Alga makes its own sunblock.

Not only are salt and sun the bane of beautiful skin, they can also make life miserable for plants. But like cosmetic companies, some plants have a secret for avoiding damage from the elements.

Molecular biologists have now learned this secret, at least for a single-cell alga called Dunaliella bardawil that thrives in the Dead Sea and the Sinai desert. The plant makes its own sunscreen and a molecular solar deflector, says Ada Zamir at the Weizmann Institute of Science in Rehovot, Israel.

To understand how this alga responds as dramatically and quickly as it does to harsh conditions, Weizmann scientists first isolated an algal protein produced when sunlight gets too intense. Zamir and her colleagues then realized that the protein, Cbr, resembles those used by plants to make molecular "antennas" to funnel light down to where photosynthesis takes place.

Although plants depend on the sun's energy to fuel photosynthesis, too much light causes them to make toxic oxygen molecules. To keep these toxins from forming and interfering with photosynthesis, this alga produces a yellow-orange pigment called zeaxanthin that joins with Cbr, says Zamir. The two substances form a "lighting rod" that helps shunt exces light away from where it could do damage, she and her colleagues report in the Oct. 5 JOURNAL OF BIOLOGICAL CHEMISTRY. Intense light also increases the alag'a production of an orange pigment, beta-carotene, which the alga can then convert to the antenna pigment or use to filter out some light, they report.

Zamir thinks that because higher plants make similar pigments and proteins, they use the same protective mechanisms as this alga, but to a lesser degree. Now that researchers know these secrets, they can figure out how to increase this protective response in other plants, she suggests.