Natural variability of metabolites in maize grain: differences due to genetic background

Understanding the impact of genetic diversity on crop biochemical composition is a prerequisite to the interpretation and potential relevance of biochemical differences experimentally observed between genotypes. This is particularly important in the context of comparative safety assessments for crops developed by new technologies such as genetic engineering. To interrogate the natural variability of biochemical composition, grain from seven maize hybrids grown at four geographically distinct sites in Europe was analyzed for levels of proximates (fat, protein, moisture, ash, and carbohydrates), fiber, amino acids, fatty acids, four vitamins, nine minerals, and secondary metabolites. Statistical evaluation of the compositional data at the p < 0.05 level compared each hybrid against every other hybrid (head-to-head) for all analytes at each site and then across all sites to understand the factors contributing to variability. Of the 4935 statistical comparisons made in this study, 40% (1986) were found to be significant. The magnitude of differences observed, as a percent, ranged between 0.84 and 149% when all individual sites and the combined sites were considered. The large number of statistically significant differences in the levels of these analytes between seven commercial hybrids emphasizes the importance of genetic background and environment as determinants of the biochemical composition of maize grain, reflects the inherent natural variability in those analytes across a representative sampling of maize hybrids, and provides a baseline of the natural range of these nutritional and antinutritional components in maize for comparative compositional assessments.     

Impact of genetics and environment on nutritional and metabolite components of maize grain

The Organization for Economic Co-operation and Development (OECD) recommends the measurement of specific plant components for compositional assessments of new biotechnology-derived crops. These components include proximates, nutrients, antinutrients, and certain crop-specific secondary metabolites. A considerable literature on the natural variability of these components in conventional and biotechnology-derived crops now exists. Yet the OECD consensus also suggests measurements of any metabolites that may be directly associated with a newly introduced trait. Therefore, steps have been initiated to assess natural variation in metabolites not typically included in the OECD consensus but which might reasonably be expected to be affected by new traits addressing, for example, nutritional enhancement or improved stress tolerance. The compositional study reported here extended across a diverse genetic range of maize hybrids derived from 48 inbreds crossed against two different testers. These were grown at three different, but geographically similar, locations in the United States. In addition to OECD analytes such as proximates, total amino acids and free fatty acids, the levels of free amino acids, sugars, organic acids, and selected stress metabolites in harvested grain were assessed. The major free amino acids identified were asparagine, aspartate, glutamate, and proline. The major sugars were sucrose, glucose, and fructose. The most predominant organic acid was citric acid, with only minor amounts of other organic acids detected. The impact of genetic background and location was assessed for all components. Overall, natural variation in free amino acids, sugars, and organic acids appeared to be markedly higher than that observed for the OECD analytes.     

Combined Application of Potassium and Zinc Improves Water Relations,Stay Green,Irrigation Water Use Efficiency,and Grain Quality of Maize under Drought Stress

Abstract

Maize (Zea mays L.) plays an important role in the global food security, but its production is threatened by climate change, especially drought stress. Potassium (K) and zinc (Zn) are considered useful to mitigate the negative consequences of drought stress in plants. Therefore, the objective of this two-year study was to identify the best combination of K and Zn application to improve the water relations, photosynthetic pigments, yield, irrigation water use efficiency (IWUE) and grain quality of maize sown under mild and severe drought stress conditions. The consisted of three drought stress levels viz. 1) well-watered as control (WW), 2) mild drought (MD) with 25?mm of potential soil moisture deficit (PSMD), 3) severe drought (SD) with 50?mm of PSMD and six K-Zn treatments: i.e. 125, 100 and 150?kg ha^?1 K with 0 and 12?kg ha^?1 Zn. The results indicated that K-Zn application improved the water relations and chlorophyll contents, biological yield and grain quality, irrespective of water stress treatment. The combined application of K-Zn under mild drought stress produced statistically same biological yield and grain quality as under well-irrigated without K-Zn fertilization and also produced compratively higher IWUE, biological yield and grain quality under sverer drought stress. Hence, the application of K at 150?kg ha^?1 in combination with Zn at 12?kg ha^?1 might be useful to improve the maize production and grain quality under drought stress. As IWUE was low in WW conditions, therefore, irrigation scheduling must be re-evaluated for optimum water use efficiency.     

不同土壤水分供应下锌对玉米叶片超微结构的影响

选择 土为供试土壤, 进行盆栽玉米试验, 设定0和5.0 mg·kg^-1两个锌处理, 按土壤饱和持水量的40%~45%和70%~75%在玉米的4叶1心期实施干旱和正常水分处理。生长50 d后, 测定不同土壤水分与锌供应状况下植株生物量和锌含量, 利用透射电子显微镜观察完全伸展新叶的超微结构变化, 以期揭示不同土壤水分供应下, 植物对施锌的响应机理。结果表明: 土壤水分供应充足条件下, 与不施锌相比, 施锌玉米地上部生物量和总干重分别增加78%和52%, 根系和地上部锌含量和锌吸收量增加较多; 而干旱条件下, 施锌对玉米生物量无显著影响。干旱条件下缺锌玉米叶片维管束鞘细胞中叶绿体结构基本保持完好, 淀粉粒和基质片层清晰可见, 但叶肉细胞中叶绿体膜受损, 基质片层结构出现皱缩, 基粒片层减少; 施锌玉米叶片维管束鞘细胞中叶绿体结构保持完好, 叶绿体周围的线粒体数目较多, 叶肉细胞中叶绿体中脂肪颗粒增多, 叶片维管束鞘细胞与叶肉细胞之间可见清晰的胞间连丝。土壤水分充足处理下, 缺锌叶片细胞膜出现皱缩, 维管束鞘细胞叶绿体淀粉粒增多, 片层结构受损, 严重时维管束鞘细胞中内溶物消失, 残存的叶绿体中仅有淀粉粒和少许片层; 叶肉细胞中叶绿体可见淀粉粒, 但片层结构少, 有些出现断裂、收缩。土壤水分充足条件下, 施锌玉米维管束鞘核叶肉细胞结构清晰, 叶绿体结构完整。结论认为: 锌对干旱胁迫下玉米叶片细胞结构的破坏有一定的缓解作用; 但土壤水分正常供应下, 缺锌导致细胞结构受损程度比干旱情况下更严重。     

Effects of drought stress and rewatering on antioxidant systems and relative water content in different growth stages of maize (Zea mays L.) hybrids

Drought is a problem of the expanding universe which seriously influences crop production and quality. Approximately one-third of the cultivated area of the world suffers from constantly inadequate supplies of water. The present study aimed to determine the effects of drought and rewatering on activities of antioxidant enzymes, chlorophyll, proline, and relative water contents (RWC). In this experiment, six maize hybrids (Sc260, Sc370, Sc500, Sc647, Sc700, and Sc704) were examined in a pot study during the maize-growing season of 2011. Results indicated that the growth of hybrids was retarded under drought stress conditions and regained growth speed during rewatering. RWC, chlorophyll, and carotenoid contents were markedly decreased by the water deficit and reached normal values during rewatering in Sc647, Sc704, and Sc700. Our findings also indicated significantly higher activity levels of peroxidase and catalase and proline content in water-stressed plants than in well-watered plants, which decreased when the plants were rewatered, showing an inverse relationship to gluthatione reductase activity. According to the results, the better upregulation of the protective mechanism in Sc704 and Sc647 probably induced higher drought resistance. We concluded that antioxidant enzyme activity could provide a useful tool for depicting drought tolerance in maize hybrids in arid and semiarid regions.     

EFFECT OF POTASSIUM NUTRITION ON SOLUTE ACCUMULATION,ION COMPOSITION AND YIELD OF MAIZE HYBRIDS GROWN UNDER SALINE CONDITIONS

An experiment was conducted to study the response of two maize hybrids to external potassium (K) application under saline conditions. The data showed that there was an increase in the organic solute contents and sodium ion under salinity stress, though potassium, calcium, nitrogen and phosphorus were decreased. There was a non-significant effect of K application on glycinebetaine and total soluble sugar, however; the proline, protein and total free amino acids were increased with the application of external K. The enzymatic activity like nitrate reductase and nitrite reductase activity were severely reduced under salinity stress and improved by K application. The maize hybrids differed significantly for all the parameters discussed in the study except sugar, phosphorus and number of grain rows per cob. The increase in yield parameters was more pronounced under control than under saline conditions. The enhanced yield and yield components of these maize hybrids might be due to the quick response to external K application, resulting in high contents of leaf potassium, calcium, nitrogen and phosphorus. The results indicated that the maize hybrid ‘Pioneer32B33’ might perform better than ‘Dekalb979’ under saline conditions when sufficient potassium is applied in the rooting medium.     

Near-Infrared Reflectance Spectroscopy (NIRS) assessment of δ(18)O and nitrogen and ash contents for improved yield potential and drought adaptation in maize

The oxygen isotope composition (δ(18)O), accumulation of minerals (ash content), and nitrogen (N) content in plant tissues have been recently proposed as useful integrative physiological criteria associated with yield potential and drought resistance in maize. This study tested the ability of near-infrared reflectance spectroscopy (NIRS) to predict δ(18)O and ash and N contents in leaves and mature kernels of maize. The δ(18)O and ash and N contents were determined in leaf and kernel samples from a set of 15 inbreds and 18 hybrids grown in Mexico under full irrigation and two levels of drought stress. Calibration models between NIRS spectra and the measured variables were developed using modified partial least-squares regressions. Global models (which included inbred lines and hybrids) accurately predicted ash and N contents, whereas prediction of δ(18)O showed lower results. Moreover, in hybrids, NIRS clearly reflected genotypic differences in leaf and kernel ash and N contents within each water treatment. It was concluded that NIRS can be used as a rapid, cost-effective, and accurate method for predicting ash and N contents and as a method for screening δ(18)O in maize with promising applications in crop management and maize breeding programs for improved water and nitrogen use efficiency and grain quality.     

RESPONSE OF NON-NODULATING,NODULATING, AND SUPER-NODULATING SOYBEAN GENOTYPES TO POTASSIUM FERTILIZER UNDER WATER STRESS

Soil moisture is a principal environmental factor limiting legume productivity in the tropics and sub-tropics. A pot experiment was conducted at the wire house of National Research Centre, Cairo, Egypt to study how potassium (K) fertilizer can mitigate the adverse effect of water stress. Three Japanese soybean (Glycine max L.) genotypes, non-nodulating (NN) (En 1282), nodulating (N) (Eneri) and super-nodulating (SN) (En-b0-1) were grown under two potassium fertilizer levels (25 and 150 mg kg^?1 soil as K1 and K2, respectively). The water stress (WS) was conducted for eight days. WS significantly reduced nodules numbers and weights, shoot dry weight, relative water content, seed yield, oil, total carbohydrate contents while protein was significantly increased in the three soybean genotypes compared with well-watered (WW). Water stress and/or K treatments caused significant increase in both free amino acids and proline as well as shoot nitrogen in the three soybean genotypes.     

太行山山前平原夏玉米优化灌溉制度研究

5年田间试验研究不同气候年型下灌水次数、灌溉时间对夏玉米生育、产量和水分利用效率的影响结果表明 ,随生育期总耗水量的增加 ,夏玉米产量逐步提高 ,当耗水量增至一定程度时产量反而递减 ;而水分利用效率随耗水量的增加呈逐步递减趋势。并确定了夏玉米最优耗水量 ,建立了不同降水年型下夏玉米优化灌溉制度。     

玉米杂交种氮效率基因型差异

利用北京地区推广的 8个主要玉米杂交种 ,在不施N和施N条件下研究了产量、N累积量及N效率的基因型差异。结果表明 ,在不施N和施N条件下 ,不同品种之间产量的变异幅度分别为 62%、57% ;N累积总量的变异幅度则分别为 55%、48%。其中以农大 108的产量和N累积总量最高 ,中单 120和中单 2号最低。随施N量增加 ,吸收效率和N效率显著下降 ,利用效率则变化不大。在 2个施N水平下 ,N效率基因型差异主要决定于吸收效率     

Qualitative characterization of benzoxazinoid derivatives in whole grain rye and wheat by LC-MS metabolite profiling

Benzoxazinoids are metabolites occurring in a restricted group of plant species including crops such as rye, wheat, and maize. Focus on the analysis of benzoxazinoid metabolites has typically been due to their importance to plant biochemistry and physiology as highly bioactive molecules that plants use as alleochemicals to defend themselves against predators and infections. However, the potential dietary contribution of these compounds has not been addressed. This study conducted a detailed qualitative characterization of benzoxazinoid metabolites present in the whole grain rye and processed fractions of rye bran, and their presence was also detected in whole grain wheat samples. Several novel benzoxazinoid metabolites of the hydroxamic acids (2,4-dihydroxy-1,4-benzoxazin-3-one, DIBOA; 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, DIMBOA), lactams (2-hydroxy-1,4-benzoxazin-3-one, HBOA), and benzoxazolinones (1,3-benzoxazol-2-one, BOA) were identified, including double-hexose derivatives of DIBOA, DIMBOA, and HBOA. This paper presents an important addition to the information on the phytochemical composition of rye and wheat grains, which deserves attention in the discussion of the potential health-promoting effects of these grains.     

太行山山前平原冬小麦和夏玉米灌溉指标研究

根据1998～2001年的田间试验,研究了太行山山前平原高产农区主要作物冬小麦和夏玉米耗水量与产量和水分利用效率的关系,确定了这两种作物不同生育期水分敏感指数和允许的土壤水分下限指标和有限供水条件下的优化供水制度。并通过对叶片水势和冠气温差的测定,建立了这两种指标与作物水分亏缺程度的关系,形成指导农田灌溉的土壤指标、冠气温差指标和叶片水势指标体系     

Evaluation of kernel yield and agronomic traits of European maize hybrids in the temperate region of Iran

The production of locally adapted maize hybrids requires parental material with adequate genetic variation in the relevant traits. The objective of the present study was to evaluate 20 European maize hybrids under temperate region for their potential use in direct cultivation or as parent material in local breeding programs. Results showed that European hybrids except BC 566 had higher kernel yield (11.4–14.3 t ha^?1) than local cultivars (KSC705 and KSC704). Korimbos, Krebs, BC 566, and BC 532 had lower kernel moisture (14–15%) compared to KSC705 (21.7%) and KSC704 (22.7%). Cluster analysis categorized these hybrids in three groups. Cluster 2 comprised of Korimbos, BC 612, DKC 6589, and 89May70. These hybrids had high plant height, thousand kernel weight, and kernel yield. Due to high kernel moisture, the hybrid 89May70 could not be proposed for direct cultivation but it can be involved in transferring high grain yield to local hybrids. Genotype × environment analysis showed that Korimbos and Krebs had low S²_i and low genotypic coefficient of variation, high and stable performance and low kernel moisture. Therefore, Korimbos and Krebs can possibly be used for direct cultivation in temperate regions of the Fars Province.     

Improving nutritional quality of maize proteins by expressing sense and antisense zein genes

The predominant proteins in maize grain are a family of alcohol-soluble prolamin storage proteins called zeins. They account for >50% of total seed proteins but are deficient in several essential amino acids. As a result, the corn grain is considered to be nutritionally poor for monogastric animals with respect to key essential amino acids, most notably lysine, tryptophan, and methionine. Thus, corn mutants with reduced levels of zeins, such as opaque-2 (o2), have been demonstrated to possess grain with improved nutritional quality characteristics. The o2 mutant has a superior amino acid composition and has been used through conventional breeding to develop Quality Protein Maize (QPM) for human and animal consumption in developing countries. With the understanding of molecular genetics of zeins and progress in biotechnology, an alternative approach to zein reduction is explored here. Through the targeted reduction of the 19-kDa alpha-zeins, increased levels of lysine, tryptophan, and methionine have been engineered in grain of transgenic hybrids. Currently, the agronomic properties and nutritional values of these transgenic lines are being evaluated.     

Fungal growth and fusarium mycotoxin content in isogenic traditional maize and genetically modified maize grown in France and Spain

Fungi of the genus Fusarium are common fungal contaminants of maize and are also known to produce mycotoxins. Maize that has been genetically modified to express a Bt endotoxin has been used to study the effect of insect resistance on fungal infection of maize grains by Fusarium species and their related mycotoxins. Maize grain from Bt hybrids and near-isogenic traditional hybrids was collected in France and Spain from the 1999 crop, which was grown under natural conditions. According to the ergosterol level, the fungal biomass formed on Bt maize grain was 4-18 times lower than that on isogenic maize. Fumonisin B(1) grain concentrations ranged from 0.05 to 0.3 ppm for Bt maize and from 0.4 to 9 ppm for isogenic maize. Moderate to low concentrations of trichothecenes and zearalenone were measured on transgenic as well as on non-transgenic maize. Nevertheless, significant differences were obtained in certain regions. The protection of maize plants against insect damage (European corn borer and pink stem borer) through the use of Bt technology seems to be a way to reduce the contamination of maize by Fusarium species and the resultant fumonisins in maize grain grown in France and Spain.     

分根区交替灌溉对玉米水分利用和土壤微生物量碳的影响

分根区交替灌溉由于创造了一个土壤水分分布不均匀的环境,从而影响土壤中微生物活性,作物水分和养分利用。为探明这种影响,该文通过盆栽试验,研究了在2种灌水水平(正常灌水W1,70%～80%田间持水率;轻度缺水W2,60%～70%田间持水率)和2种有机无机氮比例(100%无机氮,70%无机氮+30%有机氮)条件下,常规灌溉和不同生育期分根区交替灌溉(分别在苗期～灌浆初期、苗期～拔节期以及拔节期～抽雄期进行分根区交替灌溉(AI),即AI1、AI2和AI3)对玉米干物质积累、水分利用以及拔节期、抽雄期和灌浆初期土壤微生物量碳(MBC),可溶性碳(DOC)含量以及基础呼吸和诱导呼吸CO2释放量等的影响。结果表明,与常规灌溉相比,轻度缺水时,拔节期～抽雄期分根区交替灌溉总干物质质量增加23.2%～27.4%,水分利用效率提高23.3%～26.7%;相同施肥和灌水水平条件下,抽雄期时拔节期～抽雄期分根区交替灌溉土壤MBC增加,但是土壤诱导呼吸CO2释放量降低。与单施无机氮相比,有机、无机氮配施增加玉米干物质质量,在某些水分条件下(W1CI、W1AI1和W1AI2)还提高灌浆初期基础呼吸和诱导呼吸CO2释放量。因此,轻度缺水时拔节期～抽雄期进行分根区交替灌溉可以提高玉米总干物质质量、水分利用效率和微生物量碳。     

Effects of Nitrogen Application on Chlorophyll Content,Water Relations,and Yield of Maize Hybrids under Saline Conditions

An experiment was conducted to assess whether accumulation of photosynthetic pigments, proline, and maintenance of water relation attributes relate to the yield of maize hybrids differing in salt tolerance. Two maize hybrids, Pioneer32B33 and Dekalb979, were grown at three salinity levels under four nitrogen treatments. The experiment was laid out in a three-factor randomized complete block design and there were three replications of each treatment. Salt stress significantly decreased leaf chlorophyll a and a/b contents, whereas chlorophyll b and total chlorophyll were slightly increased. Under salinity stress, relative water content decreased, and water potential and osmotic potential become more negative. As a result, turgor potential also decreased. Nitrogen application improved all the chlorophyll pigments, water-related attributes, and yield components. However, chlorophyll a/b ratio was decreased. Overall, because of the differential response of maize hybrids to salt stress in terms of their performance in photosynthetic pigments, water relations, and yield, it can be concluded that hybrid Pioneer32B33 might perform better, if grown under salinity regime and sufficient nitrogen was applied in the growth medium.     

Relationships Between Carbon Isotope Discrimination and Yield of Spring Wheat Under Different Water and Nitrogen Levels

ABSTRACT

A greenhouse experiment was conducted to investigate the relationships between foliar carbon isotope discrimination (Δ) and above ground dry matter (ADM) at different stages during a plant's life cycle, and grain carbon isotope discrimination and grain yield (GY) at maturity of spring wheat (Triticum aestivum L.) under different nitrogen (N) and water levels. Results showed that ADM and GY both increased significantly with decreasing water stress, while the effects of nitrogen on ADM and GY varied with the water conditions. Foliar and grain carbon isotope discrimination decreased with increasing water stress and increasing nitrogen levels. For all water conditions, relationships between carbon isotope discrimination (foliar and grain) and yields (ADM and GY) were significantly positive (P < 0.001) at various growth stages. However, at the same water level, the correlations were complex, and under well-watered conditions, ADM and GY were strongly and negatively correlated with foliar and grain carbon isotope discrimination at all growth stages (P < 0.001). The correlations were inconsistent and not significant at moderate water level, but were positive under drought. Our results showed that water and nitrogen both significantly affected the relationships between yield and carbon isotope discrimination of spring wheat, that there are interactions between these two parameters, and that environmental conditions such as water and fertilizer must thus be considered in future research on the relationship between yield and carbon isotope discrimination of spring wheat.     

土壤干旱胁迫对玉米叶片水分状况、膜透性及酶抗氧化系统的影响

A simulation experiment on the responses of maize （Zea mays L.） from the third leaf stage to maturity for different soil water levels （well-watered, moderately stressed, and severely stressed） was conducted by controlling irrigation and using a mobile rain shelter in a neutral loam, meadow soil to determine the effects on leaf water status, membrane permeability and enzymatic antioxidant system for different growth stages. The results indicated that drought stress relied on drought intensity and duration, with more severe drought stress creating more serious effects on maize. Compared with wellwatered conditions, during the silking and blister stages moderate stress did not significantly change the relative water content （RWC） and did change significantly the relative conductivity （RC） （P 〈 0.05） of the leaves; however, severe stress did significantly decrease （P 〈 0.01） the leaf RWC and increase （P 〈 0.01） membrane permeability （leaf relative conductivity）. Furthermore, under severe drought stress antioxidant enzyme activities declined significantly （P 〈 0.01） in later stages, namely for superoxide dismutase （SOD） the tasseling and blister stages, for peroxidase （POD） the milk stage, and for catalase （CAT） during the tasseling, blister, and milk stages. Meanwhile, membrane lipid peroxidation （measured as malondialdehyde content） significantly increased （P 〈 0.01） in all stages.     

不同土壤水分供应与施锌对玉米水分代谢的影响

采用盆栽试验研究不同土壤水分状况下及施锌对玉米植株水分状况、水分生理特征的影响。结果表明,干旱胁迫下,玉米叶片含水量和水势降低,植株体内自由水分的含量减少,而束缚水含量略有增加,离体叶片失水速率小;叶片气孔阻力增加,导度下降,蒸腾作用和光合速率受到抑制。施锌后玉米叶片的水势和鲜重含水量没有明显变化,但玉米叶片气孔阻力降低,气孔导度增加,叶片蒸腾速率和光合作用速率加大。干旱胁迫下,施锌对玉米植株体内水分生理代谢有一定的调节作用,但是在土壤水分供应充足时,施锌更能增强玉米水分生理代谢,提高水分利用效率。