| ‘Xiangjiao’ plum have sweet and sour taste,moderate consumption can maintain human health.‘Xiangjiao’ plum ripen in mid-August.Due to the hot weather ‘Xiangjiao’ plum has a short life after harvest and the fruit circulation area is limited.At present,the main method to extend the storage life of fruits is low temperature storage,but ‘Xiangjiao’ plum is cold-sensitive plants,which are very resistant to storage and transportation after harvest.Cold injury of ‘Xiangjiao’ plum is easy to occur at low temperature,which will resulting in loss of flavor and sour taste,thus losing the commercial value.For fruits,sour taste is an indispensable flavor.Organic acid plays a role in safe storage.In this paper,the effects of malic acid metabolism at different temperatures,1-MCP treatment and EA treatment on malic acid metabolism enzymes and genes expression of ‘Xiangjiao’plum were studied in order to provide theoretical basis and technical support for long-term cryopreservation of ‘Xiangjiao’ plum.The main results are as follows:1.The high performance liquid chromatography method(HPLC)was used to determine the organic acids in ‘Xiangjiao’ plum.The results showed that the main organic acid in‘Xiangjiao’ plum was malic acid,which accounted for 75% of the total organic acid,followed by oxalic acid,citric acid and succinic acid.However,the content is relatively small and can be ignored.2.Cold injury promoted the degradation of malic acid in ‘Xiangjiao’ plum.The storage life of ‘Xiangjiao’ plum at temperature of 20℃should not exceed 20 d.After that,they completely lose their edible quality.Low temperature storage at 4℃ and 10℃ can extend the storage life of ‘Xiangjiao’ plum to more than 40 d.However,the storage of ‘Xiangjiao’ plum at 4℃ for15 days present cold damage symptoms,with the occurrence of fibrosis and gelation of flesh,accompanied by the decline of soluble solid content(SSC),the inhibition of respiration and superoxide dismutase(SOD)activity,the accumulation of malondialdehyde(MDA),and the aggravation of lipid peroxidation.Under cold injury titrable acid and malic acid content drops abruptly,p H value rises abruptly,solid acid ratio(RTT)drops to the minimum value.At the end of storage,the content of malic acid decrease by 1/2 comparing with that at storage,and it is 1/2 of that at the end of storage at 10℃ and 20℃.3.1-MCP treatment delayed the degradation of malic acid in ‘Xiangjiao’ plum.Compared with the control check(CK),1-MCP treatment at 4℃ and ethylene absorbent(EA)treatment have higher fruit hardness and inhibited respiratory peak.Compared with EA treatment and CK,1-MCP treatment can more effectively inhibit the accumulation of MDA,maintain the integrity of cell membrane and SOD activity,and more effectively alleviate the decline oftitrable acid content in the later stage of ‘Xiangjiao’ plum storage.At the end of storage,the content of malic acid in ‘Xiangjiao’ plum is 3/4 of that at the beginning of storage,1.5 times of that in EA treatment and CK.It is proved that 1-MCP treatment is better than EA treatment.4.NADP-Malate enzyme(NADP-ME)enzyme is the key enzyme to study malic acid degradation of postharp ‘Xiangjiao’ plum.The NAD-MDH,NADP-ME,PEPC and t DT genes are highly expressed at 4℃,with a significant rise in NAD-Malate dehydrogenase(NAD-MDH)and NADP-ME enzyme activity,collaborative control NADP-ME a significant rise in gene expression and its enzyme activity,and accelerate the degradation of malic acid.The NADP-ME gene was down-regulated in 4℃ 1-MCP-treated ‘Xiangjiao’ plum,and the NAD-MDH,PEPC and t DT genes were highly expressed.The activity of NADP-ME enzyme increased slowly,and the activity of NAD-MDH increased.It inhibits the expression of NADP-ME gene and its enzyme activity,thereby delaying the degradation of malic acid. |
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