Function and contribution of the root tip in the induction of NO₃⁻uptake along the barley root axis

The Effect of Nitrogen Nutrition on the Cellular Localization of Glutamine Synthetase Isoforms in Barley Roots

“…The number of GS polypeptides detected on western blots increased with root cell age in all N treatments, and this is analogous to the increase in GS2 activity with advancing cell age in wheat leaves (Tobin et al, 1985). Multiple isoforms of GS have been detected previously in barley roots (Marttila et al, 1993;Mack, 1995). Although our immunolocalization detected GS in the plastids, none of the observed GS polypeptides corresponded to the molecular mass of barley chloroplast GS, which implies that either root plastid GS has a different molecular mass than leaf GS2, or it is present in amounts too small to be detected by this method, and the other polypeptides present on western blots are cytosolic in origin.…”

“…There was no evidence of a NO 3~-inducible root plastid isoform, as has been reported in other species (Ernes and Fowler, 1983;Vezina and Langlois, 1989), although plastid GS labeling was lowest in NH 4 + -grown seedlings. To our knowledge, ours is the first evidence of a root plastid GS isoform in barley; other studies analyzed whole root extracts and therefore may have failed to detect small amounts of plastidic GS (Mann et al, 1980;Marttila et al, 1993;Mack, 1995).…”

“…N-inducible GS isoforms have been identified in maize roots (Sakakibara et al, 1992) and pea root plastids (Ernes and Fowler, 1983;Vezina and Langlois, 1989). Previous studies have reported conflicting effects of NH 4 + on GS activity of barley roots (Lewis et al, 1982;Mack, 1995), but these discrepancies could be due to different developmental ages of the roots used in each study. In view of these developmental influences on root GS content and the fact that differences in GS activity between N treatments were greater at the root tip than in basal regions, we sampled tissue for the immunolocalization study from just behind the tip, where cell age would be similar in all treatments.…”

“…Developmental changes in NO,-uptake can occur within millimeter-sized regions of barley roots (Siebrecht et al, 1995). It is therefore important to understand how these localized changes in root N metabolism are regulated.…”

Trans‐root potential, xylem pressure, and root cortical membrane potential of ‘low‐salt’ maize plants as influenced by nitrate and ammonium

“…Nitrate uptake appeared to be fairly uniform along the root, apart from the very tip (Lazof, Rufty & Redinbaugh 1992;Siebrecht, Mäck & Tischner 1995).An impalement was considered successful when the voltage recording attained a constant value after a few minutes. Experiments were performed at two different light regimes.…”