Evolution of amylopectin structure in developing wheat endosperm starch

Periodic changes in chain lengths distribution parameters of wheat starch during endosperm development

This study analyzed the molecular structure of developing wheat endosperm starch at different stages after anthesis (DAA) using chain length distribution analysis by size exclusion chromatography (SEC) and fluorophore-assisted carbohydrate electrophoresis. Our results revealed periodic changes in the content of both amylose and amylopectin fractions. Specifically, the content of amylose chains with a degree of polymerization (DP) > 100 significantly decreased from 5 to 10 DAA (28% to 21%) and from 15 to 20 DAA (29% to 26%), but increased between 10 and 15 DAA (21% to 29%) and 20 to 25 DAA (30.0% to 33%). Conversely, the content of short amylopectin chains with DP ≤ 32 showed the opposite trend. Interestingly, mRNA expression levels of key starch biosynthesis genes did not exhibit periodic changes. These findings contribute to our understanding of starch biosynthesis and provide important insights for the development of starch-based products.

Variation in Wheat Quality and Starch Structure under Granary Conditions during Long-Term Storage

As a globally distributed cereal, wheat is an essential part of the daily human dietary structure. Various changes in nutrient composition and starch structure can reflect the quality of wheat. In this study, we carried out a series of measurements to reveal the levels of wheat quality during long-term storage. We found that the deterioration of wheat was apparent after two years of storage: (1) the content of fatty acid increased from 12.47% to 29.02%; (2) the malondialdehyde content increased to 37.46%; (3) the conductivity significantly increased from 35.71% to 46.79%; and (4) other indexes, such as the amylopectin content, peak viscosity, and disintegration rate, increased noticeably during storage. Moreover, SEM images revealed a certain degree of damage on the surface of starch granules, and an X-ray diffraction (XRD) analysis showed A-type crystalline starch of wheat. Additionally, FTIR spectra suggested that the ratio of amylose and amylopectin decreased with a decreasing content of amylose and increasing content of amylopectin. The ratio of amylose and amylopectin can lead to variations in wheat machining characteristics. Therefore, wheat should be kept at an average of 20 °C with safe water content for less than two years to maintain reasonable quality.

Expression Pattern of Starch Biosynthesis Genes in Relation to the Starch Molecular Structure in High-Amylose Maize

The molecular structure and the expression levels of starch biosynthesis-related genes of three types of high-amylose maize (HAM) genotypes and one normal maize (NM) genotype at 5-35 days after pollination (DAP) were studied. Size exclusion chromatography (SEC) analysis showed that the molecular size of amylopectin molecules in NM increased from 5 to 35 DAP and the amylose content in HAM genotypes increased from 15 to 35 DAP. Correlation analysis for both NM and HAMs combined showed that SBEIIb and ISAII were negatively correlated with the contents of amylose and long amylopectin chains (DP > 30) and positively correlated with the content of short amylopectin chains (DP ≤ 31) and the molecular size of amylopectin molecules. Correlation analysis for only the HAMs showed that amylose content was negatively correlated with SBEI and SSIIa. In both correlation analyses, SSIIa showed a negative correlation with the average chain lengths of amylose chains.

Amylopectin Chain Length Dynamics and Activity Signatures of Key Carbon Metabolic Enzymes Highlight Early Maturation as Culprit for Yield Reduction of Barley Endosperm Starch after Heat Stress

Abiotic environmental stresses have a negative impact on the yield and quality of crops. Understanding these stresses is an essential enabler for mitigating breeding strategies and it becomes more important as the frequency of extreme weather conditions increases due to climate change. This study analyses the response of barley (Hordeum vulgare L.) to a heat wave during grain filling in three distinct stages: the heat wave itself, the return to a normal temperature regime, and the process of maturation and desiccation. The properties and structure of the starch produced were followed throughout the maturational stages. Furthermore, the key enzymes involved in the carbohydrate supply to the grain were monitored. We observed differences in starch structure with well-separated effects because of heat stress and during senescence. Heat stress produced marked effects on sucrolytic enzymes in source and sink tissues. Early cessation of plant development as an indirect consequence of the heat wave was identified as the major contributor to final yield loss from the stress, highlighting the importance for functional stay-green traits for the development of heat-resistant cereals.

Understanding Starch Structure: Recent Progress

Starch is a major food supply for humanity. It is produced in seeds, rhizomes, roots and tubers in the form of semi-crystalline granules with unique properties for each plant. Though the size and morphology of the granules is specific for each plant species, their internal structures have remarkably similar architecture, consisting of growth rings, blocklets, and crystalline and amorphous lamellae. The basic components of starch granules are two polyglucans, namely amylose and amylopectin. The molecular structure of amylose is comparatively simple as it consists of glucose residues connected through α-(1,4)-linkages to long chains with a few α-(1,6)-branches. Amylopectin, which is the major component, has the same basic structure, but it has considerably shorter chains and a lot of α-(1,6)-branches. This results in a very complex, three-dimensional structure, the nature of which remains uncertain. Several models of the amylopectin structure have been suggested through the years, and in this review two models are described, namely the “cluster model” and the “building block backbone model”. The structure of the starch granules is discussed in light of both models.

Crystal structures of Escherichia coli branching enzyme in complex with cyclodextrins

Branching enzyme (BE) is responsible for the third step in glycogen/starch biosynthesis. It catalyzes the cleavage of α-1,4 glucan linkages and subsequent reattachment to form α-1,6 branch points. These branches are crucial to the final structure of glycogen and starch. The crystal structures of Escherichia coli BE (EcBE) in complex with α-, β- and γ-cyclodextrin were determined in order to better understand substrate binding. Four cyclodextrin-binding sites were identified in EcBE; they were all located on the surface of the enzyme, with none in the vicinity of the active site. While three of the sites were also identified as linear polysaccharide-binding sites, one of the sites is specific for cyclodextrins. In previous work three additional binding sites were identified as exclusively binding linear malto-oligosaccharides. Comparison of the binding sites shed light on this apparent specificity. Binding site IV is located in the carbohydrate-binding module 48 (CBM48) domain of EcBE and superimposes with the cyclodextrin-binding site found in the CBM48 domain of 5'-AMP-activated protein kinase (AMPK). Comparison of these sites shows the similarities and differences in the two binding modes. While some of the binding sites were found to be conserved between branching enzymes of different organisms, some are quite divergent, indicating both similarities and differences between oligosaccharide binding in branching enzymes from various sources.

Diurnal changes in Sorghum leaf starch molecular structure

Control of the fine structure of transitory starch synthesized during the day in leaves is required for its normal degradation during the subsequent night. In this study, the molecular structure of transitory starch from Sorghum leaves over the diurnal cycle was characterized using size-exclusion chromatography. This is the first study of diurnal changes in the chain-length distribution (CLD) of amylopectin and amylose over the entire range of chain lengths, and in the size distribution of whole starch molecules. It was found that the outer layers of leaf starch granules, which were synthesized during the daytime and degraded during the night, contained more large molecules, including amylopectin with more short chains and more branching, than those in the inner layers. The outer layers also had lower amylose content. Starch molecular sizes in leaves are much smaller than in grain starch. The starch structures observed are likely to give optimal energy control during plant growth. Lack of this control may contribute to poor plant growth.

Starch structure in developing barley endosperm

Barley spikes of the cultivars/breeding lines Gustav, Karmosé and SLU 7 were harvested at 9, 12 and 24 days after flowering in order to study starch structure in developing barley endosperm. Kernel dry weight, starch content and amylose content increased during development. Structural analysis was performed on whole starch and included the chain-length distribution of the whole starches and their β-limit dextrins. Karmosé, possessing the amo1 mutation, had higher amylose content and a lower proportion of long chains (DP ≥38) in the amylopectin component than SLU 7 and Gustav. Structural differences during endosperm development were seen as a decrease in molar proportion of chains of DP 22-37 in whole starch. In β-limit dextrins, the proportion of Bfp-chains (DP 4-7) increased and the proportion of BSmajor-chains (DP 15-27) decreased during development, suggesting more frequent activity of starch branching enzymes at later stages of maturation, resulting in amylopectin with denser structure.

Structure of Arabidopsis leaf starch is markedly altered following nocturnal degradation

Little is known about the thermal properties and internal molecular structure of transitory starch. In this study, granule morphology, thermal properties, and the cluster structure of Arabidopsis leaf starch at beginning and end of the light period were explored. The structural properties of building blocks and clusters were evaluated by using diverse chromatographic techniques. On the granular level, starch from end of day had larger granule size, thinner crystalline lamellae thickness, lower free surface energy of crystals, and lower tendency to retrograde than that from end of night. On the molecular level, the starch had lower amylose content, larger cluster size, and higher number of blocks per cluster at the end of day than at end of night. It is concluded that the core of the granules contains a more permanent molecular and less-ordered physical structure different from the transitory layers laid down around the core at daytime.