Flowers like hibiscus use an invisible blueprint established very early in petal formation that determines the size of their floret – a crucial pre-pattern that can significantly impact their ability to attract pollinating bees.
The research from researchers at the University of Cambridge’s Sainsbury Laboratory also found that bees prefer larger florets over smaller ones and fly 25% faster between artificial flower disks with larger florets – potentially increasing efficiency for both bees and blossoms.
Patterns on plants’ flowers direct insects, such as bees, to the center of the flower, where nectar and pollen await, increasing the chances of successfully pollinating the plant. Despite their importance, surprisingly little is known about how these petal patterns form and how they evolved into the enormous diversity we see today, including spots, stripes, veins and florets.
Using a small hibiscus plant as a model, researchers compared closely related plants with the same flower size, but three different sized bullseye patterns with a dark purple center surrounded by white – H. richardsonii (small bullseye covering 4% of the flower disk), H. trionum (medium bullseye covering 16%) and a transgenic line (mutation) of H. trionum (large rose covering 36%).
They discovered that a preliminary pattern is formed on the petal surface very early in flower formation, long before the petal shows any visible color. The petal acts as a ‘paint by numbers’ canvas, with different regions predetermined to develop specific colors and textures long before they start to look different from each other.
The research also shows that plants can precisely control and adjust the shape and size of these patterns using multiple mechanisms, with potential implications for plant evolution. By refining these designs, plants can gain a competitive advantage in the fight to attract pollinators or perhaps start attracting different species of insects.
These findings were published in Scientific progress.
Dr. Edwige Moyroud, who leads a research team studying the mechanisms underlying pattern formation in petals, explains: ‘If a trait can be produced using different methods, it gives evolution more opportunities to adapt it and increase diversity. create, similar to an artist with a large palette or a builder with an extensive set of tools. By studying how bullseye patterns change, we are really trying to understand how nature generates biodiversity.”
Lead author Dr Lucie Riglet investigated the mechanism behind hibiscus petal formation by analyzing petal development in the three hibiscus flowers that had the same overall size but different bullseye patterns.
She found that the pre-pattern begins as a small, crescent-shaped area long before the rose is visible on small petals less than 0.2 mm in size.
Dr. Riglet said: “At the earliest stage we were able to dissect, the petals had about 700 cells and are still greenish in color, with no visible purple pigment and no difference in cell shape or size. When the petal further develops to 4,000 cells , it still has no visible pigment, but we identified a specific area where the cells were larger than their surrounding neighbors. This is the pre-pattern.”
These cells are important because they mark the position of the rose border, the line on the petal where the color changes from purple to white – without a border there is no rose!
A computational model developed by Dr. Argyris Zardilis provided further insights. Combining both computational models and experimental results, the researchers showed that hibiscus can vary the dimensions of the rose very early during the pre-patterning phase or modulate growth in both parts of the rose, by adjusting cell expansion or division, later in development.
Dr. Riglet then compared the relative success of the bullseye patterns in attracting pollinators using artificial flower discs that mimicked the three different bullseye dimensions. Dr. Riglet explained: “The bees not only preferred the medium and larger bullseye over the small bullseye, they also visited these larger flower discs 25% faster. Foraging takes a lot of energy and so if a bee can visit 4 flowers instead of 3 blooms at the same time, then this is probably beneficial for the bee, and also for the plants.”
The researchers think these pre-patterning strategies may have deep evolutionary roots, potentially influencing the diversity of floral patterns across species. The next step for Edwige Moyroud’s research team is to identify the signals responsible for generating these early patterns and investigate whether similar pattern formation mechanisms are used in other plant organs, such as leaves.
This research not only advances our understanding of plant biology, but also highlights the intricate connections between plants and their environments, showing how precise natural designs can play a crucial role in the survival and evolution of species.
For example, H. richardsoniiwhich has the smallest floret of the three hibiscus plants studied in this study, is a critically endangered plant native to New Zealand. H. trionum is also found in New Zealand, but is not considered native, and is widely distributed throughout Australia and Europe and has become a weedy naturalized plant in North America. Additional research is needed to determine whether increased bullseye size helps H. trionum attract more pollinators and increase its reproductive success.
