New Worlds: Air pollution tied to storm activity

Also, Weizmann Institute researcher reveals gene responsible for producing sweet, pink tomato loved by diners in the Far East.

By JUDY SIEGEL-ITZKOVICH
Where there’s smoke, there’s fire, and where there’s air pollution, local weather patterns, rainfall and thunderstorm intensity can be affected. So say Tel Aviv University researchers and colleagues in other institutions who recently published their findings in Geophysical Research Letters.
In the new study, Prof. Colin Price, head of TAU’s department of geophysics and planetary science, researched data on lightning patterns in the Amazon to show how clouds are affected by particulate matter emitted by the fires used for slash-and-burn foresting practices. His findings could be used by climate change researchers trying to understand the impact of pollution.
Along with researchers at the Weizmann Institute and the Open University, Price demonstrated how pollution’s effects on cloud development could negatively affect our environment. While low levels of particulate matter actually help thunderstorms develop, the reverse is true once a certain concentration is reached; the particles then inhibit the formation of clouds. “The clouds just dry up,” he says.
Scientists have known for some time that man-made aerosols affect cloud formation, but scientific findings have been inconclusive. How clouds and storms change in response to air pollution is central to the debate about climate change and global warming.
But how man-made pollution affects clouds, rainfall and weather patterns remains poorly understood, and natural particulates such as those generated by Iceland’s recent volcano eruptions may add to this effect. The thick volcanic ash cloud absorbs solar radiation, heating the upper atmosphere, similar to forest fire smoke, and can hence also affect the development of clouds, Price said.
While studying the climate of the Amazon forest during its dry season, the researchers noticed how thousands of man-made forest fires injected smoke into the atmosphere. Since thunderstorms still occur during the dry season, it was the perfect opportunity for studying the effects of these particulates on cloud development.
Cloud droplets form on small particles called cloud condensation nuclei (CCN). As the number of CCN increase due to fire activity, lightning activity increased in the storms ingesting the smoke. More CCN implies more small droplets that can be carried aloft into the parts of the cloud where lightning is generated. Increased lightning activity generally also implies increasing rainfall over the Amazon. But when particulate matter became too dense, they observed, clouds didn’t form, and ightning activity diminished dramatically.
These results may have significant implications for polluted regions that rely on rainfall for agriculture. “One of the most debated topics related to future climate change is what will happen to clouds, and rainfall if the earth warms up,” says Price, “and how will clouds react to more air pollution?”
EXOTIC TOMATOES
Far Eastern diners are partial to a variety of sweet, pink-skinned tomato. Dr. Asaph Aharoni of the Weizmann Institute of Science’s plant sciences department recently revealed the gene responsible for producing these pink tomatoes. Aharoni’s research focuses on plants’ thin, protective outer layers, called cuticles, which are mainly composed of fatty, wax-like substances. In the familiar red tomato, this layer also contains large amounts of antioxidants called flavonoids that are the tomatoes’ first line of defense. Some of these flavonoids also give the tomato cuticles a bright yellow cast – the color component that is missing in the translucent pink skins of the mutants.
Using a lab system that’s unique in Israel – and one of only a few in the world – Aharoni and his team are able to rapidly identify hundreds of active plant substances called metabolites. A multidisciplinary approach developed over the past decade, known as metabolomics, enables them to create a comprehensive profile of all these substances in mutant plants.
The research, carried out in Aharoni’s lab by Dr. Avital Adato, Dr. Ilana Rogachev and research student Tali Mendel, showed that the differences between pink and red tomatoes go much deeper than skin color: The scientists identified about 400 genes whose activity levels are quite a bit higher or lower in the mutants. The largest changes, appearing in both the plant cuticle and the fruit covering, were in the production of substances in the flavonoid family. The pink tomato also has less lycopene, a red pigment known to be a strong antioxidant associated with reduced risk of cancer, heart disease and diabetes. In addition, alterations in the fatty composition of the pink tomato’s outer layer caused its cuticle to be both thinner and less flexible that a regular tomato skin.
 The researchers found that all these changes can be traced to a mutation on a single gene known as SIMYB12. This gene acts as a “master switch” that regulates the activities of a whole network of other genes, controlling the amounts of yellow pigments as well as a host of other substances in the tomato. Aharoni: “Since identifying the gene, we found we could use it as a marker to predict the color of the fruit even before the plant has flowered. This ability could accelerate efforts to develop new, exotic tomato varieties.”