Thesis Abstract and Dissertation Abstracts
Biochemical And Molecular Characterization Of Cold-induced Sweetening In Potato (solanum Tuberosum L.) Varieties During Storage
Abstract Category: Science
Course / Degree: PhD Plant Biochemistry
Institution / University: Anand Agricultural University, India
Published in: 2014
Potato (Solanum tuberosum L.) is the third most important food crop, the most important non-grain food crop and one of the most essential basic vegetable worldwide as well as in Indian subcontinent. After harvest, potatoes are stored in cold storage to provide round the year supply to markets and consumers. But during storage at cold temperatures, many cultivars accumulate free reducing sugars derived from breakdown of starch to sucrose that is ultimately cleaved by acid invertase to produce glucose and fructose in a metabolic process known as cold-induced sweetening (CIS). Understanding the basis of CIS in potato tubers is of interest not only in basic research on plant adaptation to environmental stress but also in applied research, since high amounts of reducing sugars adversely affect the quality of processed food products. Investigations were carried out to characterize at biochemical and molecular levels the CIS in 11 potato varieties namely DSP 287, DSP 186, Kufri Surya, K. Chipsona-3, K. Sutlej, K. Sadabahar, K. Jyoti, K. Lauvkar, K. Himsona, K. Bahar and K. Badshah stored at 3 different temperatures viz., room temperature (25-32ºC), incubator (15ºC) and cold storage (4ºC). Samples, collected every 15 days intervals for 105 days storage were analyzed for different parameters associated with carbohydrate metabolism on one side, and antioxidant capacity on the other side. Analysis of carbohydrate dynamics showed that low temperature storage negligibly influenced dry matter, starch and maltose contents of tubers, but a significant increase in reducing sugars, total soluble sugars, fructose, glucose, hexoses:sucrose ratio and a decrease of sucrose content were observed at 4ºC as compared to room temperature. A strong positive correlation was found between reducing sugars and total soluble sugars, and between fructose and glucose. Additionally, important shrinkage and sprouting of tubers was observed at 15ºC, they were less intense at room temperature, and no any shrinkage and sprouting occurred on tubers stored at 4ºC. The potato varieties also appeared to be suitable for processing immediately after harvest or short storage at room temperature. The activity of β-amylase was considerably increased by storage at low temperature, and a weak correlation with starch content indicated an important role of other enzymes in starch degradation while absence of maltose accumulation with increased β-amylase activity implied a possible significant activity of maltase in potato tubers. Acid invertase activity drastically rose at low temperature and strongly paralleled reducing sugars, glucose, fructose and hexoses:sucrose ratio. Moreover, as acid invertase activity increased, sucrose content decreased, indicating the essential role of acid invertase in development of CIS. The above findings allowed to group the 11 potato varieties into low to high sugar-forming groups and thereby select K. Jyoti as CIS-tolerant and K. Badshah as CIS-susceptible. Banding pattern of both native and denaturated proteins of potato tubers could not clearly discriminate the varieties. Zymograms of β-amylase revealed differentially induced bands at low storage temperatures, which might justify the observed increase of enzyme activity. Screening of the 11 potato varieties with 10 SSR primers detected a total of 42 alleles arranged in 44 different configurations, among which 37 alleles (88%) were polymorphic. The polymorphic information content value of the SSR locus ranged from 0.473 to 0.787 thus indicating a high utility of these markers for study of genetic diversity in potato. The dendrogram derived from Dice’s similarity coefficients among the 11 varieties could partially but efficiently differentiate close parents and sugar-forming groups. Differential gene expression analysis showed that during storage expression of vacuolar acid invertase gene StvacINV1 and β-amylase gene BAM1 increased at low temperature and their transcripts were more expressed in the CIS-tolerant variety than the CIS-sensitive. Expression of invertase inhibitor gene INH2α however was higher in the CIS-tolerant variety than the CIS-sensitive. Correlating StvacINV1 and INH2α expressions with reducing sugar content and acid invertase activity established that post-translational regulation of acid invertase by the invertase inhibitor protein could be an important component of resistance to CIS. Besides, correlation between BAM1 expression and β-amylase activity affirmed the hypothesis of several enzymes and pathways involved in starch degradation during cold storage of potato. Analysis of antioxidant capacity parameters revealed that low temperature storage greatly influenced vitamin C content as well as the phenolic content. During storage, both parameters initially increased, then a fluctuated decline was observed but until the last day of observation, they remained above the initial level. Phenolic acids profiling by UPLC identified 12 compounds among which the most abundant was chlorogenic acid followed by gallic acid, sinapic acid and ellagic acid which is reported for the first time, while trans-cinnamic acid was the lowest. Except para-coumaric acid which decreased at 4ºC, all the phenolic acids increased with storage among which sinapic acid and ferulic acid appeared to be most enhanced. Correlation analysis showed that gallic acid, caffeic acid, chlorogenic acid and protocatechuic acid significantly contributed to total phenolic content. Evaluation of antioxidant activity showed a close relationship between DPPH and ABTS methods. Antioxidant activity estimated by both the methods increased up to 60 days storage then at 90 days, they dropped to a level comparable or lower than the original value, irrespective of the storage temperature. Correlation study revealed that chlorogenic acid, gallic acid and ferulic acid mostly contributed to antioxidant activity. Activity of the antioxidant enzymes superoxide dismutase and ascorbate peroxidase both increased initially but then decreased to values lower than the initial level and were not influenced by storage temperature. Correlation with antioxidant activity indicated that the enhancement of reactive oxygen scavenging species in tubers could result mainly from ascorbate peroxidase activity. Isoforms of the two enzymes showed interesting polymorphism and changes in bands intensity as well as differential induction or suppression of bands during storage. However, isozymes of ascorbate peroxidase showed higher similarity and better discrimination of the varieties. Although a clear relationship between CIS and antioxidant capacity was not established, nevertheless it appeared that low sugar-forming varieties K. Jyoti, K. Himsona and K. Surya were also having high antioxidant capacity whereas K. Chipsona-3 and K. Bahar both high sugar-forming had low antioxidant capacity. Hence, it is not unreasonable to suggest that antioxidant capacity of potato tubers should be taken into account in development of CIS-resistant varieties. Nonetheless, additional evidences are needed to confirm this suggestion as well as there is an urgent need to develop new varieties capable to cope with this cold stress.
Thesis Keywords/Search Tags:
Potato, Cold-induced sweetening, Storage, Phenolics, UPLC, HPLC, Gene expression, SSR, Genetic diversity
This Thesis Abstract may be cited as follows:
Galani Y.J.H. 2014. Biochemical and Molecular Characterization of Cold-Induced Sweetening in Potato (Solanum tuberosum L.) Varieties during Storage. PhD thesis, Anand Agricultural University, India. 310.
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Changes of Vitamin C content (click to enlarge) |
Submission Details: Thesis Abstract submitted by Galani Yamdeu Joseph Hubert from Cameroon on 22-Feb-2015 19:49.
Abstract has been viewed 2838 times (since 7 Mar 2010).
Galani Yamdeu Joseph Hubert Contact Details: Email: josephgalani@gmail.com Phone: +237674244181
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