Increased activities of ribonuclease and protease after challenge in tobacco plants with induced systemic resistance

Inoculation of 3-4 lower leaves of tobacco with tobacco mosaic virus (TMV) increased ribonuclease (RNase) and protease activities in inoculated leaves. Little or no increase in the activities were apparent in upper noninoculated leaves prior to challenge. After challenge with TMV or Peronospora tabacina, RNase activities increased more rapidly in the upper leaves of induced plants as compared to those of noninduced plants. Protease activities in the leaves challenged with P. tabacina or TMV also increased after challenge, but little or no differences in the activities were apparent between induced and noninduced plants. The incubation of purified TMV with leaf extracts obtained from induced challenged, noninduced challenged and noninduced unchallenged plants prior to inoculation did not affect the number of local lesions formed on tobacco plants. (C) 1995 Academic Press Limited