Role Of Lipoxygenase And Ethylene In Tomato Fruit Ripening And Aroma Synthesis

Tomato is a model crop that studies the relevant changes in fruit ripening,and is widely used because of its good development mutants,as well as ease of operation and short life cycle.Lipoxygenase(LOXs)is a non-heme ferritin present in the biological world(Brash 1999),especially higher in plants,widely involved in plant growth and development,aroma material synthesis,fruit ripening and ethylene biosynthesis.Ethylene also plays an important role in regulating ripening of fruit,Thus,the role of LOX and ethylene in fruit ripening and aroma synthesis has also received extensive attention.In this study,five pleiotropic mutant tomato(rin,nor,nr,cnr,hp-1)lines were used to test materials in comparison with wild type(AC),all those were sampled at breaker color(B+),three days after breaker(B+3)and seven days after breaker(B+7),respectively,aroma,ethylene and related genes expression of LOX,LOX activity were investigated.And take B+ when the wild type fruit AC and mutant rin made fruit discs,measured ethylene release,LOX activity and related gene expression and ethylene related gene expression,the effects of lipoxygenase and ethylene control of aroma synthesis and central regulators of ripening were studied.The results were described as follow:1.Along with fruit growth and development,single fruit weight,transverse and longitudinal diameter increased gradually and changed significantly at seven days after breaker.Sugar consistent with fruit VC and soluble solids change,maximum at seven days after breaker.2.We were detected 64 aroma compounds,such as Birch-Me,Acetic acid,Furfural,total concentration were 1388 μg/g,the aroma type and concentration in the mutants were less than wild type(such as Birch-Me,Eugenol,Acetic acid).Principal component analysis showed that the main component of 1 accounted for 63.2%,the main component of 2 accounted for 26.8%,most mutants were positively correlated with principal components 1 and 2,and a few mutants were negatively correlated with principal components.3.Determination of ethylene release at B+ to B+7 by fruit gas chromatograph,the results showed that the wild type AC,the mutant hp-1 could synthesize ethylene normally,and the ethylene content of nr fruit was less than that of the former two.The rin,cnr and nor fruits had no ethylene release or less ethylene release.4.The LOX activity,TomloxC and SIHPL gene expression of mutants and wild type fruits was determined by spectrophotometer and fluorescence quantitative PCR.The results showed that the LOX activity and expression of TomloxC and SIHPL in AC,hp-1 and nr fruits increased with the growth of fruit,and B+7 were significantly changed,but the activity of other mutant fruits decreased with fruit growth;The expression of TomloxC in AC fruit was the highest at B+3,and were significantly higher in hp-1 and nr fruit than in other periods,but the expression of genes in other mutants were lower.The expression of SlHPL was similar to that of TomloxC,but its expression was higher than that of TomloxC,which was consistent with the determination of fruit aroma.5.The expression of LOX and expression of TomloxC and SIHPL were determined by pericarp discs test with wild type AC and rin fruit.It was found that the addition of linoleic acid and linolenic acid to the discs could promote the activity and gene expression in the AC.LOX inhibitors-nordihydroguaiaretic acid(NDGA)could inhibit the activity of the enzyme and the gene expression.The addition of ACC had no effect on the activity and expression of the enzyme;In rin mutants linoleic acid or linolenic acid can promote the expression of LOX genes,has little or no effect on enzyme activity.6.The results showed that the addition of ACC,linoleic acid and linolenic acid could promote the release of ethylene in the AC fruit.NDGA inhibited the ethylene release,but had no effect on the ethylene release in rin fruit.Through the results showed that the addition of ACC,linoleic acid and linolenic acid in the pericarp discs could increase the expression of SlACO1,SlAC04,SlACS2 and SlACS4 in the AC fruit,but the addition of ACC only promote to the rin mutant SlACS2 expression,other treatments had no effect on the expression of ethylene related genes in rin.NDGA did not promote or inhibit the expression of ethylene related genes in fruit.Above all,in tomato ethylene deficient mutants the ethylene synthesis was inhibited,the aroma concentration and type were lower than that of wild type,and the expression of LOX genes were decreased,the results indicated that LOX was regulated by ethylene in aroma volatiles synthesis of fruit.The addition of ACC,linoleic acid or linolenic acid promoted the ethylene release and LOX genes and ethylene genes expression in wild type AC fruit discs,the addition of NDGA inhibited ethylene release and LOX and ethylene gene expression,but had no effect on rin mutant,indicating that AC fruit was more sensitive to exogenous treatment.After exogenous treatment of linoleic acid or linolenic acid,ethylene synthesis system could be started regulation of the formation of endogenous ethylene.