Quick and reversible inhibition of soybean root nodule growth by nitrate involves a decrease in sucrose supply to nodules

Abstract

The upper part of a nodulated soybean root hydroponically cultured in a glass bottle was monitored using a computer microscope under controlled environmental conditions, and the diameter of individual nodules was measured from 10-24 d after planting. The diameter of a root nodule attached to the primary root increased from 1 mm to 6 mm for 2 weeks under nitrogen-free conditions. The increase in diameter of the nodules was almost completely stopped after 1 d of supplying 5 mM nitrate, and was due to the cessation of nodule cell expansion. However, nodule growth quickly returned to the normal growth rate following withdrawal of nitrate from the solution. The reversible depression of nodule growth by nitrate was similar to the restriction of photoassimilate supply by continuous dark treatment for 2 d followed by normal light/dark conditions. In addition, the inhibitory effect of nitrate was partially alleviated by the addition of 3% (w/v) sucrose to the medium. Plant leaves were exposed to (11)C or (14)C-labelled carbon dioxide to investigate the effects of 5 mM nitrate on the translocation and distribution of photosynthates to nodules and roots. Supplying 5 mM nitrate stimulated the translocation rate and the distribution of labelled C in nitrate-fed parts of the roots. However, the (14)C partitioning to nodules decreased from 9% to 4% of total (14)C under conditions of 5 mM nitrate supply. These results indicate that the decrease in photoassimilate supply to nodules may be involved in the quick and reversible nitrate inhibition of soybean nodule growth.

Photoassimilate partitioning in hypernodulation mutant of soybean (Glycine max(L.) Merr.) NOD1-3 and its parent williams in relation to nitrate inhibition of nodule growth

“…Nodule respiration on a dry weight basis in Bragg showed a more pronounced decrease than in nts 1007 (Hansen et al 1992). Our results showing that the nitrate treatment resulted in a considerable shift in the partitioning of 14C from the nodules to the roots in Williams compared to NODI-3 are consistent with such findings, and suggest that nitrate inhibition of nodule growth and N2 fixation is caused by the changes in the photoassimilate flux from nodules to roots (Latimore et al 1977;Kouchi et al 1986a, b;Vessey et al 1988;Fujikake et al 2003).…”

Systemic and local effects of long-term application of nitrate on nodule growth and N2fixation in soybean (Glycine max[L.] Merr.)

“…It was reported that the nitrate supply changed the photoassimilate flux from nodules to roots (Fujikake et al 2003). Also nitrate may depress N2 fixation activity by decreasing Oc permeability through the nodule cortex to the infected region of the nodules (Becana et al 1989;Vessey and Waterer 1992;Mizukoshi et al 1995).…”

“…The results obtained also did not reveal a deprivation of soluble sugars in the nodules either directly or systemically supplied with 5 mM nitrate. However, Fujikake et al (2003) clearly showed that short-term inhibition of nitrate on nodule growth corresponded to a decrease in the photoassimilate flux to nodules and enhanced use in the roots based on lie and 14C tracer studies and supplementation of sucrose in the medium.…”

“…The local and rapid nitrate inhibition on nodule growth and nitrogen fixation was attributed to the decrease in the photoassimilate flux into nodules, COlTesponding to the increase in photoassimilate utilization in roots (Latimore et al 1977;Rabie et al 1980;Kouchi et al 1986;Vessey et al 1988;Fujikake et al 2003). Also the decrease in nitrogen fixation activity may be related to the decrease in 02 permeability caused by nitrate accumulation in the nodule cortex (Becana et al 1989;Vessey and Waterer 1992;Mizukoshi et al 1995) or the decrease in sucrose utilization which reduced nodule respiration and energy supply (Gordon et al 2(02).…”

An RNA Sequencing Transcriptome Analysis Reveals Novel Insights into Molecular Aspects of the Nitrate Impact on the Nodule Activity of Medicago truncatula

“…Fujikake et al (2003) could show that the growth of emerging soybean (Glycine max) nodules immediately and completely stopped after nitrate application (within minutes to hours). Moreover, by applying 14 C-labeled carbon dioxide, it was shown that carbon allocation within the plant was profoundly influenced by the nitrate, with less going to the nodules.…”