When a team of biochemists spliced a bacterium's gene for making hemoglobin into a tobacco plant, they expected the transgenic plant to be a tad hardier. Instead, they got veritable beanstalks: plants twice as large and bursting with much more chlorophyll and nicotine than ordinary tobacco. Some experts say that the surprising finding, reported in next month's issue of Nature Biotechnology, could lead to a revolution in transgenic agriculture.
Biologists have known for years that plants make their own hemoglobin, the oxygen-ferrying molecule that gives animal blood its red color. "The general guess is that most plants have it in a low concentration in the roots," says John Tjepkema, a plant physiologist at the University of Maine. He speculates that hemoglobin may be there because the soil-covered roots have a hard time getting oxygen. Poor oxygen flow to the roots can be fatal during a flood, when roots are covered with stagnant water.
Thinking that more hemoglobin might help plants better survive a low-oxygen environment, Leif Bülow and colleagues at the Center for Chemistry and Chemical Engineering in Lund, Sweden, inserted the Vitreoscilla bacterium's hemoglobin gene into the tobacco genome. Instead of a marginally better breather, Bülow's group got supertobacco.
While normal tobacco seeds take 6 to 8 days to germinate, the transgenic tobacco takes just three to four. After 5 weeks, the altered plants were about twice the size of their common cousins. And the amounts of compounds that require oxygen to be manufactured--like chlorophyll and nicotine--were up by a third. To top it off, the plants "appear more green," Bülow says. His group hasn't yet proven that hemoglobin levels are responsible for the phenomenal growth.
News of the finding is shaking up the field. "It's a far-out experiment, and they got far-out results. ... It would surprise anybody," says Nicholas Brewin, a plant biologist at the John Innes Center in Norwich, England. "No one had even thought before to put hemoglobin in a plant. We thought that plants are okay for oxygen; after all, they make the stuff." If the hemoglobin-enriched plants continue to perform so well, says Brewin, "it creates a whole new dimension in biotechnology."
Bülow's group is beginning to see similar results in Datura, a plant that makes the anti-motion-sickness drug scopolamine. Next, Bülow plans to turn his patent-pending process on some even bigger cash-cow crops: rice and maize.