Stress on avocado fruits regulates Δ9-stearoyl ACP desaturase expression, fatty acid composition, antifungal diene level and resistance to Colletotrichum gloeosporioides attack

The expression of the avocado homologue avfad9 encoding Delta(9)-stearoyl-ACP desaturase was enhanced by multiple stimuli: inoculation with Colletotrichum gloeosporioides, exposure to ethylene or CO2, low temperature (4 degreesC) and fruit wounding. This enhanced expression was correlated with an increase in the preformed antifungal (Z, Z)-l-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene. Treatments of fruits with ethylene that enhanced the up-regulation of avfad9 also increased the concentration of 18:2 fatty acid and the incorporation of 14C- linoleate into the antifungal diene. Fruits with enhanced Delta(9)stearoyl-ACP desaturase expression were more resistant to C gloeosporioides. It is suggested that the enhanced Delta(9)stearoyi-ACP desaturase expression is involved in elevation of unsaturated 18:2. It is also concluded that similar treatments enhance the incorporation of labeled 18:2 into the antifungal diene and elicit the concurrent enhanced resistance to fungal attack. (C) 2003 Elsevier Ltd. All rights reserved.