THE 鈥渟weat鈥� of plants could in future yield a rich harvest of drugs and
chemicals. That is the hope of researchers who have created tobacco plants that
ooze foreign proteins from their leaves each morning.
Plants can be engineered to produce everything from vaccines to plastics. But
extracting proteins from plant tissue is often complicated and expensive.
Instead, Ilya Raskin and his colleagues at Rutgers University in New Jersey
wondered if plants could excrete proteins in the 鈥渄ew drops鈥� found on
leaves.
During the night, when leaves lose less moisture by evaporation, pressure
builds up inside and squeezes fluid out鈥攁 process called guttation. This
fluid contains small amounts of protein, which Raskin guessed must come from the
fluid in the spaces between cells. So Raskin and his team genetically engineered
tobacco plants to produce three foreign proteins in this intercellular fluid,
including the green fluorescent protein from jellyfish.
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Just as they hoped, the foreign proteins showed up in the dew on the leaves.
In the future, the technique might be applied to other plants that produce large
drops of guttation fluid, such as tomatoes and grasses. The drops could be
sucked or shaken off the leaves each morning and processed to purify the
proteins (Plant Physiology, vol 124, p 927).
鈥淚t would provide a system for obtaining fluid that is already purified and
concentrated,鈥� says Hugh Mason of Cornell University in New York, who works on
vaccine expression in potatoes. The amount of protein Raskin鈥檚 team has been
able to get expressed鈥攁bout 2.8 per cent of all the protein in the
guttation fluid鈥攊s comparable to what other people have been able to
extract from the plant itself, says Mason.
Raskin thinks the method could be used in combination with another approach
he has pioneered for making plants release proteins from their roots
(快猫短视频, 1 July, p 27).