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- Title
The Effect of Nitrogen Source on Transport and Metabolism of Nitrogen in Fruiting Plants of Cowpea (Vigna unguiculata (L.) Walp.)1.
- Authors
PEOPLES, M. B.; PATE, J. S.; ATKINS, C. A.
- Abstract
Nitrogen metabolism and transport were studied during reproductive development of cowpea ( (L.) Walp. cv. Vita 3) under three contrasting nitrogen regimes: (1) nitrate supplied continuously (plants non-nodulated), (2) symbiotic N fixation (no combined nitrogen), (3) nitrogenstarvation post-anthesis of previously N-fixing plants. The last treatment involved daily flushing of the root systems with 100% oxygen which suppressed post-anthesis N-fixation by 76–79%, thereby making fruit growth almost entirely reliant upon mobilization of previously accumulated nitrogen. The bulk of the xylem nitrogen (root bleeding sap or peduncle tracheal sap) of nitrate-fed plants was nitrate and amide, that of symbiotic and O-treated plants largely ureide. The composition of fruit cryopuncture phloem sap, however, was closely similar in all treatments, with most nitrogen as amides and amino acids. The evidence suggested intense metabolic transfer of root derived nitrate-N or ureide-N to amino acids by vegetative plant parts prior to translocation to fruits. All tissues of fruits showed patterns of development of enzymic activities consistent with release of nitrogen from both ureides and amides and re-assimilation of ammonia to form amino acids. Although the levels of enzyme activities varied between treatments the differences could not be readily associated with individual patterns of nitrogen transport in the treatments. Nitrogen sufficiency in the NO-fed plants was marked by elevated vegetative biomass and low harvest indices for dry matter and nitrogen, while nitrogen deficiency of the O-treated plants was associated with seed abortion, small seed size and low seed nitrogen concentration, and efficient mobilization of nitrogen from vegetative parts to fruits.
- Publication
Journal of Experimental Botany, 1985, Vol 36, Issue 4, p567
- ISSN
0022-0957
- Publication type
Article