Hydrogen metabolism of Casuarina root nodules: A comparison of two inoculum sources
Physiologia Plantarum, 1987; 70(2): 367–372
Sellstedt A, Winship LJ

Abstract
Hydrogen metabolism was studied in three Casuarina species, C, equisetifolia Forst., C. glauca Sieb. ex. Spreng. and C. obesa Miq., either inoculated with the pure Frankia culture HFP CcI3 or inoculated with a crushed nodule inoculum made from C. glauca nodules. Nitrogenase (EC 1.7.99.2) activity and hydrogen evolution was measured on intact plants, while hydrogen uptake was measured on excised nodules and in nodule homogenates.

Nitrogenase activity was highest in C. glauca inoculated with C. glauca nodules, while no hydrogen evolution was detected. Hydrogen evolution was highest in the symbiosis between C. equisetifolia and HFP CcI3, but the nitrogenase activity showed intermediate values compared to the other symbioses. Measured at a concentration of 93 μM H2, H2 uptake was highest in C. glauca inoculated with the C. glauca inoculum. H2 uptake activity in homogenates was 83% of the intact nodule rate. With phenazinemethosulfate as the electron acceptor, H2 uptake by nodule homogenates showed typical Michaelis-Menten kinetics with a Km of 21.3 μM for H2.

The data presented here indicate a host plant effect on the endobiont which alters the hydrogen metabolism.

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