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15N-Nitrate and 35S-sulphate labelling experiments were performed with spring wheat (Triticum aestivum L. cv. Timmo) 44, 64, 79, 95 and 115 days after sowing (growth stages arbitrarily denoted I to V). Label was fed to the plants via a fraction of the root system, termed “donor root”, whereas the rest of the root (“receiver root”) was fed non-labelled nutrient solution. Net uptake rates for both nitrate and sulphate per unit root weight changed little from growth stage I to IV, but were considerably lower at stage V. On a whole-plant weight basis, uptake declined from stage I to IV, because root contribution to total plant weight declined. Between 80 and 95% of absorbed label was translocated to the shoot at all growth stages. At stage V, up to 30% of absorbed label was recovered in the ears. Labelling of the receiver root indicated that, at all growth stages, 10 to 17% of N and 12 to 32% of S translocated to the shoot was retranslocated to the root. This corresponds to between 35 and 85% of the label actually recovered in the roots. Analysis of 15N-labelling of xylem sap collected from receiver roots at growth stages I to IV indicated that about half of the reduced N in the sap is derived from cycling through roots of recently assimilated N. Evidence of cycling was also obtained at stage V. Labelled sulphate was the only form of S cycled in the plant, but it accounted for only 1 to 7% of the sulphate in the xylem sap. [ABSTRACT FROM AUTHOR]

The uptake of K+ ion was studied in the roots of wheat (Triticum aestivum L. cv. GK Szeged) and cucumber (Cucumis sativus L. cv. Budai csemege) seedlings grown in nutrient solution under nitrogen and sulfate stress conditions. Seedlings pretreated with 1 or 10 mM NaNO3, absorbed more K+ than those treated with 0.1 mM NaNO3. However, the posteffect of NaNO3 was considerably influenced by the Na2SO4, treatment. The results suggest that, at least partly, a feed‐back regulation of K+ uptake may occur. However, due to the high Na+ contents of the roots, a Na+ effect in this process cannot be excluded. The growth and dry matter yields of the roots and shoots were strongly influenced by the SO2−/4 and NO−/3 supply of the plants. Appreciable differences were experienced between wheat and cucumber seedlings. The optimum SO2−/4 concentration of the growth solution for maximal growth varied considerably between the species, and was also different for the roots and the shoots in a given species. [ABSTRACT FROM AUTHOR]

Sulfate and nitrate uptake capacity, ATP sulfurylase (ATPS) and nitrate reductase (NR) activity were determined in a set of maize hybrids representative of selection cycles carried out during the period 1930 through 1975. All the above metabolic parameters together with the grain yield were improved by the selection. The annual rate of the improvement was higher (double) for sulfate uptake than for ATPS and similar for NR and nitrate uptake. Significant correlations were evidenced between the uptake efficiency of the roots and the enzyme activity in the leaves both for sulfate and nitrate pathways, and also between the uptake and enzyme steps of nitrate and those of sulfate. This offered good evidence of a coupled genetic regulation between nitrogen and sulfur metabolism in maize. [ABSTRACT FROM AUTHOR]