Acting on impulse

 作者:鄂恧     |      日期:2019-03-08 03:18:00
By Jonathan Knight PLANTS get nervous just like the rest of us. Or at least they may have similar nervous systems, says a US government researcher. He has found hints that plant leaves send electrical signals to roots and shoots using ion channels similar to those in animal nerves. Plant physiologists have long known that there is some kind of electrical signalling in plants. For example, there are voltage changes in mimosa leaves when the leaves are touched, which makes them close. And in 1996, researchers at the University of East Anglia in Norwich recorded electrical activity in the shoots of tomato plants moments after their leaves were crushed. These signals were strongest in the phloem, the tubular tissue that carries sugars and nutrients from the leaves to the roots. In animals, nerve cells transmit electrical impulses by opening pores in their membranes that allow positive ions to rush in, changing the electrical potential across the membrane. Each pore consists of a group of five or six proteins, which span the membrane and can twist slightly to open or close the channel. Last November, researchers reported finding two ion channel genes in the thale cress (Arabidopsis). And now Frank Turano, a plant molecular biologist with the Agricultural Research Service, the research arm of the US Department of Agriculture in Beltsville, Maryland, has found 10 more. What’s more, he has also shown that at least eight of these genes appear to be most active in the phloem. The plant proteins consist of two types of channel protein found in animals: GABA receptors and glutamate receptors. The Agricultural Research Service and Auxein, the Michigan biotech company funding the research, have applied for patents on the new genes. Turano says that although the evidence so far is circumstantial, he suspects that when the receptors detect GABA or glutamate, they open the ion channels, sending an electrical signal along the phloem. Such signals could mobilise chemical defences against insects, for example. “To me it seems quite sensible that this is how they work,” he says. John Thain, one of the physiologists studying tomato plants, says such electrical signals in the phloem could explain the observations his team made. Phloem cells are open at each end and connected in a long open tube, creating a structure that could act like a nerve. “It could be the same kind of thing,” says Thain. But others are more sceptical. Richard Hooley, a biologist at the Institute for Arable Crops Research near Bristol,