Effect Of Proline Treatment On Postharvest Physiological Deterioration Of Cassava Root

The country of origin of cassava（Manihot esculenta Crantz）is South America.It is one of the three major potato crops in the world.It is not only a food crop but also an energy crop.As a cash crop,cassava is widely grown in various countries in the tropics.However,the characteristic postharvest physiological deterioration（PPD）of cassava causes considerable losses to cassava production,and the annual economic loss of cassava generation and processing due to PPD is 8%to 29%.Studies have shown that the PPD of cassava is related to the accumulation of reactive oxygen species.Amino acids are involved in various signaling and metabolic pathways in plants.Among them,proline plays a certain role in regulating osmotic pressure under dehydration conditions in plant cells and eliminating reactive oxygen free radicals.In this study,8 cassava varieties such as SC5 and SC9 were used as materials which were independently selected in China,sought the method and mechanism of exogenous treatment of cassava root to slow down the PPD.The main results are as follows:1.Assessed the storage resistance of 8 cassava varieties.Store 8 cassava varieties such as SC5 and SC9 at 25℃.According to the proportion of browning area of cassava slices,arrange their storage resistance from small to large as follows:SC8<SC9<SC205<GR891<SC10<SC124<E407<SC5.2.Determination and analysis of the amino acid content changes of cassava varieties during different storage periods.Using storage-resistant cassava variety SC5 and non-storage-resistant cassava varieties SC8 and SC9 as research materials,the changes of their 14 free amino acids（Pro,Asp,etc.）previous and after storage were measured and compared.It was found that the content of the Pro,Asp,His,Glu,Thr and Ser in SC5cassava roots had significant changes comparing to SC8 and SC9.3.sifting amino acid treatments to delay physiological deterioration of cassava.The cassava variety SC9,which was treated with 6 single amino acid exogenous supplements such as Pro and Asp,was stored for 24 hours.The results showed that Pro-treated cassava root slices had only 12.84%browning area.It is lower than the other treatments and controls,indicating that the exogenous supplementation with proline solution can significantly improve the storage resistance of cassava variety SC9.4.Sifting optimal proline concentration treatments to delay postharvest physiological deterioration of cassava.Through the comparative experiments of proline solution supplementation with 1.25 g/L,2.5 g/L,5 g/L,10 g/L,and 15 g/L,the best proline supplement was selected to be 5 g/L.5.Explaining the mechanism of proline treatment to improve the storage tolerance of non-storage-resistant cassava variety.SC9 root sections were treated with exogenous supplementation of 5 g/L proline to determine hydrogen peroxide（H₂O₂）,catalase（CAT）,superoxide dismutase（SOD）,and ascorbate peroxidase（APX）.The results showed that the H₂O₂content of the treated SC9 root sections after storage for 24 h was significantly lower than that of the control group;the content of CAT,SOD and APX was significantly higher than that of the control group.This indicates that proline can eliminate active oxygen radicals by stimulating the increase of antioxidant enzyme activity,thereby improving the storage resistance of SC9.6.Pathways of proline accumulation in storage-resistant cassava varieties at the later stage of storage.Analysis of proline biosynthetic pathway revealed that Glu and Arg are substrates for Pro biosynthesis.Analysis of the content of 14 free amino acids in SC5,SC8,and SC9 previous and after storage revealed that the content of Glu and Arg in SC5 decreased after storage.