Researchers say they have discovered the first direct demonstration that plants can salvage resources from wilted flowers and reuse those resources to promote future reproduction.
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Wilted flowers may not signal poor flower or plant health, but rather the effects of a sophisticated resource management strategy in plants, millions of years in the making.

A study published in the journal Plant biology by Macquarie University researchers and international collaborators has demonstrated for the first time that plants reuse resources from withered flowers to support future reproduction.

Lead author, Honorary Professor Graham Pyke of Macquarie University, says the findings help explain a common but poorly understood plant process.

“Our research provides the first direct demonstration that plants can salvage resources from wilted flowers and reuse these resources to promote future reproduction,” says Professor Pyke.

These resources include the energy and chemical composition of the petals, including carbohydrates and nutrients such as nitrogen and phosphorus.

Evidence management

The three-year study focused on Blandfordia grandifloracommonly known as Christmas bells, which blooms mostly in December.

This perennial plant species with colorful red and yellow flowers, native to eastern Australia, is often sold in Australian and international flower markets. Commercially grown strains of Christmas bells produce anything from two or three flowers to a dozen or more.

“Our research is taking place on a plantation containing several hectares of native wet forest where Christmas bells flower quite profusely, together with a commercial shade house,” says Professor Pyke.

The team used a variety of techniques to control pollination and flower wilting, then checked the effect on seed production and reblooming.

To their surprise, the researchers found that the plants did not use the resources from the wilted flowers to enhance short-term reproduction, either through the same flowers or through other flowers on the same plant.

“These plants save the resources invested in reproduction during one flowering season and reuse these resources during the next flowering,” says Professor Pyke.

To do this, Blandfordia grandiflora it transfers resources from its wilted flowers, storing this “chemical energy” underground in corms and roots to then help produce new flower stalks the following season, generally a year later.

Plant economy

Professor Pyke says the plant world is a fascinating area of ​​resource management and economic strategy.

“Plant economics is about trade-offs,” he says. “Plants must make decisions about where to allocate their limited resources; investing in one area means I can’t invest as much in another.”

This concept of resource allocation led Professor Pyke to investigate the phenomenon of flower wilting, which for years scientists have speculated could be a way for plants to transfer valuable resources to other processes.

“We were in for a surprise,” says Professor Pyke. “It seems that the plants were playing a longer game than we anticipated, not using their recovered resources immediately, but storing them for the next flowering season.”

Professor Pyke says plants have developed various strategies for managing flowers after they have fulfilled their primary reproductive function, with wilting just one of several possible approaches.

Not all plants follow the pattern of flower wilting; flowers will continue to bloom on some plants long after they can be fertilized and after they no longer produce nectar.

“Flowers make the whole plant more attractive to pollinators, even when they’re just there as part of the overall display,” he says.

Some plants will even drop their flowers long before they wilt. “For example, jacaranda flowers that look perfectly fine will just fall to the ground; frangipani the trees will also shed flowers intact rather than wither.”

Testing theories

The study tested resource reuse in different ways.

One experiment compared seed production between plants with flowers allowed to wilt and those with petals removed to prevent wilting. Another prevented seed production in all flowers – but allowed a group of plants to wilt.

“We can easily prevent seed production by removing the stigma,” says Professor Pyke.

The results showed that plants with wilted flowers were more likely to rebloom the following season than those where wilting was prevented.

The study also considered other factors that could influence seed production, such as flower stem height, number of flowers per stem and flower position.

Taller flowering stems, for example, produced more seeds and heavier seeds, as did stems with more flowers. But flowers positioned lower on the plant tended to have fewer seeds and seeds that weighed less.

“Our findings pave the way for further research into other plant species and how they recover and reuse resources from wilted flowers,” says Professor Pyke.

Further research could explore what these saved resources are made of, how plants move and change them, and whether the benefits of saving these resources outweigh the costs of making flowers in the first place.

Graham Pyke is an honorary professor at the School of Natural Sciences.

This article was first published on lighthouse – Macquarie University’s multimedia publishing platform – and republished here with permission.