Effects of weak-light stress during grain filling on the physicochemical properties of normal maize starch

Glycine betaine enhances tolerance of low temperature combined with low light in pepper (Capsicum annuum L.) by improving the antioxidant capacity and regulating GB metabolism

Glycine betaine (GB) is commonly used as an osmotic regulator and a donor to facilitate changes in methylation in plants and animals, thereby enhancing stress resistance. However, low temperature combined with low light stress represent the most prevalent stresses during pepper growth period in northwest China, and limited studies have focused on the potential stress-mitigating effects of GB. Therefore, to examine the regulatory mechanism of GB-induced tolerance to LL stress, pepper seedlings were pretreated with 20 mmol L-1 GB and 60 μmol L-1 3-Deazaneplanocin A hydrochloride at a temperature of 10/5 °C and illumination of 100 μmol m-2 s-1. The results demonstrated that GB significantly alleviated the detrimental effects of low temperature combined with low light stress on growth of primary and lateral roots and increased the roots absorption of mineral nutrients (N, P, Ca, Fe, and Zn). In addition, GB induced the expression of the genes for CaSOD, CaPOD, CaCAT, CaGR1, and CaDHAR, improved osmotic regulation, and increased the activities of enzymatic (superoxide dismutase, peroxidase, catalase, glutathione reductase, and dehydroascorbate reductase) and non-enzymatic antioxidants (ascorbate and glutathione). This resulted in enhanced scavenging of reactive oxygen species, thereby maintaining a balanced oxidation-reduction within the cells. Furthermore, GB substituted S-adenosylmethionine, a partial methylation donor, during the methyl group metabolism process, altering the m6A methylation level and increasing the resistance of pepper seedlings to LL stress. Overall, exogenous GB pretreatment could be used as a potential strategy for enhancing the LL tolerance of plants.

Characterization and Comparison of Structure and Physicochemical Properties of Highland Barley Starch of Different Colors

Domesticated highland barley is an important starch reserve and has differently colored grains, owing to different genotype backgrounds and cultivation environments. In this study, black, purple, blue, and yellow highland barley varieties were planted under the same cultivation conditions, and their starch distribution, structural characteristics, and physicochemical properties were analyzed. The apparent amylose content was highest in the purple variety (20.26%) and lowest in the yellow variety (18.58%). The different varieties had three subgroups and A-type crystalline structures, but the particle size and relative crystallinity (25.67-27.59%) were significantly different. In addition, the weight average molecular weight (6.72 × 107 g/mol), area ratio of APs to APL (2.88), relative crystallinity (27.59%), and 1045/1022 (0.730 cm-1) of starch were higher in yellow highland barley (YHB), forming a stable particle structure and increasing the Tp and PV of its starch. A cluster heat map showed that starches from differently colored highland barley vary in fine structure, water solubility, swelling power, and thermal and pasting properties. This study provides a reference for the high-quality breeding of colored highland barley and its utilization in food and non-food industries.

Sulfur affects multi-scale starch structures and its contribution to the cookie-baking quality of wheat subjected to shade stress

The components and structure of starch macromolecules critically determine its food-use properties. However, elemental sulfur supplementation affects the relationship between starch structure and the cookie-making quality of wheat under shaded environments remains unclear. Here, we investigated the effect of sulfur on the starch multi-scale structures and its contribution to the cookie-baking quality of wheat after pre- or post-anthesis shading. Compared with the unshaded control, shade stress decreased the amylose and total starch contents, formed smaller B-type starch granules, narrowed the molecular weight distribution, and decreased the amylopectin long-chain proportion, crystallinity, viscosity, and spread ratio of cookies. Weak-gluten cultivars are more sensitive to shade stress than strong-gluten cultivars. Under shaded environments, sulfur increased the amylopectin content, proportion of amylopectin short chains, and total starch content, increasing the mean diameter of starch granules and viscosity, ultimately decreasing the cookie hardness. The random forest model revealed that the surface area of the starch granules (18.7 %) and amylopectin B3 chain (6.7 %) contributed the most to the variation in the cookie spread ratio. Cookie hardness was determined mainly by the total starch (7.8 %), amylopectin (6.3 %), and trough viscosity (5.0 %). Our results help to design strategies for achieving superior-quality wheat in the context of global dimming.

Dynamic development of changes in multi-scale structure during grain filling affect gelatinization properties of rice starch

Rice was collected over the entire grain filling period (about 40 days) to explore the multi-structure evolution and gelatinization behavior changes of starch. During the early stage (DAA 6-14), the significant reduction in lamellar repeat distance (10.04 to 9.68 nm) and relative crystallinity (26.6 % to 22.7 %) was due to initial rapid accumulation of amylose (from 9.38 % to 14.05 %) and short amylopectin chains. Meanwhile, the decreased proportion of aggregation structure resulted in a decrease in the gelatinization temperature and a narrowed range of gelatinization temperature also indicated an increase in homogeneity as starch matured. Gelatinization enthalpy was mainly controlled by aggregation structure, which was negatively and positively related to the amylose content and the degree of order respectively. Peak viscosity of starch pasting increased and reached a maximum (924 cP) at DAA-21 due to larger granule size. Amylose and short amylopectin chains with degree of polymerization 6-12 showed positive and negative correlation with short-term retrogradation ability (setback value) respectively. The dynamics of different scale structure during grain filling had varying degrees of impact on gelatinization properties.

Effects of Low Field Temperature on the Physicochemical Properties and Fine Structure Stability of High-Quality Rice Starch during the Grain Filling Stage

The consumption of high-quality rice is increasing. Low temperatures during grain filling may affect the starch synthesis of high-quality rice and thus affect the quality of the rice itself. In this study, two high-quality conventional rice cultivars and two high-quality hybrid rice cultivars were selected and sown at a low temperature and normal temperature in the field. The low temperature during grain filling increased the amylose content, final viscosity, setback, short amylopectin chain ratio, and degree of amylopectin branching in four high-quality rice cultivars; meanwhile, the amylopectin content, gelatinization temperature, proportion of medium-long chain amylopectin, and the short-range order of starch decreased. Compared with the normal temperature, the alterations in the physicochemical and structural qualities of high-quality conventional rice cultivars YZX and NX42 were less significant at lower temperatures. The starch quality of high-quality conventional rice was more stable than hybrid high-quality rice.

Effects of soaking glutinous sorghum grains on physicochemical properties of starch

Glutinous sorghum grains were soaked (60-80 °C, 2-8 h) to explore the effects of soaking, an essential step in industrial processing of brewing, on starch. As the soaking temperature increased, the peak viscosity and crystallinity of starch gradually decreased, while the enzymatic hydrolysis rate and storage modulus first increased and then decreased. At 70 °C, the content of amylose, the enzymatic hydrolysis rate of starch, and the final viscosity first increase and then decrease with the increase of soaking time, reaching their maximum at 6 h, increased by 53.1 %, 11.0 %, and 10.4 %, respectively, as compared with the non-soaked sample. At 80 °C (4 h), the laser confocal microscopy images showed a network structure formed between the denatured protein chains and the leached-out amylose chains. The molecular weights of starch before and after soaking were all in the range of 3.82-8.98 × 107 g/mol. Since 70 °C is lower than that of starch gelatinization and protein denaturation, when soaking for 6 h, the enzymatic hydrolysis rate of starch is the highest, and the growth of miscellaneous bacteria is inhibited, which is beneficial for subsequent processing technology. The result provides a theoretical basis for the intelligent control of glutinous sorghum brewing.

The RING-Type Domain-Containing Protein GNL44 Is Essential for Grain Size and Quality in Rice (Oryza sativa L.)

Grain size in rice (Oryza sativa L.) shapes yield and quality, but the underlying molecular mechanism is not fully understood. We functionally characterized GRAIN NUMBER AND LARGE GRAIN SIZE 44 (GNL44), encoding a RING-type protein that localizes to the cytoplasm. The gnl44 mutant has fewer but enlarged grains compared to the wild type. GNL44 is mainly expressed in panicles and developing grains. Grain chalkiness was higher in the gnl44 mutant than in the wild type, short-chain amylopectin content was lower, middle-chain amylopectin content was higher, and appearance quality was worse. The amylose content and gel consistency of gnl44 were lower, and protein content was higher compared to the wild type. Rapid Visco Analyzer results showed that the texture of cooked gnl44 rice changed, and that the taste value of gnl44 was lower, making the eating and cooking quality of gnl44 worse than that of the wild type. We used gnl44, qgl3, and gs3 monogenic and two-gene near-isogenic lines to study the effects of different combinations of genes affecting grain size on rice quality-related traits. Our results revealed additive effects for these three genes on grain quality. These findings enrich the genetic resources available for rice breeders.

Transcriptome analysis reveals the mechanism of nitrogen fertilizers in starch synthesis and quality in waxy and non-waxy proso millet

Recent findings suggest that optimal application of nitrogen fertilizers can effectively improve the quality of proso millet (PM). Here, we aimed to investigate the pathways associated with starch synthesis and metabolism to elucidate the effect and molecular mechanisms of nitrogen fertilization in starch synthesis and properties in waxy and non-waxy PM varieties using transcriptomic techniques. Co-expression network analysis revealed that the regulation of starch synthesis and quality in PM by nitrogen fertilizer mainly occurred in the S2 and S3 stages during grain filling. Nitrogen fertilization inhibited glycolysis/gluconeogenesis and starch biosynthesis in grains, but increased starch degradation to maltose and dextrin and then to glucose. Moreover, nitrogen fertilization increased starch accumulation by upregulating the expression of SuS and malZ genes, thereby increasing the total starch content in grains. In contrast, nitrogen fertilization suppressed the expression of GBSS gene and decreased amylose content in PM grains, resulting in a relatively higher crystallinity, light transmittance, and breakdown viscosity in the two PM varieties. Overall, these results provided transcriptomics insights into the molecular mechanisms by which nitrogen fertilization regulates starch quality in PM, identified key genes that associated with the starch properties, and provided new insights into the quality cultivation of PM.

The potential exploitation of the Malay-red apple (Syzygium malaccense) seed as source of a phosphorylated starch

This work presents the characterization of a novel naturally phosphorylated starch extracted from an unconventional and non-utilized source, the seeds of the stone fruit Syzygium malaccense. The morphology and chemical characteristics of the extracted starch were examined by scanning electron microscopy, FTIR, 1H/13C/31P NMR and 13C-CP/MAS-NMR, HPAEC-PAD chromatography, XRD, DSC, and RVA. The extraction yielded a highly pure starch (95.6 %) with an average granule size of 13 μm. The analysis of the starch components revealed an amylose content of 28.1 % and a predominance (65 %) of B-chains (B1-B3 65 %) in the amylopectin, as shown through HPAEC-PAD chromatography. The X-ray diffractogram was compatible with B-type starch, which was confirmed by the deconvolution of the C1 peak in the 13C-CP/MAS-NMR. X-Ray diffractogram also showed that S. malaccense has 28.5 % of crystallinity. DSC analysis showed values of 82.6 °C and -12.41 J g-1 for Tc and ΔH, respectively, which is compatible with a highly ordered starch granule structure. The values observed for peak (4678 mPa•s), trough (3055 mPa•s), and final viscosity (6526 mPa•s) indicated that S. malaccense may be used as a thickener in hot food.

Strategies for starch customization: Agricultural modification

Raw starch is commonly modified to enhance its functionality for industrial applications. There is increasing demand for 'green' modified starches from both end-consumers and producers. It is well known that environmental conditions are key factors that determine plant growth and yield. An increasing number of studies suggest growth conditions can expand affect starch structure and functionality. In this review, we summarized how water, heat, high nitrogen, salinity, shading, CO2 stress affect starch biosynthesis and physicochemical properties. We define these treatments as a fifth type of starch modification method - agricultural modification - in addition to chemical, physical, enzymatic and genetic methods. In general, water stress decreases peak viscosity and gelatinization enthalpy of starch, and high temperature stress increases starch gelatinization enthalpy and temperature. High nitrogen increases total starch content and regulates starch viscosity. Salinity stress mainly regulates starch and amylose content, both of which are genotype-dependent. Shading stress and CO2 stress can both increase starch granule size, but these have different effects on amylose content and amylopectin structure. Compared with other modification methods, agricultural modification has the advantage of operating at a large scale and a low cost and can help meet the ever-rising market of clean-label foods and ingredients.

Comparison of the fine structure and physicochemical properties of proso millet (Panicum miliaceum L.) starch from different ecological regions

Field experiments were conducted to evaluate the morphology, granule size, fine structure, thermal properties, and pasting properties of starch from a waxy (139) and a non-waxy (297) varieties of proso millet grown in Yulin (YY) and Yangling (YL). Compared with the starches from the two varieties grown in YY, the starches from the two varieties grown in YL exhibited higher relative crystallinities, 1045/1022 cm-1 ratio, and amounts of amylopectin long branch chains (APL) but lower 1022/995 cm -1 ratio, amounts of amylopectin short branch chains (APs), and APs/APL ratios. Starches from YL also synthesized long branch-chain amylopectin to enhance intermolecular interactions and form a stable granular structure, which resulted in increased starch gelatinization temperature, enhanced shear resistance, and reduced setback viscosity. Starch from the waxy (139) variety has good application prospects in the food industry because of its high gelatinization temperature and light transmittance and low setback value, which can be ascribed to its extremely low amylose content, polydispersity index, high molecular weight, and dispersed molecular density. It may serve as a reference for applying proso millet starches in the food industry and developing breeding programs to improve starch quality.

Spraying exogenous hormones alleviate impact of weak-light on yield by improving leaf carbon and nitrogen metabolism in fresh waxy maize

Insufficient light during the growth periods has become one of the main factors restricting maize yield with global climate change. Exogenous hormones application is a feasible measure to alleviate abiotic stresses on crop productivity. In this study, a field trial was conducted to investigate the effects of spraying exogenous hormones on yield, dry matter (DM) and nitrogen (N) accumulation, leaf carbon and N metabolism of fresh waxy maize under weak-light stress in 2021 and 2022. Five treatments including natural light (CK), weak-light after pollination (Z), spraying water (ZP1), exogenous Phytase Q9 (ZP2) and 6-benzyladenine (ZP3) under weak-light after pollination were set up using two hybrids suyunuo5 (SYN5) and jingkenuo2000 (JKN2000). Results showed that weak-light stress significantly reduced the average fresh ear yield (49.8%), fresh grain yield (47.9%), DM (53.3%) and N accumulation (59.9%), and increased grain moisture content. The net photosynthetic rate (Pn), transpiration rate (Tr) of ear leaf after pollination decreased under Z. Furthermore, weak-light decreased the activities of RuBPCase and PEPCase, nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in ear leaves, and increased malondialdehyde (MDA) accumulation. And the decrease was greater on JKN2000. While ZP2 and ZP3 treatments increased the fresh ear yield (17.8%, 25.3%), fresh grain yield (17.2%, 29.5%), DM (35.8%, 44.6%) and N (42.5%, 52.4%) accumulation, and decreased grain moisture content compared with Z. The Pn, Tr increased under ZP2 and ZP3. Moreover, the ZP2 and ZP3 treatments improved the activities of RuBPCase, PEPCase; NR, GS, GOGAT; SOD, CAT, POD in ear leaves, and decreased MDA content during grain filling stage. The results also showed the mitigative effect of ZP3 was greater than ZP2, and the improvement effect was more significant on JKN2000.

The microstructure of the starch from the underutilized seed of jaboticaba (Plinia cauliflora)

This work presents a starch extracted from jaboticaba seeds. The extraction yielded 22.65 ± 0.63% of a slightly beige powder (a* 1.92 ± 0.03, b* 10.82 ± 0.17 and L* 92.27 ± 0.24). The starch presented low protein content (1.19% ± 0.11) and phenolic compounds (0.58 ± 0.02 GAE. g) as contaminants. The starch granules showed small, smooth, irregular shapes and sizes between 6.1 and 9.6 µm. The starch presented a high content of amylose (34.50%±0.90) and a predominance of intermediate chain length (B1-chains 51%), followed by A-chains (26%) in the amylopectin. The SEC-MALS-DRI showed the starch had a low molecular weight (5.3·106 g·mol^-1) and amylose/amylopectin content compatible with a Cc-type starch, confirmed in the X-ray diffractogram. Thermal studies showed a low onset temperature (T0 = 66.4 ± 0.46 °C) and gelatinization enthalpy (ΔH = 9.1 ± 1.19 J g^-1) but a high-temperature range (ΔT = 14.1 ± 0.52 °C). The jaboticaba starch proved to be a promising material for food and non-food applications.

Shading Stress at Different Grain Filling Stages Affects Dry Matter and Nitrogen Accumulation and Remobilization in Fresh Waxy Maize

Shading stress caused by plum rain season, which overlapped with grain filling process of fresh waxy maize in Southern China, significantly affected crop productivity. In order to investigate the effects of shading at different stages after pollination on the yield, accumulation, and remobilization of dry matter and nitrogen (N) in fresh waxy maize, field experiments were conducted, including shading at 1-7 (Z1), 8-14 (Z2), 15-21 (Z3), and 1-21 (Z4) days after pollination in 2020 and 2021. The results showed that shading reduced the fresh ear and grain yield and increased moisture content in Suyunuo5 (SYN5) and Jingkenuo2000 (JKN2000) compared to natural lighting treatment (CK). The ear yield decrease was more severe in Z4 (43.5%), followed by Z1 (29.7%). Post-silking dry matter and N accumulation and remobilization were decreased under shading stress, and those were lowest in Z4, followed by Z1. The remobilization of pre-silking dry matter and N were increased by shading stress, and the increase was highest in Z4, followed by Z1. The harvest index of dry matter and N was lowest in Z4 and second-lowest in Z1. In conclusion, shading decreased yield by affecting accumulation and remobilization of post-silking dry matter and N, and the impact was more serious when it introduced early during grain filling stage in fresh waxy maize production.

Shading affects the starch structure and digestibility of wheat by regulating the photosynthetic light response of flag leaves

Heavy haze-induced decreases in solar radiation represent an important factor that affects the structural properties of starch macromolecules. However, the relationship between the photosynthetic light response of flag leaves and the structural properties of starch remains unclear. In this study, we investigated the impact of light deprivation (60 %) during the vegetative-growth or grain-filling stage on the leaf light response, starch structure, and biscuit-baking quality of four wheat cultivars with contrasting shade tolerance. Shading decreased the apparent quantum yield and maximum net photosynthetic rate of flag leaves, resulting in a lower grain-filling rate and starch content and higher protein content. Shading decreased the starch, amylose, and small starch granule amount and swelling power but increased the larger starch granule amount. Under shade stress, the lower amylose content decreased the resistant starch content while increasing the starch digestibility and estimated glycemic index. Shading during the vegetative-growth stage increased starch crystallinity, 1045/1022 cm^-1 ratio, starch viscosity, and the biscuit spread ratio, while shading during the grain-filling stage decreased these values. Overall, this study indicated that low light affects the starch structure and biscuit spread ratio by regulating the photosynthetic light response of flag leaves.

Variation of rice starch structure and physicochemical properties in response to high natural temperature during the reproductive stage

Climate warming affects rice growth at different phenological stages, thereby increasing rice chalkiness and protein content and reducing eating and cooking quality (ECQ). The structural and physicochemical properties of rice starch played important roles in determining rice quality. However, differences in their response to high temperature during the reproductive stage have been rarely studied. In the present study, they were evaluated and compared between two contrasting natural temperature field conditions, namely, high seasonal temperature (HST) and low seasonal temperature (LST), during the reproductive stage of rice in 2017 and 2018. Compared with LST, HST significantly deteriorated rice quality, including increased grain chalkiness, setback, consistence, and pasting temperature and reduced taste values. HST considerably reduced the total starch and increased the protein content. Likewise, HST significantly reduced the short amylopectin chains [degree of polymerization (DP) <12] and increased the long amylopectin chains (DP > 12) and relative crystallinity. The starch structure, total starch content, and protein content explained 91.4%, 90.4%, and 89.2% of the total variations in pasting properties, taste value, and grain chalkiness degree, respectively. In conclusion, we suggested that rice quality variations were closely associated with the changes in chemical composition content (total starch and protein content) and starch structure in response to HST. These results indicated that we should improve the resistance of rice to high temperature during the reproductive stage to improve the fine structure of rice starch in further breeding and practice.

Low temperature and light combined stress after heading on starch fine structure and physicochemical properties of late-season indica rice with different grain quality in southern China

Late-season indica rice frequently encounters low temperature (LT) along with low light (LL) after heading in southern China, which deteriorates the grain quality by altering starch quality. However, the detailed effects on starch properties of these stressors remain unclear. Herein, two indica rice cultivars with good and poor grain quality were grown under control (CK), LT, and LT + LL conditions after heading and the structural and physicochemical properties of their starch were evaluated. Compared with CK, LT and LT + LL worsened thermal and pasting properties of starch in the two cultivars, mainly because they increased branch chain branching and A chain (DP ≤12), and decreased average branch chain length and crystallinity. Compared with LT, LT + LL deteriorated the pasting properties of the poor-quality cultivar, such as reducing breakdown (BD), final and peak viscosity, which mainly owing to decreasing the starch branching and crystallinity degrees, and increasing the small starch granules (d < 10 μm). Gelatinization enthalpy and BD both had significant and positive correlations with amylose content, the ratio of amylose and amylopectin, B3 chain and crystallinity. Taken together, these results suggest that LT and LT + LL during grain filling can deteriorate the physicochemical properties of starch in late-season indica rice cultivars by disrupting starch multilevel structure, especially upon LT + LL. In particular, while poor-quality cultivar had poorer physicochemical properties, the good-quality cultivar had poorer thermal properties under LT + LL.

Environmental Stimuli: A Major Challenge during Grain Filling in Cereals

Light, temperature, water, and fertilizer are arguably the most important environmental factors regulating crop growth and productivity. Environmental stimuli, including low light, extreme temperatures, and water stresses caused by climate change, affect crop growth and production and pose a growing threat to sustainable agriculture. Furthermore, soil salinity is another major environmental constraint affecting crop growth and threatening global food security. The grain filling stage is the final stage of growth and is also the most important stage in cereals, directly determining the grain weight and final yield. However, the grain filling process is extremely vulnerable to different environmental stimuli, especially for inferior spikelets. Given the importance of grain filling in cereals and the deterioration of environmental problems, understanding environmental stimuli and their effects on grain filling constitutes a major focus of crop research. In recent years, significant advances made in this field have led to a good description of the intricate mechanisms by which different environmental stimuli regulate grain filling, as well as approaches to adapt cereals to changing climate conditions and to give them better grain filling. In this review, the current environmental stimuli, their dose-response effect on grain filling, and the physiological and molecular mechanisms involved are discussed. Furthermore, what we can do to help cereal crops adapt to environmental stimuli is elaborated. Overall, we call for future research to delve deeper into the gene function-related research and the commercialization of gene-edited crops. Meanwhile, smart agriculture is the development trend of the future agriculture under environmental stimuli.

Starch Physicochemical Properties of Normal Maize under Different Fertilization Modes

Improving the quality with desired functions of natural starch through agronomic practice will meet the increasing need of people for natural, functional foods. A one-off application of slow-release fertilizer is a simple and efficient practice in maize production, though its influence on the starch quality is scarce. In the present study, the structural and functional properties of the starch of normal maize under two fertilization modes (one-off application of slow-release fertilizer at the sowing time (SF), and three applications of conventional fertilizer at the sowing time, and topdressing at the jointing and flowering stages (CF)) under the same fertilization level (N/P₂O₅/K₂O = 405/135/135 kg/ha) were studied using Jiangyu877 (JY877) and Suyu30 (SY30) as materials. The observed results indicate that the size of starch granules was enlarged by fertilization and the size was the largest under CF in both hybrids. The amylose content was unaffected by CF and reduced by SF in both hybrids. In comparison to no fertilizer (0F), the peak 1/peak 2 ratio was decreased by CF in both hybrids, whereas the ratio under SF was unaffected in JY877 and decreased in SY30. The amylopectin average chain-length was reduced by fertilization and the reduction was higher under CF in JY877. The relative crystallinity was increased by CF in both hybrids and the value under SF was unaffected in SY30 and increased in JY877. The peak, trough, and final viscosities of starch were increased by fertilization in both hybrids. The starch thermal characteristics in response to fertilization modes were dependent on hybrids. The retrogradation enthalpy and percentage were increased by CF in both hybrids, whereas those two parameters under SF were increased in SY30 and decreased in JY877. In conclusion, starch with similar granule size, higher peak 1/peak 2 ratio, and lower relative crystallinity was obtained under SF than under CF for both hybrids. Longer amylopectin chain-length was observed in JY877, which induced lower pasting viscosities in SY30 and lower retrogradation characteristics in JY877.

Low Light Stress Increases Chalkiness by Disturbing Starch Synthesis and Grain Filling of Rice

Low light stress increases the chalkiness of rice; however, this effect has not been fully characterized. In this study, we demonstrated that low light resulted in markedly decreased activity of ADP-glucose pyrophosphorylase in the grains and those of sucrose synthase and soluble starch synthase in the early period of grain filling. Furthermore, low light also resulted in decreased activities of granule-bound starch synthase and starch branching enzyme in the late period of grain filling. Therefore, the maximum and mean grain filling rates were reduced but the time to reach the maximum grain filling rates and effective grain filling period were increased by low light. Thus, it significantly decreased the grain weight at the maximum grain filling rate and grain weight and retarded the endosperm growth and development, leading to a loose arrangement of the amyloplasts and an increase in the chalkiness of the rice grains. Compared to the grains at the top panicle part, low light led to a greater decrease in the grain weight at the maximum grain filling rate and time to reach the grain weight at the maximum grain filling rate at the bottom panicle part, which contributed to an increase in chalkiness by increasing the rates of different chalky types at the bottom panicle part. In conclusion, low light disturbed starch synthesis in grains, thereby impeding the grain filling progress and increasing chalkiness, particularly for grains at the bottom panicle part.

Quantitative Relationship Between Solar Radiation and Grain Filling Parameters of Maize

A quantitative understanding of the factors driving changes in grain filling is essential for effective prioritization of increasing maize yield. Grain filling is a significant stage in maize yield formation. Solar radiation is the energy source for grain filling, which is the ultimate driving factor for final grain weight and grain filling capacity that determine maize yield. Here, we first confirmed the quantitative relationships between grain filling parameters and photosynthetically active radiation (PAR) by conducting field experiments using different shading and plant density conditions and cultivars in 2019 and 2020 in Xinjiang, China. The results showed that with every 100 MJ m-2 increase in PAR, the average grain filling rate (G ave), maximum grain-filling rate (G max), and the kernel weight at the time of maximum grain-filling rate (W max) increased by 0.073 mg kernel-1 day-1, 0.23 mg kernel-1 day-1, and 0.24 mg kernel-1, and the time of maximum grain-filling rate (T max) delayed by 0.91 day. Relative changes in PAR were significantly and positively correlated with relative changes in yield and G ave. With every 1% change in PAR, yield and G ave changed by 1.16 and 0.17%, respectively. From the perspective of grain filling capacity, DH618 was a more shade-resistant cultivar than XY335 and ZD958. It is urgent to breed maize cultivars with low light tolerance and high grain yield in the face of climate change, particularly the decrease in solar radiation.

Changes in chemical composition and starch structure in rice noodle cultivar influence Rapid Visco analysis and texture analysis profiles under shading

•

The pasting property of rice noodles which decreased under shade stress.

•

Pasting property is related to amylose, short chain amylopectin and crystallinity of starch.

•

Protein content and swelling factor had significant correlation with the quality of rice noodle.

GuichaoII, a rice variety with high amylose content widely used to make rice noodles, exhibits high hardness (631.07–729.43), gel consistency (8.47–9.47 mm), and hold viscosity/peak viscosity (HPV/PKV) (0.85–0.88); however, it has a low protein content (5.74–6.96%) and swelling factor (5.49–9.77). Herein, GuichaoII was subjected to low-light stress (53% reduction) during the grain filling stage. The amylose content and crystallinity of GuichaoII and the control variety Shuhui 498 decreased while the protein content, short-chain branch ratio, and degree of branching increased, which affected the ability of the rice flour to absorb water and expand during the gelatinization process. The PKV, HPV, breakdown viscosity, and final viscosity were significantly reduced, while the hardness was significantly increased, and the gel consistency and the gelatinization quality of the rice were reduced, severely limiting the processing and production of rice noodles.

Fine-tuned regulation of photosynthetic performance via γ-aminobutyric acid (GABA) supply coupled with high initial cell density culture for economic starch production in microalgae

Microalgal starch is considered as renewable and sustainable feedstock for biofuels and biorefinery. High cell density culture is favourable for photoautotrophic starch production in microalgae in the aspects of productivity and economy, but it often encounters low starch content or extra stress exposure that limits the production. This study aimed to economically enhance photosynthetic starch production from CO2 fixation in a green microalga Tetraselmis subcordiformis by regulating photosynthetic stress status with a signalling molecule γ-aminobutyric acid (GABA) combined with the application of high initial cell density culture. By increasing initial cell density (ICD) from the normal of 1.1 g L-1 (NICD) to as high as 2.8 g L-1 (HICD), the starch content, yield, and theoretical productivity were improved by 7%, 63%, and 42%, respectively. The addition of GABA under HICD resulted in 14%, 19%, and 26% of further enhancement in starch content, yield, and theoretical productivity, respectively. GABA exhibited distinct regulatory mechanisms on photosynthesis and stress status under HICD relative to NICD. GABA augmented excessive light energy absorption and electron transfer through photosystem II that reinforced the photoinhibition under NICD, while alleviated the stress reversely under HICD, both of which facilitated starch production by enabling a suitable stress status while simultaneously maintaining a sufficient photosynthetic activity. The increase of ICD and/or GABA supply particularly boosted amylopectin accumulation, leading to the changes in starch composition and was more favourable for fermentation-based biofuels production. Preliminary techno-economic analysis showed that the highest net extra benefit of 9.64 $ m-3 culture could be obtained under HICD with 2.5 mM GABA supply where high starch content (62%DW) and yield (2.5 g L-1) were achieved. The combined HICD-GABA regulation was a promising strategy for economic starch production from CO2 by microalgae for sustainable biomanufacturing.

Fertilization time of slow-release fertilizer affects the physicochemical properties of starch from spring-sown waxy maize

BACKGROUND

Slow-release fertilizer is widely used in cereal crop production because it is ecofriendly and laborsaving. Effects of different application stages (zero-, three-, and six-leaf stages, denoted as SN0, SN3, and SN6, respectively) of slow-release (N/P₂ O₅ /K₂ O = 225/75/75 kg ha^-1 ) fertilizer on physicochemical properties of starch from spring-sown waxy maize were investigated in 2018 and 2019. Application of traditional fertilizer (NCK, compound fertilizer; N/P₂ O₅ /K₂ O = 75/75/75 kg ha^-1 ) at sowing time and urea (N = 150 kg ha^-1 ) at six-leaf stage was designated as the control.

RESULTS

In comparison to the NCK, SN0 reduced grain starch content by 4.9%. Meanwhile, SN3 and SN6 did not affect this parameter. Nevertheless, all treatments, particularly SN6, increased average starch granule size. The slow-release fertilizer reduced proportion of chains with degree of polymerization (DP) > 24. Relative to NCK, SN6 increased starch crystallinity in both years, whereas SN0 and SN3 increased it in 2018 but reduced it in 2019. SN0 reduced peak, trough, and final viscosities, whereas SN3 and SN6 produced similar starch viscosities to those produced by NCK. No fertilizer mode affected gelatinization parameters, but SN6 produced a low retrogradation percentage. In comparison to data for 2018, starch produced in 2019 showed a small granule size, and a high proportion of short amylopectin chains. These properties endowed starch with high viscosity and low retrogradation percentage.

CONCLUSION

In spring-sown waxy maize production, applying slow-release fertilizer at the six-leaf stage produced starch with high viscosity and low retrogradation tendency by enlarging granule size, increasing crystallinity, and reducing the proportion of long chains. © 2021 Society of Chemical Industry.

Effects of post-silking low temperature on the physicochemical properties of waxy maize starch

Low temperature (LT) at late growth stages is an important abiotic stress that affects the grain end-use quality of summer maize. In the present work, two experiments were conducted to study the effects of LT on the structural and functional properties of starches using two waxy maize hybrids ('Suyunuo5' and 'Yunuo7'). In field trial, the plants were sown on July 1 (normal sowing date) and August 1 (late sowing date). In pot trial, the plants were sown on July 1, grown at natural environment till silking, and suffered two post-silking temperatures (normal temperature and LT were set as 28/20 and 23/15 °C, respectively). The result showed that the starch was composed of more small granules with oval polytope when sown late (August 1) or subjected to LT post-silking. The LT-stressed starch presented high proportion of short amylopectin chains and low relative crystallinity (RC). LT reduced the pasting viscosity, gelatinization enthalpy, and gelatinization temperatures but increased the retrogradation tendency. In conclusion, the low pasting viscosity and high retrogradation tendency under LT condition were caused by the decreased granule size, amylopectin chain length, and RC.

Structure and Properties of Octenyl Succinic Anhydride-Modified High-Amylose Japonica Rice Starches

Starches rich in amylose are promising functional ingredients for calory-reduced foods. In this research, a high-amylose Japonica rice starch (amylose content 33.3%) was esterified with octenyl succinic anhydride (OSA) to improve the functional properties. The OSA-modified derivatives were evaluated for structure and functional properties, with OSA-modified normal Japonica rice starch (amylose content 18.8%) used as control. Fourier transform infrared spectra confirmed the introduction of OSA groups to starch. OSA modification made little change to morphology and particle size of high-amylose starch, but decreased the relative crystallinity and pasting temperature and increased the pasting viscosity, swelling power, emulsifying stability, and resistant starch (RS) content. The changes of properties were related to the degree of substitution (DS). Typically, OSA-modified high-amylose starch at DS of 0.0285 shows polyhedral-shape granules, with a volume-average particle diameter of 8.87 μm, peak viscosity of 5730 cp, and RS content of 35.45%. OSA-modified high-amylose starch had greater peak viscosity and RS content and lower swelling power than OSA-modified normal starch of similar DS, but the two kinds of derivatives did not have a significant difference in emulsifying stability. The OSA-modified high-amylose Japonica rice starch could be used as an emulsifier, thickener, and fat replacer in food systems.

Water and heat stresses during grain formation affect the physicochemical properties of waxy maize starch

BACKGROUND

Maize is frequently subjected to simultaneous water (drought or waterlogging) and heat (HS) stresses during grain formation in southern China. This work examined the effect of high temperature combined with drought (HD) or waterlogging (HW) during grain formation on the starch physicochemical properties of two waxy maize hybrids, namely Suyunnuo5 (SYN5) and Yunuo7 (YN7).

RESULTS

Heat stress enlarged the starch granule size, and water stresses aggravated this effect. Heat stress reduced the ratio of small molecular weight fractions for both hybrids, and HD aggravated this reduction only in SYN5. Relative crystallinity in SYN5 was increased by stresses but in YN7 it was unaffected by HD, reduced by HS, and increased by HW. Fourier-transform infrared (FTIR) spectrometry results showed that the 1045/1022 cm^-1 ratio in SYN5 was not influenced by HW but was increased by other stresses, and that in YN7 it was increased by all stresses, with the highest value induced by HW. Peak viscosity was decreased, whereas gelatinization temperatures and retrogradation percentage were increased by all of these stresses. These effects were exacerbated by combined heat and water stresses. The maximum decomposition rate was severely increased by HW.

CONCLUSION

Drought or waterlogging at grain formation stage aggravated the detrimental effects of HS on the starch physicochemical properties of waxy maize. © 2020 Society of Chemical Industry.

Starch physicochemical properties of double recessive sweet-waxy maize

Sweet-waxy is a new type of maize with waxy and sugary double recessive genes. This study aims to clarify starch structural and functional properties of this maize type. Grains with sweet-waxy and waxy phenotypes were separated from an ear using the two sweet-waxy maize hybrids of ATN and NKY as materials. Compared with waxy maize starch, the sweet-waxy maize starch mainly comprises small-sized round granules despite the typical waxy character of both starches. Mw, Mn, and relative crystallinity of sweet-waxy starch were higher than those of waxy starch in both hybrids. The average chain length of waxy starch was higher in ATN but lower in NKY compared with that of sweet-waxy starch. However, polydispersity (Mw/Mn) and F1 fraction were high in sweet-waxy and waxy starches in ATN and NKY, respectively. Breakdown viscosity, gelatinization enthalpy and temperatures of both hybrids were low in sweet-waxy starch. Peak viscosity was higher in waxy starch in NKY and similar between sweet-waxy and waxy starches in ATN. Retrogradation percentage was high and low for sweet-waxy starches in ATN and NKY, respectively.

Relationship between chalkiness and the structural and thermal properties of rice starch after shading during grain-filling stage

Chalkiness is a major concern in rice production and its acceptance and is increased by shade stress. However, the relationship between rice chalkiness and the structural and thermal properties of starch is unclear. Here, we investigated the effect of shade stress on rice starch properties. The chalky grain rate and chalkiness degree significantly decreased with the amylose content, Mn, and ΔH and increased with surface area- and volume-weighted mean diameters, branching degree, ratio of 1022/995 cm^-1, and molecular weight polydispersity. Shade stress significantly increased the volume- and surface area-weighted mean diameters and Mw and decreased the amylose content, A chain proportion of amylopectin, Mn, and regularity of starch. These effects led to an increase in the molecular weight polydispersity and branching degree and a decrease in the crystallinity degree and 1045/1022 cm^-1 ratio, thereby reducing starch ΔH and uniformity. These factors contributed to increased chalkiness of rice under shade stress.

Post-Silking Shading Stress Affects Leaf Nitrogen Metabolism of Spring Maize in Southern China

Lower sunlight caused by overcast skies from June to July in Southern China is one of the main environmental stresses that frequently occur and affect the post-silking growth and grain development of spring maize. In this study, a field trial involving four maize hybrids as materials was conducted to investigate the effects of post-silking shading stress (30% and 50% light deprivation) on leaf nitrogen metabolism and biomass accumulation during maize growing seasons in 2016 and 2017. Results indicated that 30% and 50% shading stress caused the grain yield to decrease by 47.3% and 69.6%, respectively. Plant post-silking biomass accumulation was decreased by shading, whereas the translocation from pre-silking assimilates in the vegetative organs was increased by shading. This change was sharply observed when the plants were deprived of more sunlight intensity. The leaf relative chlorophyll (soil and plant analyzer development (SPAD) value) and soluble protein contents were considerably decreased by shading under 50% light deprivation condition. The activities of nitrate reductase, glutamine synthetase and glutamate synthase that are involved in nitrogen metabolism were downregulated by shading stresses. In conclusion, nitrogen metabolism was disturbed by shading, which induced the decrease in post-silking dry matter accumulation, ultimately resulting in grain yield loss.

Seasonal and diurnal patterns of non-structural carbohydrates in source and sink tissues in field maize

BACKGROUND

Carbohydrate partitioning and utilization is a key determinant of growth rate and of yield in plants and crops. There are few studies on crops in field conditions. In Arabidopsis, starch accumulation in leaves is a negative indicator of growth rate.

RESULTS

Here, we wished to establish if starch accumulation in leaves could potentially be a marker for growth rate and yield in crops such as maize. We characterized daily patterns of non-structural carbohydrate (NSC) at different growth stages over two seasons for maize hybrids in the field. In 27 commercial hybrids, we found a significant negative relationship between residual starch in leaves and plant growth, but not with final yield and biomass. We then focused on three typical hybrids and established a method for calculation of C turnover in photosynthetic leaves that took into account photosynthesis, leaf area and NSC accumulation. The ratios of stored NSC decreased from approximately 15% to less than 4% with ongoing ontogeny changes from V7 to 28 days after pollination.

CONCLUSION

The proportion rather than absolute amount of carbon partitioned to starch in leaves at all stages of development related well with yield and biomass accumulation. It is proposed that screening plants at an early vegetative growth stage such as V7 for partitioning into storage may provide a prospective method for maize hybrid selection. Our study provides the basis for further validation as a screening tool for yield.