TRANSPORT OF SALICYLIC-ACID IN TOBACCO NECROSIS VIRUS-INFECTED CUCUMBER PLANTS

The transport of salicylic acid (SA) was studied in cucumber (Cucumis sativus L.) using C-14-labeled benzoic acid that was injected in the c otyledons at the time of inoculation. Primary inoculation with tobacco necrosis virus (TNV) on the cotyledons led to an induction of systemi c resistance of the first primary leaf above the cotyledon against Col letotrichum lagenarium as early as 3 d after inoculation. [C-14]SA was detected in the phloem or in the first leaf 2 d after TNV inoculation , whereas [C-14]benzoic acid was not detected in the phloem during the first 3 d after TNV inoculation of the cotyledons, indicating phloem transport of [C-14]SA from cotyledon. In leaf 1, the specific activity of [C-14]SA decreased between 1.7 and 8.6 times compared with the cot yledons, indicating that, in addition to transport, leaf 1 also produc ed more SA. The amount of SA transported after TNV infection of the co tyledon was 9 to 160 times higher than in uninfected control plants. T hus, SA can be transported to leaf 1 before the development of systemi c acquired resistance, and SA accumulation in leaf 1 results both from transport from the cotyledon and from synthesis in leaf 1.