Abstract
When nodules of actinorhizal plants are exposed to acetylene, there is often an initial peak rate of acetylene reduction followed by a decline and a partial recovery. Treatment of hydroponically grown Myrica gale L. with water deficiency or dark stress increased the magnitude of the acetylene-induced decline and decreased the extent of the recovery. When N2 fixation was measured with 15N2 in unstressed plants, the ratio of acetylene reduction (peak) to N2 fixation prior to acetylene exposure was 3.73 [plus or minus] 0.14 (mean [plus or minus] SE). This value does not differ significantly (P < 0.05) from the theoretical minimum value of 4.0. In water-stressed plants the conversion ratio for the peak rate was greater (4.32 [plus or minus] 0.10) and in dark-stressed plants it was lower (2.54 [plus or minus] 0.33) than 4.0. The conversion ratio for the recovered rate of acetylene reduction was much lower than 4.0 in all cases, with mean values ranging from 1.16 to 2.60. We conclude that the peak rate of acetylene reduction provides the most reliable estimate of N2 fixation. The recovered rate of acetylene reduction consistently underestimates N2 fixation, sometimes severely, and thus measurements of acetylene reduction made in closed systems also underestimate N2 fixation to varying degrees.
Full Text
The Full Text of this article is available as a PDF (755.1 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Hardy R. W., Holsten R. D., Jackson E. K., Burns R. C. The acetylene-ethylene assay for n(2) fixation: laboratory and field evaluation. Plant Physiol. 1968 Aug;43(8):1185–1207. doi: 10.1104/pp.43.8.1185. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Silvester W. B., Winship L. J. Transient responses of nitrogenase to acetylene and oxygen in actinorhizal nodules and cultured frankia. Plant Physiol. 1990 Feb;92(2):480–486. doi: 10.1104/pp.92.2.480. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Simpson F. B., Burris R. H. A nitrogen pressure of 50 atmospheres does not prevent evolution of hydrogen by nitrogenase. Science. 1984 Jun 8;224(4653):1095–1097. doi: 10.1126/science.6585956. [DOI] [PubMed] [Google Scholar]
- Tjepkema J. D., Schwintzer C. R. Factors Affecting the Acetylene-Induced Decline during Nitrogenase Assays in Root Nodules of Myrica gale L. Plant Physiol. 1992 Apr;98(4):1451–1459. doi: 10.1104/pp.98.4.1451. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tjepkema J. D., Schwintzer C. R., Monz C. A. Time course of acetylene reduction in nodules of five actinorhizal genera. Plant Physiol. 1988 Feb;86(2):581–583. doi: 10.1104/pp.86.2.581. [DOI] [PMC free article] [PubMed] [Google Scholar]