AXanthomonas maltophilia isolate tolerating up to 1% sodium azide in Tris/HCl buffer.

A bacterium tolerating up to 1% NaN3 found as a contaminant of Sephadex colums being run with Tris/HCl buffer, was identified asXanthomonas maltophilia. It had low nutrient requirements, was strongly proteolytic and interfered with Sephadex columns run with Tris/HCl buffers.

Free amino Acid composition of leaf exudates and Phloem sap : a comparative study in oats and barley.

Comparisons were made between the free amino acid composition in leaf exudates and that in pure phloem sap, using twin samples taken from a single leaf of two oat (Avena sativa L.) and three barley (Hordeum vulgare L.) varieties. Leaf exudate was collected in a 5 mm EDTA-solution (pH 7.0) from cut leaf blades and phloem sap was obtained through excised aphid (Rhopalosiphum padi L.) stylets. Fluorescent derivatives of amino acids were obtained using 9-fluorenylmethyl chloroformate and were separated by means of high performance liquid chromatography. The total concentration of free amino acids varied considerably in the exudate samples. There was no correlation between the total amino acid content in the exudate samples and that of the corresponding phloem sap samples, but the amino acid composition of the corresponding samples was highly correlated (median R(2)-value 0.848). There was only limited between-plant variation in phloem sap amino acid composition. Nevertheless, in comparisons involving all samples, many of the amino acids showed significant correlations between their relative amounts in exudate and phloem sap. The results presented here indicate that the exudate technique holds great promise as an interesting alternative to the laborious and time-consuming stylet-cutting technique of obtaining samples for comparative studies of phloem sap.

Separation studies of TMV replicase.

By means of affinity chromatography RNA-agarose a partial purification of a soluble TMV replicase is obtained in addition to a poly(U) polymerase when extracts of fresh, systemically TMV-infected tobacco leaves are used. An active replicase fraction always shows a certain amount of poly(U) polymerase. The replicase is inactivated by electrophoresis and the enzyme shows a harmful adsorption to certain supporting materials. When a purified replicase fraction, or an extract from frozen infected leaves, was gel filtrated on Sephadex G-75 in 50 mM Tris-HC1 pH 7.2, three peaks of replicase activity could be detected. Peak I was found in the void volume, peak II was elute with about 1.8 times the void volume and peak III with about 2.6 times the void volume. The activities of peaks II and III had very short half-times. Peak II was not obtained with extracts of frozen healthy leaves.

A poly(U) polymerase in tobacco leaves.

A poly(U) polymerizing enzyme has been found in healthy and tobacco mosaic virus-infected tobacco leaves and has been partially purified by affinity chromatography on a gel prepared from agarose with chemically coupled RNA. The enzyme is stimulated by Mn-2+ and dependent on a polynucleotide, preferentially poly(A). The synthesis proceeds optimally at pH 7.6 and 25 degrees C. The enzyme is highly specific for UTP and is inhibited by other ribonucleoside triphosphates. The product was partly sensitive to pancreatic ribonuclease. The synthetic reaction is inhibited in the presence of pyrophosphate but insensitive to 10 mM orthophosphate and high levels of cordycepin, rifampicin and actinomycin D. A molecular weight of about 40,000 has been estimated by sucrose gradient analysis and partition cell ultracentrifugation.