Leaf starter

To grow a new leaf, a plant just needs to relax—its cell wall, that is. This conclusion comes from a new study on the regulation of leaf formation. The authors report that a protein called expansin that loosens the cell wall also sparks the growth of normal leaves.

To stimulate expansin production within the meristem that makes new leaves, a group led by Andrew Fleming of the Swiss Federal Institute of Technology in Zurich, Switzerland, created transgenic tobacco plants in which the expansin gene was coupled to a tetracycline-dependent promoter. Induction of expansin expression caused a leaf to sprout at the site. As far as they could determine, the resulting leaves were normal internally and externally, says Fleming—unlike the results from a prior experiment in which dabbing expansin on nontransgenic plants produced only spindly growths.

The authors...