NEWS OF THE WEEK Therefore, technicians are now replacing Atlantis' boosters with rockets that were slated for use on the next shuttle flight, in November. And those boosters are being assembled using the TCAbased adhesive and cleaning fluid. NASA still has more than 100 gal of the old adhesive and only a few gallons are used per shuttle mission, notes a spokesman. So "there's enough for a while" until NASA figures out whether it can use the new materials or will have to find, test, and certify alternatives. Meanwhile, Lucid will have more time to continue microgravity and life sciences experiments on Mir with two Russian cosmonauts, Yuri Onufrienko and Yuri Usachev, to prepare for an international space station (C&EN, April 1, page 7). On July 15, Lucid, 53, surpassed the longest previous U.S. stay in space, 115 days. Richard Seltzer
Curbs urged on air transport of oxidizers The Federal Aviation Administration (FAA) is calling for tighter limits on transport of oxygen-yielding hazardous materials on passenger aircraft. It has asked the Department of Transportation (DOT) to ban the materials from class D cargo holds—those without smoke detectors or fire extinguishers. FAA also wants DOT to shift $14 million within its 1997 budget, mostly to fund more hazardous materials inspectors. The National Transportation Safety Board (NTSB), an independent federal agency that investigates transportation accidents, urged these changes in May, shortly after a Valujet Airlines plane crashed in the Everglades near Miami, killing all 110 passengers and crew. The crash is still under investigation but is believed to have been caused by an intense fire in the cargo hold involving oxygen generators being shipped as cargo. The Valujet plane had a class D cargo hold—designed to be airtight and thereby smother any fire that may start. But that system doesn't work if oxidizers are in the compartment. DOT issued a temporary ban in May on transport of chemical oxygen generators as cargo on passenger airlines. The new recommendations would make 12
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the ban permanent and extend it to other oxidizing materials, such as hydrogen peroxide. The Valujet cargo included many poorly packed and mislabeled oxygen generator canisters of the type used to supply airplane passengers with emergency oxygen. They contain sodium chlorate and iron, two stable solids which, when heated, produce oxygen by the general reaction Fe + NaC103 -> FeO + NaCl + 0 2 . Heat is ordinarily supplied by a percussion cap activated by a hammer that is part of the canister. Without safety caps—which were missing from some of the canisters on the Valujet plane—it's fairly easy to activate the system by accident. NTSB knows of two other incidents in recent years involving fires associated with chemical oxygen generators shipped by air without proper identification as hazardous materials, board chairman James E. Hall told a House subcommittee last month. He also said undeclared and improperly packaged hydrogen peroxide shipped as cargo has been involved in at least two aircraft fires in the past decade. Rebecca Rawls
Algae grow using one-step photosynthesis Experiments with mutant algae are challenging some of the fundamental concepts of plant photosynthesis. Two mutant strains of algae can carry out photosynthesis and grow even though they lack one of the two photosystems generally held to be critical for photosynthesis to occur, according to work by Elias Greenbaum, a group leader in the biotechnology research division at Oak Ridge National Laboratory, Oak Ridge, Term., and colleagues there, and by Thomas G. Owens, a spectroscopist and plant biologist at Cornell University [Science, 273,364 (1996)]. "The traditional model of the way plants convert light energy into chemical energy requires two light reactions—called photosystem I and photosystem II—working in series/' Greenbaum explains. "These mutants do not have any detectable level of photosystem I, yet they perform the basic reactions of photosynthesis. They fix carbon dioxide, they can produce hydrogen and oxygen, and they grow."
In work published a year ago [Nature, 376,438 (1995)], the group demonstrated that the mutants could photoassimilate carbon dioxide from the atmosphere and simultaneously produce hydrogen and oxygen from water in a light-driven reaction—the two basic reactions of photosynthesis. The new work demonstrates, in addition, that the algae can use these reactions to divide and grow. "That completes the triad of what a photosynthetic organism should be required to do," Greenbaum notes. "We're not saying that [the traditional two-step model of photosynthesis, called] the Z scheme is wrong," Greenbaum points out. "Certainly Z-scheme photosynthesis is correct in the sense that that is the way plants do it today. . . . We're saying that the Z scheme may not be the unique pathway by which autotrophic photosynthesis occurs." The mutant strains, he notes, may help in understanding how photosynthesis evolved. The mutants and Greenbaum's claims about them have caused quite a stir among photosynthesis researchers during the past year. Many questions need to be answered about whaf s going on in these organisms—including the quantum efficiency of the process and a detailed description of the reaction pathways involved—before the findings are likely to be widely accepted. "Most people have an open mind, but are skeptical," says Gary W. Brudvig, chemistry professor at Yale University. The system is an interesting novelty that deserves wider attention and study, says James Barber, professor of biochemistry at Imperial College, London. Although most plants clearly use two photosystems for photosynthesis, "there may be a variation on the theme" represented by these algae, he adds. "It's not inconceivable, given the thermodynamics . . . but it's unexpected, to say the least." "I think the observation is real, and it deserves an explanation," says Bruce A. Diner, a research fellow at DuPont's central research laboratories in Wilmington, Del. "It will certainly stimulate further work." The mutants must be inefficient in their incorporation of solar energy into chemical bonds, he says, noting that photosystem I overcomes a bottleneck in electron flow in classic photosynthesis. Rebecca Rawls
