PJB-1994-32
SEASONAL FLUCTUATIONS IN NITROGEN-FIXING ABILITY (C2H2 REDUCTION) AND HYDROGEN UPTAKE BY ROOT NODULES OF CORlARIA NEPALENSIS ANDDATISCA CANNABINAI
M. SAJJAD MIRZA, A.H. CHAUDHARY1 AND A.D.L. AKKERMANS2
Abstract
A study was made on the seasonal fluctuations in N2-fixing (C2H2 reduction) activity and uptake hydrogenase activity of the root nodules of Coriaria nepalensis and Datisca cannabina. Nitrogenase activity of the nodules of both plants showed biphasic curves with peaks in spring and late summer. Acetylene reduction by the root nodules of Coriaria nepalensis was highest (16.4 µ mol. C2H4 g-1 fresh nodule Wt. h-1) during July while the peak acetylene reduction activity (14.8 µ mol. C2H4 g-1 fresh nodule wt. h-1) of Dansca cannabina nodules was determined in April. Less than 15% of the enzyme activity was retained by the nodules in winter. The nodules of both plant species consumed hydrogen on incubation with a gas mixture containing H2 indicating an uptake hydrogenase activity. The H2 uptake by the excised nodules of both Coriaria and Dalisca was highest (2.16 and 1.95 µ mol. H2 consumed g-1 fresh nodule Wt. h-1, respectively) in May. The presence of an uptake hydrogenase was confirmed in nodule homogenates with phenazine metasulphate as an artificial electron acceptor. Purified vesicle cluster suspensions (20 µm residue) showed highest hydrogenase activity, indicating that the enzyme is associated with the endophyte.
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