Structural studies of a rhamnogalacturonan from the stipules of Musanga cercropoides.

The major water-soluble polysaccharide isolated from the stipules of Musanga cercropoides has been investigated, using n.m.r.

Ammonium inactivation of nitrate reductase in Lemna minor L.

The addition of ammonium to nitrate induced plants of Lemna minor L. brings about a rapid loss in extractable nitrate reductase activity. This inactivation is reversible both in vivo and in vitro.

Ammonium repression of nitrate reductase formation in Lemna minor L.

The presence of ammonium is shown to inhibit the nitrate-promoted formation of nitrate reductase in Lemna minor L. The ammonium inhibition does not result from an inhibition of nitrate accumulation. The kinetics of the ammonium inhibition suggest it is not a direct effect of ammonium.

Some characteristics of nitrate reductase induction in Lemna minor L.

Low levels of nitrate reductase can be detected in plants of Lemna minor grown on some organic nitrogen sources. Nitrogen-starvation does not lead to a derepression of nitrate reductase activity. Nitrate ions are necessary for the development of maximum enzyme activity and the maintenance of high enzyme levels.