METHYL JASMONATE INDUCES PAPAIN INHIBITOR(S) IN TOMATO LEAVES

Leaves of 18- to 24-d-old tomato (Lycopersicon esculentum) plants expo sed to gaseous methyl jasmonate (MJ) for 24 h at 30-degrees-C in conti nuous light contained high levels of soluble protein that inhibited pa pain. Chromatographic analysis demonstrated that the active protein ha d a molecular mass of 80 to 90 kD. Induction of papain inhibitor was d irectly related to the concentration of airborne MJ up to a maximum of 0.1 muL MJ per treatment and depended on the duration of exposure up to 18 h. Inhibitor activity in plants treated for less than 18 h incre ased with time after treatment. Levels remained constant for up to 4 d after treatment, after which time activity decreased. The youngest le af, leaf 5, consistently lost activity at a faster rate than older, lo wer leaves. Inhibitor concentration in all leaves was reduced to minim um levels by 11 d after MJ treatment, but did not return to control le vels. Treatment with MJ in the dark did induce inhibitor activity, but at a significantly lower rate. Polyclonal antibodies raised to purifi ed potato tuber skin cysteine proteinase inhibitors (CPI) cross-reacte d with the tomato inhibitor, suggesting that the tomato papain inhibit or and the potato CPI are closely related. No papain inhibitor activit y was observed in extracts from wounded tomato leaves, nor was there a ny immunoreactivity with antibodies raised to potato tuber skin CPI.