Dependence of methyl jasmonate- and wound-induced cysteine proteinase inhibitor activity on nitrogen concentration

Papain inhibitor activity was induced in leaves of wounded potato plants in direct relationship to the concentration of nitrogen supplied. Virtually no inhibitory activity was observed when plants were deprived of nitrogen altogether, even after 12 d of wounding. However, in plants supplied N at 21 mg/d, inhibitory activity increased gradually with time after wounding was started until day seven, when maximal activity was attained at a level that: inhibited about 16 micromoles of papain per liter of leaf extract. When N supplementation was stopped immediately prior to wounding, inhibitor levels increased with time but never reached the maximum levels observed with continuous fertilization. There was no inhibitory activity measured in tomato leaf extracts following cutting for 6 d, at any of the N levels. A slight increase was observed if cutting was continued for more than 10 d, but only at 21 mg/d, N. Following treatment with gaseous methyl jasmonate (MJ), inhibitors were induced in potato leaves, increasing from 12 mu mol/L in plants with no N supplement, to a maximum inhibition of 20 mu mol/L with the addition of 3.5 mg/d, N. MJ also induced papain inhibitor activity in tomatoes, even in those plants that had been deprived of nitrogen, with activity increasing in direct relationship to nitrogen concentration, reaching a maximum of 22 mu mol/L. These data demonstrate the importance of ensuring that plants are adequately fertilized with nitrogen when investigating proteinase inhibitor induction after wounding. They also suggest that gaseous MJ can circumnavigate the normal plant response to nitrogen deprivation.