Depression of nitrate and ammonium transport in barley plants with diminished sulphate status. Evidence of co-regulation of nitrogen and sulphate intake

• Published in: Journal of experimental botany 1989-09, Vol.40 (218), p.953-963
• Main Authors: Clarkson, D.T, Saker, L.R, Purves, J.V
• Format: Article
• Language: English
• Subjects: 13N; ammonium; ammonium nitrogen; Barley; Biological and medical sciences; concentrations; deficiency; deprivation; Fundamental and applied biological sciences. Psychology; growth; Hordeum vulgare; ion-uptake; Metabolism; Metabolism. Physicochemical requirements; nitrate; Nitrates; Nitrogen; nutrient solutions; nutrient uptake; Phosphates; Plant physiology and development; Plant roots; Plants; Potassium; Quaternary ammonium compounds; radiolabeling; responses; roots; sulfates; Sulfur; sulphate; transport
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/40.9.953

When barley plants were grown in a solution with nitrate as the sole N-source but deprived of sulphate (-S plants) for 1 to 5 d, the capacity for sulphate transport by the roots increased very markedly; subsequent measurement of influx using 35S-labelled SO4(-2) showed increases of greater than 10-fold compared to plants continuously supplied with sulphate (+S plants). There were only small effects on plant growth over a 5 d period and yet the influx of NO3-, labelled with the short-lived tracer 13N, was diminished by approximately 30%. By contrast, the influx of phosphate was little affected by sulphate-deprivation. When a sulphate supply was restored to -S plants, the sulphate influx was quickly repressed over the subsequent 24 h and the nitrate influx was restored to greater than 90% of the value in +S plants. When plants were grown in a solution with a mixed nitrate and ammonium supply and deprived of sulphate for 1 d or 5 d the depression of nitrate influx was more strongly marked (up to 55% depression). The influx of ammonium was also depressed after 5 d of sulphate-deprivation, but not at 1 d, nor where the concentration of ammonium in the uptake solution was lowered to 20 mmol m-3 or less. Additional measurements with 15N-labelled nitrate and ammonium over longer periods were used to determine net uptake. Net uptake of nitrate was depressed to a similar extent to efflux, but net ammonium uptake was depressed only in unbuffered uptake solution where the pH decreased to pH 4.9 during the uptake period. The 15N-tracer experiments showed that the translocation of label to the shoot, from both nitrate and ammonium, was depressed to a greater extent than net uptake in -S plants. The depression of nitrate influx, caused by 5 d of sulphate deprivation, could be relieved almost completely by providing plants with 1.0 mol m-3 L-methionine during the day prior to influx measurement. This treatment substantially decreased sulphate and potassium (86Rb-labelled) influx in both +S and -S plants, but greatly increased total S-status of the plants. This methionine treatment had no effect on ammonium influx or net uptake in -S plants but increased influx significantly in +S ones. When plants were grown with sulphate but deprived of nitrate for 4 d there was a marked depression of the sulphate influx (by 48-65%) but a smaller effect on phosphate influx (21-37% of +N). The results are discussed in relation to the effects of sulphate-deprivation on growth rate and the