Effect of high temperature on grain filling period, yield, amylose content and activity of starch biosynthesis enzymes in endosperm of basmati rice

Effects of high temperature during two growth stages on caryopsis development and physicochemical properties of starch in rice

Global warming may affect the development of rice at different growth stages, thereby decreasing rice yield and deteriorating grain quality. The difference in rice responses to high temperature during primordial differentiation (PD) and pollen filling (PF) stages has been rarely studied. In this paper, two temperature treatments (40 °C and 30 °C) at the two stages (PD and PF) were imposed to four rice groups under the controlled temperature chambers. Compared with rice under normal temperature, high temperature-stressed rice showed accelerated growth rate, smaller caryopsis and decreased yield. Moreover, high temperature affected the starch physicochemical properties, resulting in lower apparent amylose content and higher order degree, gelatinization temperatures, and thereby increased peak, trough and final viscosities in starch. High temperature during PD stage inhibited cell development and starch deposition, thus leading to small starch granule and low retrogradation. However, temperature-stressed rice during PF stage showed increased starch accumulation and larger granule size. Therefore, effects of high temperature during the two stages on caryopsis development and starch properties were partly similar but also notably different. These results enriched and deepened the study of high temperature-stressed rice and served as an important reference for the processing and utilization of rice starch in food industry.

Improvement and stabilization of rice production by delaying sowing date in irrigated rice system in central China

BACKGROUND

Climate change has posed great challenges to rice production. Temperature and solar radiation show significant variations in central China. This study aims to analyze the responses of different rice genotypes to the variations of temperature and solar radiation in central China, and to find the way of identifying the optimal sowing date to improve and stabilize rice production. For this end, four rice genotypes (two Indica and two Japonica cultivars) were cultivated at two locations under irrigation conditions in 2 years with six sowing dates.

RESULTS

We investigated variations of rice grain yield, resource use efficiency, average daily temperature and solar radiation during different phenological stages. Rice grain yield could increase by about 2-17% in central China. Compared with solar radiation, temperature was a more important factor affecting rice grain yield in central China. The grain yield showed great correlation with the means temperature during different phenological stages, especially during the first 20 days after heading (GT20). Besides our results demonstrated that the grain yield displayed slender variations when the GT20 was within 24.9-26.4 °C. However, GT20 was higher than 26.4 °C in most cases, which became more frequent due to climate changes. Analysis of climate change during the last 25 years revealed that the frequency of GT20 within 24.9-26.4 °C was increased by the delay of sowing date.

CONCLUSION

We propose that delaying sowing date to achieve the optimal GT20 (24.9 °C-26.4 °C) can be an effective strategy to stabilize and improve rice grain yield and resource use efficiency in central China. © 2019 Society of Chemical Industry.

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

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

Biochemical composition distribution in different grain layers is associated with the edible quality of rice cultivars

Clarifying the association of differences in endosperm biochemical composition with nutrient and edible quality can guide rice breeding and cultivation. In this study, very-low-amylose-content (LAC), Japanese good-taste (JTC), Northeast China good-taste (CTC), and Northeast China high-yield (CHC) cultivars were milled to obtain four layers (L1-L4) from outside-in, and then analyzed for apparent amylose content (AAC), protein content (PC), amino acids, soluble sugars, and minerals. The association of these compositions and Rapid-Visco analysis values with taste was also examined. LAC had low AAC, high amino acid and mineral content, and the highest taste value. Taste was significantly affected by AAC and soluble sugar in L3, and by PC in the L2 layer. High levels of amino acid in L2 and L3 improved the taste, as did Mg, P, and Ca in L1. On the whole, starch factors had the highest contribution to taste, followed by minerals, amino acids, and PC.

Anthocyanin Accumulation in Black Kernel Mutant Rice and its Contribution to ROS Detoxification in Response to High Temperature at the Filling Stage

Effect of high temperature (HT) on anthocyanin (ANS) accumulation and its relationship with reactive oxygen species (ROS) generation in color rice kernel was investigated by using a black kernel mutant (9311bk) and its wildtype (WT). 9311bk showed strikingly higher ANS content in the kernel than WT. Just like the starch accumulation in rice kernels, ANS accumulation in the 9311bk kernel increased progressively along with kernel development, with the highest level of ANS at kernel maturity. HT exposure evidently decreased ANS accumulation in 9311bk kernel, but it increased ROS and MDA concentrations. The extent of HT-induced decline in kernel starch accumulation was genotype-dependent, which was much larger for WT than 9311bk. Under HT exposure, 9311bk had a relatively lower increase in ROS and MDA contents than its WT. This occurrence was just opposite to the genotype-dependent alteration in the activities of antioxidant enzymes (SOD, CAT and APX) in response to HT exposure, suggesting more efficiently ROS detoxification and relatively stronger heat tolerance for 9311bk than its WT. Hence, the extent of HT-induced declines in grain weight and kernel starch content was much smaller for 9311bk relative to its WT. HT exposure suppressed the transcripts of OsCHS, OsF3’H, OsDFR and OsANS and impaired the ANS biosynthesis in rice kernel, which was strongly responsible for HT-induced decline in the accumulation of ANS, C3G, and P3G in 9311bk kernels. These results could provide valuable information to cope with global warming and achieving high quality for color rice production.

The interaction between amylose and amylopectin synthesis in rice endosperm grown at high temperature

Starch is the abundant component in rice endosperm, and its microstructure determines the quality and functional properties of rice grain. It is well known that the starch fine structure is markedly influenced by high temperature during grain filling. However, it is poorly understood on the competition among starch synthesis related enzymes as well as the interaction between amylose and amylopectin biosynthesis under increased growing temperature. In this study, the non-waxy and waxy rice were planted under normal and high temperatures. Parameterizing analysis of the starch microstructure using mathematical models proved that amylose synthesis competed with the elongation of long amylopectin chains (DP＞60); Short chains of amylopectin can be used as the substrate for elongation of longer amylopectin chains; High temperature eliminated the consistency and regularity of the synthesis of amylose and amylopectin. In addition, enzyme assay proved the validity of fitting results from mathematical modeling analysis of starch.

Effects of high temperature on the fine structure of starch during the grain-filling stages in rice: mathematical modeling and integrated enzymatic analysis

BACKGROUND

High temperature during the grain-filling stage is an important factor that can affect grain quality by altering the composition and structure of starch in rice. Therefore, it is important to study the regulatory mechanism of high temperature on rice starch biosynthesis.

RESULTS

Two japonica cultivars, the waxy rice Taihunuo and non-waxy Nangeng 5055 were used to examine the effect of high temperature on the fine structure of starch during the grain-filling stage. Analysis of starch chain length distribution indicated that exposure to a high temperature increased the content of starch with medium-long chains and decreased the starch with short chains in both rice varieties. The differences of amylopectin synthesis responding to high temperature between waxy and non-waxy rice can shed light on the interactions of amylose and amylopectin synthesis under high temperature conditions. In the non-waxy variety, the amylose biosynthesis may affect the short and medium-long amylopectin biosynthesis under high temperature. A mathematical fitting model was used to interpret the fine structure of amylopectin and a series of parameters with enzymatical significance (β and γ) were obtained. The fitting results showed that the waxy and non-waxy rice had similar responses to high temperature. The variations of the parameter response to high temperature was more remarkable in Taihunuo. Activity analysis of starch synthesis-related enzymes during the grain-filling stage demonstrated the reliability of model fitting results.

CONCLUSION

The influences of high temperature on the fine structure of starch are similar between waxy and non-waxy rice. Amylose biosynthesis may affect amylopectin biosynthesis under high temperature. © 2018 Society of Chemical Industry.

Concurrent Drought and Temperature Stress in Rice-A Possible Result of the Predicted Climate Change: Effects on Yield Attributes, Eating Characteristics, and Health Promoting Compounds

Despite the likely increasing co-occurrence of drought and heat stress, not least in equatorial regions, due to climate change, little is known about the combinational effect of these stresses on rice productivity and quality. This study evaluated the impact of simultaneous drought and temperature stress on growth, grain yield, and quality characteristics of seven rice cultivars from Rwanda, grown in climate chambers. Two temperature ranges—23/26 °C night/day and 27/30 °C night/day—together with single or repeated drought treatments, were applied during various plant developmental stages. Plant development and yield were highly influenced by drought, while genotype impacted the quality characteristics. The combination of a high temperature with drought at the seedling and tillering stages resulted in zero panicles for all evaluated cultivars. The cultivar ‘Intsindagirabigega’ was most tolerant to drought, while ‘Zong geng’ was the most sensitive. A “stress memory” was recorded for ‘Mpembuke’ and ‘Ndamirabahinzi’, and these cultivars also had a high content of bioactive compounds, while ’Jyambere’ showed a high total protein content. Thus, climate change may severely impact rice production. The exploitation of genetic diversity to breed novel rice cultivars that combine drought and heat stress tolerance with high nutritional values is a must to maintain food security.

Amino acid content in rice grains is affected by high temperature during the early grain-filling period

Amino acid content in grains is an important nutritional quality trait in rice. High temperature can affect rice quality by accelerating grain filling. However, there is limited information available on the influence of high temperature on amino acid content in rice grains, especially under natural conditions. In this study, grain-filling traits and amino acid content in the grain of two rice cultivars (Luliangyou 996 and Lingliangyou 268) were compared between two years (2016 and 2017) with contrasting temperatures during the early grain-filling period under field conditions. Average daily mean temperature during the period of 0–5 days after full heading in 2016 (30.1 °C) was 5.4 °C higher than that in 2017. Initial, maximum, and mean grain-filling rates were 42–307% higher in 2016 than in 2017 for Luliangyou 996 and Lingliangyou 268. The time taken to reach the maximum grain-filling rate and active grain-filling duration were 6.3–10.7 d shorter in 2016 compared to 2017 for Luliangyou 996 and Lingliangyou 268. Grain weight was equal to or significantly higher in 2016 than in 2017 for Luliangyou 996 and Lingliangyou 268. N accumulation and N content in the grain were significantly lower in 2016 than in 2017 for both cultivars. The grain contents of all detected amino acids, except for methionine in Luliangyou 996, were significantly lower in 2016 than in 2017. Our study suggests that high temperature during the early grain-filling period can result in an accelerated grain-filling process, reduced N accumulation and content in rice grains, and consequently reduced amino acid content in the grain.

Mechanism Underlying Heat Stability of the Rice Endosperm Cytosolic ADP-Glucose Pyrophosphorylase

Rice grains accumulate starch as their major storage reserve whose biosynthesis is sensitive to heat. ADP-glucose pyrophosphorylase (AGPase) is among the starch biosynthetic enzymes severely affected by heat stress during seed maturation. To increase the heat tolerance of the rice enzyme, we engineered two dominant AGPase subunits expressed in developing endosperm, the large (L2) and small (S2b) subunits of the cytosol-specific AGPase. Bacterial expression of the rice S2b with the rice L2, potato tuber LS (pLS), or with the mosaic rice-potato large subunits, L2-pLS and pLS-L2, produced heat-sensitive recombinant enzymes, which retained less than 10% of their enzyme activities after 5 min incubation at 55°C. However, assembly of the rice L2 with the potato tuber SS (pSS) showed significantly increased heat stability comparable to the heat-stable potato pLS/pSS. The S2b assembled with the mosaic L2-pLS subunit showed 3-fold higher sensitivity to 3-PGA than L2/S2b, whereas the counterpart mosaic pLS-L2/S2b showed 225-fold lower sensitivity. Introduction of a QTC motif into S2b created an N-terminal disulfide linkage that was cleaved by dithiothreitol reduction. The QTC enzyme showed moderate heat stability but was not as stable as the potato AGPase. While the QTC AGPase exhibited approximately fourfold increase in 3-PGA sensitivity, its substrate affinities were largely unchanged. Random mutagenesis of S2b^QTC produced six mutant lines with elevated production of glycogen in bacteria. All six lines contained a L379F substitution, which conferred enhanced glycogen production in bacteria and increased heat stability. Modeled structure of this mutant enzyme revealed that this highly conserved leucine residue is located in the enzyme's regulatory pocket that provides interaction sites for activators and inhibitors. Our molecular dynamic simulation analysis suggests that introduction of the QTC motif and the L379F mutation improves enzyme heat stability by stabilizing their backbone structures possibly due to the increased number of H-bonds between the small subunits and increased intermolecular interactions between the two SSs and two LSs at elevated temperature.

Heat stress during grain filling affects activities of enzymes involved in grain protein and starch synthesis in waxy maize

High temperature (temperature over 35 °C) is an extremely important environmental factor that affects the maize grain quality in Southern China. The effects of heat stress after pollination on grain protein and starch deposition and activities of involved enzymes were studied in a pot trail in 2014 and 2015. Results showed that grain dry weight reductions at maturity were 19.8% and 19.1%, whereas starch contents (mg g⁻¹) were reduced by 3.0% and 3.3%, and starch accumulation (mg grain⁻¹) were reduced 22.2% and 21.8% in 2014 and 2015, respectively. Protein content was decreased by heat stress before 15 DAP and increased thereafter. At maturity, protein contents (mg g⁻¹) were increased by 24.5% and 25.3% in 2014 and 2015, while protein accumulation (mg grain⁻¹) were not affected by heat stress. In response to heat stress, glutamate synthase activity was enhanced by 29.1–82.9% in 2014 and 2.0–141.8% in 2015, whereas glutamine synthetase activity was reduced by 1.9–43.5% in 2014 and 0.1–27.4% in 2015 throughout the grain filling. The activities of sucrose phosphate synthase were decreased by heat stress at 10–25DAP (12.7–32.0%) in 2014 and 15–20 DAP (23.2–27.5%) in 2015, and activities of sucrose synthase were decreased by heat stress at 5–15 DAP (20.0–45.0%) in 2014 and 15 DAP (22.0%) in 2015, repectively. The activities of enyzmes that involved in starch synthessis were all suppressed by heat stress during grain filling, and the reduction of adenosine diphosphate-glucose pyrophosphorylase, soluble starch synthase, and starch branching enzyme were decreased by 21.3–43.1%, 19.1–29.2%, and 7.0–45.6% in 2014 and 1.8–78.5%, 21.4–51.2%, and 11.0–48.0% in 2015, respectively. Conclusively, grain weight and starch deposition were suppressed by heat stress due to the decreased activities of enzymes involved in starch synthesis, and the increased protein content was due to the enhanced activity of glutamate synthase.

Quantitative iTRAQ-based proteomic analysis of rice grains to assess high night temperature stress

Rice yield and quality are adversely affected by increasing global surface temperature, and are strongly attributed to high night temperature (HNT) than high daytime temperature. However, the molecular mechanism underlying the heat‐tolerant characteristics of rice remains unclear. In the present study, we compared the proteomes of heat‐tolerant and ‐sensitive lines of rice at early milky stage using an iTRAQ method. We have identified 38 differentially expressed proteins between the two lines, of which 32 proteins have been functionally annotated in NCBI and/or the UniProt database. These proteins were then classified into seven functional subgroups, which include signal transduction, transcript regulation, oxidation, defense response, transport, energy metabolism, and biosynthesis. Further analysis indicated that HNT stress could disrupt the redox equilibrium of plant cells, which in turn triggers the calcium‐dependent protein kinase and COP9 signalosome, thereby regulating downstream genes/proteins that are involved in the HNT response. The candidate proteins may provide genetic resources for the improvement of heat‐tolerant characteristics in rice, and the proposed model for signal transduction and transcriptional regulation may facilitate in the elucidation of the molecular mechanism underlying the response to HNT stress in rice.

High temperature stress during flowering and grain filling offsets beneficial impact of elevated CO2 on assimilate partitioning and sink-strength in rice

Elevated [CO2] (e[CO2]) environments have been predicted to improve rice yields under future climate. However, a concomitant rise in temperature could negate e[CO2] impact on plants, presenting a serious challenge for crop improvement. High temperature (HT) stress tolerant NL-44 and high yielding basmati Pusa 1121 rice cultivars, were exposed to e[CO2] (from panicle initiation to maturity) and a combination of e[CO2] + HT (from heading to maturity) using field based open top chambers. Elevated [CO2] significantly increased photosynthesis, seed-set, panicle weight and grain weight across both cultivars, more prominently with Pusa 1121. Conversely, e[CO2] + HT during flowering and early grain filling significantly reduced seed-set and 1000 grain weight, respectively. Averaged across both the cultivars, grain yield was reduced by 18 to 29%. Despite highly positive response with e[CO2], Pusa 1121 exposure to e[CO2] + HT led to significant reduction in seed-set and sink starch metabolism enzymatic activity. Interestingly, NL-44 maintained higher seed-set and resilience with starch metabolism enzymes under e[CO2] + HT exposure. Developing rice cultivars with higher [CO2] responsiveness incorporated with increased tolerance to high temperatures during flowering and grain filling using donors such as NL-44, will minimize the negative impact of heat stress and increase global food productivity, benefiting from [CO2] rich environments.

Pickering emulsifiers based on hydrophobically modified small granular starches - Part I: Manufacturing and physico-chemical characterization

Small granular starches from rice, quinoa and amaranth were hydrophobized by esterification with octenyl succinic anhydride (OSA) in an aqueous alkaline slurry to obtain series of modified starches at defined intervals (i.e. 0.6, 1.2, 1.8, 2.4, 3.0%). The physical and the physico-chemical properties of the starch particles were characterized by proximate analysis including protein level, amylose level and dry matter. The shape and size of the starch granules were characterized by scanning electron microscopy and light scattering. The gelatinization properties were characterized by differential scanning calorimetry. The degree of modification was determined by titration with NaOH. With regard to the emulsion formulation and in order to assess the emulsifying capacity of the small granular starches, the effect of starch type, degree of modification and starch concentration on the resulting emulsion droplet size were evaluated by light scattering and optical microscopy. Emulsifying properties were found to depend on the degree of substitution, size of the granules and the starch to oil ratio of the formulation. Quinoa starch granules, in general, had the best emulsifying capacity followed by amaranth and rice. However, in higher starch concentrations (>400mg/mL oil) and adequate levels of OSA (3.0%) amaranth performed best, having the smallest size of starches studied.

Effects of short-term high temperature on grain quality and starch granules of rice (Oryza sativa L.) at post-anthesis stage

High temperature causes negative effects on grain yield and quality of rice (Oryza sativa L.). In this study, the effects of short-term high temperature (SHT) on grain quality and starch granules were investigated in two rice cultivars Nanjing 41 (NJ41, heat-sensitive) and Wuxiangjing 14 (WJ14, heat-tolerant) at post-anthesis stage (anthesis and early grain-filling stage). The results of rice quality analysis showed that chalky rate and chalkiness increased while brown rice rate, milled rice rate, and head rice rate decreased in two rice cultivars with the increase of high temperature and prolonged duration. Moreover, SHT stress reduced the accumulation of amylose as well as starch accumulation. The starch accumulation and eating quality were more sensitive to SHT than the appearance and milling quality. The starch structure data observed by scanning electron microscope further showed that the starch granules are arranged loosely and more single starch granules appeared after SHT treatment. The extent of change in rice quality and starch traits of WJ14 under SHT was lower than that of NJ41. The effects of SHT at anthesis stage were greater than that at grain-filling stage. Taken together, the results could help further understand the physiological and biochemical processes governing rice quality under high-temperature conditions.

Heat Stress Is More Damaging to Superior Spikelets than Inferiors of Rice (Oryza sativa L.) due to Their Different Organ Temperatures

In general, the fertility and kernel weight of inferior spikelets of rice (Oryza Sativa L.) are obviously lower than those of superior spikelets, especially under abiotic stress. However, different responses to heat stress are seemed to show between the superior and inferior spikelet, and this response is scarcely documented that the intrinsic factors remain elusive. In order to reveal the mechanism underlying, two rice plants with different heat tolerance were subjected to heat stress of 40°C at anthesis. The results indicated that a greater decrease in fertility and kernel weight was observed in superior spikelets compared to inferior spikelets. This decrease was primarily ascribed to their different organ temperatures, in which the temperature of the superior spikelets was significantly higher than that of inferior spikelets. We inferred the differences in canopy temperature, light intensity and panicle types, were the primary reasons for the temperature difference between superior and inferior spikelets. Under heat stress, the fertility and kernel weight of superior and inferior spikelets decreased as the panicle numbers per plant were reduced, which was accompanied by significantly increasing the canopy temperatures. Thus, it was suggested that the rice plant with characteristic features of an upright growth habit and loose panicles might be more susceptible to heat stress resulting from their higher canopy and spikelets temperatures.

Characterization of Grain Quality and Starch Fine Structure of Two Japonica Rice (Oryza Sativa) Cultivars with Good Sensory Properties at Different Temperatures during the Filling Stage

Temperature during the growing season is a critical factor affecting grain quality. High temperatures at grain filling affect kernel development, resulting in reduced yield, increased chalkiness, reduced amylose content, and poor milling quality. Here, we investigated the grain quality and starch structure of two japonica rice cultivars with good sensory properties grown at different temperatures during the filling stage under natural field conditions. Compared to those grown under normal conditions, rice grains grown under hot conditions showed significantly reduced eating and cooking qualities, including a higher percentage of grains with chalkiness, lower protein and amylose contents, and higher pasting properties. Under hot conditions, rice starch contained reduced long-chain amylose (MW 10(7.1) to 10(7.4)) and significantly fewer short-chain amylopectin (DP 5-12) but more intermediate- (DP 13-34) and long- (DP 45-60) chain amylopectin than under normal conditions, as well as higher crystallinity and gelatinization properties.

Effects of ripening temperature on starch structure and gelatinization, pasting, and cooking properties in rice (Oryza sativa)

The effect of ripening temperature on rice (Oryza sativa) grain quality was evaluated by assessing starch structure and gelatinization, pasting, and cooking properties. As the ripening temperature increased, the amylose content and number of short amylopectin chains decreased, whereas intermediate amylopectin chains increased, resulting in higher gelatinization temperatures and enthalpy in the starch. These results suggested that an increase in cooking temperature and time would be required for rice grown at higher temperatures. A high ripening temperature increased the peak, trough, and final viscosities and decreased the setback due to the reduction in amylose and the increase in long amylopectin chains. With regard to starch crystallinity and amylopectin molecular structure, the highest branches and compactness were observed at 28/20 °C. Rice that was grown at temperatures above 28/20 °C showed a deterioration of cooking quality and a tendency toward decreased palatability in sensory tests.