Sulphate deprivation depresses the transport of nitrogen to the xylem and the hydraulic conductivity of barley (Hordeum vulgare L.) roots

Abstract

During the first 4 d after the removal of SO 4 (2-) from cultures of young barley plants, the net uptake of (15)N-nitrate and the transport of labelled N to the shoot both decline. This occurred during a period in which there was no measurable change in plant growth rate and where the incorporation of [(3)H]leucine into membrane and soluble proteins was unaffected. Reduced N translocation was associated with six- to eightfold increases in the level of asparagine and two- to fourfold increases in glutamine in root tissue; during the first 4 d of SO 4 (2-) deprivation there were no corresponding increases in amides in leaf tissue. The provision of 1 mol · m(-3) methionine halted, and to some extent reversed the decline in NO 3 (-) uptake and N translocation which occurred during continued SO 4 (2-) deprivation. This treatment had relatively little effect in lowering amide levels in roots. Experiments with excised root systems indicated that SO 4 (2-) deprivation progressively lowered the hydraulic conductivity, Lp, of roots; after 4 d the Lp of SO 4 (2-) -deprived excised roots was only 20% of that of +S controls. In the expanding leaves of intact plants, SO 4 (2-) deprivation for 5 d was found to lower stomatal conductance, transpiration and photosynthesis, in the order given, to 33%, 37% and 18% of control values. The accumulation of amides in roots is probably explained by a failure to export either the products of root nitrate assimilation or phloem-delivered amino-N. This may be correlated with the lowered hydraulic conductivity. Enhanced glutamine and-or asparagine levels probably repressed net uptake of NO 3 (-) and (13)NO 3 (-) influx reported earlier (Clarkson et al. 1989, J. Exp. Bot. 40, 953-963). Attention is drawn to the similar hydraulic signals occurring in the early stages of several different types of mineral-nutrient stresses.

Sulphate uptake and xylem loading of mycorrhizal beech roots

“…Similar effects were obtained by Kreuzwieser et al (1996) with excised, non-mycorrhizal roots of beech trees. A correlation between sulphur and N supply was also described for barley plants where nitrogen depletion diminished sulphate influx (Clarkson et al, 1989 ;Karmoker et al, 1991). It might therefore be suggested that plants regulate sulphate uptake in a way that is balanced to N nutrition.…”

Plant Hydraulic Conductivity: The Aquaporins Contribution

“…This suggests that the lowered root Lp r of N-, or Pdeficient plants may be due to the decreaseds water channel activity or abundance on the plasma membrane (Carvajal et al 1996(Carvajal et al , 1998Clarkson et al, 2000;Shangguan et al, 2005). Such a decrease has also been observed in SO 4 2--deprived barley (Hordeum vulgare) roots, where Lp r decreased to 20% of controls over a 4-d period (Karmoker et al 1991) On the other hand, Mg 2+ and K + starvation produced a positive effect on L 0 (Cabañero & Carvajal, 2007) and Lp r (Benlloch-González et al, 2010) respectively. Nevertheless, available data regarding the effect of K + deprivation on aquaporin activity are sparse and contradictory.…”

Biosensor-Mediated In Situ Imaging Defines the Availability Period of Assimilatory Glutamine in Maize Seedling Leaves Following Nitrogen Fertilization

“…In addition to transporter regulation, increased Gln was shown to control at least 35 general stress response genes in rice [39,40]. Increased Gln has also been implicated in coordinating sulphate and N nutrition in barley [41], and to exert control over the C4 photosynthetic pathway in maize [42]. Therefore, the~24 h period of Gln availability may be an important interval during which free Gln (or lack thereof) can affect a range of plant metabolic processes.…”