Abstract
The inulin-type fructans in Jerusalem artichoke (Helianthus tuberosus L.) tubers exhibit different degrees of polymerization and are critical for germination. We aimed to characterize the sugar metabolism dynamics in the tubers without bud eyes or shoots (T) and BE/S of indoor- and field-grown Jerusalem artichokes during germination. Ht1-FEH II and Ht1-FEH III (1-fructan exohydrolases II and III, inulin-degrading enzymes) expression increased 5 days after planting indoors, whereas Ht1-FEH II expression increased 72 days after planting in the field in T and BE/S. Ht1-SST (sucrose:sucrose 1-fructosyl transferase, inulin synthesis initiator), and Ht1-FFT (fructan:fructan 1-fructosyl transferase, inulin elongator) expression generally decreased in indoor-grown T. The enzyme activities of 1-FEH and 1-FFT were unchanged during germination in both indoor- and field-grown T and BE/S, whereas 1-SST activity decreased in indoor-grown T, while 1-FEH and 1-FFT activities increased as a function of germination time in BE/S of both indoor- and field-grown tubers. The total soluble sugar content gradually decreased in T after germination indoors or in the field, while at the end of germination, the sucrose and fructan contents decreased, and fructose content increased in the field. The enzyme activities of soluble vacuolar (VI) or neutral invertase (NI) did not change significantly, except at the late germination stage. Sucrose synthase (SS) and sucrose-phosphate synthase (SPS) activities were not significantly changed in T and BE/S in indoor-grown artichokes, while SS activity gradually increased, and SPS activity gradually decreased in field-grown artichokes, alongside sucrose degradation. Compared to T, BE/S generally had higher enzyme activities of 1-FEH and 1-FFT, promoting inulin hydrolysis. This work shows that the process of tuber germination is similar indoors and in the field, and germination studies can therefore be conducted in either environment.
Highlights
MATERIALS AND METHODSJerusalem artichoke (Helianthus tuberosus L.) is a herbaceous perennial plant that grows to around 2 m in height
Tubers were germinated in two environments, indoors at a constant temperature of 20◦C and in the field under regular production conditions
Ht1-Fructan exohydrolase (FEH) I expression decreased in T, while remaining stable in Bud eyes plus shoots (BE/S), up to 5 Days after planting (DAP) in tubers grown indoors (Figure 1; Primers for Quantitative PCR (qPCR) are listed in Supplementary Table S2)
Summary
Jerusalem artichoke (Helianthus tuberosus L.) is a herbaceous perennial plant that grows to around 2 m in height. Due to its high biomass yield and tolerance to abiotic stress, Jerusalem artichoke is extensively cultivated on marginal lands for vegetable production or for wind prevention and sand fixation (Conde et al, 1991; Puangbut et al, 2015). A type of fructan, in the tuber, and this accounts for approximately 85% of the tuber’s dry weight (Marx et al, 1997). Jerusalem artichoke inulin consists of linear β (2, 1)-linked fructofuranosyl units terminated by Glc. The DP, fructofuranosyl units) of inulin varies throughout the growing season, with inulin in mature tubers containing 3 to 35 fructofuranosyl units but fructan DP 2–10 constituting the majority (Luo et al, 2018). Inulin is commonly included in bread and yogurt products as a prebiotic, as it stimulates the growth of beneficial bacteria in the colon (Ritsema and Smeekens, 2003; Drabinska et al, 2016)
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