Systemic resistance induced by localized virus infections: Extent of changes in uninfected plant parts

Abstract

Necrotic lesions caused by tobacco mosaic virus (TMV) in 3–4 lower leaves of a tobacco plant induced resistance to TMV in up to 16 noninoculated leaves; the resistance was characterized by the development of fewer and much smaller lesions in response to subsequent inoculation with TMV than developed in comparably inoculated normal leaves. Similar resistance was not induced by Pseudomonas tabaci or by mechanical or chemical injury. No resistance developed unless leaves containing the initial TMV infections remained on the plant for about 3 days. Leaving the initially inoculated leaves on the plant for longer periods resulted in progressively higher levels of resistance up to periods of about 7 days, but delaying the removal for still longer periods resulted in no further increase in resistance. Once a leaf became resistant, it remained so for at least 42 days, the longest period tested. When the 3 lower leaves of tobacco plants were inoculated with TMV and then removed 7–10 days later, the next 9–16 leaves, but not those above the 16th, became resistant regardless of whether the tested leaves had developed before or after removal of the originally inoculated leaves. Some leaves that became resistant were no more than leaf initials when the leaves containing the original infections were removed. The respiration rate of disks cut from resistant tissues did not differ significantly from that of disks from normal tissues, nor did resistant and normal tissues differ in quantity of total or individual free amino acids. Polyphenoloxidase activity, as determined manometrically, was essentially the same in extracts from resistant leaves as in extracts of normal leaves.