By D. B. Layzell, S. Hunt, B. J. King (auth.), John G. Torrey, Lawrence J. Winship (eds.)
This e-book presents an outstanding representation of the interrelationship among growth in clinical method and conceptual advances, and its publica tion should still give a contribution to extra advances. it's renowned that significant advances in figuring out usually stick to the improvement of recent tools. the improvement of the acetylene aid assay for nitrogenase task offers an excellent instance of this interrelationship among concept and strategies. Theoretical wisdom ended in a look for substrates for nitro genase which may be assayed for extra simply than ammonium, the conventional made from the enzyme. the invention of the aid of acetylene to ethylene by means of nitrogenase supplied the fitting resolution to the matter by means of provid ing a speedy, particular, nondestructive, and cheap assay for nitrogenase task. This assay is now utilized by virtually each laboratory doing examine on nitrogen fixation. although, extra use and improvement of the acetylene aid assay has proven that it will probably underestimate nitrogenase task and will even provide wrong relative values below a few situations. the foremost challenge is that publicity of legume nodules to acetylene could cause a wide raise within the resistance to oxygen diffusion into the nodule. This decreased provide of oxygen decreases the speed of nitrogenase job inside a number of minutes.
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Extra info for Applications of Continuous and Steady-State Methods to Root Biology
Plant Physiol 84: 900-905. Weisz PR, TR Sinclair 1987b Regulation of soybean nitrogen fixation in response to rhizosphere oxygen. II. Quantification of nodule gas permeability. Plant Physiol 84: 906910. Winship LJ, JD Tjepkema 1982 Simultaneous measurement of acetylene reduction and respiratory gas exchange of attached root nodules. Plant Physiol 70: 361-365. Witty JF, FR Minchin, JE Sheehy, MI Minguez 1984 Acetylene-induced changes in the oxygen diffusion resistance and nitrogenase of legume root nodules Ann Bot 53: 13-20.
1988, Hunt et al. 1988) suggest that a barrier to gas diffusion exists in the nodule cortex. Since nodules are able to maintain high rates of nitrogenase activity at p02 of 80 kPa or more without increasing their rate of respiration (Sheehy et al. 1983, Hunt et al. 1987, Weisz and Sinclair 1987a, b) it has been suggested that this diffusion barrier is variable, and increases its resistance in response to increased external pOz (Sheehy et al. 1983, Hunt et al. 1987). Other factors reported to affect the nodule's resistance to Oz diffusion include 24 atmospheres of 10% C 2H 2 or Ar:0 2 leading to the declines in nitrogenase activity described above (Minchin et al.
This model uses a one-dimensional diffusion equation to describe steady-state acetylene flux into the nodule such that (8) where V is the steady-state ethylene production rate (mm 3 S-I), k is the nodule gas conductivity (mm 3 S-I), Aex is the acetylene concentration external to the nodule (mm 3 mm- 3), and Ain is the acetylene concentration at the inner surface of the diffusion barrier (mm 3 mm- 3). Additionally, a 37 Michaelis-Menten equation is used to describe nodule acetylene reduction such that (9) where Vrnax is the maximum ethylene production rate at saturating acetylene concentrations (mm 3 S-I), and KM is the nitrogenase Michaelis-Menten constant for acetylene divided by the acetylene solubility (mm 3 mm- 3).