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Why do petals have rounded ends while leaves are more pointed?
The shape of petals is controlled by a hidden map located within the plant’s growing buds.
Leaves and petals perform different functions related to their shape. Leaves acquire sugars for a plant via photosynthesis, which can then be transported throughout the plant. Petals develop later in the life cycle and help attract pollinators. In earlier work, this team had discovered that leaves in the plant Arabidopsis contain a hidden map that orients growth in a pattern that converges towards the tip of the bud, giving leaves their characteristic pointed tips. In the new study, the researchers discover that Arabidopsis petals contain a similar, hidden map that orients growth in the flower’s bud. However, the pattern of growth is different to that in leaves - in the petal growth is oriented towards the edge giving a more rounded shape - accounting for the different shapes of leaves and petals. Researchers discovered that molecules called PIN proteins are involved in this oriented growth, which are located towards the ends of each cell.
Unlike animal cells, plant cells are unable to move and migrate to form structures of a particular shape, and so these findings help to explain how plants create differently shaped organs - by controlling rates and orientations of cell growth. From an evolutionary perspective, this system creates the flexibility needed for plant organs to adapt to their environment and to develop different functions.
http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001550

Why do petals have rounded ends while leaves are more pointed?

The shape of petals is controlled by a hidden map located within the plant’s growing buds.

Leaves and petals perform different functions related to their shape. Leaves acquire sugars for a plant via photosynthesis, which can then be transported throughout the plant. Petals develop later in the life cycle and help attract pollinators. In earlier work, this team had discovered that leaves in the plant Arabidopsis contain a hidden map that orients growth in a pattern that converges towards the tip of the bud, giving leaves their characteristic pointed tips. In the new study, the researchers discover that Arabidopsis petals contain a similar, hidden map that orients growth in the flower’s bud. However, the pattern of growth is different to that in leaves - in the petal growth is oriented towards the edge giving a more rounded shape - accounting for the different shapes of leaves and petals. Researchers discovered that molecules called PIN proteins are involved in this oriented growth, which are located towards the ends of each cell.

Unlike animal cells, plant cells are unable to move and migrate to form structures of a particular shape, and so these findings help to explain how plants create differently shaped organs - by controlling rates and orientations of cell growth. From an evolutionary perspective, this system creates the flexibility needed for plant organs to adapt to their environment and to develop different functions.

http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001550