Useful piece, Gill, thanks.
Afaik, salt acts as an inhibitor on the yeast (while the sugar acts to feed it), and this produces a better gluten, making the loaf rise evenly, with small bubbles and no collapse. We've found we can reduce the salt to about 75% before it has a bad effect, but we use malt extract and lemon juice to enhance the flavour. The malt also produces a slower rise - thus taking over from salt. We're looking to add some extra gluten next, which is how we found the flour bin. It seems to be more freely available in America than here.