THE INFLUENCE OF ETHYLENE AND TISSUE AGE ON THE SENSITIVITY OF XANTHITOBACCO-LEAVES TO A TRICHODERMA-VIRIDE XYLANASE

A xylanase produced by Trichoderma viride induced defense responses in cluding ethylene biosynthesis and necrosis in Nicotiana tabacum cv. Xa nthi leaves. Ethylene pretreatment accentuated the level of ethylene a nd necrosis produced in response to xylanase. The sensitivity of leave s to xylanase and ethylene was influenced by tissue age. Young leaves were relatively insensitive to both ethylene and xylanase. Mature leav es were relatively insensitive to xylanase but became very sensitive t o xylanase after treatment with ethylene. Senescing leaves were more s ensitive to xylanase than young or mature leaves. Ethylene alone had l ittle if any effect on ethylene biosynthesis or ACC synthase transcrip t levels in the absence of xylanase treatment but stimulated accumulat ion of pathogenesis related protein PR-1 basic transcripts directly. E thylene-pretreated leaves subsequently treated with xylanase had great ly elevated ACC synthase transcript levels compared to levels in xylan ase treated air-pretreated leaves. The time course of PR-1 basic trans cript accumulation in response to ethylene was similar to the time cou rse for ethylene enhanced-sensitivity to xylanase as expressed by ethy lene biosynthesis, ACC synthase transcript level and necrosis. All the measured effects of ethylene were lost within a similar time frame of 48 h after removing plants from the ethylene atmosphere. A second eth ylene treatment of tobacco plants, following the loss of the initial e thylene treatment, restored the enhanced sensitivity of the tissues to xylanase. The continual presence of ethylene is required for maintena nce of the effects of ethylene studied here and, the timing of the ind uction and subsequent loss of the ethylene effects are closely coordin ated whether at the molecular or whole tissue level.