Wines from the USA are famous and coveted worldwide. With more than 4,500 square kilometers of vineyards, the United States is the fourth largest wine-growing country in the world after Italy, Spain and France. California alone produces about 84 percent of all U.S. wine. However, concern is increasingly spreading among winegrowers due to the abnormally high summer temperatures caused by climate change. This puts the vines under drought stress.

Winegrowers are therefore forced to harvest the grapes before they are perfectly physiologically ripe, which can lead to unbalanced wines and atypical aging notes. Artificial irrigation provides a remedy in some cases, but it involves high costs and is not exactly environmentally friendly.

For Andrew McElrone, professor in the Department of Viticulture and Enology at the University of California at Davis, research into the water transport physiology of grapevine roots is crucial to the future of California's viticulture industry. The plant biologist's ultimate goal is to develop sustainable water use strategies for grape growers. To do this, he wants to provide them with hard data on how much drought their plants can withstand and which species are ideal for an agricultural future with an uncertain water supply.

High Resolution X-Ray Tomography

In his research, McElrone used Beamline 8.3.2 of the "Advanced Light Source" - ALS for short (see infobox). To gain a better understanding of the grapevine's water transport system, McElrone used the high-resolution X-ray tomography available there. Thanks to the brilliant scans, he and his research partners were able to see for the first time exactly how pressure from drought affects the xylem vessels in a plant's water transport network. This is important because the xylem network transports water and nutrients from the roots to the rest of the plant–. The more a drought stresses the network, the greater the tension in the system and therefore the more susceptible the individual vessels and tubes ni the plant are to rupture, and thus to bacterial invasion.

McElrone discovered during his work on the ALS that some grapevines can actually repair this break by forming droplets on the walls of the xylem tubes. Scientists had speculated about this process, but McElrone and his fellow researchers were the first to actually observe it in action. They found that droplet formation does not occur randomly, but rather follows the orientation of the remaining living cells. McElrone continued the research with a number of grape varieties and realized that that the more drought-resistant grape varieties were more likely to be able to resist breakage or have better repair capabilities.

"Our goal is to find out how far we can push drought in different grape varieties before they break, which we can then apply to water use in the fields," McElrone says. "At the ALS, we were able to actually observe the breakage and repair."

Another important finding from McElrone's research on the ALS beamline was that the vines' bridging cells - which provide better connectivity within the plants' vascular architecture - also determine which species are most resistant to pathogens. Thanks to high-resolution electron microscopy scans from the University's Davis lab combined with ALS scans, McElrone's team observed the presence and orientation of bridge cells.

Additional research should also reveal whether there are intact barriers between the bridge cells. The more susceptible vines actually had more open bridge cells, McElrone said. Pathogens were able to penetrate through the network and further into the plant structure. "The resistant species, on the other hand, isolated the pathogens by forming bridge cells with barriers, stopping the bacteria from spreading," the researcher says. McElrone sums up by saying that, "as far as plant biology goes, the images are decidedly revealing."


The Advanced Light Source (ALS) is a research facility at Lawrence Berkeley National Laboratory in Berkeley, California. It is one of the world's brightest sources of ultraviolet and soft X-ray light. The latter has a much lower photon energy than hard X-rays, enabling imaging of solids as a homogeneous "unexposed" medium. In addition, the ALS has the first "third generation" synchrotron light source in its energy range.

The ALS provides multiple extremely bright sources of intense and coherent short-wavelength light that researchers from around the world use for scientific experiments. It is funded by the U.S. Department of Energy (DOE) and managed by the University of California (UC).

How ALS Works

Electron bunches moving almost at the speed of light are forced into an almost circular path by magnets in the ultra-high vacuum of the ALS storage ring. Between these magnets, there are straight sections with dozens of magnets with alternating polarity, the so-called "undulators". They force the electrons onto a slalom-like path. Under the influence of the deviations from the straight path, electromagnetic rays are emitted, ranging from the infrared through the visible and ultraviolet range to X-ray wavelengths. The resulting beams can be guided to the instruments of the experimental stations via branching tubes - the beamlines.

The ALS has a complex vacuum system with a total length of more than one kilometer of vacuum tubes for the electron and photon beams. The vacuum pressure in the beam tubes is 100 mbar at some experimental stations and goes up to 1x10-11 mbar in the storage ring.

The extreme vacuum is necessary for a very simple reason: If the tubes were ventilated normally, the elementary particles would collide with the air molecules immediately after leaving the electron or photon source and interact with them. Accelerated radiation would not even occur.

In order to be able to hermetically seal certain sections of the high and ultra-high vacuum range for maintenance work, sector valves are primarily used. They can be used to hermetically seal certain sections of the high and ultrahigh vacuum range. In addition, there are quick-acting valves that quickly isolate affected ring or tube sections in the event of leakage, thus maintaining the vacuum and preventing possible contamination by intruding air.

The vacuum valves used are all-metal valves. These are a class of vacuum valves that operate completely without elastomer seals. Here, sealing is achieved with metal on metal - and the surfaces of the seals are designed with corresponding precision. Elastomer seals, which are often used even on valves in vacuum, degrade very quickly under the high temperatures and high-energy radiation prevailing in the beamlines and storage ring.      

"Vacuum gate valves are essential to the protection, maintenance and construction of ALS vacuum beamlines," said Sol Omolayo, ALS vacuum systems manager. "Beamline 8.3.2, on which Andrew McElrone conducted research, has a high vacuum pressure requirement and operates at an average vacuum pressure of 1x10-7 mbar.