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The nitrogen balance of Raphanus sativus X raphanistrum plants. I. Daily nitrogen use under high nitrate supply
Author(s) -
SCHULZE E.D.,
KOCH G.,
PERCIVAL F.,
MOONEY H. A.,
CHU C.
Publication year - 1985
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11611835
Subject(s) - xylem , petiole (insect anatomy) , raphanus , transpiration , nitrogen , nitrate , chemistry , horticulture , botany , nutrient , dry weight , biology , photosynthesis , hymenoptera , organic chemistry
Growth‐chamber cultivated Raphanus plants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m −3 (NO − 3 ) in a balanced nutrient solution, the oldest leaves (eight‐leaf stage) accumulated 2.5% NO − 3 ‐nitrogen (NO 3 ‐N) in their lamina, and almost 5% NO 3 ‐N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol −3 m −3 concentration of NO − 3 in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO − 3 uptake, NO − 3 fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by an in vivo test. NO − 3 uptake by roots and mesophyll cells was greater in the light than in the dark. The NO − 3 concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO − 3 was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty‐four per cent of the NO − 3 influx was turned into organic nitrogen, with the remaining NO − 3 accumulating in both the light and the dark.