DEPENDENCE OF METHYL-JASMONATE-INDUCED AND WOUND-INDUCED CYSTEINE PROTEINASE-INHIBITOR ACTIVITY ON NITROGEN CONCENTRATION

Papain inhibitor activity was induced in leaves of wounded potato plan ts in direct relationship to the concentration of nitrogen supplied. V irtually no inhibitory activity was observed when plants were deprived of nitrogen altogether, even after 12 d of wounding. However, in plan ts supplied N at 21 mg/d, inhibitory activity increased gradually with time after wounding was started until day seven, when maximal activit y was attained at a level that: inhibited about 16 micromoles of papai n per liter of leaf extract. When N supplementation was stopped immedi ately prior to wounding, inhibitor levels increased with time but neve r reached the maximum levels observed with continuous fertilization. T here was no inhibitory activity measured in tomato leaf extracts follo wing cutting for 6 d, at any of the N levels. A slight increase was ob served if cutting was continued for more than 10 d, but only at 21 mg/ d, N. Following treatment with gaseous methyl jasmonate (MJ), inhibito rs were induced in potato leaves, increasing from 12 mu mol/L in plant s with no N supplement, to a maximum inhibition of 20 mu mol/L with th e addition of 3.5 mg/d, N. MJ also induced papain inhibitor activity i n tomatoes, even in those plants that had been deprived of nitrogen, w ith activity increasing in direct relationship to nitrogen concentrati on, reaching a maximum of 22 mu mol/L. These data demonstrate the impo rtance of ensuring that plants are adequately fertilized with nitrogen when investigating proteinase inhibitor induction after wounding. The y also suggest that gaseous MJ can circumnavigate the normal plant res ponse to nitrogen deprivation.