Evidence that α-farnesene biosynthesis during fruit ripening is mediated by ethylene regulated gene expression in apples

Abstract

The effect of ethylene regulation on α-farnesene biosynthesis in preclimateric ‘Delicious’ and ‘Granny Smith’ apples was studied using an ethylene inducer and inhibitor, α-farnesene biosynthesis precursors, and protein transcription and translation inhibitors. α-Farnesene was not detectable when internal ethylene concentrations were less than 1 μl l −1 . Correlations between internal ethylene and α-farnesene production fit the exponential growth equation and were significant in ‘Delicious’ ( y = e 0.17 ; r 2 =0.68) and ‘Granny Smith’ ( y = e 0.18 ; r 2 =0.83). When applied at harvest, aminoethoxyvinylglycine (AVG) at 200 mg l −1 inhibited both internal ethylene accumulation and α-farnesene production, whereas ethephon at 200 mg l −1 accelerated both. Adding ethephon to AVG-treated fruit after 18 days at 20°C induced internal ethylene accumulation and α-farnesene production. Ethephon induced α-farnesene production in discs from preclimacteric fruit peel as well as AVG-treated fruit peel, but α-farnesene was undetectable when cycloheximide (CHI, 50 mM), actinomycin D (Act D, 50 mM), or silver nitrate (150 mg l −1 ) were added to the ethephon-treated discs. In preclimacteric fruit discs at harvest, with or without AVG treatment, α-farnesene biosynthesis was induced by 50 μM mevalonic acid lactone (MAL) or farnesyl pyrophosphate (FPP), but not by hydroxymethylglutaric acid (HMG). Adding CHI or Act D to these discs did not affect the induction of α-farnesene by MAL or FPP.