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MONSTER plants that are all flower and no leaf could soon be with us, now
biologists have discovered how to make plants grow petals in place of
leaves.

As long ago as 1790, the German philosopher and playwright Johann Wolfgang
von Goethe suggested that flower petals might be modified leaves. Over the past
decade, biologists have uncovered three groups of genes that govern flower
formation. If these genes are disabled, all the flower鈥檚 petals, stamens and
carpels are turned into leaf-like sepals.

But the reverse exercise of activating these genes in leaves failed to turn
them into petals. Then last year researchers from the National Autonomous
University of Mexico and the University of California at San Diego discovered
three more 鈥渇lower鈥� genes they named SEPALLATA. When these genes are disabled,
the flowers also form only sepals (Nature, vol 405, p 200). 鈥淒ouble flowers鈥�
with this mutation have long been prized by gardeners, but the genetic
basis was unknown.

Now the same team has shown that by activating two of the SEPALLATA genes
along with the three original groups of genes, they can create petals in place
of leaves in the cress Arabidopsis (Current Biology, vol 11, p 182). Researchers
at Kyoto University have come up with similar results (Nature, vol 409, p
525).

鈥淏eing able to produce petals in leaves is a fairly big deal. It tells us
there aren鈥檛 any other essential genes,鈥� says Hong Ma, a biologist at
Pennsylvania State University.

The new discovery could allow growers to create new kinds of flowers, such as
roses with petals all along the stem. 鈥淲e should be able to do this in any
plant, and convert any leaf into a petal,鈥� says Martin Yanofsky, a member of the
San Diego team.