Now, in an article in the Journal of the American Chemical Society, one team reports on the mechanics of how these natural plant sunscreens work.

Timothy Zwier and colleagues at Purdue University note that the harsh ultraviolet radiation plants are exposed to daily can cause serious damage to plant DNA and, as a result, hinder plant growth.  Biochemical tests have shown that plants produce special molecules and send them to the outer layer of their leaves to protect themselves. These molecules, called sinapate esters, appear to block ultraviolet-B radiation from penetrating deeper into leaves where it might otherwise disrupt a plant's normal development. Although researchers have been amassing evidence that points to sinapate esters as the protective molecules, no one had investigated in detail what happens to them under UV exposure. Zwier's team wanted to understand this process.

The researchers coaxed these molecules into the gas phase and zapped them with UVB radiation from a laser in the laboratory. They found that the particular sinapate ester that plants use as a screen against UVB was inherently capable of soaking up radiation at every wavelength across the UVB spectrum. Thus, it is remarkably efficient at absorbing harsh radiation that could otherwise damage the plant. Their findings further shore up the idea that this class of molecules does indeed comprise plant-made sunblock, the researchers say.