Changes in concentration of free amino acids and amides induced in tobacco plants by potato virus X and potato virus Y

Abstract

Abstract Tobacco plants grown under controlled conditions were inoculated with potato virus X (PVX), potato virus Y (PVY), or a combination of the two (PVX & PVY) and analyzed for free amino acids, amides, and PVX titer. Inoculated leaves were analyzed 1 week after inoculation, and secondarily invaded leaves 1 and 2 weeks after inoculation. In inoculated leaves, infection with PVX resulted in a slight increase in the concentration of serine. Infection with PVY and with PVX & PVY caused increases in the concentrations of glutamic acid, glutamine, serine, asparagine, γ-aminobutyric acid, and proline as compared with healthy controls. Infection with PVY did not stimulate PVX synthesis. In secondarily invaded leaves, infection with PVX resulted in decreased concentrations of alanine, glutamine, and proline 1 week after inoculation, whereas 2 weeks after inoculation only an accumulation of asparagine could be found. Infection with PVY led to an accumulation of asparagine and proline 1 week after inoculation and of asparagine and glutamine 2 weeks after inoculation. Deficiencies in the concentrations of alanine, serine, and glutamine and an increased concentration of asparagine were found in secondarily invaded leaves of doubly infected plants 1 week after inoculation when symptom expression was most severe and the PVX concentration was 5 times that in leaves infected with PVX alone. Proline accumulated in leaves infected with PVY, but not in doubly infected leaves. Two weeks after inoculation, increased concentrations of γ-aminobutyric acid and of asparagine were detected in doubly infected leaves. Pipecolic acid was sometimes found in leaves from doubly infected plants, but not in leaves from either healthy or singly infected plants. Derangements in the concentrations of the free amino acids and amides were not correlated with symptom production.