Conserving synaptic weight

roduction of reactive oxygen species (ROS) by an NADPH oxidase induces a calcium channel to open and root hair elongation to occur, according to a report from Starting with the rhd2 Arabidopsis mutant, which has stunted root growth and very short root hairs, the authors used transposon-tagging methods to identify the RHD2/AtrbohC gene, which encodes an NADPH oxidase that produces ROS. " When we cloned this gene, we were completely dumbfounded, " says Dolan. But at around the same time, other groups were finding that plants use ROS as second messengers in response to pathogen invasion and to control the movement of guard cells to open and close stomata. What is unusual about the new work is that both the activity and the protein controlling it have been identified, whereas in the other systems, the proteins that produce the ROS are not yet known. In rhd2 mutant plants, ROS production is decreased by 50%, there is little accumulation of intracellular calcium in the root hair tip, and little growth occurs. Upon addition of exogenous ROS to the system, however, the calcium concentration rises and root hair elongation occurs, indicating that an increase in ROS concentration causes the rise in calcium. What is not yet clear is how this occurs. Whether P Conserving synaptic weight ong-term potentiation (LTP), a phenomenon by which previously stimulated synapses become increasingly sensitive to stimulation such that the same level of presynaptic input induces a larger postsynaptic output, and long-term depression (LTD), which conversely reduces efficacy at such synapses, have been implicated in memory formation and storage. But computer models predict that without a balancing force of some kind, LTP and LTD will cause neural circuits to go haywire. Now, Sébastien Royer and Denis Paré have identified just such a force that can maintain balance in a network—and might imply that humans have a limited memory capacity. " There have been lots of studies about what happens in LTP and LTD, but little attention has been paid to the synapses that are not stimulated when you induce LTP, " says Paré, despite the fact that each cell has thousands of synapses, only a few of which gain LTP or LTD. L the effect is direct or indirect " is a complete black box as yet, " says Dolan. The group is already looking for genetic suppressors of the rhd2 mutant, which will identify other components in …