Changes in the free amino acids and amides in tomato plants inoculated with tomato spotted wilt virus

Abstract

SUMMARYLeaves of tomato plants grown in water culture in growth rooms were inoculated with sap from healthy tomato leaves or with sap containing tomato spotted wilt virus (t.s.w.v.). Changes in the free amino acids and amides of stems and of inoculated leaves, stem growth and infectivity were determined. Samples were analysed 5, 9, 13 and 17 days after inoculation using two‐dimensional paper chromatography.Inoculation with sap from healthy leaves, mixed with celite and sodium sulphite, caused small increases in glutamic acid, asparagine, glycine and serine in the inoculated leaves, and in glutamic and aspartic acids in the stems.In leaves inoculated with t.s.w.v., glutamine and asparagine increased greatly, reaching maxima at day 13. Both infectivity and amide levels were greater with more concentrated inoculum. The total free amino acids increased in leaves inoculated with t.s.w.v. by 150–180%. Increases were found in α‐alanine (day 9, 13 and 17) and in aspartic acid, valine, glycine and the leucines (day 13).Systemic infection of stems increased total free amino acids by 200–300% and amides by more than 400%. Serine, threonine, phenyl‐alanine, proline and the leucines increased at day 9 and reached maxima at day 13. Glutamine, asparagine, glutamic acid, aspartic acid, valine, tyrosine, α‐alanine, glycine and γ‐amino‐butyric acid increased at days 13 and 17.Changes in total free amino acids in stems and leaves were closely correlated with changes in infectivity.Five days after inoculation and 3 days before symptoms appeared, the levels of serine and threonine in the stems of plants receiving a dilute inoculum were less than those in controls.It is suggested that accumulation of NH2 compounds in an infected plant may interfere with virus synthesis; this may explain the observed cyclical changes in infectivity.Free tyrosine and hydroxylysine were recorded for the first time in leaves and stems of healthy tomato plants and tyrosine and methionine in healthy roots.