The influence of ethylene and tissue age on the sensitivity of xanthi tobacco leaves to a trichoderma viride xylanase

A xylanase produced by Trichoderma viride induced defense responses including ethylene biosynthesis and necrosis in Nicotiana tabacum cv. Xanthi leaves. Ethylene pretreatment accentuated the level of ethylene and necrosis produced in response to xylanase. The sensitivity of leaves to xylanase and ethylene was influenced by tissue age. Young leaves were relatively insensitive to both ethylene and xylanase. Mature leaves were relatively insensitive to xylanase but became very sensitive to xylanase after treatment with ethylene. Senescing leaves were more sensitive to xylanase than young or mature leaves. Ethylene alone had little if any effect on ethylene biosynthesis or ACC synthase transcript levels in the absence of xylanase treatment but stimulated accumulation of pathogenesis related protein PR-1 basic transcripts directly. Ethylene-pretreated leaves subsequently treated with xylanase had greatly elevated ACC synthase transcript levels compared to levels in xylanase treated air-pretreated leaves. The time course of PR-1 basic transcript accumulation in response to ethylene was similar to the time course for ethylene enhanced-sensitivity to xylanase as expressed by ethylene 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 ethylene treatment of tobacco plants, following the loss of the initial ethylene treatment, restored the enhanced sensitivity of the tissues to xylanase. The continual presence of ethylene is required for maintenance of the effects of ethylene studied here and, the timing of the induction and subsequent loss of the ethylene effects are closely coordinated whether at the molecular or whole tissue level.