Variation of Fructan and Its Metabolizing Enzymes in Onions with Different Storage Characteristics

Sugar accumulation and activities of enzymes involved in fructan dynamics from seedling to bulb formation in onion (Allium cepa L.)

Improved fructan accumulation in perennial ryegrass transformed with the onion fructosyltransferase genes 1-SST and 6G-FFT

High fructan content in the grain of cereals is an important trait in agriculture such as environmental resilience and dietary fiber food production. To understand the mechanism in determining final grain fructan content and achieve high fructan cereal, a cross breeding strategy based on fructan synthesis and hydrolysis activities was set up and have achieved barley lines with 11.8% storage fructan in the harvested grain. Our study discovered that high activity of fructan hydrolysis at later grain developmental stage leads to the low fructan content in mature seeds, simultaneously increasing fructan synthesis at early stage and decreasing fructan hydrolysis at later stage through crossing breeding is an efficient way to elevate grain diet-fiber content. A good correlation between fructan and beta glucans was also discovered with obvious interest. Field trials showed that the achieved high fructan barley produced over seven folds higher fructan content than control barley and pull carbon-flux to fructan through decreasing fructan hydrolysis without disruption starch synthesis will probably not bring yield deficiency.

Fructans are easily mobile storage carbohydrate in crops. In barley (Hordeum vulgare L.), a variable amount of fructans is stored in the stem or remobilized to the grain after flowering, which might be impacted by the photosynthetic performance. The aim of this work was to analyze the connection between photosynthetic performance, fructan content and activity of genes involved in the synthesis (1-SST, sucrose:sucrose-1-fructosyltransferase and 6-SFT, sucrose:fructan-6-fructosyltransferase) and remobilization (1-FEH, fructan 1-exohydrolase) of fructans at three developmental growth stages: flowering, grain filling and ripening stage in two spring barley cultivars differing in their yield. Photosynthetic performance was assessed by using chlorophyll a fluorescence measurement expressed as total performance index (PItotal) and maximum quantum yield (Fv/Fm), fructan content was determined spectrophotometrically using resorcinol reagent and gene activity by semi-quantitative RT-PCR. The PItotal was higher in cultivar Jaran than in Astor, indicating its better photosynthetic performance. Cultivar Jaran accumulated significantly less fructans in three basal internodes compared to cultivar Astor. Such observations could be explained by concurrent synthesis and remobilization and better sink strength in cultivar Jaran due to congruent expression of genes regulating biosynthesis and fructan remobilization. On the other hand, the higher fructan content in basal internodes of cultivar Astor could possibly be the consequence of lower expression of 1-FEH gene responsible for fructan remobilization. Our results showed that fructan synthesis and remobilization to the grain are dependent on synchronized activity of regulatory genes, indicating a strong influence of photosynthetic performance and genotype.

The relationship between fructan (fructose polymer) level in early winter and overwintering ability in wheat varieties was studied by using 15 varieties and 14 lines related to pedigree of breeding. 1. The concentration of fructan in the shoot predominated over that of glucose, fructose or sucrose in all varieties or lines. Fructan concentration in stem base including leaf sheath was approximately twice as much as leaf blade, and the varieties were divided into two groups in accordance with the fructan concentration. 2. The fructan concentration was closely correlated with the overwintering ability. This result implies that this polysaccharide is influentially involved in the winter survival. 3. All the genotypes containing high fructan have a close linkage to the genotypes bred in cold regions, Turkey Red II, Hon-iku 49, Hokuriku 17, Yukichabo, F7 and Hokuriku 49, on pedigree.

Early sprouting is a main cause of onion spoilage during storage. However, limited knowledge is available on which factors trigger sprouting. Here, this was studied in the Hyfive and Exhibition cultivars, which largely differ in sprouting time. Sprouting progress was compared to the fructan and abscisic acid (ABA) profiles in the bulb scales and basal plates. Fructan concentrations decreased in the scales from harvest time onwards in the late-sprouting cultivar Hyfive, while remaining constant in the cultivar Exhibition until internal sprouting. In the basal plates, fructan concentrations increased in both cultivars from approximately one month after harvest, but reached maximum concentrations at moments that could not be related to the difference in internal sprouting. ABA levels generally decreased in the scales of both cultivars, while increasing in their basal plates. Nevertheless, for fructans, the measured variation in ABA concentrations was not consistently associated with differences in internal sprouting. A subsequent perturbation of internal sprouting by Maleic Hydrazide treatment in the cultivar Hyfive confirmed a lack of correlation. Altogether, this indicates that fructan and ABA levels in the scales and basal plate tissue change independent of internal sprouting and cannot be regarded as predictive markers for sprouting and storability.

Wholemeal flours from blends of bread wheat, emmer and spelt were processed into bread using yeast-based and sourdough fermentation. The bread wheat flour contained significantly higher concentrations of total dietary fibre and fructans than the spelt and emmer flours, the latter having the lowest contents. Breadmaking using sourdough and yeast systems resulted in changes in composition from flour to dough to bread including increases in organic acids and mannitol in the sourdough system and increases in amino acids and sugars (released by hydrolysis of proteins and starch, respectively) in both processing systems. The concentrations of fructans and raffinose (the major endogenous FODMAPs) were reduced by yeast and sourdough fermentation, with yeast having the greater effect. Both systems resulted in greater increases in sugars and glycerol in emmer than in bread wheat and spelt, but the significance of these differences for human health has not been established.

An up-close and early look at lamellar pathology characteristic of oligofructose-induced laminitis

Fructans are fructose polymers derived from sucrose and like starch are naturally present in many plants as reserve carbohydrates. The aims of this study were to determine the content of fructans in both grain and malt barley samples and to examine the relationships between fructan content and malt quality parameters such as hot water extract (HWE), apparent attenuation limit (AAL) and viscosity. The relationships between fructan content and malt quality parameters were first investigated using Pearson correlations. A positive and statistically significant (p < 0.05) correlation between fructan content and HWE (r = 0.73) and a negative and statistically significant with viscosity (r = −0.45) was found; however, there was no relationship between fructan content and AAL in the malt sample set analysed. The results from this study showed that diverse barley varieties have different fructan contents in grain and corresponding malt which may determine differences in final malt quality.

Fructans and arabinoxylans (AXs) are prebiotics naturally occurring in cereal grains which have well-known beneficial effects on human health. However, the majority of grains consumed by humans are processed prior to the consumption. The effect of baking on fructan and AX levels has been studied in rye breads, but there is a scarcity of data on the presence of fructans and AXs in wheat breads. Therefore, the aim of this study was to investigate the effect of baking on stability of fructans and total AXs in breads made from both wheat and rye flours. Bread loaves were baked using an automatic bread maker Breville BBM100 (Sydney, Australia). Sugar analysis was performed using high-performance liquid chromatography on a Dionex ICS-3000 unit. This study showed slight loss of total AXs (6–10 %) during preparation processes of leavened, yeast-free and unleavened breads. In contrast, there was 40–60 % degradation in fructan content of leavened, but no significant losses of fructans in unleavened breads. Yeast-free breads had higher contents of both fructans and AXs than leavened breads. Generally, smaller changes in the content of these prebiotics were apparent in wholemeal and rye than in white breads. It seems that differences in the structures of AXs and fructans in cereals, and the presence of yeast play significant role in determining stabilities of these components during baking.

The influence of climatic variations on fructan content in tropical regions is not well known. The present study deals with the effects of temperature on fructan contents in rhizophores of plants of Vernonia herbacea, a native species from the Brazilian cerrado vegetation. Intact plants and fragmented rhizophores were subjected to different temperatures under natural and controlled environmental conditions. Rhizophores of plants in pre-dormant stage (aerial parts showing some yellowish leaves) presented higher fructan content at 5oC than those kept at 25oC, whereas in dormant plants (aerial parts absent) temperature treatments did not affect fructan contents. Fragmented rhizophores obtained from dormant plants presented higher levels of fructo-polysaccharides at the end of the experiment than at the beginning of the treatment, regardless of the temperature they were stored, whereas fragments obtained from vegetative plants showed a decrease in fructan content under the same treatments. It was concluded that variations observed in fructan contents are related to the phenological state of the plants prior to the treatment rather than to extraneous temperatures they are subjected to during this stage.

Grain fructans play an important role in the physiology of wheat plants and also impact on the health of consumers of wheat-sbased products. Given the potential economic importance of fructan levels, if genetic variability could be identified for this trait, it may be a potentially useful breeding target for developing climate-resilient and nutritionally enhanced wheat varieties. The aim of the current study was to screen 78 genetically diverse Australian wheat varieties released between 1860 and 2015 to determine if historic breeding targets have resulted in changes in fructan levels and to identify potential breeding parents for the development of varieties with specific fructan levels. The impact of seasonal conditions on grain fructan levels were also investigated. Analysis of the varieties in this study indicated that historic breeding targets have not impacted on grain fructan levels. Fructan content in flours varied between 1.01 to 2.27%, showing some variation among the varieties. However, a significant variation in fructan levels was observed between different harvest years (mean values for 2015 and 2016 samples were 1.38 and 1.74%, respectively). While large variations in fructan contents of different varieties were not found, there were some varieties with consistently higher or lower fructan contents which could be used to breed varieties with specific fructan levels.

The non-structural dry matter content of onion bulbs consists principally of fructose, glucose, sucrose and fructans. The objective of this study was to understand the genetic basis for the wide variation observed in the relative amounts of these carbohydrates. Bulb carbohydrate composition was evaluated in progeny from crosses between high dry matter storage onion varieties and sweet, low dry matter varieties. When samples were analysed on a dry weight basis, reducing sugar and fructan content exhibited high negative correlations and bimodal segregation suggestive of the action of a major gene. A polymorphic SSR marker, ACM235, was identified which exhibited strong disequilibrium with bulb fructan content in F(2:3) families from the 'W202A' x 'Texas Grano 438' mapping population evaluated in two environments. This marker was mapped to chromosome 8 in the interspecific population 'Allium cepa x A. roylei'. Mapping in the 'Colossal Grano PVP' x 'Early Longkeeper P12' F2 population showed that a dominant major gene conditioning high-fructan content lay in the same genomic region. QTL analysis of total bulb fructan content in the intraspecific mapping population 'BYG15-23' x 'AC43' using a complete molecular marker map revealed only one significant QTL in the same chromosomal region. This locus, provisionally named Frc, may account for the major phenotypic differences in bulb carbohydrate content between storage and sweet onion varieties.

Fructans are the main soluble carbohydrate in onion (Allium cepa) bulbs and their concentrations show significant correlations with dry weights and pungency. In previous research, we identified regions on chromosomes 5 and 8 associated with higher amounts of soluble carbohydrates in onion bulbs. In this research, we estimated the genetic effects and interactions between these two chromosome regions using larger inbred families grown in field trials over 3 years. Bulbs were evaluated 30 and 90 days after harvest (DAH) for dry weights and soluble carbohydrates. Fructan concentrations decreased significantly between 30 and 90 DAH, consistent with loss of bulb dormancy over this period. Dry weights were negatively correlated with fructose and positively correlated with sucrose and fructans. Analyses of variance and interval mapping revealed that the region on chromosome 5 affected bulb dry weight, whereas the region on chromosome 8 significantly affected both dry weight and fructan concentrations. Regions on chromosomes 5 and 8 showed dominance for increased dry weights and/or soluble solids. Interactions between regions on chromosomes 5 and 8 were significant only for sucrose and the fructan neokestose, indicating that these regions independently contribute to higher amounts of soluble carbohydrates. These results demonstrate that onions with low concentrations of soluble carbohydrates were developed by selecting for relatively few recessively inherited chromosome regions.

Bulbing was studied in shallot plants cultured in vitro. Bulbing occurred under a 16 h photoperiod with fluorescent + incandescent light and 30-50 g 1(-1) sucrose in the culture medium. Exogenous gibberellin (10 microM GA3) inhibited leaf and root growth and bulbing. When added to the medium at a concentration of 10 microM, three inhibitors of gibberellin biosynthesis (ancymidol, flurprimidol and paclobutrazol) promoted bulb formation and the percentage of bulbing. When ancymidol was used in combination with GA3, it did not reverse the effect of GA3 applied alone. Under treatments with 30-70 g l(-1) sucrose, bulbing ratios greater than those found in control plants were achieved by addition of ancymidol, and bulb fresh weight was increased in the same way. Ancymidol caused a 66% decrease in sucrose content in leaf bases but greatly increased the glucose, fructose and fructan contents. The increase in fructan content by ancymidol could result from the three-fold rise in total [14C]sucrose uptake per plant from the culture medium associated with a marked increase in leaf base labelling at the expense of root labelling. The possible role of ancymidol is discussed and evidence supports a major regulatory role for gibberellins in bulbing.