Effect of soil salinity on fructan content and polymerization degree in the sprouting tubers of Jerusalem artichoke (Helianthus tuberosus L.)

In addition to their role as reserve carbohydrates, fructans have been recognized as compounds that are protective against adverse environments. The aim of this study was to identify changes in the content and the degree of polymerization (DP) of fructan in sprouting tubers of Jerusalem artichoke under salt stress. Fructan was extracted from tubers at 1, 3, 5, and 7 days after planting in sandy loam soil irrigated with NaCl solution. Fructan accumulation and polymerization and the expression of genes encoding enzymes for fructan synthesis and degradation were evaluated. No significant differences between the control and treatment groups were observed until 5 days after sowing. The highest level of salinity (250 mM) not only inhibited sprouting and root growth but also decreased the level of fructan in the tubers. The proportion of fructan at DP 2-5 rapidly increased one day after sowing and then decreased over time. Under various NaCl treatments, at 7 days after sowing, all fructans except fructan at DP 6-10 were present in proportions less than or equal to the control. The variation in the DP of fructan was related to the transcription level of fructan metabolism genes. Fructan may support sprouting or resistance to salt stress by changing the DP of fructan molecules through hydrolysis without changing the total amount of fructan. The low-molecular-weight oligosaccharides (DP < 5) may be the major carbohydrates that support tuber sprouting or that are involved in protection from salt stress.