This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Knight, T. J. Articles by Langston-Unkefer, P. J. Search for Related Content PubMed PubMed Citation Articles by Knight, T. J. Articles by Langston-Unkefer, P. J. Agricola Articles by Knight, T. J. Articles by Langston-Unkefer, P. J.

Articles

Effects of Tabtoxinine--Lactam on Nitrogen Metabolism in Avena sativa L. Roots ¹

Isotope and Nuclear Chemistry Division, INC-4, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States Department of Agriculture, Agricultural Research Service, and Department of Plant Pathology, University of Wisconsin, Madison, Wisconsin 53706

The effects of tabtoxinine--lactam (T--L) on nitrate uptake and glutamine synthetase (GS) and nitrate reductase (NR) activities in roots of Avena sativa seedlings were determined. Seven-day-old oat seedlings placed in a 10 mM KNO₃ and 0.5 mM T--L solution for 24 hours took up T--L and lost approximately 90% of their root GS activity. [³H]-T--L taken up by roots of seven-day-old oat seedlings was associated with GS immunoprecipitated from the extract of these roots. Total nitrate uptake and in vivo NR activity were decreased approximately 50% in the T--L treated roots. However, T--L uptake did not affect the induction phases of nitrate uptake or reduction, nor did it inhibit in vitro NR activity. Thus, the decrease in nitrate uptake and reduction is a secondary effect of T--L action. Roots of seven-day-old oat seedlings were inoculated with Pseudomonas syringae pv tabaci (Tox+) and the pathogen population in the rhizosphere was estimated by dilution plate count; 6 x 10¹³ bacteria were recovered after 3 days, as compared to the original inoculation with 7 x 10⁹ bacteria, indicating a significant growth of the pathogen in the rhizosphere. The bacteria recovered from the rhizosphere caused chlorosis in tobacco leaves and produced T--L in culture; 1 x 10¹⁴ bacteria were recovered from roots of seedlings inoculated with P. syringae pv tabaci (Tox–) using the same inoculation and assay procedure as for the pv tabaci (Tox+). Extracts of surface-sterilized roots previously inoculated with P. syringae pv tabaci (Tox+) did not produce viable bacterial cultures when plated out on a complete medium. Oat seedlings growing in sand culture and inoculated with P. syringae pv tabaci (Tox+) had developed chlorosis, and root GS activity had declined to less than 10% of controls after 3 days. Conversely, seedlings inoculated with P. syringae pv tabaci (Tox–) never developed chlorosis and maintained normal levels of GS activity. All oat plants inoculated with P. syringae pv tabaci (Tox+) died within 7 days after inoculation as compared to the plants inoculated with P. syringae pv tabaci (Tox–) which grew to maturity.

This article has been cited by other articles:

				T. J. KNIGHT and P. J. LANGSTON-UNKEFER Enhancement of Symbiotic Dinitrogen Fixation by a Toxin-Releasing Plant Pathogen Science, August 19, 1988; 241(4868): 951 - 954. [Abstract] [PDF]