Effects of high temperature on starch morphology and the expression of genes related to starch biosynthesis and degradation

Relationship between Chalkiness and the Structural and Physicochemical Properties of Rice Starch at Different Nighttime Temperatures during the Early Grain-Filling Stage

The chalkiness, starch fine structure, and physiochemical properties of rice starch were analyzed and their correlations were investigated under different nighttime temperatures during the early grain-filling stage. Compared to MT, medium temperature (MT) and low (LNT) and high (HNT) nighttime temperatures resulted in an increased chalky grain rate (CGR) and chalkiness degree (CD). LNT mainly affected the chalkiness by increasing peak1 (short branch chains of amylopectin), the branching degree, and the proportion of small starch granules but decreasing peak2 (long branch chains of amylopectin) and peak3 (amylose branches). This altered the pasting properties, such as by increasing the peak viscosity and final viscosity. However, HNT mainly affected the chalkiness by increasing peak2 and the crystallinity degree but decreasing peak1 and peak3. Regarding the thermal properties, HNT also elevated peak and conclusion temperatures. The CGR and CD were significantly and positively correlated with the proportions of small and medium starch granules, peak1, branching degree, gelatinization enthalpy, setback viscosity, and pasting time but markedly and negatively correlated with the proportion of large starch granules, amylose content, peak3, peak viscosity, and breakdown viscosity. These findings suggest that LNT and HNT disrupted the starch structure, resulting in increased chalkiness. However, their mechanisms of action differ.

Structural and physicochemical effects on the starch quality of the high-quality wheat genotype caused by delayed sowing

Background

Bread wheat is one of the most important food crops associated with ensuring food security and human nutritional health. The starch quality is an important index of high-quality wheat. It is affected by a complex series of factors; among which, suitable sowing time is a key factor.

Aim and methods

To analyze the integrative effects of sowing time on the starch quality of high-quality wheat, in the present study, we selected a high-quality bread wheat cultivar Jinan 17 and investigated the effect of different sowing times on the starch properties and the related genes by analyzing X-ray diffraction patterns, apparent amylose content, thermal properties, pasting properties, in vitro starch digestibility, and qRT-PCR. Meanwhile, we also investigated the agronomic and yield performance that may be associated with the starch properties.

Results

Delayed sowing had little effect on starch crystalline morphology, but there was a tendency to reduce the formation of crystals within wheat starch granules: (1) delayed sowing for 15 days altered the thermal properties of starch, including onset, peak and termination temperatures, and enthalpy changes; (2) delayed sowing for 30 days changed the thermal characteristics of starch relatively insignificant; (3) significant differences in pasting characteristics occurred: peak viscosity and hold-through viscosity increased, while final viscosity, breakdown viscosity, and setback viscosity tended to increase and then decrease, suggesting that delayed sowing caused changes in the surface of the starch granules resulting in a decrease in digestibility. Analysis of related genes showed that several key enzymes in starch biosynthesis were significantly affected by delayed sowing, leading to a reduction in apparent straight-chain starch content. In addition to starch properties, thousand-kernel weight also increased under delayed sowing conditions compared with normal sowing.

Conclusion

The impact of delayed sowing on starch quality is multifaceted and complex, from the fine structure, and functional properties of the starch to the regulation of key gene expression. Our study holds significant practical value for optimizing wheat planting management and maximizing the potential in both quality and yield.

Effects of exogenous salicylic acid on starch physicochemical properties and in vitro digestion under heat stress during the grain-filling stage in waxy maize

Waxy maize starch serves as a pivotal component in global food processing and industrial applications, while high temperature (HT) during the grain-filling stage seriously affects its quality. Salicylic acid (SA) has been recognized for its role in enhancing plant heat resistance. Nonetheless, its regulatory effect on the quality of waxy maize starch under HT conditions remains unclear. In this study, two waxy maize varieties, JKN2000 (heat-tolerant) and SYN5 (heat-sensitive) were treated with SA after pollination and then subjected to HT during the grain-filling stage to explore the effect of SA on grain yield and starch quality. The results indicate that exogenous SA under HT treatment led to an increase in kernel weight and starch content in both varieties. Moreover, SA reduced the HT-induced holes on the surfaces of starch granules, enlarged the starch granule size, elevated the amylopectin branching degree, and reduced amylopectin average chain length. Consequently, improvements of pasting viscosity and the decrease of retrogradation percentage of starch were observed with SA under HT. Exogenous SA reduced HT-induced rapidly digestible starch content in SYN5, but had no significant effect on that in JKN2000. In summary, SA pretreatment effectively alleviated the detrimental effects of HT on starch pasting and thermal properties of waxy maize.

Strategies for starch customization: Agricultural modification

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

Effects of Post Anthesis High Temperature Stress on Carbon Partitioning and Starch Biosynthesis in a Spring Wheat (Triticum aestivum L.) Adapted to Moderate Growth Temperatures

This study investigates carbon partitioning in the developing endosperm of a European variety of spring wheat subjected to moderately elevated daytime temperatures (27°C/16°C day/night) from anthesis to grain maturity. Elevated daytime temperatures caused significant reductions in both fresh and dry weights and reduced starch content of harvested grains compared to plants grown under a 20°C/16°C day/night regime. Accelerated grain development caused by elevated temperatures was accounted for by representing plant development as thermal time (°CDPA). We examined effects of high temperature stress (HTS) on uptake and partitioning of [U-14C]-sucrose supplied to isolated endosperms. HTS caused reduced sucrose uptake into developing endosperms from the second major grain filling stage (approximately 260°CDPA) up to maturity. Enzymes involved in sucrose metabolism were unaffected by HTS, whereas key enzyme activities involved in endosperm starch deposition such as ADP-glucose pyrophosphorylase and soluble isoforms of starch synthase were sensitive to HTS throughout grain development. HTS caused a decrease in other major carbon sinks such as evolved CO2, ethanol-soluble material, cell walls and protein. Despite reductions in labelling of carbon pools caused by HTS, the relative proportions of sucrose taken up by endosperm cells allocated to each cellular pool remain unchanged, except for evolved CO2, which increased under HTS and may reflect enhanced respiratory activity. The results of this study show that moderate temperature increases in some temperate wheat cultivars can cause significant yield reductions chiefly through three effects: reduced sucrose uptake by the endosperm, reduced starch synthesis, and increased partitioning of carbon into evolved CO2.

Heat Stress Tolerance 2 confers basal heat stress tolerance in allohexaploid wheat (Triticum aestivum L.)

Heat stress substantially reduces the yield potential of wheat (Triticum aestivum L.), one of the most widely cultivated staple crops, and greatly threatens global food security in the context of global warming. However, few studies have explored the heat stress tolerance (HST)-related genetic resources in wheat. Here, we identified and fine-mapped a wheat HST locus, TaHST2, which is indispensable for HST in both the vegetative and reproductive stages of the wheat life cycle. The studied pair of near isogenic lines (NILs) exhibited diverse morphologies under heat stress, based on which we mapped TaHST2 to a 485 kb interval on chromosome arm 4DS. Under heat stress, TaHST2 confers a superior conversion rate from soluble sugars to starch in wheat grains, resulting in faster grain filling and a higher yield potential. A further exploration of genetic resources indicated that TaHST2 underwent strong artificial selection during wheat domestication, suggesting it is an essential locus for basal HST in wheat. Our findings provide deeper insights into the genetic basis of wheat HST and might be useful for global efforts to breed heat-stress-tolerant cultivars.

From source to sink: mechanistic insight of photoassimilates synthesis and partitioning under high temperature and elevated [CO2]

Photosynthesis is the vital metabolism of the plant affected by abiotic stress such as high temperature and elevated [CO₂] levels, which ultimately affect the source-sink relationship. Triose phosphate, the primary precursor of carbohydrate (starch and sucrose) synthesis in the plant, depends on environmental cues. The synthesis of starch in the chloroplasts of leaves (during the day), the transport of photoassimilates (sucrose) from source to sink, the loading and unloading of photoassimilates, and the accumulation of starch in the sink tissue all require a highly regulated network and communication system within the plant. These processes might be affected by high-temperature stress and elevated [CO₂] conditions. Generally, elevated [CO₂] levels enhance plant growth, photosynthetic rate, starch synthesis, and accumulation, ultimately diluting the nutrient of sink tissues. On the contrary, high-temperature stress is detrimental to plant development affecting photosynthesis, starch synthesis, sucrose synthesis and transport, and photoassimilate accumulation in sink tissues. Moreover, these environmental conditions also negatively impact the quality attributes such as grain/tuber quality, cooking quality, nutritional status in the edible parts and organoleptic traits. In this review, we have attempted to provide an insight into the source-sink relationship and the sugar metabolites synthesized and utilized by the plant under elevated [CO₂] and high-temperature stress. This review will help future researchers comprehend the source-sink process for crop growth under changing climate scenarios.

Starch structural and functional properties of waxy maize under different temperature regimes at grain formation stage

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Excessive high temperature (>35 °C) enlarges and corrodes the starch granules.

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Heat stress increases the proportion of amylopectin long chains.

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Extremely high temperature induces the lowest pasting viscosity and the highest retrogradation of starch.

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This study provides scientific basis for the deterioration of waxy maize starch under severe high temperature.

Global warming affects crop productivity, but the influence is uncertain under different temperature regimes. The impact of growth temperatures (T0, 28 °C/20 °C; T1, 32 °C/24 °C; T2, 36 °C/28 °C; T3, 40 °C/32 °C) at grain formation stage on the waxy maize starch physicochemical properties of Suyunuo5 (heat-sensitive hybrid) and Yunuo7 (heat-tolerant hybrid) was studied. Compared with T0, T2 and T3 resulted in a higher number of starch granules with more pitted or uneven surface due to the enhanced enzymatic activities of α-amylase and β-amylase. Meanwhile, large starch granule size, long amylopectin chain-length, and high relative crystallinity under T2 and T3 resulted in low pasting viscosities and gelatinization enthalpy and high retrogradation percentage, especially under T3. The low coefficient variation of gelatinization temperatures indicated that the differences were meaninglessness. The influence of T1 on the pasting viscosities were more obvious in Suyunuo5. In conclusion, high temperatures at grain formation stage deteriorated the starch pasting and retrogradation properties.

Overcoming Reproductive Compromise Under Heat Stress in Wheat: Physiological and Genetic Regulation, and Breeding Strategy

The reproductive compromise under heat stress is a major obstacle to achieve high grain yield and quality in wheat worldwide. Securing reproductive success is the key solution to sustain wheat productivity by understanding the physiological mechanism and molecular basis in conferring heat tolerance and utilizing the candidate gene resources for breeding. In this study, we examined the performance on both carbon supply source (as leaf photosynthetic rate) and carbon sink intake (as grain yields and quality) in wheat under heat stress varying with timing, duration, and intensity, and we further surveyed physiological processes from source to sink and the associated genetic basis in regulating reproductive thermotolerance; in addition, we summarized the quantitative trait loci (QTLs) and genes identified for heat stress tolerance associated with reproductive stages. Discovery of novel genes for thermotolerance is made more efficient via the combination of transcriptomics, proteomics, metabolomics, and phenomics. Gene editing of specific genes for novel varieties governing heat tolerance is also discussed.

Unmodified cassava starches with high phosphorus content

Our study was based on the fact that physiological changes in the plant resulting from the growth conditions alter the properties of the starch. An experimental trial was installed with cassava plants in poor phosphorus soil. A part of plants received phosphate fertilization at a level three times higher than the recommended dose, in order to provide high availability of phosphorus in the soil. The plants grew for two years and the starches were isolated at three times in the second vegetative cycle. The starches had A-type X-ray pattern. Starches isolated from cassava plants grown in soils with high phosphorus had increases of more than 100% in the content of bound phosphorus, which caused changes in the size of the granules, amylose, swelling power, solubility, pasting and thermal properties. These results indicate possibilities of increasing the commercial value of native cassava starch due to the expansion of use, considering the range of uses of phosphate starches for food and non-food purposes.

Contribution of starch to the flavor of rice-based instant foods

Increased consumption of instant foods has led to research attention, especially rice-based instant foods. Starch, one of the most important components of rice, significantly affects food quality. However, the mechanisms by which starch contributes to rice-based instant foods flavor are poorly understood in many cases. The review aims to describe the common mechanisms by which starch contributes to food flavor, including participating in flavor formation, and affecting flavor release throughout starch multiscale structure: particle morphology, crystal structure, molecular structure. Five specific examples of rice-based instant foods were further analyzed to summarize the specific contribution of starch to flavor, including instant rice, fermented rice cake, rice noodles, fried rice, and rice dumplings. During foods processing, reducing sugars produced by heating or enzymatic hydrolysis of starch participate in Maillard reaction, caramelization and thermal degradation, which directly or indirectly affect the formation of flavor compounds. In addition, adsorption by granules, encapsulation by retrograded V-type crystal, and controlled release by starch gel all contribute to rice-based instant food flavor qualities. These mechanisms jointly contribute to flavor compounds formation and release. Proper theoretical application and improved processing methods are needed to promote the high-quality, mechanization, and automation of rice-based instant foods production.

Characterization of the starch synthase under terminal heat stress and its effect on grain quality of wheat

Terminal heat stress (HS) is a key barrier for wheat grain yield and quality. Various physiochemical and molecular parameters such as photosynthetic rate, expression analysis and activity of starch synthase (SS), total starch, amylose and amylopectin content, total amylolytic activity, and total antioxidant capacity (TAC) were analysed in wheat cvs.HD3059 (thermotolerant) and BT-Schomburgk (thermosusceptible) at grain-filling stage under HS (32 °C and 40 °C, 1 h). The decrease in photosynthetic rate was observed under HS. Expression analysis of the SS gene at transcript level showed downregulation in both the wheat cvs.HD3059 and BT-Schombugk under HS (32 °C and 40 ºC, 1 h) as compared to the control. Although the downregulation of SS gene transcript expression was less in HD3059 than BT-Schombugk. Both the cultivars showed decrease in starch synthase activity and starch content under HS and the overall content was higher in HD3059, compared to BT-Schomburgk. Higher total amylolytic activity and amylose content were observed in BT-Schomburgk. Scanning electron microscopy (SEM) showed un-structured starch granules under HS. Total antioxidant capacity (TAC) was found higher in HD3059 (14.07 mM FeSO₄ gm^-1 FW) compared to BT-Schomburgk (8.89 mM FeSO₄ gm^-1 FW) under HS (40 ºC, 1 h). Findings suggest that HS during grain filling stage had more severe impact on the overall physiochemical properties of the wheat grain. Thus the starch bisynthesis pathway associated gene(s) could be exploit to enhance the yield and quality of wheat under heat stress.

High night temperature induced changes in grain starch metabolism alters starch, protein, and lipid accumulation in winter wheat

Unlike sporadic daytime heat spikes, a consistent increase in night-time temperatures can potentially derail the genetic gains being achieved. Ten winter wheat genotypes were exposed to six different night-time temperatures (15-27°C) during flowering and grain-filling stages in controlled environment chambers. We identified the night-time temperature of 23^o C as the critical threshold beyond which a consistent decline in yields and quality was observed. Confocal laser scanning micrographs of central endosperm, bran, and germ tissue displayed differential accumulation of protein, lipid, and starch with increasing night-time temperatures. KS07077M-1 recorded a decrease in starch and an increase in protein and lipid in central endosperm with increasing night-time temperatures, whereas the same was significantly lower in the tolerant SY Monument. Expression analysis of genes encoding 21 enzymes (including isoforms) involved in grain-starch metabolism in developing grains revealed a high night-time temperature (HNT)-induced reduction in transcript levels of adenosine diphosphate glucose pyrophosphorylase small subunit involved in starch synthesis and a ≥2-fold increase in starch degrading enzymes isoamylase III, alpha-, and beta-amylase. The identified critical threshold, grain compositional changes, and the key enzymes in grain starch metabolism that lead to poor starch accumulation in grains establish the foundational knowledge for enhancing HNT tolerance in wheat.

Effects of High Temperature and Drought Stress on the Expression of Gene Encoding Enzymes and the Activity of Key Enzymes Involved in Starch Biosynthesis in Wheat Grains

High temperature (HT) and drought stress (DS) play negative roles in wheat growth, and are two most important factors that limit grain yield. Starch, the main component of the wheat [][endosperm, accounts for 65-75% of grain weight, and is significantly influenced by environmental factors. To understand the effects of post-anthesis HT and DS on starch biosynthesis, we performed a pot experiment using wheat cultivar "Zhengmai 366" under field conditions combined with a climate-controlled greenhouse to simulate HT. There were two temperature regimes (optimum day/night temperatures of 25/15°C and high day/night temperatures of 32/22°C from 10 days after anthesis to maturity) accompanied by two water treatments (optimum of ∼75% relative soil water content, and a DS of ∼50% relative soil water content). Optimum temperature with optimum water treatment was the control (CK). We evaluated the expression patterns of 23 genes encoding six classes of enzymes involved in starch biosynthesis in wheat grains using real-time qPCR. HT, DS, and HT+DS treatments altered gene expression profiles. Compared to the CK, expression of 22 of the 23 genes was down regulated by HT, and only one gene (ISA2) was up-regulated by HT. Actually ISA2 was the only gene up-regulated by all three stress treatments. The expression of 17 genes was up-regulated, while six genes, including granule-bound starch synthase (GBSSI), AGPS2, BEIII, PHOL, ISA1, and AGPL2, were down-regulated by DS. Eleven genes were down-regulated and 12 were up-regulated by HT+DS. The activity of ADP-Glc pyrophosphorylase, starch synthases, GBSS, SS, and starch branching enzymes in the stress treatments (HT, DS, and HT+DS) often appeared to peak values in advance and declined significantly to be lower than that in the CK. The genes that coordinated participation in the enzymes formation can serve as an indicator of the enzymes activity potentially involved in starch biosynthesis. HT, DS, and HT+DS altered the timing of starch biosynthesis and also influenced the accumulation of amylose, amylopectin, total starch, and sucrose. Under HT, DS, and HT+DS, the key enzymes activity and their genes expression associated with the conversion of sucrose to starch, was reduced, which was the leading cause of the reductions in starch content. Our study provide further evidence about the effects of stress on starch biosynthesis in wheat, as well as a physiological understanding of the impact of post-anthesis heat and DS on starch accumulation and wheat grain yield.

Starch accumulation in rice grains subjected to drought during grain filling stage

Drought stress during the grain filling stage severely affects the quality and quantity of starch in rice grains. The enzymes such as ADP-glucose pyrophosphorylase (AGPase, EC 2.7.7.27) and starch synthase (SS, EC 2.4.1.21) are the key regulatory enzymes involved in the starch biosynthesis. In this study, the activity of the AGPase and starch synthase (SS) was correlated with the qualitative and quantitative parameters such as sucrose, starch, amylose, amylopectin, and resistant starch in leaves, roots, and grains of drought tolerant (N22) and drought susceptible (IR64) cultivars under applied water deficit stress (WDS). Drought stress enhanced the remobilization of stored starch from leaves to developing rice grains which was positively correlated with a decrease in the starch and starch synthase activity in leaves. Starch accumulation in developing grains was positively correlated with an increase in the AGPase and SS activity under drought. It was found that starch, amylopectin, and sucrose content in developing grains increased under water deficit stress (WDS), while amylose content decreased in both the varieties. However, in leaves, the SS activity decreased while AGPase activity was found to be increased under WDS in both varieties. Decreased starch content in matured grains was due to shortening of grain filling stage as drought stress caused early plant senescence. Yield reduction under drought was more in susceptible variety IR64 as compared to tolerant genotype N22.

Use of X-ray micro computed tomography imaging to analyze the morphology of wheat grain through its development

BACKGROUND

Wheat is one of the most important staple source in the world for human consumption, animal feed and industrial raw materials. To deal with the global and increasing population demand, enhancing crop yield by increasing the final weight of individual grain is considered as a feasible solution. Morphometric analysis of wheat grain plays an important role in tracking and understanding developmental processes by assessing potential impacts on grains properties, size and shape that are major determinants of final grain weight. X-ray micro computed tomography (μCT) is a very powerful non-invasive imaging tool that is able to acquire 3D images of an individual grain, enabling to assess the morphology of wheat grain and of its different compartments. Our objective is to quantify changes of morphology during growth stages of wheat grain from 3D μCT images.

METHODS

3D μCT images of wheat grains were acquired at various development stages ranging from 60 to 310 degree days after anthesis. We developed robust methods for the identification of outer and inner tissues within the grains, and the extraction of morphometric features using 3D μCT images. We also developed a specific workflow for the quantification of the shape of the grain crease.

RESULTS

The different compartments of the grain could be semi-automatically segmented. Variations of volumes of the compartments adequately describe the different stages of grain developments. The evolution of voids within wheat grain reflects lysis of outer tissues and growth of inner tissues. The crease shape could be quantified for each grain and averaged for each stage of development, helping us understand the genesis of the grain shape.

CONCLUSION

This work shows that μCT acquisitions and image processing methodologies are powerful tools to extract morphometric parameters of developing wheat grain. The results of quantitative analysis revealed remarkable features of wheat grain growth. Further work will focus on building a computational model of wheat grain growth based on real 3D imaging data.

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.

Programmed cell death in wheat (Triticum aestivum L.) endosperm cells is affected by drought stress

Drought frequently occurs during wheat (Triticum aestivum L.) grain filling. The objectives of this study were (i) to investigate the effect of post-anthesis drought on programmed cell death (PCD) in wheat endosperm cells and (ii) to examine the role of ethylene (ETH) receptors and abscisic acid (ABA) in regulating wheat endosperm PCD. Two winter wheat cultivars ('Xindong 18' and 'Xindong 22') were used in this study. Grain samples were collected from normal and drought stressed plants at 5-day intervals between 5 and 35 days post-anthesis. The samples were then compared with respect to cell viability, nuclear morphometry, cell ultrastructure, DNA integrity, nucleic acid content, and nuclease activity. Analysis was also conducted about gene transcripts related to PCD, ETH receptors, and ABA biosynthesis and degradation. Drought stress reduced cell viability, accelerated nuclear deformation, and increased mitochondrial dissolution. The activity of nucleic acid hydrolase was greater, and the nucleic acid concentrations were less in the drought treatments than in the control. As a result, the peak in DNA fragmentation occurred earlier in the drought treatment. Drought stress significantly increased the expression of four genes related to ABA (nced1, nced2, ao1, ao2). In contrast, drought significantly reduced the expression of four genes related to ETH receptors (ers1, ers2 etr1, etr2) and one gene related to PCD (dad1). In summary, the results indicated that drought stress caused PCD to occur earlier in the endosperm of winter wheat.

Phosphorus Alters Starch Morphology and Gene Expression Related to Starch Biosynthesis and Degradation in Wheat Grain

Phosphorus is an essential plant macronutrient which profoundly affects the yield and quality of wheat starch. In this study, scanning electron microscopy showed that P fertilizer amount (0, 46, and 92 kg P ha-1) had no significant effect on the shape of starch granules in wheat (cv. Xindong 20) grain. However, confocal laser scanning microscopy with 3-(4-carboxybenzoyl) quinoline-2-carboxaldehyde and methanolic merbromin stains indicated that P amount influenced the microstructure of the starch granules. Starch granules from the 46 kg P ha-1 treatment released significantly more reducing sugars than those from the 0 and 92 kg P ha-1 treatments during digestion with alpha-amylase and amyloglucosidase digestion. Phosphorus application (especially the 46 kg P ha-1 treatments) significantly increased the relative expression of genes related to starch synthesis (especially during early to mid-grain filling) and starch degradation (especially during mid- and late grain filling). Phosphorus application also increased the transcript abundance of amylase genes at the periphery of the endosperm. We propose that P application, especially the 46 kg P ha-1 treatment, enhanced channels in wheat starch granules. These channels facilitated the transport of substances required for starch biosynthesis, thus increasing starch accumulation in wheat endosperm. These results provide insight into the potential mechanisms through which P influences the microstructure and biosynthesis of wheat starch.