Back to Contents

FREE FULL TEXT PDF

SEASONAL FLUCTUATIONS IN NITROGEN-FIXING ABILITY (C₂H₂ REDUCTION) AND HYDROGEN UPTAKE BY ROOT NODULES OF CORlARIA NEPALENSIS AND DATISCA 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.

National Institute for Biotechnology and Genetic Engineering (NIBGE), P. O. Box 577, Jhang Road, Faisalabad, Pakistan.

Department of Biological Sciences, Quaid-i-Azam University, Islamabad.
Department of Microbiology, Wageningen Agricultural University, Hesselink van Suchtelenweg 4, 6703 CT  Wageningen, The Natherlands.