Soluble Starch Synthase Activity Research Articles

Nitrogen Level Impacts the Dynamic Changes in Nitrogen Metabolism, and Carbohydrate and Anthocyanin Biosynthesis Improves the Kernel Nutritional Quality of Purple Waxy Maize

Waxy corn is a special type of maize primarily consumed as a fresh vegetable by humans. Nitrogen (N) plays an essential role in regulating the growth progression, maturation, yield, and quality of waxy maize. A reasonable N application rate is vital for boosting the accumulation of both N and carbon (C) in the grains, thereby synergistically enhancing the grain quality. However, the impact of varying N levels on the dynamic changes in N metabolism, carbohydrate formation, and anthocyanin synthesis in purple waxy corn kernels, as well as the regulatory relationships among these processes, remains unclear. To explore the effects of varying N application rates on the N metabolism, carbohydrate formation, and anthocyanin synthesis in kernels during grain filling, a two-year field experiment was carried out using the purple waxy maize variety Jinnuo20 (JN20). This study examined the different N levels, specifically 0 (N0), 120 (N1), 240 (N2), and 360 (N3) kg N ha−1. The results of the analysis revealed that, for nearly all traits measured, the N application rate of N2 was the most suitable. Compared to the N0 treatment, the accumulation and content of anthocyanins, total nitrogen, soluble sugars, amylopectin, and C/N ratio in grains increased by an average of 35.62%, 11.49%, 12.84%, 23.74%, 13.00%, and 1.87% under N2 treatment over five filling stages within two years, respectively, while the harmful compound nitrite content only increased by an average of 30.2%. Correspondingly, the activities of related enzymes also significantly increased and were maintained under N2 treatment compared to N0 treatment. Regression and correlation analysis results revealed that the amount of anthocyanin accumulation was highly positively correlated with the activities of phenylalanine ammonia-lyase (PAL) and flavanone 3-hydroxylase (F3H), but negatively correlated with anthocyanidin synthase (ANS) and UDP-glycose: flavonoid-3-O-glycosyltransferase (UFGT) activity, nitrate reductase (NR), and glutamine synthetase (GS) showed significant positive correlations with the total nitrogen content and lysine content, and a significant negative correlation with nitrite, while soluble sugars were negatively with ADP-glucose pyrophosphorylase (AGPase) activity, and amylopectin content was positively correlated with the activities of soluble starch synthase (SSS), starch branching enzyme (SBE), and starch debranching enzyme (SDBE), respectively. Furthermore, there were positive or negative correlations among the detected traits. Hence, a reasonable N application rate improves purple waxy corn kernel nutritional quality by regulating N metabolism, as well as carbohydrate and anthocyanin biosynthesis.

Response of blue light in different proportions on the growth & flowering in sunflower

Due to the light sensitivity of sunflowers, regulating spectral composition holds significant potential for optimizing sunflower growth and flowering to meet market demands. In this study, sunflower plants were exposed to white light (W200, control) and three levels of blue light (B40R80Fr80 with blue light intensity of 40 µmol m−2 s−1; B67R67Fr67 with blue light intensity of 67 µmol m−2 s−1; B100R50Fr50 with blue light intensity of 100 µmol m−2 s−1) under an overall irradiance level of 200 µmol m−2 s−1 for 60 days. The aim was to investigate the effects on sunflower morphology regulation, leaf growth, and flowering. Results demonstrated that the growth of sunflowers under B40R80Fr80 treatment with 20 % blue light inhibited plant height compared with B67R67Fr67 and B100R50Fr50 treatments. The highest total leaf dry weight was observed in sunflower leaves under the B100R50Fr50 treatment. Leaves under B67R67Fr67 treatment enhanced activities of Glyceraldehyde 3-phosphate dehydrogenase, Fructose-1,6-bisphosphate aldolase, and soluble starch synthase, along with a 10.4 % increase in Rubisco activity compared with B100R50Fr50 treatment. The sucrose and starch content under B67R67Fr67 treatment increased by 41.0 % and 19.1 % than those of B100R50Fr50 treatment, respectively. Sunflower plants under B67R67Fr67 treatment significantly improved flower disk diameter and No. of petal per flower compared with W200 treatment. Phenotype-assisted transcriptome analysis revealed that B67R67Fr67 treatment on sunflower leaves had positive effects on circadian rhythm-related genes associated with flowering [CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and FLOWERING LOCUS T (FT)], compared with B100R50Fr50 treatment. Additionally, four genes related to GA metabolism were identified for flower development regulation; LOC110884159 and LOC110890361 (GID1B) were up-regulated under B67R67Fr67 treatment. Sunflower leaves under B67R67Fr67 treatment increased GA content and induced the GA pathway related to circadian rhythm, compared with those of B100R50Fr50 treatment. Consequently, the implementation of B67R67Fr67 treatment led to improved circadian rhythm and GA pathway activation, resulting in induced flowering to fulfill market demands for sunflowers.

Unraveling the effect of drought and heat stresses on grain quality of wheat (Triticum aestivum)

Drought stress (DS) and heat stress (HS) have adverse effects on wheat (Triticum aestivum L.) growth, serving as the primary constraints that significantly limit grain yield. Present study was carried out during 2020–21 and 2021–22 at the research farm of ICAR-Indian Agricultural Research Institute, New Delhi to evaluate the effects of drought and heat stress on grain quality parameters of 4 contrasting wheat genotypes. Several physiological and biochemical parameters were analyzed in wheat cv. C306 (thermotolerant), HD3271 (thermosusceptible), H11500 (drought tolerant) and HD3226 (drought susceptible) under DS and HS. Our study found that disintegration of chlorophyll pigments was higher in wheat cv. HD3226 (43%) under combined stress. Grain weight per spike was reduced by 30% in C306 and 47.3% in HD 3271 under combined drought and heat stress treatment. All cultivars showed reduction in starch, amylose, amylopectin, AGPase and Soluble starch synthase activity under DS and HS. Additionally, a significant increase in total soluble protein and free amino acid content were observed in all genotypes under combined stress. Chlorophyll content and grain weight per spike were positively correlated with the starch, amylose, amylopectin, soluble starch synthase and AGPase activity, while negatively related to the total soluble protein and free amino acid content. The tolerant genotypes maintained higher chlorophyll content, grain weight per spike, starch, amylose, amylopectin, soluble starch synthase and AGPase activity could be used for breeding, for the adaptation to drought and heat under climate change.

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.

Effects of Rice Straw Combined with Inorganic Fertilizer on Grain Filling and Yield of Common Buckwheat

This study aims to clarify the effect of rice straw combined with inorganic fertilizer on the grain-filling characteristics and yield formation of common buckwheat (Fagopyrum esculentum Moench) and provide a scientific basis for straw fertilizer utilization and the scientific fertilization of common buckwheat in Guizhou Province.Common buckwheat ‘Fengtian1’ was field-grown and treated with no straw and no fertilization (CK), no straw with normal fertilizer (SF), full straw with 20% reduction in conventional fertilization (SH), full straw with 40% reduction in conventional fertilization (SM), full straw with 80% reduction inconventional fertilization (SL), and full straw with no fertilization (HT). The results showed that the initial growth power (R0), maximum and average grain-filling rate, and starch synthase activity of the superior grains were higher than those of the inferior grains. Compared with CK, the treatments with straw and inorganic fertilizers remarkably increased the contents of available nitrogen, available potassium, available phosphorus, and organic matter in the rhizosphere of common buckwheat. SH and SF treatments remarkablyimproved the fertilizer contribution rate and fertilizer agronomic utilization rate, promoted root growth, and enhanced the starch branching enzyme and soluble starch synthase activities of superior and inferior grains. Compared with CK, SH treatment considerably increased the number of grains per plant, grain weight per plant, 100-grain weight, and final yield. Thus, straw combined with inorganic fertilizers, particularlythe SH treatment, should be recommended as an agronomic method for promoting grain filling and increasing the yield of common buckwheat.

Physiological Biochemistry-Combined Transcriptomic Analysis Reveals Mechanism of Bacillus cereus G2 Improved Salt-Stress Tolerance of Glycyrrhiza uralensis Fisch. Seedlings by Balancing Carbohydrate Metabolism.

Salt stress severely threatens the growth and productivity of Glycyrrhiza uralensis. Previous results found that Bacillus cereus G2 enhanced several carbohydrate contents in G. uralensis under salt stress. Here, we analyzed the changes in parameters related to growth, photosynthesis, carbohydrate transformation, and the glycolysis Embden-Meyerhof-Parnas (EMP) pathway-tricarboxylic acid (TCA) cycle by G2 in G. uralensis under salt stress. Results showed that G2 helped G. uralensis-accumulating photosynthetic pigments during photosynthesis, which could further increase starch, sucrose, and fructose contents during carbohydrate transformation. Specifically, increased soluble starch synthase (SSS) activity caused to higher starch content, which could induce α-amylase (AM) and β-amylase (BM) activities; increased sucrose content due to the increase of sucrose synthase (SS) activity through upregulating the gene-encoding SS, which decreased cell osmotic potential, and consequently, induced invertase and gene-encoding α-glucosidase that decomposed sucrose to fructose, ultimately avoided further water loss; increased fructose content-required highly hexokinase (HK) activity to phosphorylate in G. uralensis, thereby providing sufficient substrate for EMP. However, G2 decreased phosphofructokinase (PFK) and pyruvate kinase (PK) activities during EMP. For inducing the TCA cycle to produce more energy, G2 increased PDH activity that enhanced CA content, which further increased isocitrate dehydrogenase (ICDH) activity and provided intermediate products for the G. uralensis TCA cycle under salt stress. In sum, G2 could improve photosynthetic efficiency and carbohydrate transformation to enhance carbohydrate products, thereby releasing more chemical energy stored in carbohydrates through the EMP pathway-TCA cycle, finally maintain normal life activities, and promote the growth of G. uralensis under salt stress.

A novel mechanism study of microplastic and As co-contamination on indica rice (Oryza sativa L.)

Although the compound pollution of microplastics and arsenic (As) in paddy soil can affect the growth and quality of rice, relevant research on this phenomenon was limited. Therefore, we combined a pot experiment with computational chemistry to explore the effects and mechanism of polystyrene (PSMP) and polytetrafluoroethylene (PTFE) microplastics on As bioavailability. PSMP and PTFE interacted with rice root exudates through van der Waals forces, approached the rice root system, inhibited root activity, reduced the relative abundance of Geobacteria and Anaeromyxobacter, and consequently reduced the iron plaques on the root surfaces. Consequently, As uptake by the rice was inhibited. PSMP and PTFE reduced the hemoglobin content by directly destroying its tertiary structure, thereby retarding rice growth. In contrast, As increased the hemoglobin content by inducing reactive oxygen species in rice. Under the influence of PSMP, PTFE, and As, the activities of soluble starch synthase and pyrophosphorylase in rice grains were inhibited, and starch accumulation decreased. Thus, PSMP, PTFE, and As reduced rice biomass and yield owing to their physiological toxicity and adverse impacts on root activity. Grain yields in soil with an As content of 86.3 mg·kg–1, 0.5% small particle-sized PSMP, and 0.5% small particle-sized PTFE decreased by 30.7%, 20.6%, and 19.4%, respectively, compared to the control. This study determined the comprehensive mechanism through which PSMP and PTFE affect As bioavailability, which is critical for managing rice biomass and low yields in As and microplastic co-contaminated soil.

Variation of carbon partitioning in newly expanded maize leaves and plant adaptive growth under extended darkness

Plants must maintain a balance between their carbon (C) supply and utilization during the day–night cycle for continuous growth since C starvation often causes irreversible damage to crop production. It is not well known how C fixation and allocation in the leaves of crops such as maize adapt to sudden environmental changes. Here, to quantify primary C fixation and partitioning in photosynthetic maize leaves under extended darkness and to relate these factors to plant growth, maize seedlings were subjected to extended darkness (ED) for three successive days at the 6th leaf fully expanded stage (V6). ED reduced plant growth and leaf chlorophyll levels but not the rate of net CO2 exchange. As a result of the reduction in photoassimilates, the accumulation of starch and total soluble carbohydrates (TSC) in mature leaves also decreased under ED. However, the percentage of the daily C fixation reserved in mature leaves increased. These transient C pools were largely composed of TSC and were mainly used for consumption by increased nocturnal respiration rather than for transport. As the days went on, both the amount of C accumulated and the percentage of the daily fixed C that was reserved in leaves decreased, which could be largely accounted for by the attenuated starch synthesis in all treatments. The activities of ADP-glucose pyrophosphorylase and soluble starch synthase decreased significantly over time. Therefore, this study concluded that both starch and TSC are involved in the coordination of the C supply and plant growth under a sudden C shortage but that they may be involved in different ways. While the ratio of reserved C to daily fixed C increased to maintain blade function under acute C starvation, both the amount and the proportion of C reserved in mature leaves decreased as plant growth continued in order to meet the growth demands of the plant.

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.

Effect of biochar on rice starch properties and starch-related gene expression and enzyme activities

We determined the effects of biochar on starch properties and the activities of enzymes and expression levels of genes related to starch in two Japonica rice cultivars. The two rice varieties were subjected to five biochar treatments (0, control; and 5, 10, 20, and 40 t/hm2). In both rice varieties, the content of apparent amylose and resistant starch were lower in biochar treatments than in the control. The proportion of fa chains was higher and that of fb3 chain was lower in the biochar treatments than in the control. Starch viscosity and cooking taste quality were improved by the biochar treatments. In both rice varieties, the activity of granule-bound starch synthase was significantly decreased by biochar treatments, and the activities of soluble starch synthase, starch branching enzyme, and starch debranching enzyme were significantly increased. The transcript levels of genes encoding starch synthases and starch branching enzymes were significantly increased by biochar treatments. We conclude that biochar at a dose of 5–10 t/hm2 can regulate the activity of starch-related enzymes, and this affects the type, content, and fine structure of starch. Therefore, the addition of biochar to soil can improve the viscosity and taste quality of rice starch.

Drought-induced disturbance of carbohydrate metabolism in anthers and male abortion of two Gossypium hirsutum cultivars differing in drought tolerance.

Cotton pollen abortion, under drought stress, was closely associated with changes in anther carbohydrate metabolism, and pollen abortion rate due to drought was higher in drought-sensitive cultivars than drought-tolerant cultivars. Cotton reproductive failure under drought stress is intrinsically connected with altered male fertility, however, studies investigating the effect of drought stress on cotton male fertility are nonexistent. Thus, a drought stress experiment was conducted with two cotton cultivars, differing in drought tolerance, to study pollen fertility and anthers' physiology. Results indicated that drought stress reduced pollen fertility of both cultivars due to decreases in anther starch and adenosine triphosphate (ATP) synthesis. Lower assimilate supply capacity in conjunction with impaired activities of ADP-glucose pyrophosphorylase and soluble starch synthase were the main reasons for the decreased starch levels in drought-stressed anthers. The decreased activities of sucrose synthetase and acid invertase were responsible for the higher sucrose level in drought-stressed anthers than well-watered anthers and the changing trend of sucrose was intensified by the decreased expressions of sucrose synthase genes (GhSusA, GhSusB, GhSusD) and acid invertase genes (GhINV1, GhINV2). However, despite sucrose degradation being limited in drought-stressed anthers, glucose level was higher in droughted anthers than well-watered ones, and that might be attributed to the down-regulated respiration since decreased anther ATP levels were detected in drought-stressed plants. Furthermore, compared to the drought-tolerant cultivar, pollen fertility was more suppressed by drought stress for the drought-sensitive cultivar, and that was attributed to the larger decrease in starch and ATP contents.

Drought limits pollen tube growth rate by altering carbohydrate metabolism in cotton (Gossypium hirsutum) pistils

It has been reported that drought stress (DS) reduces cotton yield by negatively affecting reproductive activities. Some studies have investigated the effects of DS on pollen physiology and biochemistry, but studies exploring the impact of drought on pistil biochemistry and its relationship with pollen tube growth rates in vivo are scarce. In order to investigate these objectives, a greenhouse study was conducted with a drought sensitive cotton cultivar, Yuzaomian 9110. Two water treatments were imposed at flowering stage, 1. control, where plants were irrigated with optimum quantity of water and 2. DS treatment, where plants were irrigated with 50% of the optimum quantity of water. Results indicated that stored starch content at the early stage of pollen tube growth (12:00 h) was 31.6% lower in drought-stressed pistils than control pistils, and it was highly correlated with pollen tube growth rate. The decline in starch accumulation of drought-stressed pistils could be attributed to the impeded transport of photosynthetic carbon assimilates. Moreover, decreased ADP-glucose pyrophosphorylase and soluble starch synthase activities also resulted in curtailing starch accumulation in drought-stressed pistils. Furthermore, pistil sucrose concentration was significantly higher in droughted plants relative to control plants at 12:00 and 18:00 h (during the rapid growth period), which was due to lower activities of sucrose synthase and acid invertase, and the down-regulated expressions of sucrose synthase genes, GhSusA, GhSusB and GhSusD, and acid invertase genes, GhINV1 and GhINV2, in drought-stressed pistils, limiting as a result the hydrolysis of sucrose into hexose. Drought-stressed pistils sampled at 18:00 h had lower α-amylase activity compared to control pistils, resulting in decreased starch decomposition, which, in conjunction with the decreased hydrolysis of sucrose, led to lower glucose and fructose contents in drought-stressed pistils at 18:00 h. Finally, lower pyruvate level in drought-stressed pistils could not produce enough acetyl-CoA in the tricarboxylic acid cycle to yield sufficient energy (ATP) for pollen tube growth. We conclude that DS disrupts the carbohydrate balance of pistil, reducing as a consequence carbon and energy supply for pollen tube elongation in the style, which will ultimately result in reproductive failure.

Mulching with plastic film improved the root quality of summer-sown sweet potato (Ipomoea batatas (L). Lam.) in northern China

The root quality of sweet potato cultivated during the summer season is poor in northern China; thus, this study was conducted to determine whether root quality could be improved through mulching with plastic film (MPF). The effect of MPF on root starch and its composition, the activity of starch synthesis enzymes, and other quality-related parameters were investigated in two purple flesh sweet potato cultivars, Jishu 18 and Ayamurasaki (Aya). The results indicated that root dry matter, anthocyanin content, adenosine triphosphate (ATP), and starch content were higher in both cultivars under the MPF treatment than those under the control treatment. The root adenosine diphosphate glucose pyrophosphorylase/uridine diphosphate glucose pyrophosphorylase (ADPGPPase/UDPGPPase) activity and adenosine triphosphatease (ATPase) activity were increased using MPF. However, under the MPF treatment, the amylose content, soluble sugar content, and granule-bound synthase (GBSS) activity increased in Jishu 18 but decreased in Aya, and the amylopectin content, protein content, and soluble starch synthase (SSS) activity decreased in Jishu 18 but increased in Aya. Therefore, MPF seems benifit to improve the quality of sweet potato, but the effects of this treatment condition may be dependent on the cultivar.

Acid pretreatment improves microtuberization of potato plantlets

To efficiently produce potato (Solanum tuberosum L.) microtubers, in vitro plantlets were pretreated with an acid solution before culturing in Murashige and Skoog medium supplemented with 60 g L−1 sucrose. The first tubers were formed at 36 h of acid pretreatment (AT), which was 6.2 d earlier than the untreated control. The maximum number of tubers (3.2), and highest fresh weight per tuber (282.5 mg) were also achieved with the AT. During microtuberization, the leaf dry weight of the control was higher than the AT from 1 to 5 d of culture. However, the dry weight of AT leaves increased rapidly after 5 d of culture and reached the same level as the control. The tuber dry weight in the AT was significantly higher (α = 0.05) than the control during the same culture period. Sucrose and starch content, and the enzyme activity of sucrose synthase (SS), ADP-glucose pyrophosphorylase (AGPase), and soluble starch synthase (SSS) in the AT and control exhibited a similar pattern as culture time progressed. However, levels of these biochemical indexes statistically differed (α = 0.05) between the AT and control. In addition to the sucrose content in AT, the starch content and activities of SS, AGPase, and SSS in the leaves were lower, whereas those in tubers were higher than those in the control. The present study suggests that acid pretreatment can efficiently promote microtuber formation and growth, which can be used for industrial production of potato seeds.

Waterlogging and simulated acid rain after anthesis deteriorate starch quality in wheat grain

The synthesis and accumulation of starch is greatly affected by environmental stress. Wheat grown in the downstream area of the Yangtze River is easily subjected to stress of waterlogging and acid rain. In order to probe the effect of waterlogging and acid rain on yield and starch characteristic, we used winter wheat cultivars of Yangmai 16 (more resistant) and Wennong 17 (relatively sensitive) to sole stress of acid rain or waterlogging and to their combinations during grain filling. The responses of grain yield, the physiochemical properties and morphology of starch granules in endosperm to the stresses were investigated. Compared with CT (control), grain yield in Wennong 17 were significantly decreased by both pH 4.0 acid rain and pH 2.5 acid rain, while in Yangmai 16 only by pH 2.5 acid rain. Waterlogging combined with acid rain significantly reduced grain weight and grain yield in both wheat cultivars. Acid rain, waterlogging and their combination depressed activities of ADP glucose pyrophosphorylase and soluble starch synthase (SSS) in grains of both cultivars. Acid rain and waterlogging damaged endosperm cell structure and caused abnormal starch granules. Starch granules at maturity became fragile and failed to keep in shape and some granules were even totally submerged in the protein matrix and other tissue under acid rain and waterlogging. Content of amylopectin and amylopectin/amylose ratio was also decreased, while content of amylose was increased under acid rain and waterlogging. As a result, swelling power and most viscosity parameters decreased, while the pasting temperature increased in both cultivars due to stresses. In sum, acid rain and waterlogging and their combination damaged cell structure and depressed synthesis of amylopectin, and led to the formation of abnormal fragile starch granules, and finally reduced grain weight and then yield, and deteriorated starch quality.

Analyses of starch biosynthetic protein complexes and starch properties from developing mutant rice seeds with minimal starch synthase activities

BackgroundStarch is the major component of cereal grains and is composed of essentially linear amylose and highly branched amylopectin. The properties and composition of starch determine the use and value of grains and their products. Starch synthase (SS) I, SSIIa, and SSIIIa play central roles in amylopectin biosynthesis. These three SS isozymes also affect seed development, as complete loss of both SSI and SSIIIa under reduced SSIIa activity in rice lead to sterility, whereas presence of minimal SSI or SSIIIa activity is sufficient for generating fertile seeds. SSs, branching enzymes, and/or debranching enzymes form protein complexes in cereal. However, the relationship between starch properties and the formation of protein complexes remain largely unknown. To better understand this phenomenon, properties of starch and protein complex formation were analyzed using developing mutant rice seeds (ss1L/ss2aL/ss3a) in which all three major SS activities were reduced.ResultsThe SS activity of ss1L/ss2aL/ss3a was 25%–30% that of the wild-type. However, the grain weight of ss1L/ss2aL/ss3a was 89% of the wild-type, 55% of which was starch, showing considerable starch synthesis. The reduction of soluble SS activity in ss1L/ss2aL/ss3a resulted in increased levels of ADP-glucose pyrophosphorylase and granule-bound starch synthase I, which are responsible for substrate synthesis and amylose synthesis, respectively. Together, these features led to an increase in apparent amylose content (34%) in ss1L/ss2aL/ss3a compared with wild-type (20%). Gel filtration chromatography of the soluble proteins in ss1L/ss2aL/ss3a showed that the majority of the starch biosynthetic enzymes maintained the similar elution patterns as wild-type, except that the amounts of high-molecular-weight SSI (> 300 kDa) were reduced and SSIIa of approximately 200–300 kDa were present instead of those > 440 kDa, which predominate in wild-type. Immuno-precipitation analyses suggested that the interaction between the starch biosynthetic enzymes maybe reduced or weaker than in wild-type.ConclusionsAlthough major SS isozymes were simultaneously reduced in ss1L/ss2aL/ss3a rice, active protein complexes were formed with a slightly altered pattern, suggesting that the assembly of protein complexes may be complemented among the SS isozymes. In addition, ss1L/ss2aL/ss3a maintained the ability to synthesize starch and accumulated less amylopectin and more amylose in starch.

Responses of Landoltia punctata to cobalt and nickel: Removal, growth, photosynthesis, antioxidant system and starch metabolism

Landoltia punctata has been considered as a potential bioenergy crop due to its high biomass and starch yields in different cultivations. Cobalt and nickel are known to induce starch accumulation in duckweed. We monitored the growth rate, net photosynthesis rate, total chlorophyll content, Rubisco activity, Co2+ and Ni2+ contents, activity of antioxidant enzymes, starch content and activity of related enzymes under various concentrations of cobalt and nickel. The results indicate that Co2+ and Ni2+ (≤0.5mgL−1) can facilitate growth in the beginning. Although the growth rate, net photosynthesis rate, chlorophyll content and Rubisco activity were significantly inhibited at higher concentrations (5mgL−1), the starch content increased sharply up to 53.3% dry weight (DW) in L. punctata. These results were attributed to the increase in adenosine diphosphate-glucose pyrophosphorylase (AGPase) and soluble starch synthase (SSS) activities and the decrease in α-amylase activity upon exposure to excess Co2+ and Ni2+. In addition, a substantial increase in the antioxidant enzyme activities and high flavonoid contents in L. punctata may have largely resulted in the metal tolerance. Furthermore, the high Co2+ and Ni2+ contents (2012.9±18.8 and 1997.7±29.2mgkg−1 DW) in the tissue indicate that L. punctata is a hyperaccumulator. Thus, L. punctata can be considered as a potential candidate for the simultaneous bioremediation of Co2+- and Ni2+-polluted water and high-quality biomass production.

Characteristics of starch synthesis and grain filling of common buckwheat

The common buckwheat ‘cv. Fengtian 1’ (FT1), ‘cv. Yuqiao 4’ (YQ4), ‘cv. Dingtian 2 (DT2)’, and ‘cv. Tongliao (TL)’ were selected to investigate the characteristics of starch synthesis and grain filling. The chlorophyll and chlorophyll a/b contents of leaves in the third stem showed a steady downward trend with the growth of common buckwheat. Whereas, FT1, YQ4 and DT2 showed higher chlorophyll content than that of TL at 7d and 14d. The activity of soluble starch synthase(SSS) and adenosine diphosphate glucose pyrophosphorylase (ADPGP) in the four tested varieties showed a rapid upward trend until 14 days after heading but then rapidly decreased until 21 days after heading. The average adenosine diphosphate glucose pyrophosphorylase activities of FT1, YQ4 and DT2 were higher than TL, while the average soluble starch synthase activities were similar among the four tested varieties. Consistently, the four tested varieties showed rapid accumulation of starch, amylose, and amylopectin during the prefilling stage, but no difference of starch content was found at maturity. The filling process of the four common buckwheat varieties exhibited an “S” curve. The Richards equation was utilized to evaluate the grain-filling process of common buckwheat. YQ4 showed the largest values of initial growth power (R0). The time reaching the maximum grain-filling rate (tmax.G) of FT1 was the longest, and the maximum grain-filling rate (Gmax) of DT2 was the fastest.

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.

Polyamines mediate the effect of post-anthesis soil drying on starch granule size distribution in wheat kernels

Polyamines (PAs) are important endogenous plant growth regulators responding to environmental stress and mediating many physiological processes including grain filling in cereals. This study investigated whether PAs mediate the effect of post-anthesis soil drying on starch granule size distribution, starch content, and weight of superior and inferior kernels of wheat (Triticum aestivum L.). Two wheat cultivars were grown in pots. Three treatments, well-watered (WW), moderate soil drying (MD) and severe soil drying (SD), were imposed from 9days post-anthesis until maturity. PA levels in kernels and small, medium and large granules were measured. The results showed that superior kernels had much higher free spermidine (Spd) and free spermine (Spm) concentrations, larger volumes of medium starch granules, and smaller-sized large granules than did inferior kernels under all the treatments. Compared to WW, MD significantly increased the concentrations of free Spd and free Spm, activities of soluble starch synthase and granule-bound starch synthase, volume of medium granules, and starch content and kernel weight of inferior kernels, and decreased the size of large granules. SD produced the opposite effect. Application of Spd or Spm to spikes produced effects similar to those of MD, and application of an inhibitor of Spd and Spm synthesis produced effects similar to those of SD. These results suggest that PAs mediate the effect of post-anthesis soil drying on starch biosynthesis in wheat kernels by regulating key enzymes in starch synthesis and that elevated PA levels under MD increase the volume of medium granules and kernel weight of inferior kernels.