Sun-Protection Mechanism of Plants Unraveled

 

Agricultural crops resistant to strong sunlight may one day be cultivated in the hottest and most drought-ridden parts of the world thanks to recent finding of Weizmann Institute researchers.

The scientists have unraveled the protective mechanism allowing a particularly sturdy salt-water alga, Dunaliella bardawil, to thrive in scorching sunlight. In the future, it may be possible to manipulate a similar mechanism existing in higher plants, including crop, in order to enhance their resistance to the sun, according to Prof. Ada Zamir of the Institute's Department of Biochemistry. She deciphered the mechanism together with department members Haim Levy, Tamar Tal, Dr. Aviv Shaish, Dr. Irena Gokhman and Dr. Amnon Lers.

Dunaliella bardawil is known for its legendary resistance to the salt and sun, which allows it to thrive in the brackish marshes of the Sinai desert and even in the Dead Sea. It was first isolated from the Bardawil marsh in Sinai and studied by the late Institute Professor Mordhay Avron, together with his then student, Prof. Ami Ben-Amotz.

The dunaliella alga fascinates scientists because it is both a remarkable survivor and functionally very similar to higher plants. These two properties make it an excellent model for studying survival strategies that may be relevant for growing useful crops under harsh conditions, according to Prof. Zamir.

Excessive sunlight causes most plants to produce toxic oxygen molecules that damage and eventually destroy the plant's photosynthetic machinery. Zamir and her associates have discovered a protein, now known as Cbr, that is formed in dunaliella whenever this machinery is threatened. Using genetic engineering, the researchers have cloned the gene coding for this protein.

They further observed a close link between Cbr and a carotenoid pigment called zeaxanthin, also formed under the stressful conditions of intense light. The scientists have concluded that the protein binds with the pigment to form a light-protective "antenna" or "lightening rod," which diverts the excessive, harmful light from the sensitive components of the photosynthetic machinery. While producing Cbr and zeaxanthin, the alga also forms large quantities of beta-carotene, an orange pigment that serves as the plant's natural sunscreen.

Prof. Zamir holds the Carl and Dorothy Bennett Chair of Biochemistry.

The research was supported by grants from the Minerva and the German-Israel Foundations.