Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2006
Publication Date: 6/29/2006
Citation: Kondo, S., Isuzugawa, K., Kobayashi, S., Mattheis, J.P. 2006. Aroma volatile emission and expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase genes in pears treated with 2,4-DP. Postharvest Biology and Technology. v 41. P. 22-31.
Interpretive Summary: Ripening of many fruit is controlled by the odorless gas ethylene produced naturally by fruit tissues. What factors control production of ethylene and initiation of the ripening process is as yet uncharacterized. Auxins are another naturally occurring plant growth regulator, and auxin activity can stimulate ethylene production in other plant tissues. Using a synthetic auxin, we demonstrated an advancement of pear fruit ripening after application of auxin to fruit. Accelerated ripening was observed in fruit color, aroma, ethylene production, and also by earlier development of internal breakdown that is typical of overripe fruit.
Technical Abstract: Effects of the synthetic auxin 2,4-dichlorophenoxy-propionic acid (2,4-DP) on 1-aminocyclopropane-1-carboxylate (ACC) synthase and oxidase gene expression by ‘La France’ and aroma production by ‘Bartlett’ pears (Pyrus communis L.) were investigated. In non-stored, non-treated ‘LaFrance’ fruit, the accumulation of ACC synthase and ACC oxidase transcripts was not observed. In 2,4-DP treated ‘La France’ fruit, the levels of mRNAs hybridizing to ACS4 probes increased strongly while ACS1, ACS3, and ACO1 mRNA levels were similar between 2,4-DP treated fruit and stored nontreated fruit. The result indicates that ACS4 may be an ACC synthase gene which is induced by auxin in pears. Thirty-eight volatile compounds were detected from ‘Bartlett’ pears. The composition and amount of aroma volatiles were similar between 2,4-DP treated fruit and stored nontreated fruit. Esters were the most prevalent compounds and butyl-, ethyl-, and hexyl acetate were produced in the largest amounts. In non-stored, non-treated fruit, aldehydes were quantitatively the largest group of volatiles produced. Internal browning in 2,4-DP treated ‘Bartlett’ fruit developed on the tree within 30 days of application. Possible effects of pre-harvest temperatures are discussed.