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.

For more details, read the news release from Max Planck.