| Frying processing is an important way to increase the added value of potato,and the lack of special varieties for frying has become an important factor that influence the development of potato processing industry.Cold-induced sweetening(CIS)phenomenon occurred in cold-storage of potato tubers puts forward higher requirements to the fried processed varieties.At present,there is no really popular variety of potato resistance to CIS,and the formation mechanism of CIS from different varieties is still unclear.In this paper,tubers from 12 different potato varieties were treated at 4℃ for 0,2,4 and 8 weeks,and were used to study the differences of CIS and their formation mechanism.The results of our research will benefit for potato resistance breeding on CIS and for development and utilization of known varieties.The main results were as follows:I.Real-time quantitative PCR(q RT-PCR)was used to analyze the differences in the expression patterns of 6 enzyme genes related to starch-sugar metabolism.The results showed that the expression levels of both genes VInv and SPS present trends of rising firstly and then falling on the whole during the cold storage,and the peak at2 rd or 4th week,but different varieties had obvious differences in time and amplitude.However,the expression levels of genes INH,Su Sy,AGPase and GBSS all showed trend of falling or stabilizing on the whole during the cold storage,and the expression levels of these genes were lowest at the later stage.Further in-depth analysis of the VInv gene revealed that the expression levels of the VInv gene were highest in 2-week of cold-stored tubers from 9 varieties,among which 1/3 of the varieties had more than100-fold of expression levels compared to those in 0-week of cold-stored tubers.Interestingly,the expression patterns and expression levels of the VInv gene in tubers of Hongmei,Zaodabai and Zhongshu No.5 were similar to those in Atlantic which showed certain resistance to CIS,and all the expression patterns showed rising with low amplitude and then falling on the whole during the cold storage.It was speculated that the 3 varieties also had certain resistance to CIS.II.The activities of five enzymes related to starch-sugar metabolism were estimated,and the results showed that the enzyme activities of acid invertase(AI)in tubers of 12 potato varieties increased gradually on the whole during the cold storage,but the enzyme activities of AI were relatively low in tubers of Hongmei and Zhongshu No.5,and the variation trends were similar to that in Atlantic.More interestingly,the activity of AI in Hongmei was lower than that in Atlantic.The activities of enzymes SPS and Su Sy present trends of rising firstly and then falling on the whole during the cold storage,and the peak at 2rd or 4th week in tubers of all varieties except Zhongshu No.3 and Xingjia No.2.However,the enzyme activity of AGPase showed trends of stabilizing on the whole,and 50% of the varieties showed no significant difference during the cold storage,which indicated that cold temperature had little effect on the activity of enzyme AGPase in these varieties.The enzyme activity of GBSS increased on the whole during the cold storage,and the activities in 50% of the varieties increased gradually,so these results revealed that the activities of enzyme GBSS were greatly affected by the cold temperature.III.Sugar contents were measured in tubers of all 12 potato varieties,the results indicated that the contents of reducing sugars were low and the fold changes among 12 varieties were less than 3 at the beginning of cold storage.However,the contents of reducing sugars in tubers of 11 potato varieties increased gradually and the peak at 8th week during the cold storage,and the contents of sucrose in tubers of 8 potato varieties present trends of rising firstly and then falling.The accumulation of reducing sugars could be used as the index of CIS resistance,and we all known that Atlantic has certain resistance to CIS,we found that the contents and variation trends of reducing sugars in Hongmei were very similar to those in Atlantic.We also noticed that the contents of reducing sugars in 8-week of cold-stored tubers of Hongmei were less than that in Atlantic,and accounts for 88.2% of the Atlantic.Both USDA chip color chart and precise chromatic aberration meter were used to identify the phenotypes of CIS,and results showed that the chip color got darker during the cold storage,but large differences were observed among different varieties,and the lightest chip color was found in both Hongmei and Atlantic.IV.Correlation analysis was conducted in data generated from all 12 potato varieties.Significant or extremely significant positive correlation were found between the expression levels of genes VInv and SPS in Atlantic,Zhongshu No.3,Zaodabai,Favorita,Zhongshu No.5,Huishu No.2,Huishu No.1,Huangbaoshi and Hongmei,,including all 7 varieties with certain resistance to CIS and 2 varieties susceptible to CIS(Huishu No.2 and Hui shu No.1).It is speculated that the common low expression of VInv and SPS may play a key role in the resistance to CIS.Significant or extremely significant negative correlation of the expression levels of GBSS gene and the phenotypes of CIS were detected in Atlantic,Zhongshu No.3,Favorita,Zhongshu No.5,Xingjia No.2,Huangbaoshi and Heijingang.There was significant or extremely significant positive correlation between the enzyme activities of AI and the contents of reducing sugars in Zhongshu No.3,Zaodabai,Favorita,Zhongshu No.5,Huishu No.2,Huishu No.1,Shepody,Xingjia No.2,Huangbaoshi and Heijingang,and extremely significant positive correlation were observed between the enzyme activities of AI and the phenotypes of CIS in Zaodabai,Favorita,Zhongshu No.5,Huishu No.2,Shepody,Xingjia No.2,Huangbaoshi and Heijingang.The results of the above correlation analysis showed that the enzyme activity of AI had important influence on the contents of reducing sugars and the phenotypes of CIS in most of varieties used in this study. |
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