Sellstedt A, Reddell P, Rosbrook PA, Ziehr A
The Relations of Hemoglobin and Lignin-Like Compounds to Acetylene-Reduction in Symbiotic Casuarina
Journal of Experimental Botany: 1991 42:1331-1337
Nodules from six Casuarina symbioses (Casuarina cunninghamiana, C. equisetifolia, and C. glauca inoculated with each of two different Frankia sources) were evaluated for (i) concentrations of haemoglobin (measured as CO-reactive haem) at 124, 144 and 165 d after inoculation, (ii) acetylene reduction and (iii) occurrence of lignin-like compounds in cell walls of the nodules at 165 d after inoculation. Haemoglobin concentration and the occurrence of lignin-like compounds were related to acetylene reduction at final harvest. Concentration of haemoglobin in nodules ranged from 1.56 to 22.27 nmol haem (g FW)-1. There were marked plant species-Frankia interactions. At final harvest plant growth was greatest in C. cunninghamiana inoculated with Frankia inoculum designated SI, while haemoglobin concentration was intermediate in this symbiosis. Acetylene reduction activity was detected in all the symbioses except C. equisteifolia inoculated with SI, and was highest in C. glauca inoculated with SI. Haemoglobin concentration per fresh weight nodule and acetylene reduction per plant were positively correlated (r = 0.84, n = 12). The highest levels of cumulative nitrogen fixation were always associated with the highest haemoglobin concentrations and the highest rates of acetylene reduction activity. Nitrogen content was lowest in C. equisetifolia inoculated with SI (23.89 +/- 3.07 mg) and highest in C. cunninghamiana inoculated with the same inoculum (217.2 +/- 22.5 mg). Irrespective of symbiotic performance, lignin-like compounds were found in the cell walls of the nodules in all symbioses in this study. The cells containing these compounds were mainly localized in the infected areas of the nodule. The roles of haemoglobin and occurrence of lignin-like compounds in relation to nitrogen fixation in Casuarina symbioses are discussed.
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