Starch Synthesis In Grains Research Articles

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.

Abscisic acid synergizes with sucrose to enhance grain yield and quality of rice by improving the source-sink relationship

BackgroundAbscisic acid (ABA) and sucrose act as molecular signals in response to abiotic stress. However, how their synergy regulates the source-sink relationship has rarely been studied. This study aimed to reveal the mechanism underlying the synergy between ABA and sucrose on assimilates allocation to improve grain yield and quality of rice. The early indica rice cultivar Zhefu802 was selected and planted in an artificial climate chamber at 32/24 °C (day/night) under natural sunlight conditions. Sucrose and ABA were exogenously sprayed (either alone or in combination) onto rice plants at flowering and 10 days after flowering.ResultsABA plus sucrose significantly improved both the grain yield and quality of rice, which was mainly a result of the higher proportion of dry matter accumulation and non-structural carbohydrates in panicles. These results were mainly ascribed to the large improvement in sucrose transport in the sheath-stems in response to the ABA plus sucrose treatment. In this process, ABA plus sucrose significantly enhanced the contents of starch, gibberellic acids, and zeatin ribosides as well as the activities and gene expression of enzymes involved in starch synthesis in grains. Additionally, remarkable increases in trehalose content and expression levels of trehalose-6-phosphate synthase1, trehalose-6-phosphate phosphatase7, and sucrose non-fermenting related protein kinase 1A were also found in grains treated with ABA plus sucrose.ConclusionThe synergy between ABA and sucrose increased grain yield and quality by improving the source-sink relationship through sucrose and trehalose metabolism in grains.

Approach and mechanism in enhancing the remobilization of assimilates and grain-filling in rice and wheat

Monocarpic plants such as rice and wheat need to initiate the whole plant senescence before their pre-stored assimilates can be remobilized for the grain filling. However, plant senescence and photosynthesis are a pair of trade-off processes. How to coordinate plant senescence, photosynthesis, and remobilization of assimilates is a long-term unsolved problem in cereals. Solving this problem would have great significance in not only understanding the mechanism of the remobilization of assimilates to grain and grain-filling but also effectively coping with the poor remobilization of assimilates from vegetative tissues to grain and slow grain-filling for some cultivars or under the condition of heavy use of nitrogen in the current rice and wheat production systems. This paper reviewed crop management and physiological mechanism in enhancing the remobilization of assimilates to grain and grain-filling in rice and wheat. There are three important findings. (i) Moderate soil-drying (MSD) during post-anthesis can regulate the relationship of plant senescence, photosynthesis, and remobilization of assimilates, and accelerate grain-filing. With post-anthesis MSD, plant can rehydrate overnight but not severely inhibit leaf photosynthesis at day time. More importantly, it can timely and appropriately initiate the process of plant senescence, trigger assimilate remobilization from vegetative tissues to grain, accelerate grain-filling, especially for the late-flowering inferior caryopses, and lead to increases in grain yield, harvest index, and water use efficiency. The MSD therefore provides a new way to coordinate the relationship among plant senescence, photosynthesis, and remobilization of assimilates during grain-filling and to achieve the dual goal of increasing grain yield and saving water in cereals. (ii) Abscisic acid (ABA) and its interaction with ethylene and gibberellins (GAs) regulate assimilate remobilization and grain-filling. During the active grain-filling period, the filling of grain requires a higher level of endogenous ABA and higher ratios of ABA to ethylene and to GAs. Post-anthesis MDS enhances the remobilization of assimilates to grain and grain-filling through increases in ABA levels and the ratios of ABA to ethylene and/or to GAs, which reveals the mechanism in which plant hormones regulate assimilate remobilization and grain-filling, and provides a physiological regulation to improve grain-filling in cereals. (iii) A modest increase in ABA level in plants can enhance activities of the key enzymes involved in carbon metabolism, and thereby increase assimilate loading and unloading capacity. An elevated ABA level through MSD or applying ABA with a low concentration can increase activities of the key enzymes in starch or fructan degradation and sucrose synthesis in vegetative tissues, leading to the enhancement in assimilate loading capacity, and enhance activities of the key enzymes in sucrose-to-starch conversion in the sink organ, and consequently, increase assimilate unloading capacity and starch synthesis in grain, which reveals the mechanism in which ABA regulates assimilate remobilization and grain-filling. Further research is needed to understand the molecular mechanism, such as from the aspect of signal transduction, in which assimilate remobilization and grain filling are regulated in cereals, to investigate the regulatory mechanism underlying nitrogen remobilization from vegetative tissues to grain, and to elucidate the mechanism in which the MSD reduces spikelet degeneration and improves grain quality of cereals.

Effects of Low Light on Agronomic and Physiological Characteristics of Rice Including Grain Yield and Quality

Light intensity is one of the most important environmental factors that determine the basic characteristics of rice development. However, continuously cloudy weather or rainfall, especially during the grain-filling stage, induces a significant loss in yield and results in poor grain quality. Stress caused by low light often creates severe meteorological disasters in some rice-growing regions worldwide. This review was based on our previous research and related research regarding the effects of low light on rice growth, yield and quality as well as the formation of grain, and mainly reviewed the physiological metabolism of rice plants, including characteristics of photosynthesis, activities of antioxidant enzymes in rice leaves and key enzymes involved in starch synthesis in grains, as well as the translocations of carbohydrate and nitrogen. These characteristics include various grain yield and rice quality components (milling and appearance as well as cooking, eating and nutritional qualities) under different rates of shading imposed at the vegetative or reproductive stages of rice plants. Furthermore, we discussed why grain yield and quality are reduced under the low light environment. Next, we summarized the need for future research that emphasizes methods can effectively improve rice grain yield and quality under low light stress. These research findings can provide a beneficial reference for rice cultivation management and breeding program in low light environments.

Activities of key enzymes involved in starch synthesis in grains of wheat under different irrigation patterns

SUMMARYIt is generally accepted that sucrose phosphate synthase (SPS), sucrose synthase (SuSy), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS), granule-bound starch synthase (GBSS) and starch branching enzyme (SBE) play a key role in starch synthesis in wheat grains. Starch synthesis in wheat grains is influenced by genotype and environment. However, what is not known is the degree of variation in enzyme activities during starch accumulation of wheat cultivars field-grown in different water regimes. The present study was undertaken to determine whether irrigation patterns could cause differences in starch accumulation and activities of key enzymes involved in starch synthesis. Starch accumulation and related enzyme activities were investigated in two winter wheat varieties, JM20 and BY535, differing in grain starch content, under two irrigation patterns. Results showed that soil water deficit led to an increase at early grain filling and decrease during late grain filling in starch accumulation rate (SAR) and activities of key enzymes involved in starch synthesis, especially AGPase, SSS and SBE. Water deficit enhanced grain starch accumulation in two wheat cultivars, suggesting that rainfed treatments increase physiological activities during early grain filling and promote starch accumulation. Furthermore, the change of SAR is consistent with SuSy, AGPase, SSS and GBSS. The results suggest that these enzymes play a key role in starch synthesis, and the decrease of photosynthate produced in the source organ is not the factor inhibiting starch accumulation.

Characteristics of Starch Synthesis in Grains and Translocation of Car-bohydrate in Leaves and Sheaths at Filling Stage for Low Phytic Acid Mutant Rice

Characteristics of Starch Synthesis in Grains and Translocation of Car-bohydrate in Leaves and Sheaths at Filling Stage for Low Phytic Acid Mutant Rice

Modeling plant carbon flow and grain starch accumulation in wheat

The process of starch accumulation in grain directly influences the yield and quality formation in wheat. Since few studies have been aimed at modeling the grain starch accumulation, this study was undertaken to develop a simplified process model for predicting the rate of starch accumulation in wheat grain by focusing on the variation of plant carbon dynamics post-anthesis. Five different experiments involving genotypes, nitrogen rates and water regimes were conducted to support model development and model evaluation. The model proposed that the starch accumulation rate (STR) in individual grain was determined by the availability of carbon source in plant (GCA i ) and the ability of starch synthesis in grain ( f( A i )), as influenced by the factors of temperature, water and nitrogen conditions within plants. The f( A i ) could be described in a two-section curve with post-anthesis growing degree days (GDD), first exponential increase and then linear decrease. The GCA i was determined by post-anthesis carbon assimilation and carbon remobilization from vegetative organs to grains. A genotypic parameter was incorporated into the model algorithm, i.e. the maximum rate of individual grain starch accumulation, to differentiate the ability of starch accumulation among cultivars. The overall performance of the model was validated with different data sets from three field experiments spanning 3 years and comprising various genotypes, nitrogen and water levels. The RMSE values for all treatments were averaged as 12.51%, indicating a good fit between the simulated and observed data. It appears that the model can give a reliable prediction for grain starch accumulation of different wheat cultivars under various growing conditions.

Activities of key enzymes for starch synthesis in relation to growth of superior and inferior grains on winter wheat (Triticum aestivum L.) spike

Weight of individual grains is a major yield component in wheat. The non-uniform distribution of single grain weight on a wheat spike is assumed to be closely associated with starch synthesis in grains. The present study was undertaken to determine if the enzymes involved in starch synthesis cause the differences in single grain weight between superior and inferior grains on a wheat spike. Using two high-yield winter wheat (Triticum aestivum L.) varieties differing in grain weight and three nitrogen rates for one variety, the contents of amylose and amylopectin, and activities of enzymes involved in starch synthesis in both superior and inferior grains were investigated during the entire period of grain filling. Superior grains showed generally higher starch accumulation rates and activities of enzymes including SS (sucrose synthase), UDPGPPase (UDP-glucose pyrophosphorylase), ADPGPPase (ADP-glucose pyrophosphorylase), SSS (soluble starch synthase) and GBSS (starch granule bound starch synthase) and subsequently produced much higher single grain weight than inferior grains. Nitrogen increased enzyme activities and starch accumulation rates, and thus improved individual grain weight, especially for inferior grains. The SS, ADPGPPase and SSS were significantly correlated to amylopectin accumulation, while SS, ADPGPPase, SSS and GBSS were significantly correlated to amylose accumulation. This infers that SS, ADPGPPase and starch synthase play key roles in regulating starch accumulation and grain weight in superior and inferior grains on a wheat spike.

Starch synthesis by isolated amyloplasts from wheat endosperm

The aim of this work was to discover which compound(s) cross the amyloplast envelope to supply the carbon for starch synthesis in grains of Triticum aestivum L. Amyloplasts were isolated, on a continuous gradient of Nycodenz, from lysates of protoplasts of endosperm of developing grains, and then incubated in solutions of (14)C-labelled: glucose, glucose 1-phosphate, glucose 6-phosphate, fructose 6-phosphate, fructose-1,6-bisphosphate, dihydroxyacetone phosphate and glycerol 3-phosphate. Only glucose 1-phosphate gave appreciable labelling of starch that was dependent upon the integrity of the amyloplasts. Incorporation into starch was linear with respect to time for 2 h. At the end of the incubations, 98% of the (14)C in the soluble fraction of the incubation mixture was recovered as [(14)C]glucose 1-phosphate. Thus it is unlikely that the added [(14)C glucose 1-phosphate was extensively metabolized prior to uptake by the amyloplasts. It is argued that the behaviour of the isolated amyloplasts, and previously published data on the labelling of starch by [(13)C]glucose, are consistent with the view that in wheat grains it is a C-6, not a C-3, compound that enters the amyloplast to provide the carbon for starch synthesis.