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International Botanical Congress 1999
NS 14 Aug 99
A COMMON form of anaemia and vitamin A deficiency could potentially be banished among people whose staple diet is rice, thanks to new breeds of genetically modified plants. At least a quarter of the world's population-and 58 per cent of women in southern Asia-suffer from anaemia as a result of iron deficiency, which can also lead to physical and mental retardation, premature births and increased susceptibility to infectious diseases. "You will not find any illness worldwide which is so widely distributed," says Ingo Potrykus, a plant scientist at the Swiss Federal Institute of Technology in Ziirich Rice contains the least iron of any cereal grain. In addition, it is rich in a compound called phytate, which can prevent the uptake of up to 98 per cent of iron from other dietary sources by binding to it in the gut. Potrykus and his colleagues mounted a three-pronged attack on the problem. First, they inserted into rice plants a fungal gene for an enzyme called phytase, which destroys phytate. To other plants, they added a gene for an iron-storage compound called ferritin, so that their rice grains would store more iron. Finally, they introduced a gene for a protein rich in the amino acid cysteine, which helps the gut to absorb iron, into a third set of plants. Each of the three strategies works, says Potrykus. Plants with the phytase gene produce enough of the enzyme to eliminate all the phytate in rice; the grains of ferritincontaining plants store at least twice as much iron as normal rice grains; and the third gene boosts cysteine levels by 25 per cent. The researchers now plan to cross these plants to combine all three traits. Rice also lacks vitamin A, leading to blindness and reduced disease resistance in about 400 million children worldwide.
Working with Peter Beyer of the University of Freiburg in Germany, Potrykus and his colleagues inserted three genes that promote the production of beta-carotene, which is converted to vitamin A in the body. The result is "golden rice"-Yellow grains that contain enough beta-carotene to supply all of a person's vitamin A needs. Several hurdles remain before either new rice appears in farmers' fields, however. So far, Potrykus has inserted the genes into short-grained rice because these japonica varieties are easier to modify genetically. Breeders must now cross the genes into the long-grained indicas that are the preferred rice in tropical regions, where the deficiencies are most common. That, together with field trials of the new varieties, should take about three years. Some critics of engineered, crops have given the work a cautious welcome, as it is designed to aid the developing world, rather than to boost profits of multinational companies. "This is a potentially good use of the technology," says Jane Rissler of the Union of Concerned Scientists in Washington DC.
FORGET the botany you leamt in school - even if it was only last year. It looks as if a brand-new family tree, unveiled in St Louis, will overtum many old ideas about who's related to whom in the world of green plants. "Ever since Darwin, people have been speculating on this stuff, but it was more akin to art criticism than to science," says Brent Mishler, a botanist at the University of Califomia at Berkeley and one of the leaders of a five-year, 200-person effort to build a more rigorous plant family tree. In the past, botanists had to rely on their intuition and plants' physical appearance to classify species. But now molecular biologists have worked out the DNA sequences of dozens of genes in a rapidly growing list of plants, creating a rich new source of evolutionary information. And in the past few years, botanists have developed objective ways of combining all the available information to determine the phylogeny, or family tree, that best fits all the observations. Mishler and his colleagues chose representative species spanning the breadth of green plant diversity, and completed their work just in time for the botanical congress. "Now we have a bigger, more comprehensive phylogeny for the green plants than we have for the animals," he says.
The new family tree looks different from the old one in several important ways. For example, the broad-leaved plants, or dicots-once thought to represent a single group of flowering plants-turn out to be several separate lineages, some of which are more primitive than both other dicots and narrow leaved grasses, or monocots. Water lilies, for instance, are one such group. The new family tree also identifies the most primitive "living fossil" among the flowering plants, a small flower called Amborella-so little known that it has no common name-that grows only on the Pacific island of New Caledonia. Until recently, many botanists also thought that land plants evolved twice, with one lineage leading to mosses and liverworts and the other to ferns and higher plants. But the new tree shows unequivocally that all land plants evolved from a single common ancestor. However, other experts on classification wam that the new family tree is unlikely to be the last word on green plants. "We're at the stage where it looks very simple," says John Taylor, who studies fungi at the University of California at Berkeley. "As we learn more, we're not going to be so smug."
Rooting for acid
CROPS genetically modified to leak citric acid from their roots can produce higher yields with less fertiliser. So claims their Mexican creator, who wants to make the crops freely available to small farmers in developing countries. Many tropical soils ar6 either so acidic or so alkaline that phosphate, an essential plant nutrient, is tied up in an insoluble form. The roots of some plants excrete citric acid to make the phosphate soluble, but most crops can't do this. Luis Herrera-Estrelia, a botanist at the Centre for Research and Advanced Studies in lrapuato, Mexico, has inserted a gene for citric acid production into tobacco plants and studied how they grow in alkaline soils. When lightly fertilised, the plants grew 20 per cent more than tobacco plants without the new gene. The plants also achieved maximum growth using half the fertiliser required by normal plants. Herrera-Estrelia and his team have also inserted the gene into rice and maize. Preliminary tests suggest that it is even more effective in these crops, he says, though he will not have complete results of large-scale greenhouse experiments for another 18 months. Commercial development is likely to take three more years after that. If trials are successful, cash-strapped farmers in developing countries could reap the benefits of fertillser for a fraction of the cost. "Insoluble sources of phosphate fertillser are cheaper and we could use much less," says Herrera-Estrelia. Insoluble phosphates would also be less likely to contaminate the water table. Herrera-Estrelia's team has filed for patents on the genetically modified plants but say they will only enforce them against people who can easily afford to pay. "We want to give it for free to small farmers," says Herrera-Estrelia, "but if it's going to be used by large farmers in developed countries we would like to get some money to continue our research."
Ebola drug found in forest
AN EXTRACT of seeds from an African rainforest tree is showing promise as a treatment for the deadly Ebola virus. "From the same African forests that gave us Ebola, we could have a cure," claims Maurice lwu of the Bioresources Development and Conservation Programme in Nsukka, Nigeria. Nigerian traditional' healers use seeds of the Garcinia kola tree, known as bitter kola, as a remedy for many ailments. "When the healer does not know what is wrong, the drug of choice is an extract of Garcinia kola," says lwu, who arranged
for the extracts to be tested as antiviral drugs. In tests conducted by the US Army's Medical Research Institute of Infectious Diseases in Fort Detrick, [email protected] of the few centres worldwide equipped to handle Ebola-a mixture of chemicals extracted from bitter kola has emerged as one of several dozen substances that inhibit the growth of the virus in laboratory cultures of monkey cells. Unlike most other candidates, it doesn't appear to be toxic. "It's very unusual to see this strong an antiviral activity in a compound that is nontoxic," says James Miller, head of applied research at the Missouri Botanical Garden in St Louis.