S. Yoshida et al., “Stem cell activation by light guides plant organogenesis,” Genes Dev, 25:1439-50, 2011. Free 1000 Evaluation
For 150 years it was assumed that an unknown internal stimulus drove leaf genesis. But Saiko Yoshida and colleagues in the lab of Cris Kuhlemeier at the University of Bern have now determined that even though the location where new leaf development occurs—stem cells at the tip of a plant shoot—is shrouded by a dense covering of leaves, enough light can penetrate to activate growth hormones.
The authors looked at two hormones—cytokinin and auxin—known to react to environmental stimuli. Cytokinin promotes cell division, while auxin is responsible for leaf formation.
When researchers grew tomato plants in the dark, new leaf production ceased even when sugar was added to make up for the lack of photosynthesis. Instead, the auxin transporter protein gradually disappeared from cell membranes with a consequent drop in auxin levels. Applying auxin externally and allowing it to diffuse into the cells did not restore leaf formation, but cytokinin application did, suggesting that auxin does not work alone.
For the first time, external stimuli were found to affect leaf initiation. This light trigger could be used to manipulate leaf arrangement to optimize light capture and potentially provide higher crop yields. In addition, it suggests researchers might want to take another look at signals that were assumed to be independent of environmental cues, says Karen Halliday, at the University of Edinburgh.