Economy of Carbon and Nitrogen in Nodulated and Nonnodulated (NO₃-grown) Cowpea [Vigna unguiculata (L.) Walp.]

Abstract

The response of non-nodulated cowpea ( Vigna suguicalata (L.) Walp. cv Caloona) to a wide range of NO3 levels in the rooting medium was studied 40 days after sowing by in vitro assays of plant organs for NO3 reductase (EC 1.6.6.1) and analyses of root bleeding (xylem) sap for nitrogenous solutes. Plants fed 1, 5, 10, 20, and 40 millimolar NO3 showed, respectively, 64, 92, 94, and 91% of their total reductase activity in shoots and 34, 30, 66,62, and 58% of the total N of their xylem sap as NO3. These data, and the absence in the plants of significant pools of stored NO3, indicated that shoots were major organs of NO3 assimilation, especially at levels of NO3 (10 to 40 millimolar) that maintained plant growth at near maximum rates. Partitioning and utilization of C and N were studied in nodulated, minus NO3 plants and non-nodulated plants fed 10 or 20 millimolar NO3, the levels of NO3 which gave rates of growth and N assimilation closest to those of the symbiotic plants. The

Pathways of Nitrogen Assimilation in Cowpea Nodules Studied using 15N2 and Allopurinol

“…3A) is rather similar to previously published data for asn soybean nodules exposed to'5N or'3N2 (14)(15)(16) (13,20) and the amide shown to accumulate as a significant proportion glu of the fixed N in '5N2 feeding studies (15). It 3 4 whether in the assimilation of NO3- (2) (Fig. 4).…”

Spontaneous Phloem Bleeding from Cryopunctured Fruits of a Ureide-Producing Legume

“…Despite the preliminary nature ofthe present observations, the labeling studies and comparisons of relative amounts of nitrogepous solutes in xylem root bleeding sap and phloem-cryopuncture fruit exudate of N03-fed and symbiotic (-N) plants, suggest several interesting features relating to the assimilation and translocation processes for N in cowpea. Confirming earlier studies of xylem transport in this and other ureide-producing legumes (3,17,20), utilization of NO3 is characterized by high (78%) "spillover" of free N03-to the shoot from the root, low ureide transport from roots relative to amides and amino acids, and a high ratio of Asn:Gln in xylem sap. By contrast, the xylem transport of plants using symbiotically fixed N shows a marked preponderance of ureide-N over amino N and a high ratio of Gln:Asn.…”

“…Some plants (symbiotic, N2-dependent treatment) were inoculated with the effective Rhizobium strain CB756 and received N-free culture solution. Other plants (non-nodulated, N03-fed treatment) were not inoculated and received culture solution containing 10 mM N03 ; a NO3-regime previously shown (3) to suppress nodulation and support a rate of growth and N accumulation comparable to that of companion N2-dependent plants. All Fig.…”

Mesure de l'activité nitrate réductase durant le cycle cultural du soja (Glycine max L Merr). Répartition dans la plante et relation avec l'activité nitrogénase

“…This complementarity suggests that a substantial yield increase can be obtained through optimization of both ways of nitrogen nutrition in nodulated legumes. Pagan, 1977 ;Pate et al, 1979 ;Atkins et al, 1980) parce que très coûteuses en pouvoir réducteur fourni par la photosynthèse . Au champ, l'assimilation du nitrate du sol et la fixation de l'azote de l'air se succèdent générale-ment au cours du cycle de développement du soja (Harper, 1974 ;Thibodeau et Jaworski, 1975 ;Obaton et al, 1982) Corman, 1985) ou le dosage des uréides (Herridge, 1982 ;Zengbé et al, 1982) (Vincent, 1970) Nos résultats en serre suggèrent qu'il peut aussi exister une complémentarité plus tardive entre les 2 sources de nutrition azotée.…”