How the daisy got its spots

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Washington, December 19 (ANI): In a new research, scientists have studied how the dark spots on the petals of flowers like daisies are formed.

Dr. Meredith Thomas from the University of Cambridge and associates from England and South Africa have carried out the research.

They focused on the South African endemic beetle daisy Gorteria diffusa, which has a unique, raised, dark spot at the base of some of its ray florets.

"The spots on the flowers mimic the plant's pollinator, a small fly, which is attracted to the plant because of the spots. The plant is dependent on the pollinator for reproductive success, so it's incredibly important that the plant attracts the flies," said Thomas.

"What we found surprising was how complex the petal spots are in a few populations, when other populations seem to get by with a very simple spot or even no petal spot at all," said Thomas.

By peeling away layers of the tissues that make up the spots on mature ray florets and examining them under a simple dissecting scope, Thomas and associates found that the spots of G. diffusa are more complex than most.

These spots are composed of three different types of specialized epidermal cells: the central highlight cells that reflect UV and lack pigment; the interior cells that are shorter, rounder, variously pigmented, and raised above the highlight cells; and, surrounding the spot, a circle of multicellular papillae that are swollen, shiny, and filled with anthocyanin.

Moreover, each spot spans four congenitally fused petal lobes, meaning that each lobe contained only part of the spot (and only some cell types) in its genetic makeup.

As to what attracts the pollinators, the researchers hypothesized that because there is a lot of spot variation in this species, the elements that are found in common among the various populations, such as the presence of anthocyanin pigment or UV reflectivity, might do the trick.

The researchers also wanted to know how only a subset of the floral rays develops a spot.

Using scanning electron microscopy, the authors looked at how the spot developed, or its ontogeny, over time.

They found that only the first few ray florets that develop contain the spots, whereas the rest do not.

The scientists hypothesize that the genes that control the appearance of the spot are turned on initially and then fade with time, such that only the first, and oldest, rays to develop have the spots.

Thus, the development of the spots is complex not only at the cellular level, but at the organismal level as well. (ANI)

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