Scientists at the Max Planck Institute for Plant Breeding Research in
Cologne have discovered how a protein called LMI1 controls leaf growth and
shape. Francesco Vuolo and colleagues are investigating the mechanisms
underlying leaf shape variations, but have recently looked into the little
understood leaf parts called stipules. These outgrowths form at the base of
a leaf during development and vary greatly in size and function in different
plant species. In the model plant Arabidopsis, the mature stipules remain
tiny, although they make up a substantial part of the young leaf. In other
plants, such as garden pea, the stipules form a large part of the leaf.
The research team used a combination of tools and showed that the protein
LMI1 keeps the stipules small. Vuolo explains that if the protein is
produced in a cell during leaf development, it simply continues to grow
instead of dividing, prevents the cell from developing into other cell
types, and limits the pool of cells available for further tissue growth.
LMI1 also plays a key role in the regulation of leaf morphology in other
plants. Vuolo's team discovered that LMI1 is not produced in the large
leaf-like stipule of pea plants, but instead in the upper part of the pea
leaf, where tendrils form. These findings shed new light on the
developmental origin of stipules, suggesting that they are in fact cryptic
leaves that are maintained in a repressed state by LMI1.