Biologists Uncover Rules that Govern Leaf Design

Biologists from the University of California Los Angeles (UCLA) have discovered fundamental rules of leaf design that underlie plants' ability to produce leaves that vary in size. In their mathematical design, leaves are the "perfect machines," said Lawren Sack, UCLA professor of ecology and evolutionary biology and senior author of the research, published in the October issue of the American Journal of Botany.

The team discovered the mathematical relationships using "allometric analysis," which looks at how the proportions of parts of an organism change with differences in total size. The biologists focused on how leaf anatomy varies across leaves of different sizes and examined plant species from around the world. They tested the underlying relationship between cell and tissue dimensions and leaf size across species, and discovered that larger cells of thicker leaves are surrounded by thicker cell walls.

The team hypothesized that these strong mathematical relationships arise from leaf development. Because light can penetrate only so many layers of cells, leaves cannot vary much in the number of cells arranged vertically. The expansion of individual cells and their cell walls occurs simultaneously and is reflected in the thickness of the whole leaf. On the other hand, the number of cells arranged horizontally in the leaf continues to increase as the leaves expand, regardless of the size of the individual cells.

For more details about this study, read the UCLA news release available at http://newsroom.ucla.edu/portal/ucla/ucla-biologists-discover-new-mathematical-249097.aspx.