Joe R. Cowles

Effect of Induced Nodule Senescence on Parameters Related to Dinitrogen Fixation, Bacteroid Size and Nucleic Acid Content

Summary: Darkness and treatment with combined nitrogen (NH4Cl or KNO3) were used to induce nodule senescence in alfalfa and soybeans. Nodule senescence was assessed by determinations of the acetylene-reducing activity and leghaemoglobin and sugar contents of the nodules. Bacteroids from nodules of the treated plants were compared using flow microfluorimetry. Upon induced nodule senescence, alfalfa bacteroids decreased both in nucleic acid content and cell size while the soybean bacteroids were essentially unaffected.

Demonstration of two tyrosyl-tRNA synthetases of pea roots

Abstract Tyrosyl-tRNA synthetase ( l -tyrosine: tRNA ligase (AMP), EC 6.1.1.1) from pea roots was fractionated into two activity regions by DEAE-cellulose chromatography. The two fractions also eluted from a Sephadex G-200 column at different positions. The two synthetase activities from the Sephadex G-200 fractionation rechromatographed on a second DEAE-cellulose column in the same respective positions as on the first DEAE-cellulose column. The synthetase which eluted first from the DEAE-cellulose column (T 1 synthetase) was much less stable than the synthetase which eluted later (T 2 synthetase). Both enzymes had similar pH, ATP and MgCl 2 optima. The two enzymes acylated tyrosyl-tRNA from various plant tissues and calf liver but did not significantly acylate Escherichia coli tRNA . T 1 and T 2 synthetase catalyzed the acylation of the two major isoaccepting tyrosyl-tRNA species of pea. A third tyrosyl-tRNA of pea was acylated by either T 1 or T 2 synthetase at only a very low rate relative to the rate of the crude (ammonium sulfate) synthetase preparation.