Tabtoxin, produced by Pseudomonas tabaci, decreases Nicotiana tabacum glutamine synthetase in vivo and causes accumulation of ammonia

• Published in: Physiological plant pathology Vol. 19; no. 1; pp. 57 - 67
• Main Author: Turner, J.G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1981
• Subjects: tobacco
• ISSN: 0048-4059
• DOI: 10.1016/S0048-4059(81)80008-2

Tabtoxin caused the rapid loss of activity of Nicotiana tabacum glutamine synthetase in vivo. Following infiltration of leaves with a solution of tabtoxin (0·5 mg ml −1) glutamine synthetase was detectably reduced after 1 h and was 5% of control levels after 4 h. No recovery of activity was detected. Ammonia started to accumulate in leaves between 3 and 4 h after treatment with tabtoxin. An inverse relation was demonstrated between glutamine synthetase activity and ammonia levels in leaves infiltrated with different concentrations of tabtoxin. The smallest dose of tabtoxin, 85 ng cm −2 leaf, which caused accumulation of ammonia was also the smallest dose causing chlorosis. Doses of tabtoxin greater than 1·35 mg cm −2 leaf caused necrosis. The ammonia accumulating in tabtoxin-treated leaves was accounted for quantitatively by the inhibition, of ammonia assimilation resulting from the loss of glutamine synthetase activity. Glutamate dehydrogenase was unaffected by tabtoxin. Necrosis occurring in tissues infiltrated with P. tabaci was not preceded by a reduction in glutamine synthetase activity or by accumulation of ammonia and it is doubtful therefore that tabtoxin is causally involved in this symptom. However, the chlorosis which is characteristic of P. tabaci infections was associated with loss of glutamine synthetase activity and accumulation of ammonia, confirming the causal role of tabtoxin in this symptom.