In plants, the pigment chlorophyll plays a central role in photosynthesis: the process of converting sunlight to energy. This process involves creating a flow of electrons by removing one from a molecule and transferring it to another. The first step happens when an electron is transferred from chlorophyll molecule to a compound called pheophytin a. Autumn leaf colors occur when chlorophyll degrades as a normal part of leaf aging or "senescence," playing an important role in nitrogen recycling. The process of chlorophyll degradation is triggered when an enzyme extracts magnesium (Mg) from chlorophyll. Researchers have named the enzyme Mg-dechelatase, but have never been able to detect its actual presence in experiments. Yousuke Shimoda, Hisashi Ito, and Ayumi Tanaka at Hokkaido University in Japan have demonstrated that a gene with known involvement in chlorophyll degradation, called Stay-Green (SGR), codes for Mg-dechelatase. Stay-Green mutants allow leaves to retain greenness during senescence. This gene was among several that led Gregor Mendel to establish the basic laws of genetics in the 19th century while studying the characteristics of peas over several generations. However, it has long been unknown what the gene actually encodes. The Hokkaido team transiently induced SGR in fully green leaves of a small flowering plant called thale cress. They found this resulted in a reduction of chlorophyll levels. They also incubated chlorophyll in a test tube with SGR, which resulted in its conversion to pheophytin a. Chlorophyll can only be converted to pheophytin a by extracting Mg from it. The experiments strongly suggest that Mg-dechelatase is involved in chlorophyll degradation via SGR. The new results were published online on September 7, 2016 in The Plant Cell.
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