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Translocation and cycling through roots of recently absorbed nitrogen and sulphur in wheat ( Triticum aestivum ) during vegetative and generative growth
Author(s) -
Larsson C.M.,
Larsson M.,
Purves J. V.,
Clarkson D. T.
Publication year - 1991
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1991.tb02916.x
Subject(s) - xylem , shoot , dry weight , nitrogen , cycling , seedling , labelling , biology , meristem , chromosomal translocation , sowing , nutrient , horticulture , agronomy , botany , chemistry , history , ecology , biochemistry , archaeology , organic chemistry , gene
15 N‐Nitrate and 35 S‐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 15 N‐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.