Ethylene-mediated plant responses to severe water deficit in strawberry

The research described in this thesis focussed on the potential effect of ethylene produced under severe water deficit conditions (SWD) on the concentration of phenolic compounds in fruit and leaves of commercial strawberry (Fragaria x ananassa Duch.). An increased ethylene production rate was detected in green fruit and leaves at midday of the second day of wilting in response to SWD. The stress-induced rise in ethylene production was successfully inhibited by applications of aminoethoxyvinylglycine (AVG) and subsequently re-instated by 1-aminocyclopropane- 1-carboxylic acid (ACC) or replaced by abscisic acid (ABA) in fruits. Initially, fruit total ellagic acid concentration increased along with ethylene production but conclusive evidence for the causal role of ethylene in the accumulation of individual phenolics in fruit from the inhibition, re-instatement and replacement of the ethylene signal was not obtained. The quantitative expression of selected genes in leaves was investigated, and a significant reduction in the relative expression of FaACS1 (coding for ACC synthase), an increase in FaACO1, FaACO4 (coding for ACC oxidase) expression and no change on the expression FaPAL (coding for Phenylalanine ammonia lyase) was observed. Increased leaf ethylene production rate was likely due to increased expression of genes regulating ACC oxidase activity. However, no evidence was found from these genetic studies to confirm the role of stress-induced ethylene production in accumulation of phenolics in fruit or leaves