University of Manchester, UK
A physiologist notes the similarities between animal and plant electricity.
Almost all organisms run on electricity. As an undergraduate, I was intrigued by the fact that the long, single cells of the freshwater plant Nitella are nearly identical to those of single nerve fibres. These plant cells generate slow action potentials that are similar to those of human or animal nerves. But the electrical components that span plant and animal membranes — the ion channels and transporter proteins — are usually quite different, as are some of the ions they transport.
Earlier this year, however, two researchers in Italy found that a single mutation can turn an important transport protein from a component that is compatible with animal electrical systems into one that is appropriate for plants. They studied the protein CLC-5, which is abundant in the intracellular vesicles of kidney cells. There, it exchanges chloride ions for protons, and in so doing regulates the vesicles’ acid content (G. Zifarelli and M. Pusch EMBO J. 28, 175–182; 2009).
The researchers knew that CLC-5 resembled the plant transporter atCLCa, but they had no idea how closely. In plant vacuoles, which are formed by the fusion of several vesicles, atCLCa exchanges not chloride but nitrate ions for protons. The difference is vital: nitrate is necessary for plants to grow and is stored in the vacuoles of root and shoot cells, whereas chloride has a very different role. It is needed for photosynthesis and for the opening and closing of stomata, which matters mostly in the leaves.
Merely substituting one serine amino acid in CLC-5 with a proline changed the protein from a chloride transporter into a nitrate transporter. I find this fascinating because it provides an even more striking example of the similarities that animals and plants can share, even though their biologies are generally very different.