewhere.

“The second experiment, where plants could reuse resources in other flowers of the same plant, also showed no difference between wilting plants and non-wilting plants,” says Pyke.

In the third experiment, they removed all the stigmas from plants, and then removed petals on some plants and left them on others – so the Christmas bells couldn’t make any seeds that year, but some of them could still wilt. The team then returned a year later to see how the plants produced seeds in the next season.

“We found that yes, indeed, the plants from which flowers have been allowed to wilt were more likely to flower again a year later,” says Pyke.

This means that the wilting flowers are a long-term move for the plant: they allow the plant to conserve resources for another year.

“This is the first direct demonstration that flowering plants store resources from wilting flowers, and reuse of resources for subsequent reproduction,” says Pyke.

“A lot of people have suggested that in the past – we’re the first ones to come along and give a great demonstration.”

The researchers don’t yet know how this reallocation works, although they have ideas for ways to figure it out.

“I want to look, for example, at what happens with tissues labelled with radioisotopes in different parts of the flowers, [to] see where those radioisotopes move,” says Pyke.

“That will shed a lot of light on that some of the physiological mechanisms by which the plant does things.

“As for how it actually pulls it off chemically – we need a clever biochemist to come along and look at that.”

As well as possibly being useful knowledge for florists – Christmas bells are a very popular bouquet addition – Pyke says the research might lead to ways to make fruit more productive.

“It’d be very interesting to follow up from our research and do similar research on a plant like the blueberry, and see if the same kinds of phenomena are occurring, and see if that could lead to some way of manipulating what blueberries do in order to enhance the quantity or quality of their fruit production,” he says.

“This is really just the tip of the iceberg in terms of looking at how plants allocate resources.”