Stimulation of callose synthesis in the leaves of samsun NN tobacco showing systemic acquired resistance to tobacco mosaic virus.

When the lower leaves of Samsun NN tobacco were inoculated with tobacco mosaic virus (TMV) and were kept at 20C for 12-14 days under continuous light, callose accumulation of the wound leaf surfaces in the non-inoculated upper leaves was stimulated. Challenge-inoculation with TMV to the upper leaves 10-14 days after the first inoculation resulted in the limited lesion formation; the diameter of lesions was much smaller than those on control plants. Heavy callose deposition could be detected around the tiny lesions formed on the leaves showing acquired resistance. The relation between the limited expansion of lesion and the accumulation of callose in the resistant leaves is discussed.