Embryo and endosperm development in wheat (Triticum aestivum L.) kernels subjected to drought stress

ABA-mediated regulation of rice grain quality and seed dormancy via the NF-YB1-SLRL2-bHLH144 Module

Abscisic acid (ABA) plays a crucial role in promoting plant stress resistance and seed dormancy. However, how ABA regulates rice quality remains unclear. This study identifies a key transcription factor SLR1-like2 (SLRL2), which mediates the ABA-regulated amylose content (AC) of rice. Mechanistically, SLRL2 interacts with NF-YB1 to co-regulate Wx, a determinant of AC and rice quality. In contrast to SLR1, SLRL2 is ABA inducible but insensitive to GA. In addition, SLRL2 exhibits DNA-binding activity and directly regulates the expression of Wx, bHLH144 and MFT2. SLRL2 competes with NF-YC12 for interaction with NF-YB1. NF-YB1 also directly represses SLRL2 transcription. Genetic validation supports that SLRL2 functions downstream of NF-YB1 and bHLH144 in regulating rice AC. Thus, an NF-YB1-SLRL2-bHLH144 regulatory module is successfully revealed. Furthermore, SLRL2 regulates rice dormancy by modulating the expression of MFT2. In conclusion, this study revealed an ABA-responsive regulatory cascade that functions in both rice quality and seed dormancy.

Melatonin as a key regulator in seed germination under abiotic stress

Seed germination (SG) is the first stage in a plant's life and has an immense importance in sustaining crop production. Abiotic stresses reduce SG by increasing the deterioration of seed quality, and reducing germination potential, and seed vigor. Thus, to achieve a sustainable level of crop yield, it is important to improve SG under abiotic stress conditions. Melatonin (MEL) is an important biomolecule that interplays in developmental processes and regulates many adaptive responses in plants, especially under abiotic stresses. Thus, this review specifically summarizes and discusses the mechanistic basis of MEL-mediated SG under abiotic stresses. MEL regulates SG by regulating some stress-specific responses and some common responses. For instance, MEL induced stress specific responses include the regulation of ionic homeostasis, and hydrolysis of storage proteins under salinity stress, regulation of C-repeat binding factors signaling under cold stress, starch metabolism under high temperature and heavy metal stress, and activation of aquaporins and accumulation of osmolytes under drought stress. On other hand, MEL mediated regulation of gibberellins biosynthesis and abscisic acid catabolism, redox homeostasis, and Ca2+ signaling are amongst the common responses. Nonetheless factors such as endogenous MEL contents, plant species, and growth conditions also influence above-mentioned responses. In conclusion, MEL regulates SG under abiotic stress conditions by interacting with different physiological mechanisms.

Effects of the duration of post-silking drought on the starch physicochemical properties of waxy maize

BACKGROUND

Drought is a major abiotic stress that affects the physicochemical properties of cereal starch. However, quantitative information on the effects of drought duration on the starch quality of waxy maize, a special maize-type starch composed of nearly pure amylopectin, has been lacking. The effects of post-silking drought duration 1-10 (DS10), 1-20 (DS20), and 1-30 (DS30) days after pollination on the physicochemical properties of starch were assessed from 2019 to 2020 using two waxy maize hybrids as materials.

RESULTS

With extending drought duration, the starch granule size and average amylopectin chain length of Jingkenuo2000 (JKN2000) gradually increased, with those of Suyunuo5 (SYN5) being the highest for DS20, followed by DS30. All drought durations decreased the degree of branching of both hybrids, with the lowest value obtained for DS30 and DS20 in JKN2000 and SYN5, respectively. Relative crystallinity increased for DS30 in both hybrids but its responses for DS10 and DS20 differed. Pasting viscosities and gelatinization enthalpy were decreased and retrogradation percentage was increased by drought stress. The lowest pasting viscosities were observed for DS30, and the highest retrogradation percentage was found for DS10 in general.

CONCLUSION

Post-silking drought led to the pasting and retrogradation properties deteriorating, with decreased pasting viscosities and increased retrogradation percentage. The decrease in viscosity was caused by enlarged granules. Meanwhile, the increased proportion of amylopectin chains with a degree of polymerization of 25-36 resulted in lower viscosity and higher retrogradation. © 2022 Society of Chemical Industry.

Effects of post-silking drought stress degree on grain yield and quality of waxy maize

BACKGROUND

Drought stress (DS) induced by post-silking have a major impact on the yield and quality of maize. In this study, the effects of different degrees of DS after pollination on grain filling, starch and protein metabolism, and functional properties were investigated using two waxy maize cultivars as materials. The levels of DS that were investigated were 'mild water stress' (WS1), 'moderate water stressed' (WS2), and 'severe waterstressed' (WS3).

RESULTS

Drought stress decreased grain fresh weight, dry weight, and moisture content in both cultivars during grain filling, and reduced kernel number, kernel weight, and grain yield at maturity. The effect on grain development and yield formation gradually increased with drought aggravation. The water stress (WS) treatment downregulated the enzymatic activities related to starch biosynthesis during grain-filling process, accompanied by a decrease in soluble sugar and starch deposition. The WS treatment increased the enzymatic activities involved in protein synthesis during grain-filling process, thereby increasing the protein content of grains. On average, WS2 and WS3 treatments reduced the pasting viscosities and increased the gelatinization temperatures of grains, with WS3 having the greatest effect. However, the changes of setback viscosity, gelatinization enthalpy, retrogradation enthalpy, and retrogradation percentage under WS treatment were inconsistent in both cultivars. Pearson correlation analysis showed that starch content was negatively correlated with gelatinization temperatures and positively correlated with pasting viscosities in both cultivars. However, grain pasting  and gelatinization properties have opposite correlations with protein content and starch content.

CONCLUSIONS

These findings suggest that post-silking DS regulated the grain-filling process and starch and protein biosynthesis, which influenced grain yield and quality. © 2022 Society of Chemical Industry.

Parental drought priming enhances tolerance to low temperature in wheat (Triticum aestivum) offspring

Low temperature is one of the major environmental stresses that limit crop growth and grain yield in wheat (Triticum aestivum L.). Drought priming at the vegetative stage could enhance wheat tolerance to later cold stress; however, the transgenerational effects of drought priming on wheat offspring's cold stress tolerance remains unclear. Here, the low temperature responses of offspring were tested after the parental drought priming treatment at grain filling stage. The offspring plants from parental drought priming treatment had a higher abscisic acid (ABA) level and lower osmotic potential (Ψo) than the control plants under cold conditions. Moreover, parental drought priming increased the antioxidant enzyme activities and decreased hydrogen peroxide (H2 O2 ) accumulation in offspring. In comparison to control plants, parental drought priming plants had a higher ATP concentration and higher activities of ATPase and the enzymes involved in sucrose biosynthesis and starch metabolism. The results indicated that parental drought priming induced low temperature tolerance in offspring by regulating endogenous ABA levels and maintaining the redox homeostasis and the balance of carbohydrate metabolism, which provided a potential approach for cold resistant cultivation in wheat.

Ionomic and metabolic responses of wheat seedlings to PEG-6000-simulated drought stress under two phosphorus levels

Background

Wheat (Triticum aestivum L.) is a major food crop worldwide. Low soil phosphorus content and drought are the main constraints on wheat production in Xinjiang, China.

Methods

In this study, the ionic and metabolic responses of one wheat variety (“Xindong20”) to drought stress simulated by using polyethylene glycol 6000 (PEG-6000) were investigated under low phosphorus (LP) and conventional phosphorus (CP) conditions by analysing wheat mineral elements and metabolites. Besides, due to xanthohumol was the metabolite with the most significant difference in expression detected in “Xindong 20”, two wheat variety “Xindong20 and Xindong 23” were selected to conduct the germination test simultaneously, to further verify the function of xanthohumol in wheat growth. Xanthohumol was mixed with PEG solution (20%) to prepare PEG solutions with different concentrations (0%, 0.1%, 0.5%, and 1%) of xanthohumol. Then wheat grains were soaked in the solutions for 20 hours, followed by a germination test. After 7 days, the indicators including shoot length, max root length, and root number were determined to identify whether the metabolite was beneficial to improve the drought tolerance of wheat.

Results

The results showed that the root density and volume of wheat in LP treatment were higher than those in CP treatment. The roots underwent programmed cell death both in LP and CP treatments under PEG-6000-simulated drought stress, however, the DNA degradation in root cells in LP treatment was lower than that in CP treatment after rehydration for 3 d. Before drought stress, the malondialdehyde (MDA) content in shoot and the peroxidase (POD) activity in root in LP treatment were significantly higher than those in CP treatment, while the soluble sugar content and chlorophyll content in LP treatment were significantly lower than those in CP treatment. During drought stress, the POD activity maintained at a high level and the soluble sugar content gradually increased in LP treatment. After rehydration, the MDA content still maintained at a high level in LP treatment, the superoxide dismutase (SOD) activity increased, and the contents of soluble sugar and chlorophyll were significantly higher than those in CP treatment. The analysis of mineral elements and metabolites showed that the wheat in CP treatment was more sensitive to drought stress than that in LP treatment. Besides, the effect of drought stress was greater on shoot than on root in CP treatment, while it was opposite in LP treatment. The effect of drought stress on sugar metabolism gradually increased. Germination assays showed that 0.1% exogenous xanthohumol addition could significantly increase the shoot length of the two wheat varieties under drought stress.

Conclusion

Appropriate low phosphorus supply could increase antioxidant enzyme activity in wheat, and enhance sugar metabolism to regulate osmotic balance, as well as the accumulation of various organic acids to maintain the intracellular ion homeostasis. Therefore, compared to the conventional phosphorus supply level, appropriate low phosphorus supply can significantly improve the drought tolerance of wheat. Additionally, addition of 0.1% exogenous xanthohumol, an important differential expressed metabolite in drought-stressed wheat, could effectively promote wheat shoot growth under drought stress.

Climate Change Impact on Wheat Performance—Effects on Vigour, Plant Traits and Yield from Early and Late Drought Stress in Diverse Lines

Global climate change is threatening wheat productivity; improved yield under drought conditions is urgent. Here, diverse spring-wheat lines (modern, old and wheat-rye introgressions) were examined in an image-based early-vigour assay and a controlled-conditions (Biotron) trial that evaluated 13 traits until maturity. Early root vigour was significantly higher in the old Swedish lines (root length 8.50 cm) and introgressed lines with 1R (11.78 cm) and 1RS (9.91 cm) than in the modern (4.20 cm) and 2R (4.67 cm) lines. No significant correlation was noted between early root and shoot vigour. A higher yield was obtained under early drought stress in the 3R genotypes than in the other genotype groups, while no clear patterns were noted under late drought. Evaluating the top 10% of genotypes in terms of the stress-tolerance index for yield showed that root biomass, grains and spikes per plant were accountable for tolerance to early drought, while 1000-grain weight and flag-leaf area were accountable for tolerance to late drought. Early root vigour was determined as an important focus trait of wheat breeding for tolerance to climate-change-induced drought. The responsible genes for the trait should be searched for in these diverse lines. Additional drought-tolerance traits determined here need further elaboration to identify the responsible genes.

Goyal A, Chaudhury A. Molecular and Transcriptional Regulation of Seed Development in Cereals: Present Status and Future Prospects

Cereals are a rich source of vitamins, minerals, carbohydrates, fats, oils and protein, making them the world’s most important source of nutrition. The influence of rising global population, as well as the emergence and spread of disease, has the major impact on cereal production. To meet the demand, there is a pressing need to increase cereal production. Optimal seed development is a key agronomical trait that contributes to crop yield. The seed development and maturation is a complex process that includes not only embryo and endosperm development, but also accompanied by huge physiological, biochemical, metabolic, molecular and transcriptional changes. This chapter discusses the growth of cereal seed and highlights the novel biological insights, with a focus on transgenic and new molecular breeding, as well as biotechnological intervention strategies that have improved crop yield in two major cereal crops, primarily wheat and rice, over the last 21 years (2000–2021).

Drought and crop yield

Episodes of water shortage occur in most agricultural regions of the world. Their durations and intensities increase, and their seasonal timing alters with changing climate. During the ontogenic cycle of crop plants, each development stage, such as seed germination, seedling establishment, vegetative root and shoot growth, flowering, pollination and seed and fruit development, is specifically sensitive to dehydration. Desiccation threatens yield and leads to specific patterns, depending on the type of crop plant and the harvested plant parts, e.g. leafy vegetables, tubers, tap roots or fruits. This review summarizes the effects of drought stress on crop plants and relates the dehydration-dependent yield penalty to the harvested organ and tissue. The control of shoot transpiration and the reorganization of root architecture are of core importance for maintaining proper plant water relationships. Upon dehydration, the provision and partitioning of assimilates and the uptake and distribution of nutrients define remaining growth activity. Domestication of crops by selection for high yield under high input has restricted the genetic repertoire for achieving drought stress tolerance. Introgression of suitable alleles from wild relatives into commercial cultivars might improve the ability to grow with less water. Future research activities should focus more on field studies in order to generate more realistic improvements to crops. Robotic field phenotyping should be integrated into genetic mapping for the identification of relevant traits.

Effects of supplemental irrigation on winter wheat starch structure and properties under ridge-furrow tillage and flat tillage

Supplemental irrigation (SI) is an important strategy to improve the water-use efficiency (WUE) of crops without compromising the yield. However, such strategy can influence the starch and grain quality. Hence, the effects of SI on winter wheat starch structure and functionality were studied on ridge-furrow (RF) and flat tillage (FT) treated fields. Flat irrigation was set as control. RF + SI significantly increased the grain yield throughout the study period (2016-2018). SI decreased the amylose content and the content of amylopectin chains with DP 13-24 but increased the proportions of amylopectin chains with DP 6-12 and 25-36. The starch granule relative crystallinity decreased, and more B-type granules were produced by SI treatment. SI significantly increased the resistant starch content in both raw and cooked starch systems. Flat tillage enhanced the effect of SI on granule specific surface area (SSA) and viscosity, which increased starch paste viscosity, while SI + RF showed the opposite effects. Our study demonstrates important combined effects of SI and tillage on wheat starch quality.

Sorghum mitigates climate variability and change on crop yield and quality

Global food insecurity concerns due to climate change, emphasizes the need to focus on the sensitivity of sorghum to climate change and potential crop improvement strategies available, which is discussed in the current review to promote climate-smart agriculture. Climate change effects immensely disturb the global agricultural systems by reducing crop production. Changes in extreme weather and climate events such as high-temperature episodes and extreme rainfalls events, droughts, flooding adversely affect the production of staple food crops, posing threat to ecosystem resilience. The resulting crop losses lead to food insecurity and poverty and question the sustainable livelihoods of small farmer communities, particularly in developing countries. In view of this, it is essential to focus and adapt climate-resilient food crops which need lower inputs and produce sustainable yields through various biotic and abiotic stress-tolerant traits. Sorghum, "the camel of cereals", is one such climate-resilient food crop that is less sensitive to climate change vulnerabilities and also an important staple food in many parts of Asia and Africa. It is a rainfed crop and provides many essential nutrients. Understanding sorghum's sensitivity to climate change provides scope for improvement of the crop both in terms of quantity and quality and alleviates food and feed security in future climate change scenarios. Thus, the current review focused on understanding the sensitivity of sorghum crop to various stress events due to climate change and throws light on different crop improvement strategies available to pave the way for climate-smart agriculture.

Genetic and Environmental Variation in Starch Content, Starch Granule Distribution and Starch Polymer Molecular Characteristics of French Bread Wheat

This study investigates genetic and environmental variation in starch content and characteristics of 14 French bread cultivars. Understanding the impact of these factors on wheat quality is important for processors and especially bakers to maintain and meet the requirements of industrial specifications. Different traits were evaluated: starch content, distribution of starch granules, percentage of amylose and amylopectin and their molecular characteristics (weight-average molar mass, number-average molar mass, polydispersity and gyration radius). Genetic, environment and their interaction had significant effects on all parameters. The relative magnitude of variance attributed to growth conditions, for most traits, was substantially higher (21% to 95%) than that attributed to either genotype (2% to 73%) or G × E interaction (2% to 17%). The largest environmental contribution (95%) to total variance was found for starch dispersity. The highest genetic influence was found for the percentage of A-type starch granules. G × E interaction had relatively little influence (≈7%) on total phenotypic variance. All molecular characteristics were much more influenced by environment than the respective percentages of amylose and amylopectin were. This huge difference in variance between factors obviously revealed the importance of the effect of growing conditions on characteristics of cultivars.

Quantifying the influence of water deficit on root and shoot growth in wheat using X-ray Computed Tomography

The potential increased frequency and severity of drought associated with environmental change represents a significant obstacle to efforts aimed at enhancing food security due to its impact on crop development, and ultimately, yield. Our understanding of the impact of drought on crop growth in terms of plant aerial tissues is much more advanced than knowledge of the below-ground impacts. We undertook an experiment using X-ray Computed Tomography that aimed to support measurements of infrared gas exchange from plant shoots with quantification of 3D root architecture traits and the associated soil structural characteristics. Winter wheat (cv. Zebedee) was assessed at two early growth stages (14 and 21 days) under four water treatments (100, 75, 50 and 25 % of a notional field capacity (FC) and across two soil types (sandy loam and clay loam)). Plants generally grew better (to a larger size) in sandy loam soil as opposed to clay loam soil, most likely due to the soil structure and the associated pore network. All plants grew poorly under extreme water stress and displayed optimal growth at 75 % of FC, as opposed to 100 %, as the latter was most likely too wet. The optimal matric potential for root and shoot growth, inferred from the water release curve for each soil type, was higher than that for photosynthesis, stomatal conductance and transpiration suggesting root and shoot growth was more affected by soil water content than photosynthesis-related characteristics under water deficit conditions. With incidences of drought likely to increase, identification of wheat cultivars that are more tolerant of these conditions is important. Studies that consider the impact of water stress on both plant shoots and roots, and the role of the soil pore system such as this offer considerable potential in supporting these efforts.

Wheat Cultivars With Contrasting Root System Size Responded Differently to Terminal Drought

In the Mediterranean-type environment of Australia and other parts of the world, end-of- season or terminal drought is the most significant abiotic stress affecting wheat grain yields. This study examined the response of two wheat cultivars with contrasting root system size to terminal drought and the effect of terminal drought on grain yield and yield components. The cultivars were grown in 1.0 m deep PVC columns filled with soil in a glasshouse under well-watered conditions until the onset of ear emergence (Z51) when well-watered and terminal drought treatments were imposed. Terminal drought reduced stomatal conductance, leaf photosynthesis, and transpiration rates faster in Bahatans-87 (larger root system size) than Tincurrin (smaller root system size). Terminal drought reduced grain yield in both cultivars, more so in Bahatans-87 (80%) with the large root system than Tincurrin (67%) with the small root system, which was mainly due to a reduction in grain number and grain size in Bahatans-87 and grain size in Tincurrin. In the terminal drought treatment, Bahatans-87 had 59% lower water use efficiency than Tincurrin, as Bahatans-87 used 39% more water and reduced grain yield more than Tincurrin. The lesser reduction in grain yield in Tincurrin was associated with slower water extraction by the small root system and slower decline in stomatal conductance, leaf photosynthesis, and transpiration rates, but more importantly to faster phenological development, which enabled grain filling to be completed before the severe effects of water stress.

Effects of low temperature at stem elongation stage on the development, morphology, and physicochemical properties of wheat starch

The low temperature in spring is a meteorological problem in wheat production because it leads to yield reduction and alteration of wheat quality. In this study, an artificial low-temperature treatment (LTT) at the stem elongation stage was implemented to investigate the starch granule development and physical and chemical properties of wheat starch. Results showed that the agronomic traits of spike, such as spike length, spikelet number per spike, and grain number per spikelet, decreased after LTT. LTT promoted the development of starch granules in developing grains at 15 days post-anthesis, resulting in increased B-type granules and reduced C-type granules with an irregular shape in mature grains. The swelling power of the starch granules was reduced, but their solubility was enhanced by LTT. The proportion of the amorphous structure within the granules increased, but the crystalline component decreased after LTT, leading to a significant reduction in the relative degree of crystallinity and double- and single-helix structures. Three types of hydrolysis showed that starch in LTT was easy to hydrolyze, resulting in a high degree of hydrolysis. The findings suggest that low temperature at the stem elongation stage can not only reduce the yield parameters of spike but also alter starch accumulation, thereby affecting the processability and structure characteristics of starch in wheat grains.

Proteins and Metabolites as Indicators of Flours Quality and Nutritional Properties of Two Durum Wheat Varieties Grown in Different Italian Locations

Durum wheat is an important food source in Mediterranean countries, and Italy is the major producer of durum wheat in Europe. The quality of durum wheat flours depends on the type and amount of gluten proteins and starch while flour nutritional value rests on metabolite contents such as polyphenols. In this work, two Italian cultivars, Iride and Svevo, were analyzed for two years (2016-2017) in four Italian regions to explore how the environment affects: (i) reserve proteome; (ii) starch content and composition; and (iii) free, conjugated, bound phenolics and antioxidant capacity. The impact of environmental and meteorological conditions was significant for many traits. Regardless of the cultivation site, in 2017, a year with less rainfall and a higher temperature during grain filling, there was an increase in low molecular weight glutenins, in the glutenin/gliadin ratio and in the A-type starch granules size, all parameters of higher technological quality. In the same year, the cultivars showed higher amounts of polyphenols and antioxidant capacity. In conclusion, the two wheat cultivars, selected for their medium to high yield and their good quality, had higher performances in 2017 regardless of their sowing locations.

Effects of water-deficit and high-nitrogen treatments on wheat resistant starch crystalline structure and physicochemical properties

This work investigated the effects of water-deficit and high-nitrogen (N) treatments on wheat resistant starch (RS) formation, molecular structure, and physicochemical properties. The results of consecutive 2-year field experiments revealed that water deficit significantly reduced starch granule number and diameter, amylose, RS content, RS particle size distribution, and physicochemical properties, including peak and trough viscosities, oil absorption capacity, and freeze-thaw stability. Water deficit also altered the long- and short-range structures of RS. In contrast, high-N fertilizer application significantly improved the RS content, long- and short-range structures, and physicochemical properties. Pearson correlation analysis revealed that RS content was positively correlated with total starch, amylose, rapidly digesting starch, 90^th percentile of RS particle size, relative crystallinity, infrared 1047/1022 cm^-1 ratio, peak and breakdown viscosities, oil absorption capacity, and freeze-thaw stability, and was negatively correlated with slowly digestible starch content, 1022/995 cm^-1 ratio, and final viscosity.

Insights into transcriptional characteristics and homoeolog expression bias of embryo and de-embryonated kernels in developing grain through RNA-Seq and Iso-Seq

Bread wheat (Triticum aestivum L.) is an allohexaploid, and the transcriptional characteristics of the wheat embryo and endosperm during grain development remain unclear. To analyze the transcriptome, we performed isoform sequencing (Iso-Seq) for wheat grain and RNA sequencing (RNA-Seq) for the embryo and de-embryonated kernels. The differential regulation between the embryo and de-embryonated kernels was found to be greater than the difference between the two time points for each tissue. Exactly 2264 and 4790 tissue-specific genes were found at 14 days post-anthesis (DPA), while 5166 and 3784 genes were found at 25 DPA in the embryo and de-embryonated kernels, respectively. Genes expressed in the embryo were more likely to be related to nucleic acid and enzyme regulation. In de-embryonated kernels, genes were rich in substance metabolism and enzyme activity functions. Moreover, 4351, 4641, 4516, and 4453 genes with the A, B, and D homoeoloci were detected for each of the four tissues. Expression characteristics suggested that the D genome may be the largest contributor to the transcriptome in developing grain. Among these, 48, 66, and 38 silenced genes emerged in the A, B, and D genomes, respectively. Gene ontology analysis showed that silenced genes could be inclined to different functions in different genomes. Our study provided specific gene pools of the embryo and de-embryonated kernels and a homoeolog expression bias model on a large scale. This is helpful for providing new insights into the molecular physiology of wheat.

Stigma Functionality and Fertility Are Reduced by Heat and Drought Co-stress in Wheat

As a consequence of climate change, unpredictable extremely hot and dry periods are becoming more frequent during the early stages of reproductive development in wheat (Triticum aestivum L.). Pollen sterility has long been known as a major determinant of fertility loss under high temperature and water scarcity, but it will be demonstrated here that this is not the exclusive cause and that damage to female reproductive organs also contributes to losses of fertility and production. Changes in the phenology, morphology, and anatomy of female reproductive cells and organs, in the ROS and RNS generation of stigmatic papilla cells, and in fertility and yield components in response to simultaneous high temperature and drought at gametogenesis were studied in two wheat genotypes with contrasting stress responses. The combination of high temperature (32/24°C) and total water withdrawal for 5 days at gametogenesis altered the phenology of the plants, reduced pollen viability, modified the morphology and the anatomy of the pistils, enhanced the generation of ROS and RNS, intensified lipid peroxidation and decreased the NO production of stigmatic papilla cells, all leading to reduced fertility and to production loss in the sensitive genotype, depending on the position of the floret on the spike. Reduced functionality of female and male reproductive parts accounted for 34% and 66%, respectively, of the total generative cell- and organ-triggered fertility loss.

Molecular aspects of sucrose transport and its metabolism to starch during seed development in wheat: A comprehensive review

Wheat is one of the most important crops globally, and its grain is mainly used for human food, accounting for 20% of the total dietary calories. It is also used as animal feed and as a raw material for a variety of non-food and non-feed industrial products such as a feedstock for the production of bioethanol. Starch is the major constituent of a wheat grain, as a result, it is considered as a critical determinant of wheat yield and quality. The amount and composition of starch deposited in wheat grains is controlled primarily by sucrose transport from source tissues to the grain and its conversion to starch. Therefore, elucidation of the molecular mechanisms regulating these physiological processes provides important opportunities to improve wheat starch yield and quality through biotechnological approaches. This review comprehensively discusses the current understanding of the molecular aspects of sucrose transport and sucrose-to-starch metabolism in wheat grains. It also highlights the advances and prospects of starch biotechnology in wheat.

Differential effects of a post-anthesis heat stress on wheat (Triticum aestivum L.) grain proteome determined by iTRAQ

Heat stress, a major abiotic stressor of wheat (Triticum aestivum L.), often results in reduced yield and decreased quality. In this study, a proteomic method, Tags for Relative and Absolute Quantitation Isobaric (iTRAQ), was adopted to analyze the protein expression profile changes among wheat cultivar Jing411 under heat stress. Results indicated that there were 256 different proteins expressed in Jing411 under heat stress. According to the result of gene annotation and functional classification, 239 proteins were annotated by 856 GO function entries, including growth and metabolism proteins, energy metabolism proteins, processing and storage proteins, defense-related proteins, signal transduction, unknown function proteins and hypothetical proteins. GO enrichment analysis suggested that the differentially expressed proteins in Jing411 under heat stress were mainly involved in stimulus response (67), abiotic stress response (26) and stress response (58), kinase activity (12), and transferase activity (12). Among the differentially expressed proteins in Jing411, 115 were attributed to 119 KEGG signaling/metabolic pathways. KEGG pathway enrichment analysis in Jing411 showed that heat stress mainly affected the starch and sucrose metabolism as well as protein synthesis pathway in the endoplasmic reticulum. The protein interaction network indicated that there were 8 differentially expressed proteins that could form an interaction network in Jing411.

Effects of water stress on the composition and immunoreactive properties of gliadins from two wheat cultivars: Nawra and Tonacja

BACKGROUND

Water shortage during wheat vegetation causes changes in the composition of gliadins in grains, which can lead to changes in their immunoreactive properties.

RESULTS

The investigated wheat cultivars exposed to water stress accumulated significantly lower amounts (P < 0.05) of gliadins and glutenins in grains. The composition of proteins accumulated in grains was also modified. Water shortage results in a decreased share of αβ and γ fractions in total gliadins. Grains of wheat cultivated under water stress contain significantly higher (P < 0.05) levels of ω-gliadins by 4.5% and 43.3% for Nawra and Tonacja cultivars, respectively. Water stress promotes an increase in the share of P and Q/E residues in gliadins. In protein samples R5 antibodies recognized increased amounts of gliadins matching the QQPFP sequence. Wheat proteins also reacted with IgE antibodies isolated from subjects allergic to gluten.

CONCLUSION

Cultivation of wheat under conditions of water stress results in the qualitative and quantitative changes of gliadins by increasing their immunoreactivity. © 2016 Society of Chemical Industry.

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.

Developmental program impacts phenological plasticity of spring wheat under drought

BACKGROUND

Developing drought-tolerant crops critically depends on the efficient response of a genotype to the limited water availability, a trait known as phenological plasticity. Our understanding of the phenological plasticity remains limited, in particular, about its relationships with plant developmental program. Here, we examined the plastic response of spring wheat at tillering, booting, heading, and anthesis stages to constant or periodic drought stress. The response was assessed by morphological and physiological parameters including symptoms.

RESULTS

The dynamics of morphological symptoms were indicators of the plasticity identification of drought. We found that spring wheat exhibits higher phenological plasticity during tillering stage followed by the heading stage, while booting and anthesis stages are the most sensitive. Also, the adaptive response is thought to be influenced with the plant height genes. Furthermore, periodic stress caused more pronounced inhibition of yield than the constant stress, with limited resistance resolution under long period.

CONCLUSIONS

Our study shows the importance of considering the phenological plasticity in designing screens for drought tolerance in spring wheat and proposes tillering as the most informative stage for capturing genotypes with tolerance to limit water availability.

Effect of drought stress on the development of endosperm starch granules and the composition and physicochemical properties of starches from soft and hard wheat

BACKGROUND

The objectives of this study were to: (1) observe the effects of drought stress (DS) on the structural development of endosperm starch granules; (2) investigate the effects of DS on composition and physicochemical properties of starches; and (3) compare the different responses to DS between soft and hard wheat.

RESULTS

DS resulted in large A-type starch granules at 12 d after anthesis (DAA) and a high percentage of B-type starch granules at 18 DAA in endosperm cells of the two wheat cultivars. DS decreased the 1000-grain weight, total starch and amylose contents, and amylose-to-amylopectin ratio of both starches. DS also decreased the percentage of B-type starch granules in NM13 and increased the number of hollows on the surface of A-type starch granules in XM33. DS further increased the swelling power and affected pasting properties of both starches. DS also significantly enhanced the hydrolysis degrees of starches by pancreatic α-amylase, Aspergillus niger amyloglucosidase, and HCl in NM13. DS altered the contents of rapidly digestible, slowly digestible, and resistant starches in native, gelatinised, and retrograded starches.

CONCLUSION

Overall, DS can affect the development of endosperm starch granules and the physicochemical properties of starches, thus affecting the qualities of the final wheat products. © 2015 Society of Chemical Industry.

Contrasting response of biomass and grain yield to severe drought in Cappelle Desprez and Plainsman V wheat cultivars

We report a case study of natural variations and correlations of some photosynthetic parameters, green biomass and grain yield in Cappelle Desprez and Plainsman V winter wheat (Triticum aestivum L.) cultivars, which are classified as being drought sensitive and tolerant, respectively. We monitored biomass accumulation from secondary leaves in the vegetative phase and grain yield from flag leaves in the grain filling period. Interestingly, we observed higher biomass production, but lower grain yield stability in the sensitive Cappelle cultivar, as compared to the tolerant Plainsman cv. Higher biomass production in the sensitive variety was correlated with enhanced water-use efficiency. Increased cyclic electron flow around PSI was also observed in the Cappelle cv. under drought stress as shown by light intensity dependence of the ratio of maximal quantum yields of Photosystem I and Photosystem II, as well by the plot of the Photosystem I electron transport rate as a function of Photosystem II electron transport rate. Higher CO2 uptake rate in flag leaves of the drought-stressed Plainsman cv. during grain filling period correlates well with its higher grain yield and prolonged transpiration rate through spikes. The increase in drought factor (DFI) and performance (PI) indices calculated from variable chlorophyll fluorescence parameters of secondary leaves also showed correlation with higher biomass in the Cappelle cultivar during the biomass accumulation period. However, during the grain filling period, DFI and PI parameters of the flag leaves were higher in the tolerant Plainsman V cultivar and showed correlation with grain yield stability. Our results suggest that overall biomass and grain yield may respond differentially to drought stress in different wheat cultivars and therefore phenotyping for green biomass cannot be used as a general approach to predict grain yield. We also conclude that photosynthetic efficiency of flag and secondary leaves is correlated with grain yield and green biomass, respectively. In addition, secondary trait associated mechanisms like delayed senescence and higher water-use efficiency also contribute to biomass stability. Our studies further prove that photosynthetic parameters could be used to characterize environmental stress responses.

A morpho-physiological approach differentiates bread wheat cultivars of contrasting tolerance under cyclic water stress

Leaf micromorphological traits and some physiological parameters with potential relevance to drought tolerance mechanisms were investigated in four selected winter wheat varieties. Plants were subjected to two cycles of drought treatment at anthesis. Yield components confirmed contrasting drought-sensitive and -tolerant behavior of the genotypes. Drought tolerance was associated with small flag leaf surfaces and less frequent occurrence of stomata. Substantial variation of leaf cuticular thickness was found among the cultivars. Thin cuticle coincided with drought sensitivity and correlated with a high rate of dark-adapted water loss from leaves. Unlike in Arabidopsis, thickening of the cuticular matrix in response to water deprivation did not occur. Water stress induced epicuticular wax crystal depositions preferentially on the abaxial leaf surfaces. According to microscopy and electrolyte leakage measurements from leaf tissues, membrane integrity was lost earlier or to a higher extent in sensitive than in tolerant genotypes. Cellular damage and a decline of relative water content of leaves in sensitive cultivars became distinctive during the second cycle of water deprivation. Our results indicate strong variation of traits with potential contribution to the complex phenotype of drought tolerance in wheat genotypes. The maintained membrane integrity and relative water content values during repeated water limited periods were found to correlate with drought tolerance in the selection of cultivars investigated.

Development of barley (Hordeum vulgare L.) lines with altered starch granule size distribution

Microscope analysis of starches prepared from 139 barley genotypes identified a Japanese genotype, Kinai Kyoshinkai-2 (KK-2), with altered starch granule size distribution. Compared to normal barley starch, KK-2 produced consistently higher volumes of starch granules with 5-15 μm diameter and reduced volumes of starch granules with >15 μm diameter when grown in different environments. A cross between KK-2 and normal starch cultivar CDC Kendall was made and led to the production of 154 F5 lines with alterations to the normal 7:3:1 distribution for A-:B-:C-type starch granule volumes. Three F5 lines showed unimodal starch granule size distribution due to apparent lack of very small (<5.0 μm diameter) C-type starch granules, but the phenotype was accompanied by reduced grain weight and total starch concentration. Five F5 lines produced a significantly larger population of large (>15 μm diameter) A-type starch granules as compared to normal starch and showed on average a 10:4:1 distribution for A-:B-:C-type starch granule volumes. The unusual starch phenotypes displayed by the F5 lines confirm starch granule size distribution in barley can be genetically altered.

Stress-related genes distinctly expressed in unfertilized wheat ovaries under both normal and water deficit conditions whereas differed in fertilized ovaries

In this study, a proteomic approach was utilized to identify differentially accumulated proteins in developing wheat ovaries before and after fertilization and in response to water deficit. Proteins were extracted, quantified, and resolved by 2-DE at pH4-7. Statistical analysis of spot intensity was performed by using principal component analysis and samples were clustered by using Euclidean distance. In total, 136 differentially accumulated protein spots representing 88 unique proteins were successfully identified by MALDI-TOF/TOF MS. Under normal conditions, stress-related proteins were abundant in unfertilized ovaries while proteins involved in the metabolism of energy and matter were enriched in fertilized ovaries just 48h after fertilization. Similar trends were observed in unfertilized and fertilized wheat ovaries under water deficit conditions, except for increased accumulation of stress-related proteins in fertilized ovaries. Some proteins required for normal development were not present in ovaries subjected to water deficit. Our comprehensive results provide new insights into the biochemical mechanisms involved in ovary development before and after fertilization and in tolerance to water deficit.

BIOLOGICAL SIGNIFICANCE

Fertilization initiates the most dramatic changes that occur in the life cycle of higher plants; research into differences in gene expression before and after ovary pollination can make a substantial contribution to understanding the physiological and biochemical processes associated with fertilization. To date, a small number of studies have examined changes in transcriptional activity of the developing plant embryo sac before and after fertilization. However, comparative proteomic analysis of wheat ovary development before and after fertilization, and in response to water deficit, has not yet been reported. Our comprehensive results provide new insights into the biochemical mechanisms involved in ovary development before and after fertilization and in tolerance to water deficit.

Seed-development programs: a systems biology-based comparison between dicots and monocots

Seeds develop differently in dicots and monocots, especially with respect to the major storage organs. High-resolution transcriptome data have provided the first insights into the molecular networks and pathway interactions that function during the development of individual seed compartments. Here, we review mainly recent data obtained by systems biology-based approaches, which have allowed researchers to construct and model complex metabolic networks and fluxes and identify key limiting steps in seed development. Comparative coexpression network analyses define evolutionarily conservative (FUS3/ABI3/LEC1) and divergent (LEC2) networks in dicots and monocots. Finally, we discuss the determination of seed size--an important yield-related characteristic--as mediated by a number of processes (maternal and epigenetic factors, fine-tuned regulation of cell death in distinct seed compartments, and endosperm growth) and underlying genes defined through mutant analyses. Altogether, systems approaches can make important contributions toward a more complete and holistic knowledge of seed biology and thus support strategies for knowledge-based molecular breeding.

Electron paramagnetic resonance (EPR) spectroscopy characterization of wheat grains from plants of different water stress tolerance

Grains of five genotypes of wheat (four Polish and one Finnish), differing in their tolerance to drought stress were chosen for this investigation. Electron paramagnetic resonance spectroscopy allowed observation of transition metal ions (Mn, Fe, Cu) and different types of stable radicals, including semiquinone centers, present in seed coats, as well as several types of carbohydrate radicals found mainly in the inner parts of grains. The content of paramagnetic metal centers was higher in sensitive genotypes (Radunia, Raweta) than in tolerant ones (Parabola, Nawra), whereas the Finnish genotype (Manu) exhibited intermediate amounts. Similarly, the concentrations of both types of radicals, carbohydrates and semiquinone were significantly higher in the grains originating from more sensitive wheat genotypes. The nature of carbohydrate radicals and their concentrations were confronted with the kinds and amounts of sugars found by the biochemical analyses and microscopy observations. It is suggested that some long lived radicals (semiquinone and starch radicals) occurring in grains could be indicators of stress resistance of wheat plants.

Response of Aegilops species to drought stress during reproductive stages of development

Drought stress is an important abiotic factor limiting wheat yield. Thirty-one accessions of Aegilops species belonging to five species were screened to identify species/accessions tolerant to drought stress and to measure traits associated with the tolerance. Plants were grown at full irrigation, 25/19°C day/night temperature and an 18h photoperiod. At anthesis (Feekes 10.5.1), drought stress was imposed by withholding water for 16 days. Controls were continuously irrigated. Drought stress decreased chlorophyll content, grain number, individual grain weight and grain yield by 31, 25, 68 and 76% compared with the control. Aegilops geniculata Roth had greater tolerance to drought stress for yield (48% decline from control) compared with other species (>73% decline from control). The tolerance was associated with higher grain number spike-1 and heavier grains. A. geniculata, GenBank accession number TA 10437, was highly tolerant to drought stress with <20% yield decline and a drought stress susceptibility index (DSI) <0.5, whereas TA 1802, TA 2061, TA 1814, TA 1819 were identified as moderately tolerant to drought stress (20-40% yield decline and DSI<1.0). Our results suggest a presence of genetic variability among Aegilops species that can be utilised in breeding wheat for tolerance to drought stress at reproductive stages.