Regulation Of Trans-2-hexenal On Chloroplast Degradation And Fruit Softening In Tomato

Trans-2-hexenal is a naturally occurring volatile substance,which is closely related to tomato ripening.It is speculated that it may play a regulatory role in tomato ripening.To verify this hypothesis,tomatoes were treated with appropriate concentration of exogenous trans-2-hexenal,then the signal intensity was improved,the changes in gene expression,physiological indexes and subcellular structure in response to trans-2-hexenal signal were observed.The results showed that trans-2-hexenal could regulate chloroplast degradation in tomato fruits and leaves by different mechanisms,and soften tomato fruits after harvest by regulating the mechanism related to pectin degradation.The main results are as follows:(1)In this study,an association was established between trans-2-hexenal and chloroplast degradation in tomato fruits.It was found that trans-2-hexenal inhibited tomato color transformation.The initial mechanism is that trans-2-hexenal specifically destroys chloroplast structure in a way independent of autophagy gene ATG,but has relatively little effect on the chromosomes.Due to the violent decomposition of chloroplast thylakoid membranes,chlorophyll was not enzymatically reacted.However,a large number of chloroplasts were degraded and did not form chloroplasts with sufficient accumulation of carotenoids,so that the fruit showed inhibited color transformation.The decreased level of unsaturated fatty acids and the less affected saturated fatty acids also supported the hypothesis of the decomposition of the chloroplast intimal system.LOX,AOS,AOC genes were upregulated,and HPL gene was downregulated,that indicated the fatty acids released by the decomposed chloroplast intimal system were degraded along the LOX and jasmonic acid pathways without the synthesis of more endogenous trans-2-hexenal.In conclusion,trans-2-hexenal may be a regulatory factor targeting the non-ATG-dependent degradation of chloroplasts in tomato fruit.(2)In this study,an association was established between trans-2-hexenal and chloroplast degradation in tomato leaves,rapid and intense senescence of tomato leaves after trans-2-hexenal treatment.The decrease of β-carotene content and the increase of lutein compared with the control group indicated that the effect of trans-2-hexenal on tomato leaves wilt was not directed to the pigment synthesis and decomposition process.In the low concentration treatment group,the autophagosomes were formed and the ATG5,ATG7 and ATG10 genes were upregulated,showed that the apoptosis reaction occurred,the programmed autophagy was initiated.In the high concentration treatment group,apoptosis and autophagy did not occur,the cell structure was destroyed in a more violent way,resulting in cell death.MDA content and conductivity were not significantly affected by low concentration treatment,which also indicated that the integrity of cells was not severely damaged by trans-2-hexenal.But the MDA content and conductivity were increased by high concentration treatment,which indicated that high concentration treatment damaged the integrity of cells in a more severe way and led to plant death.The OR gene was highly responsive to the treatment of trans-2-hexenal.At the same time,the upregulated expression of LOX and HPL gene was observed,which suggested that the decomposition of fatty acids in the membrane structure was initiated during chloroplast transformation.In conclusion,trans-2-hexenal may play a role in regulating chloroplast degeneration in leaves.The downregulation of AOS and AOC indicated that 13-HPOT catalyzed by a large number of LOX enzymes did not flow to the jasmonic acid pathway,but synthesized more trans-2-hexenal through the catalyzed HPL pathway,suggesting that a cascade amplification mechanism may be activated to accelerate the lipolysis of chloroplast membrane and form more trans-2-hexenal.Through this cascade amplification mechanism,drastic and rapid leaf wilt was achieved.In addition,trans-2-hexenal may be a very promising natural herbicide.(3)In this study,an association was established between trans-2-hexenal and tomato fruit softening.The antifungal effects of trans-2-hexenal were widely studied.This study found that high concentration of trans-2-hexenal increased the incidence of Botrytis Cinerea inoculated tomatoes.Based on this phenomenon,the negative effect of trans-2-hexenal on tomatoes was further explored.The results showed that trans-2-hexenal promoted the decrease of tomato hardness,and the combination with 1-MCP excluded the effect of endogenous ethylene,which proved that this phenomenon was not related to endogenous ethylene synthesis.After treatment,the polygalacturonse(PG)and pectin methylesterase(PME)activity increased,the PG and PME2.1 genes were upregulated,the content of pectin decreased,and the middle layer of cell wall shrunk.The results indicated that the change of pectin related enzyme activity and gene were the internal cause of fruit softening,and this phenomenon could help the tomato fruit peel off.