Starch Branching Enzyme Activity Research Articles

Rheological properties of indica rice determined by starch structure related enzymatic activities during after-ripening

The processing quality of indica rice must undergo ripening after harvest to achieve stability and improvement. However, the mechanism underlying this process remains incompletely elucidated. Starch, the predominant component in indica rice, plays a crucial role in determining its properties. This study focused on analyzing the rheological properties and starch fine structure, as well as the related biosynthetic enzymes of indica rice during the after-ripening process. The results showed that after-ripened rice exhibited increased elastic modulus (G′) and viscous modulus (G″), accompanied by a decrease in the loss tangent (Tan δ), indicating an enhancement in viscoelasticity and the gel network structure. Moreover, the proportions of amylopectin super long chains (DP 37–60) decreased, while those of medium chains (DP 13–24 and DP 25–36) or short chains (DP 6–12) of amylopectin increased. Additionally, the activities of starch branching enzyme (SBE) and starch debranching enzyme (DBE) declined over the after-ripening period. Pearson correlation analysis revealed that the rheological properties of after-ripened rice were correlated with the chain length distribution (CLD) of starch, which, in turn, was associated with its related endogenous enzymes. These findings provied new insights into understanding the quality changes of after-ripened indica rice.

Grain Chalkiness Is Decreased by Balancing the Synthesis of Protein and Starch in Hybrid Indica Rice Grains under Nitrogen Fertilization.

The important reason for the commercial value of hybrid rice suffering is due to excessive chalkiness, and the biosynthesis of starch and proteins is critical for regulating chalkiness; however, it is currently unclear how the application of N fertilizer affects grains to reduce their chalkiness and improve their quality. The 2019, 2020, and 2021 trials were conducted in a split-plot design, with high and low chalky varieties as the main plot and N fertilizer rate as the split-plot. The effects of fertilization with 75, 150, and 225 kg N ha-1 on the dynamic synthesis of starch, protein, and endogenous hormones and on the amino acid of hybrid indica rice kernels with different degrees of chalkiness were investigated. Grain physiological activity was higher in low-chalky varieties than in high-chalky varieties, and these physiological parameters were strongly associated with chalkiness formation. Higher N fertilization (150 and 225 kg N ha-1) significantly reduced the proportion of chalky grains (8.93-28.02%) and chalkiness (8.61-33.99%) compared with 75 kg N ha-1. Increased N fertilization decreased the activities of granule-bound starch synthase and starch-debranching enzyme, but significantly increased adenosine diphosphate glucose pyrophosphorylase, soluble starch synthase, and starch-branching enzyme activities, synergistically improving glutamate synthetase and glutamine synthetase enzyme activities, which tended to support the synthesis of amylopectin, α-ketoglutarate, and 3-phosphoglyceric acid-derived amino acids in the endosperm cells of the grains; this favored starch and protein accumulation in the grains at 6-30 days after anthesis. Additionally, N application promoted the synthesis of endogenous hormones 1-aminocyclopropane-1-carboxylic acid, gibberellins, and abscisic acid in grains. Hence, N fertilization reduced the rice chalkiness in hybrid indica rice varieties by balancing grain protein and starch composition and enhancing some endogenous hormone synthesis.

The Response of Grain Yield and Quality of Water-Saving and Drought-Resistant Rice to Irrigation Regimes

Of all the crops, rice is the one that consumes the most water. Rice yields and quality are significantly influenced by irrigation. However, it is still unknown how different irrigation practices would affect the grain yield and quality of water-saving and drought-resistant rice. Hyou 518 (high-yielding rice variety) and Hanyou 73 (water-saving and drought-resistant rice variety) were employed as materials. Three irrigation regimes were set up in the field: conventional flooding irrigation (CF), alternate wetting and moderate soil drying irrigation (AWD), and dry cultivation (D). It was investigated how various irrigation regimes affected the two varieties’ yield and quality. The results revealed the following: 1. D considerably increased water-use efficiency while drastically reducing the yield, compared to CF and AWD. In comparison to other irrigation regimes, the grain yield and water use efficiency of Hanyou 73 enhanced synergistically under AWD treatment. 2. In contrast to CF treatment, AWD and D (especially) treatments decreased perfect rice kernel, total starch content, amylose content, amylopectin content, amylose/amylopectin, gel consistency, and breakdown, but increased green rice kernel, chalky kernel, protein content, and setback. 3. After heading, AWD and D lowered, and D treatment decreased more, the activities of ADP-glucose pyrophosphorylase (AGP), soluble starch synthase (SSS), and starch branching enzyme (SBE). AGP, SSS, and SBE were strongly inversely linked with perfect rice kernel, amylopectin content, gel consistency, and breakdown, but significantly negatively correlated with green rice kernel, chalky kernel, protein content, and setback. The results indicate that with AWD treatment, Hanyou 73 might provide a synergistic boost grain production, water-use efficiency, and quality. D treatment could significantly improve water-use efficiency. Compared with Hyou518, Hanyou 73 could maintain higher AGP, SSS, and SBE activities, head milled rice, perfect rice kernel, amylopectin content, and gel consistency under AWD and D treatment.

Response of Rice with Overlapping Growth Stages to Water Stress by Assimilates Accumulation and Transport and Starch Synthesis of Superior and Inferior Grains.

Drought stress at jointing–booting directly affects plant growth and productivity in rice. Limited by natural factors, the jointing and booting stages of short-growth-period rice varieties are highly overlapped in high-latitude areas, which are more sensitive to water deficit. However, little is known about the dry matter translocation in rice and the strategies of starch synthesis and filling of superior and inferior grains under different drought stress was unclear. In this study, the rice plants were subjected to three degrees of drought stress (−10 kPa, −25 kPa, −40 kPa) for 15 days during the jointing–booting stage; we investigated dry matter accumulation and translocation, grain filling and enzyme activities to starch synthesis of superior and inferior grains in rice with overlapping growth stages from 2016 to 2017. The results showed that drought stress significantly reduced dry matter accumulation in the stems and leaves. Mild and moderate drought increased dry matter translocation efficiency. However, severe drought stress largely limited the dry matter accumulation and translocation. A large amount of dry matter remains in vegetative organs under severe drought stress. The high content in NSC in stem and sheath plays a key role in resisting drought stress. The drought stress at jointing–booting directly caused a change in the grain filling strategy. Under moderate and severe drought, the grain-filling active period of the superior grains was shortened to complete the necessary reproductive growth. The grain-filling active period of the inferior grains was significantly prolonged to avoid a decrease in grain yield. The significant decrease in the grain-filling rate of the superior and inferior grains caused a reduction in the thousand-grain weight. In particular, the influence of the grain-filling rate of inferior grains on the thousand-grain weight was more significant. Drought stress changed the starch synthesis strategies of the superior and inferior grains. Soluble starch synthase and starch branching enzyme activities of inferior grains increased significantly under drought stress. GBSS activity was not sensitive to drought stress. Therefore, amylose content was decreased and amylopectin synthesis was enhanced under drought stress, especially in inferior grains.

Agronomic and Physicochemical Properties Facilitating the Synchronization of Grain Yield and the Overall Palatability of Japonica Rice in East China

Understanding the agronomic and physicochemical characteristics related to grain yield and grain quality is an ongoing hotspot. In 2018 and 2019, high-yielding rice with good palatability (HYGP), high-yielding rice with poor palatability (HYPP), and low-yielding rice with good palatability (LYGP) were grown in paddy fields to explore the main traits underlying the better grain yield and overall palatability of HYGP. HYGP and HYPP demonstrated a 18.1–20.7% higher grain yield (p < 0.05) than LYGP; HYGP and LYGP gave an overall palatability from 75.2 to 77.0, higher (p < 0.05) than HYPP. The higher grain yield of HYGP compared to that of LYGP resulted from a larger sink size because of the spikelets per panicle and the higher total shoot biomass weight (p < 0.05). HYGP exhibited more (p < 0.05) panicles per m2 but lower spikelets per panicle and 1000-grain weight than HYPP and maintained a similar grain yield to HYPP. Compared with HYPP and LYGP, HYGP exhibited more (p < 0.05) biomass accumulation from heading to maturity, supported by the higher leaf area index, post-heading leaf photosynthetic rate, and SPAD values. HYGP had higher (p < 0.05) adenosine diphosphate glucose pyrophosphorylase and starch branching enzyme activities at the middle and late grain-filling stages than HYPP and LYGP. HYGP and LYGP had a lower (p < 0.05) chalky area, chalky degree, amylose content, setback, grain protein content, and prolamin content than HYPP, while it had a higher (p < 0.05) gel consistency, breakdown, and ratio of glutelin content to prolamin content. Our results suggested that optimized yield components, more biomass accumulation through improved leaf photosynthetic capacities, a lower amylose content with coordinated enzyme activities involved in starch synthesis, and a lower grain protein content with a better composition were the main traits facilitating the better grain yield and overall palatability of rice in east China.

Activities of Key Enzymes Involved in Starch Accumulation In Sorghum (Sorghum Bicolor L. Moench) Grains With Different Starch Contents

Starch accumulation and the seven metabolic enzyme activities in sorghum grains with different starch contents were investigated under field conditions in Shenyang Agricultural University. The results indicated that the starch accumulation in Tieza17 (high starch content variety) and Liaoza11 (low starch content variety) grains could be fitted with logistic equation. The activities of sucrose synthase (SS), soluble starch synthase (SSS) and uridine diphosphate glucose pyrophosphorylase (UGPase) in Tieza17 were similar to those in Liaoza11. Adenosine diphosphate glucose pyrophosphorylase (AGPase) and granule-bound starch synthase (GBSS) activities in Tieza17 grains were consistently higher than those in Liaoza11 grains. Starch branching enzyme (SBE) and starch debranching enzyme (DBE) activities increased or decreased significantly between the two varieties at different filling stages. It is suggested that the differences in the activities of AGPase, GBSS, SBE and DBE and their tradeoff played an important role in regulating starch accumulation in sorghum grains. Bangladesh J. Bot. 51(2): 217-222, 2022 (June)

Effects of Early- and Late-Sowing on Starch Accumulation and Associated Enzyme Activities During Grain Filling Stage in Rice

The environmental temperature occurring during the grain filling stage is an important factor affecting starch synthesis and accumulation in rice. We investigated starch accumulation, amylase activity and starch granule size distribution in two low-amylose japonica rice varieties, Nanjing 9108 and Fujing 1606, grown in the field at different filling temperatures by manipulating sowing date. The two rice varieties exhibited similar performances between two sowing dates. Total starch, amylose and amylopectin contents were lower at the early-filling stage of T1 treatment (Early-sowing) compared with those at the same stage in T2 treatment (Late-sowing). In contrast, at the late-filling stage, when field temperatures were generally decreasing, total starch and amylopectin contents in T1 were higher compared to those in T2. The ideal temperature for strong activity of ADP-glucose pyrophosphorylase and soluble starch synthase was about 22°C. A higher temperature from the heading to maturity stages in T1 increased the activities of starch branching enzyme and suppressed the activities of granule bound starch synthetase and starch debranching enzyme. We found that rice produced larger-sized starch granules under the T1 treatment. These results suggested that due to the early-sowing date, the high temperature (30°C) occurring at the early-filling stage hindered starch synthesis and accumulation, however, the lower temperatures (22°C) at the late-filling stage allowed starch synthesis and accumulation to return to normal levels.

Partial substitution of organic nitrogen with synthetic nitrogen enhances rice yield, grain starch metabolism and related genes expression under the dual cropping system.

Improving grain filling in the presernt farming systems is crucial where grain filling is a concern due to the extreme use of chemical fertilizers (CF). A field experiment was conducted at the experimental station of Guangxi University, China in 2019 to test the hypothesis that cattle manure (CM) and poultry manure (PM) combined with CF could improve rice grain filling rate, yield, biochemical and qualitative attributes. A total of six treatments, i.e., no fertilizer (T1), 100% CF (T2), 60% CM + 40% CF (T3), 30% CM + 70% CF (T4), 60% PM + 40% CF (T5), and 30% PM + 70% CF (T6) were used in this study. Results showed that the combined treatment T6increased starch metabolizing enzymes activity (SMEs), such as ADP-glucose phosphorylase (ADGPase) by 8 and 12%, soluble starch synthase (SSS) by 7 and 10%, granule bound starch synthesis (GBSS) by 7 and 9%, and starch branching enzyme (SBE) by 14 and 21% in the early and late seasons, respectively, compared with T2. Similarly, higher rice grain yield, grain filling rate, starch, and amylose content were also recorded in combined treatments. In terms of seasons, higher activity of SMEs , grain starch, and amylose content was noted in the late-season compared to the early season. The increment in these traits was mainly attributed to a lower temperature in the late season during the grain filling period. Furthermore, our results suggested that an increment in starch accumulation and grain filling rate were mainly associated with the enhanced sink capacity by regulating key enzyme activities involved in Suc-to-starch conversion. In-addition, RT-qPCR analysis showed higher expression levels of AGPS2b, SSS1, GBSS1, and GBSE11b genes, which resultantly increased the activities of SMEs during the grain filling period under combined treatments. Linear regression analysis revealed that the activity of ADGPase, SSS, GBSS, and SBE were highly positively correlated with starch and amylose accumulation. Thus, we concluded that a combination of 30% N from PM or CM with 70% N from CF is a promising option in terms of improving rice grain yield and quality. Our study provides a sustainable fertilizer management strategy to enhance rice grain yield and quality at the lowest environmental cost.

The NAC Transcription Factors OsNAC20 and OsNAC26 Regulate Starch and Storage Protein Synthesis.

Starch and storage proteins determine the weight and quality of cereal grains. Synthesis of these two grain components has been comprehensively investigated, but the transcription factors responsible for their regulation remain largely unknown. In this study, we investigated the roles of NAM, ATAF, and CUC (NAC) transcription factors, OsNAC20, and OsNAC26 in starch and storage protein synthesis in rice (Oryza sativa) endosperm. OsNAC20 and OsNAC26 showed high levels of amino acid sequence similarity. Both were localized in the aleurone layer, starchy endosperm, and embryo. Mutation of OsNAC20 or OsNAC26 alone had no effect on the grain, while the osnac20/26 double mutant had significantly decreased starch and storage protein content. OsNAC20 and OsNAC26 alone could directly transactivate the expression of starch synthaseI (SSI), pullulanase (Pul), glutelin A1 (GluA1), glutelin B4/5 (GluB4/5), α-globulin, and 16 kD prolamin and indirectly influenced plastidial disproportionating enzyme1 (DPE1) expression to regulate starch and storage protein synthesis. Although they could also bind to the promoters of ADP-Glc pyrophosphorylase small subunit 2b (AGPS2b), ADP-Glc pyrophosphorylase large subunit 2 (AGPL2), and starch branching enzymeI (SBEI), and the expression of the three genes was largely decreased in the osnac20/26 mutant, ADP-Glc pyrophosphorylase and starch branching enzyme activities were unchanged in this double mutant. In addition, OsNAC20 and OsNAC26 are main regulators of Pul, GluB4, α-globulin, and 16 kD prolamin In conclusion, OsNAC20 and OsNAC26 play an essential and redundant role in the regulation of starch and storage protein synthesis.

Dynamics of starch synthesis enzymes and their relationship with chalkiness of early indica rice under different postanthesis temperature regimes

An experiment on an early indica rice cv. ‘Shenyou9576’ was conducted in the Key Laboratory of Phytohormones and Growth Development of Hunan Agricultural University, Changsha, Hunan, PR China in 2014 to investigate the influence of varying post-anthesis temperatures on chalkiness rate, head rice rate, and on major 6 starch synthesis enzymes i.e., SuSy (EC 1.9.3.1), ADPG-Ppas (EC 2.7.7.27), SSS (EC 2.4.1.21) and GBSS, (EC 2.4.1.21), SBE (EC 2.4.1.18) and SDBE (EC 3.2.1.70). The treatments comprised of three temperature regimes which are designated as the high (35/28oC- day/night), low (25/20oC- day/night) and natural condition (35/25oC-day/night) as the control. Under high temperature maximum chalkiness rate was 61.11% and minimum was 22.59% under low temperature treatment. The lowest head rice rate was 42.76% under high temperature treatment followed by 49.91% in the control, while the highest rate was 62.33% under low temperature treatment. Maximum grain filling rate (Gmax) was found highest (1.69 mg/day) in the high temperature and average grain filling rate (Gavg) was found highest (1.36 mg/day) under the control. The activity of SuSy, ADPG-Ppase, SSS and GBSS were decreased gradually from 14 to 35 days after flowering (DAF). Irrespective of the treatments, an increasing trend of ADPG-Ppase activity was observed from 7 to 14 DAF and then declined. Correlation between the chalkiness and the enzymes activity of SuSy, ADPG-Ppase and SSS were significantly negative at 21, 28 and 35 DAFs, i.e., higher activity of SuSy, ADPG-Ppase and SSS at the mid-late to the late caryopsis development stage mediated by low temperature treatment played an important role for the reduction of chalkiness. The correlation between GBSS activity and chalkiness was significantly negative and stronger at 14, 21 and 28 DAF indicating that GBSS played a cardinal role to reduce chalkiness in the mid to mid-late stage of rice grain development. Significantly negative correlation was found between starch branching enzyme (SBE) and chalkiness at 21, 28 and 35 DAF, i.e., the higher SBE activity under low temperature treatment at the later grain filling stage also had a positive role in reduction of chalkiness.
 Bangladesh J. Agril. Res. 44(2): 223-238, June 2019

Heat stress-reduced kernel weight in rice at anthesis is associated with impaired source-sink relationship and sugars allocation

Heat stress is one of the most limiting factors in rice plant growth and development. However, the impairment in the whole-plant carbohydrate partitioning at anthesis caused by heat stress is seldom documented. Two rice genotypes with different heat tolerance, namely Nipponbare (NIPP) and its high-temperature susceptible (HTS) mutant were subjected to heat stress of 40 °C for 12 d at anthesis. Heat stress significantly decreased the spikelet fertility and kernel weight, and a larger decline was found in HTS than in NIPP plants compared with their respective controls. However, there was no significant difference in photosynthesis in flag leaf and starch branching enzyme activity in grain between the control and heat-stress groups. Thus, heat stress-induced decline in kernel weight was most likely due to the inhibition of the assimilate distribution rather than the limitation of the source and sink. This assumption was confirmed by the distribution of dry mater weight, nonstructural carbohydrates (NSC) and starch in grain, leaf and sheath-stem observed under heat stress. Indeed, the sucrose transporter (SUT) genes, sucrose synthase (SUS) genes and phytohormones in grain and the callose deposition in plasmodesmata of leaf and sheath were involved in the process. However, the patterns of change in phytohormones in leaf and sheath-stem were different from those of carbohydrates, but exogenous sucrose alleviated the heat-stress effect on the spikelet fertility, kernel weight, dry matter weight accumulation and allocation. Thus, sugars rather than phytohormones might act as a signal molecule to mediate the source-sink relationship in rice under heat stress.

Low Nitrogen Application Enhances Starch-Metabolizing Enzyme Activity and Improves Accumulation and Translocation of Non-structural Carbohydrates in Rice Stems.

More than 4 billion inhabitants in Asia depend on rice for 35–60% of the calories consumed in their diets, but new rice cultivars frequently do not reach expected yields because of poor rice grain filling. Here, we quantified the activities of enzymes involved in starch metabolization in rice to investigate the mechanisms regulating the accumulation and translocation of stem non-structural carbohydrates (NSC) under different levels of nitrogen fertilizer application. A pot experiment was conducted using two rice cultivars, Liangyoupeijiu (LYPJ) and Shanyou63 (SY63), under high and low nitrogen applications. Compared with high nitrogen application (HN), low nitrogen application (LN) increased stem NSC concentration before the heading stage and NSC translocation during the grain filling stage; concomitantly, LN significantly shortened the active grain filling period and increased the grain filling rate in superior spikelets. Compared with the LYPJ cultivar, SY63 exhibited a higher grain weight, higher grain filling percentage, and higher stem NSC concentration before heading and greater NSC translocation after heading. During the period between panicle initiation and heading, the activities of adenosine diphosphate-glucose pyrophosphorylase (AGP), starch synthase (StS), and starch branching enzyme (SBE), all enzymes involved in starch synthesis, increased under the LN treatment and positively correlated with increases in stem NSC. During grain filling, the activities of enzymes involved in starch-to-sucrose conversion [α-amylase, β-amylase, and sucrose phosphate synthase (SPS)] increased under the LN treatment and positively correlated with stem NSC remobilization. Overall, the investigated enzymes exhibited higher activities in SY63 than in LYPJ. Our results suggest that low nitrogen increases the activities of AGP, StS, SBE, α-amylase, β-amylase, and SPS, leading to increased accumulation and remobilization of stem starch and NSC in SY63. We conclude that calculated reductions in nitrogen application and the choice of an appropriate cultivar may improve rice grain yields via enhanced stem NSC accumulation and translocation, thereby reducing the costs and increasing the sustainability of rice production.

Effects of open-field warming during grain-filling stage on grain quality of two japonica rice cultivars in lower reaches of Yangtze River delta

To evaluate the actual and comprehensive response of rice grain quality to global warming in lower reaches of Yangtze River delta, a 3-year open-field warming experiment was conducted with two japonica rice cultivars using Free-air temperature enhancement (FATE) facility. Ningjing3 and Wuyunjing24 were planted under two temperature regimes (NT: natural temperature; ET: elevated temperature) during grain-filling. FATE facility increased rice canopy temperature by 2.7 °C (daytime 1.5 °C/nighttime 3.9 °C), 2.0 °C (daytime 1.6 °C/nighttime 2.5 °C) and 3.4 °C (daytime 2.0 °C/nighttime 4.9 °C) in 2012, 2013 and 2014, respectively. Compared with NT, head rice rate, occurrence of perfect grains, amylose content, setback and consistency were decreased by ET, while occurrence of chalky grains, breakdown, cool paste viscosity, pasting temperature were increased under ET. Response of different chalky types to warming were unstable among cultivars and years. Based on Wu-Gilbert model, we found that the relative activity of starch branching enzyme (SBE) to starch synthase (SS) was decreased by ET, which may contribute to longer average amylopectin chain length. ET increased protein content of rice grain but performed no influence on the relative proportion of amino acids. These results revealed that low-amplitude warming during grain-filling could deteriorate rice milling, appearance and cooking quality, but improved its nutritional quality.

Starch accumulation in hulless barley during grain filling

BackgroundStarch consists of two types of molecules: amylose and amylopectin. The objective of this study was increase understanding about mechanisms related to starch accumulation in hulless barley (Hordeum vulgare L.) grain by measuring temporal changes in (i) grain amylose and amylopectin content, (ii) starch synthase activity, and (iii) the relative expressions of key starch-related genes.ResultsThe amylopectin/amylose ratio gradually declined in both Beiqing 6 and Kunlun 12. In both cultivars, the activities of adenosine diphosphate glucose pyrophosphorylase, soluble starch synthase (SSS), granule bound starch synthase (GBSS), and starch branching enzyme (SBE) increased steadily during grain filling, reaching their maximums 20–25 days after anthesis. The activities of SSS and SBE were greater in Ganken 5 than in either Beiqing 6 or Kunlun 12. The expression of GBSS I was greater in Beiqing 6 and Kunlun 12 than in Ganken 5. In contrast, the expression of SSSI, SSSII and SBEI was greater in Ganken 5 than in Beiqing 6 and Kunlun 12. The peak in GBSSI expression was later than that of SSSI, SSSII, SBEIIa and SBEIIb. The GBSSI transcript in Kunlun 12 was expressed on average 90 times more than the GBSSII transcript.ConclusionsThe results suggest that SBE and SSS may control starch synthesis at the transcriptional level, whereas GBSSI may control starch synthesis at the post transcriptional level. GBSSI is mainly responsible for amylose synthesis whereas SSSI and SBEII are mainly responsible for amylopectin synthesis in amyloplasts.

Abscisic Acid-Induced Starch Accumulation in Bioenergy Crop Duckweed Spirodela polyrrhiza

Spirodela polyrrhiza, a fast-growing duckweed with high starch and low lignin content, shows promise as a feedstock for bioenergy. Abscisic acid (ABA) is a biological hormone that controls plant growth and stress response. The effects of different ABA concentrations (0, 1.0 × 10−5, 1.0 × 10−4, 1.0 × 10−3, 1.0 × 10−2, and 1.0 × 10−1 mg/L) on duckweed biomass growth, carbon dioxide fixation, formation of photosynthetic pigments (Chlorophyll a (Chla), Chlorophyll b (Chlb), and carotenoids), the activities of soluble starch synthase (SSS) and starch branching enzyme (SBE), and the starch content of biomass were investigated in this study. ABA at concentrations lower than 1.0 × 10−3 mg/L promoted carbon dioxide fixation, whereas it inhibited carbon dioxide fixation at concentrations over 1.0 × 10−3 mg/L. ABA enhanced SSS and SBE activities at concentrations lower than 1.0 × 10−2 mg/L. ABA treatment increased the content of Chla, Chlb, and carotenoids and resulted in the enhancement of starch content. Chla content gradually increased with the increasing concentration of ABA (1.0 × 10−5 to 1.0 × 10−2 mg/L). After culturing for 10 days, starch content in 1.0 × 10−2 mg/L ABA medium reached 35.3% of dry weight (DW), which was the highest level in this study. This suggests that there is a great potential to develop a technology to increase starch accumulation in duckweed which can be used as an alternative to corn, sugarcane, or other food crops as a starch source.

Biochemical analysis of new type mutants of japonica rice that accumulate water‐soluble α‐glucans in the endosperm but retain full starch debranching enzyme activities

Amylopectin has a highly regulated branched structure called cluster structure, which causes the glucan to be hydrophobic and to form a semicrystalline architecture of starch granules. It is known that lesions of the isoamylase1 (ISA1) gene result in accumulation of a water‐soluble glucan (WSG) called phytoglycogen instead of amylopectin in various plant species. This type of cereal mutant is referred to as sugary‐1 and accumulates a large amount of phytoglycogen in the endosperm. In this study, another WSG‐synthesizing mutant has been isolated from japonica rice. This mutant accumulated a significant amount of WSG in the center of endosperm. No significant changes were found in activities of ISA and pullulanase and in the compositions of ISA1 homomer and ISA1‐ISA2 heteromer. In addition, activities of starch branching enzyme and starch synthase isoforms were not altered. The accumulated WSG had a specific fine structure, that differed from that of phytoglycogen. Thus, we designated this new mutant as the sugary‐2 mutant. Our study results strongly suggest that the Sugary‐2 gene product plays an important role in amylopectin synthesis of rice endosperm and identifies a new factor that controls the normal amylopectin structure, especially at the early developmental stage of the endosperm.

Progress in controlling starch structure by modifying starch-branching enzymes.

This paper reviews the progress of development of plants with desirable starch structure by modifying starch branching enzymes. Starch-branching enzyme (SBE) is responsible for the creation of branches during starch biosynthesis in plastids, and is a major determinant of the final fine structure and physical properties of the starch. Multiple isoforms of SBE have been found in plants, with each playing a different role in amylopectin synthesis. Different methods have been used to develop desirable starch structures by modifying the SBE activity. These can involve changing its expression level (either up-regulation or down-regulation), genetically modifying the activity of the SBE itself, and varying the length of its transferred chains. Changing the activity and the transferred chain length of SBE has been less studied than changing the expression level of SBE in vivo. This article reviews and summarizes new tools for developing plants producing the next generation of starches.

Comparison of amylopectin structure and activities of key starch synthesis enzymes in the grains of rice single-segment substitution lines with different Wx alleles

The Wx gene is the major gene controlling amylose synthesis in rice endosperm. So far, the Wx gene can be mainly classified into five common alleles, wx, Wx t, Wx g1, Wx g2, and Wx g3, according to their amylose phenotypes. Besides, the Wx allelic variation was also found to play an important role in regulating other physicochemical properties of rice starch. However, the specific physiological and starch structural mechanisms are not clear yet. With a set of single-segment substitution lines harboring five different Wx alleles, the genotype differences in amylopectin structure and dynamic changes of activities of key starch synthesis enzymes were investigated. The distinct Wx genotype difference in chain length distribution of amylopectin was confirmed by size exclusion chromatography. There were clear allelic differences in activities of starch synthesis enzymes during grain filling. The Wx allelic variation had the highest impact on the activities of starch branching enzyme, followed by pullulanase, and soluble starch synthase, while no influence on isoamylase activity. Differences in structural features of amylopectin and mean enzyme activities during grain filling period correlated well with most of the variations in starch property traits. These findings indicate that the Wx allelic variation may affect starch structure and physicochemical properties through selectively influencing activities of starch synthesis enzymes in developing rice grains. The present results will contribute to our understanding of the regulation of starch biosynthesis in rice endosperm.

Changes in Carbohydrate Accumulation and Activities of Enzymes Involved in Starch Synthesis in Maize Kernels at Different Positions on an Ear during Grain Filling

Kernels at the upper position of a maize ear usually show slower filling rate and lower weight than those at the basal and middle positions. The mechanism is little understood. The objective of this study was to understand if changes in carbohydrate accumulation and activities of the enzymes involved in starch synthesis in the kernels at different positions on a maize ear were associated with grain filling. A maize cultivar Denghai 11 was planted in spring and summer. Contents of the soluble sugar,sucrose and starch and the activities of the adenosine diphosphoglucose pyrophosphorylase(AGPase),starch synthase(St S),and starch branching enzyme(SBE) in kernels at different positions on an ear and their relationships with grain filling rate were determined. The results showed that kernel number per ear,100-kernel weight,and grain yield were more or higher for the spring maize than for the summer maize. Although the grain yield was different between the spring maize and the summer maize,the maximum kernel filling rate,mean kernel filling rate,100-kernel weight,the contents of both soluble sugar and sucrose in kernels,the maximum starch accumulation rate and mean starch accumulation rate in kernels all exhibited an order of basal position middle position upper position. The activities of AGPase,St S,and SBE in kernels at different positions on an ear showed the changes of single peak curves,and the peak and mean enzymatic activities in kernels at the upper position were significantly lower than those at both middle and basal positions. The starch accumulation rate and kernel filling rate were very significantly and positively correlated with activities of AGPase,St S,and SBE in kernels. The results suggested that a smaller starch accumulation rate and lower weight for the kernels at the upper position on a maize ear are mainly attributed to lower activities of the enzymes involved in starch synthesis in these kernels. A higher kernel weight for the spring maize is closely associated with its stronger ability of starch synthesis in the kernels.

Effects of Elevated Ozone Concentration on Starch and Starch Synthesis Enzymes of Yangmai 16 Under Fully Open-Air Field Conditions

O3 is not only greenhouse gas but also a primary gaseous contaminant in the atmosphere. It has long-lasting effects on crop growth, yield and quality, and brings a series of ecological and environmental problems. A free-air controlled enrichment (FACE) system was applied to study the effect of elevated ozone concentration on activities of key enzymes of starch synthesis of Yangmai 16 in 2009-2010. The main-plot treatment had two levels of O3: ambient level (A-O3) and 50% higher than ambient level (E-O3). The main results were that accumulation rate of amylose, amylopectin and starch were represented in a single peak curve, and their content and accumulation amount rose gradually. The O3 elevation decreased the accumulation rate of amylose, amylopectin and starch amylase, reduced the accumulation amount of amylopectin and starch, and decreased the content of amylopectin and starch, but increased the content of amylose. With the increase of O3 concentration, the enzyme activity of grain granule-bound starch synthase (GBSS), soluble starch synthase (SSS) and starch branching enzyme (SBE) decreased after anthesis. The activities of GBSS and SSS had highly significant correlations with amylose, amylopectin and starch accumulation rate, and the activity of SBE had significant correlations with these items. So the O3 elevation decreased the activity of key enzymes of starch synthesis, which led to the variation of starch synthesis.