Ammonium and amino acid metabolism in excised leaves of wheat (Triticum aestivum) senescing in the dark

Several parameters of amino acid metabolism were studied in detached primary leaves of wheat (Triticum aestivum L. cv. Castell) during a 14 day incubation period in the dark. Protein loss was accompanied by a 5-fold increase in the total amount of free amino acids during the first 4 days of the incubation period with asparagine being the most important. Beyond this stage a pronounced intracellular accumulation of ammonium occured. A gradual decrease in the levels of free amino acids and ammonium at the later stages of senescence could in part be accounted for by leakage from the leaves. Additionally, some nitrogen was lost due to ammonia volatilization. The rapid decay of the glutamine synthetase (GS; EC 6.3.1.2)-glutamate synthase (Fd-GOGAT; EC 1.4.7.1) system and the fast decline of glutamate-pyruvate transaminase (GPT; EC 2.6.1.2) activity appear to be predominant features of senescence in the dark. Decreasing Fd-GOGAT activity was slightly compensated by a small and temporary increase in the activity of NADH-GOGAT (EC 1.4.1.14). Glutamateoxalocetate transaminase (GOT: EC 2.6.1.1) activity, although declining continuously, proved to be much more persistent. Changes in glutamate dehydrogenase (GDH; EC 1.4.1.3) activity closely resembled the profile of ammonium evolution in the leaves and NADP-isocitrate dehydrogenase (IDH; EC 1.1.1.42) activity revealed a temporary maximum during the period of rapid increase in GDH activity. Increased activity of GDH could also be induced by exogenous ammonium. Ammonium accumulation could, at least partly, be caused by increased asparaginase (EC 3.5.1.1) activity which accompanied the rapid conversion of asparagine to aspartic acid. Asparagine aminotransferase (EC 2.6.1.14) activity declined sharply from the beginning of the senescence period. Although the activity profile of glutaminase (EC 3.5.1.2) was similar to that of asparaginase, glutamine was of little importance quantitatively and an analogous relationship between glutamine and glutamic acid could not be detected.     

Effects of different levels of nitrogen fertilization on soil respiration during growing season in winter wheat (Triticum aestivum)

 在目前全球氮沉降不断增加的背景下, 研究农田土壤呼吸对氮沉降的响应有助于理解未来生态系统碳循环对全球变暖的潜在影响。为探讨不同施氮浓度对华东地区冬小麦(Triticum aestivum)生长期土壤呼吸的影响, 该实验设计了对照组(不施加氮肥)和3种浓度施氮处理组(低浓度施氮15 g·m^–2·a^–1, 中等浓度施氮30 g·m^–2·a^–1, 高浓度施氮45 g·m^–2·a^–1)。使用便携式土壤CO₂通量观测仪LI-8100测定不同施氮浓度处理下冬小麦生长期(2013年12月至2014年5月)的土壤呼吸速率, 并探讨土壤呼吸与土壤温度、湿度等环境因素的关系。结果表明: 低、中、高3种浓度施氮处理的土壤呼吸速率平均值分别为5.29、6.17和6.75 μmol·m^–2 ·s^–1, 与对照组(土壤呼吸速率平均值为4.90 μmol·m^–2·s^–1)相比, 分别增加了7.8%、23.6%和37.8%; 地上生物量分别增加39.9%、104.4%和200.2%, 并与冬小麦生长季的总土壤呼吸正相关。5 cm深度土壤的温度与土壤呼吸速率呈指数关系(p < 0.05), 土壤呼吸季节变化的65%–75%由土壤温度引起, 其温度敏感性为2.09–2.32。结果表明, 添加氮肥促进了植物的生长, 增加了生物量, 从而增加了冬小麦农田的土壤呼吸速率。     

不同施氮水平对冬小麦生长期土壤呼吸的影响

在目前全球氮沉降不断增加的背景下, 研究农田土壤呼吸对氮沉降的响应有助于理解未来生态系统碳循环对全球变暖的潜在影响。为探讨不同施氮浓度对华东地区冬小麦(Triticum aestivum)生长期土壤呼吸的影响, 该实验设计了对照组(不施加氮肥)和3种浓度施氮处理组(低浓度施氮15 g·m^-2·a^-1, 中等浓度施氮30 g·m^-2·a^-1, 高浓度施氮45 g·m^-2·a^-1)。使用便携式土壤CO₂通量观测仪LI-8100测定不同施氮浓度处理下冬小麦生长期(2013年12月至2014年5月)的土壤呼吸速率, 并探讨土壤呼吸与土壤温度、湿度等环境因素的关系。结果表明: 低、中、高3种浓度施氮处理的土壤呼吸速率平均值分别为5.29、6.17和6.75 μmol·m^-2 ·s^-1, 与对照组(土壤呼吸速率平均值为4.90 μmol·m^-2·s^-1)相比, 分别增加了7.8%、23.6%和37.8%; 地上生物量分别增加39.9%、104.4%和200.2%, 并与冬小麦生长季的总土壤呼吸正相关。5 cm深度土壤的温度与土壤呼吸速率呈指数关系(p < 0.05), 土壤呼吸季节变化的65%-75%由土壤温度引起, 其温度敏感性为2.09-2.32。结果表明, 添加氮肥促进了植物的生长, 增加了生物量, 从而增加了冬小麦农田的土壤呼吸速率。     

Distribution of gluten proteins in bread wheat (Triticum aestivum) grain

Background and Aims

Gluten proteins are the major storage protein fraction in the mature wheat grain. They are restricted to the starchy endosperm, which forms white flour on milling, and interact during grain development to form large polymers which form a continuous proteinaceous network when flour is mixed with water to give dough. This network confers viscosity and elasticity to the dough, enabling the production of leavened products. The starchy endosperm is not a homogeneous tissue and quantitative and qualitative gradients exist for the major components: protein, starch and cell wall polysaccharides. Gradients in protein content and composition are the most evident and are of particular interest because of the major role played by the gluten proteins in determining grain processing quality.

Methods

Protein gradients in the starchy endosperm were investigated using antibodies for specific gluten protein types for immunolocalization in developing grains and for western blot analysis of protein extracts from flour fractions obtained by sequential abrasion (pearling) to prepare tissue layers.

Key Results

Differential patterns of distribution were found for the high-molecular-weight subunits of glutenin (HMW-GS) and γ-gliadins when compared with the low-molecular-weight subunits of glutenin (LMW-GS), ω- and α-gliadins. The first two types of gluten protein are more abundant in the inner endosperm layers and the latter more abundant in the subaleurone. Immunolocalization also showed that segregation of gluten proteins occurs both between and within protein bodies during protein deposition and may still be retained in the mature grain.

Conclusions

Quantitative and qualitative gradients in gluten protein composition are established during grain development. These gradients may be due to the origin of subaleurone cells, which unlike other starchy endosperm cells derive from the re-differentiation of aleurone cells, but could also result from the action of specific regulatory signals produced by the maternal tissue on specific domains of the gluten protein gene promoters.     

Sucrose metabolism during endosperm development in wheat (Triticum aestivum)

This work reports changes in sucrose synthase and invertase activities throughout endosperm development in wheat, together with the associated substrates and metabolites, sucrose, UDP, glucose, fructose and UDP-glucose. Throughout endosperm development, sucrose synthase had consistently higher activity than invertase and indeed invertase activity did not change appreciably. The observed variation in pattern and amounts of glucose and fructose present during the mid- and late stages of endosperm development confirmed the suggestion that invertase was not the preferred pathway of sucrose catabolism. Kinetic parameters for sucrose synthase were determined in crude extracts. Estimates of UDP and sucrose concentrations suggest that sucrose synthase is unlikely to achieve its potential maximum velocity. This limitation may however be overcome in part by the apparent excess catalytic activity measured during endosperm development.     

Allelopathy in wheat (Triticum aestivum)

Wheat (Triticum aestivum) allelopathy has potential for the management of weeds, pests and diseases. Both wheat residue allelopathy and wheat seedling allelopathy can be exploited for managing weeds, including resistant biotypes. Wheat varieties differ in allelopathic potential against weeds, indicating that selection of allelopathic varieties might be a useful strategy in integrated weed management. Several categories of allelochemicals for wheat allelopathy have been identified, namely, phenolic acids, hydroxamic acids and short‐chain fatty acids. Wheat allelopathic activity is genetically controlled and a multigenic model has been proposed. Research is underway to identify genetic markers associated with wheat allelopathy. Once allelopathic genes have been located, a breeding programme could be initiated to transfer the genes into modern varieties for weed suppression. The negative impacts of wheat autotoxicity on agricultural production systems have also been identified when wheat straws are retained on the soil surface for conservation farming purposes. A management package to avoid such deleterious effects is discussed. Wheat allelopathy requires further study in order to maximise its allelopathic potential for the control of weeds, pests and diseases, and to minimise its detrimental effects on the growth of wheat and other crops.     

Effects of foliar applied benzyladenine on grain yield and grain protein in wheat (Triticum aestivum L.)

The effects of foliar applications of nitrogen and benzyladenine (BA) on grain yield and grain protein of wheat grown under field conditions were studied over 2 years with 5 cultivars at 2 locations. Nitrogen (N) at 20 kg.ha^–1, and BA at 100 or 800 mg.l^–1 were applied alone or combined at pre and post-anthesis; applications of BA at 8 mg.l^–1 were also made on individual ears in order to study the effect on cell number. Weekly determinations of the chlorophyll content of the flag leaf were conducted after anthesis to study leaf senescence. At harvest, yield, yield components and grain protein percentage were determined. N and BA applications delayed chlorophyll loss in the flag leaf, but modified neither yield nor yield components. Foliarly applied BA increased grain protein in four of the five cultivars tested. It is concluded that delay of the senescence induced by BA might allow more energy to be available for N uptake by the crop leading to an increase in grain protein.Research supported by a CAFPTA grant 1656/86 and by CONICET, PID 30017700/85.CONICETComisión de Investigaciones Cientificas de la Provincia de Buenos AiresInstituto de Fisiologia Vegetal     

低磷和干旱胁迫对小麦生长发育影响的研究初探

研究了低磷和干旱胁迫对小麦（Triticum aestivum L.）生长发育的影响。结果表明,低磷胁迫能显著降低小麦的分蘖数、叶片相对含水量和叶绿素含量,进而抑制小麦的生长发育,降低其生物产量和经济产量,不耐低磷品种中国春受影响的程度要大于耐低磷品种烟中144。在相同条件下,干旱能够强化磷胁迫效应,表现出明显的胁迫叠加现象。     

Antioxidative enzymes and the Russian wheat aphid (Diuraphis noxia) resistance response in wheat (Triticum aestivum)

A crucial function of antioxidative enzymes is to remove excess reactive oxygen species (ROS), which can be toxic to plant cells. The effect of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), infestation on the activities of antioxidative enzymes was investigated in the resistant (cv. Tugela DN) and the near-isogenic susceptible (cv. Tugela) wheat (Triticum aestivum L.). RWA infestation significantly induced the activity of superoxide dismutase, glutathione reductase and ascorbate peroxidase to higher levels in the resistant than in susceptible plants. These findings suggest the involvement of antioxidative enzymes in the RWA-wheat resistance response, which was accompanied by an early oxidative burst. The results are consistent with the role of ROS in the resistance response and the control of their levels to minimise toxic effects.     

Lignin deposition induced by aluminum in wheat (Triticum aestivum) roots

We investigated the relation between the toxic effect of aluminum (Al) on root growth and the lignin deposition in wheat ( Triticum aestivum L. cvs Atlas 66 and Scout 66). In the Al-tolerant cultivar Atlas 66, control treatment without AlCl₃ at pH 4.75, cell length increased dramatically in the portion of the root that was 0.6 to 3.2 mm from the root cap junction (approximately 1.0 to 3.6 mm from the root tip). However, treatment with 20 μ M AlCl₃ for 24 and 48 h completely inhibited root elongation and markedly decreased the length and increased the diameter of the cells in the same portion of the root. Moreover, marked deposition of lignin was observed in the cells that corresponded to the portion 1.5 to 4.5 mm from the root tip in Atlas 66 roots treated with 20 μ M AlCl₃, while no deposition of lignin was detected in control roots. Treatment with 5 μ M AlCl₃ slightly inhibited root growth and there was no deposition of lignin in the root. On the other hand, in roots of the Al-sensitive cultivar Scout 66, treatment with 5 μ M AlCl₃ completely inhibited root growth and markedly induced deposition of lignin. These results suggest that lignification in the elongating region coincided with the extent of inhibition of root growth by Al in two wheat cultivars that differed in their sensitivity to Al.     

Amino acid metabolism associated with N-mobilization from the flag leaf of wheat (Triticum aestivum L.) during grain development

Field-grown winter wheat (Triticum aestivum L. cv. Castell) was used to study changes in the free amino acid pools of different plant parts and related enzyme activities in the flag leaf throughout the grain-filling period in three consecutive growing seasons. Amino acid analysis data indicated that, during senescence, the nitrogen flow in the flag leaf was directed towards the synthesis of glutamine as a specific nitrogen transport form. Of the enzymes involved, total glutamine synthetase (GS; EC 6.3.1.2) and especially ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) activities declined continuously as senescence progressed. Unlike (chloroplastic) GS₂, (cytosolic) GS₁ was shown to be very persistent suggesting a special role for this isoenzyme in the N-reallocation process. Glutamate-oxaloacetate transaminase (GOT; EC 2.6.1.1), glutamate-pyruvate transaminase (GPT; EC 2.6.1.2) and isocitrate dehydrogenase (IDH; EC 1.1.1.42) showed a characteristic biphasic activity profile after anthesis. It is proposed that these enzymes, for each of which at least two isoenzymes were demonstrated, are involved in glutamate synthesis at the later stages of leaf senescence. Ammonium levels were fairly constant throughout the flag leafs life span, an ultimate rise often following peak values of glutamate dehydrogenase (GDH; EC 1.4.1.4) activity. The enzymology of flag leaf amino acid metabolism during grain development is further discussed in relation to observations of NH₃-volatilization from naturally senescing wheat plants.     

冬小麦根系时空分布动态及产量对不同氮源配施的响应

为了解不同氮(N)源(有机/无机肥)配施对冬小麦(Triticum aestivum)根系时空分布特征和产量的影响, 采用微根管(minirhizotron)动态监测技术, 以强筋小麦品种‘豫麦34’为试验材料, 在等养分条件下, 设置不施肥(T₀)、100%尿素N (T₁)、75%尿素N + 25%鸡粪N (T₂)、50%尿素N + 50%鸡粪N (T₃)、25%尿素N + 75%鸡粪N (T₄)和100%鸡粪N (T₅)等6个有机N与化肥N配施处理, 研究分析了‘豫麦34’在不同生育时期及0-100 cm土层中根系直径、根长密度、根长生长量和死亡量等根系特征参数的变化及其产量表现。结果表明, 施肥不仅有利于各生育时期及不同土层中根系直径、根长密度和根长生长量的增加, 而且增加了根长死亡量, 促进了根系的周转。对不同配施处理进行比较, 发现T₃处理(尿素和鸡粪等氮配施)的效果最为显著, 全生育期平均根长密度、周期生长量与周期死亡量分别较对照T₀增加了55.52%、57.79%和61.61%, 有效分蘖数、穗粒重、经济产量和经济系数也以T₃处理增加最多, 分别较T₀增加了52.63%、43.90%、40.16%和12.02%; 穗粒数在T₄处理下最大, 较T₀增加了45.79%; 生物产量在T₅处理下最高, 比T₀增加了26.95%。因此, 不同氮源合理配施有利于促进冬小麦根系的生长及在不同土层中的扩展, 提高冬小麦产量。尿素和鸡粪为N源时等氮配施(50 : 50)的效果最佳。     

干旱胁迫下冬小麦(Triticum aestivum)高光谱特征和生理生态响应

2006年于冬小麦(Triticum aestivum)孕穗期、开花期和灌浆期,采用ASD Fieldspec HH光谱仪测定了不同水分胁迫下冬小麦高光谱反射率、红边参数和对应的冬小麦生理生态参数叶绿素a(Chla)、叶绿素b(Chlb)、叶绿素a b(Chla b),叶片水分含量(LWC),叶面积指数(LAI).结果表明,冬小麦生理生态参数随生长发育呈现先上升后下降趋势,Chla、Chlb和Chla b开花期达最大值;LWC和LAI孕穗期达最大值.随干旱胁迫程度增加,Chla、Chlb和Chla b、LWC和LAI减少.不同水分处理下冬小麦高光谱反射率具有绿色植物特征.用红边一阶微分光谱特征参数分析,冬小麦孕穗期和开花期红边(λred)位于728～730nm,灌浆期红边(λred)移到734nm.Chla、Chlb和Chla b与Dλ730:Dλ702、Dλ730:Dλ718,LWC与Dλred、Dλ718以及LAI与Dλ718、Dλred、Sred均呈正相关,相关系数大于0.5(p<0.05).经回归分析,Chl与Dλ730:Dλ702、LWC与Dλred呈线性关系(R2=0.87),LAI与Sred呈二次关系(R2=0.68).因此,用冬小麦高光谱特征及红边参数能判断冬小麦生育后期长势和农田水分胁迫程度.     

Translocation and cycling through roots of recently absorbed nitrogen and sulphur in wheat (Triticum aestivum) during vegetative and generative growth

¹⁵N-Nitrate and ³⁵S-sulphate labelling experiments were performed with spring wheat ( Triticum aestivum L. cv. Timmo) 44. 64, 79, 95 and 115 days after sowing (growth stages arbitrarily denoted I to V). Label was fed to the plants via a fraction of the root system, termed "donor root", whereas the rest of the root ("receiver root") was fed non-labelled nutrient solution. Net uptake rates for both nitrate and sulphate per unit root weight changed little from growth stage I to IV, but were considerably lower at stage V. On a whole-plant weight basis, uptake declined from stage I to IV, because root contribution to total plant weight declined. Between 80 and 95% of absorbed label was translocated to the shoot at all growth stages. At stage V, up to 30% of absorbed label was recovered in the ears. Labelling of the receiver root indicated that, at all growth stages, 10 to 17% of N and 12 to 32% of S translocated to the shoot was retranslocated to the root. This corresponds to between 35 and 85% of the label actually recovered in the roots. Analysis of ¹⁵N-labelling of xylem sap collected from receiver roots at growth stages I to IV indicated that about half of the reduced N in the sap is derived from cycling through roots of recently assimilated N. Evidence of cycling was also obtained at stage V. Labelled sulphate was the only form of S cycled in the plant, but it accounted for only 1 to 7% of the sulphate in the xylem sap.     

Nitrate accumulation by wheat (Triticum aestivum) in relation to growth and tissue N concentrations

The accumulation of nitrate in relation to total N concentrations ([N]_i) in tissues of wheat (Triticum aestivum L., cv Sicco) grown in solution culture was investigated. Root, shoot and leaf tissues showed qualitatively similar relationships between internal nitrate concentrations and [N]_i, both expressed on a tissue water basis. At low [N]_i, no nitrate was detectable but once a particular [N]_i was exceeded, nitrate accumulated as a linear function of [N]_i. The threshold [N]_i values for nitrate accumulation were 110, 450, and 550 mM for roots, total shoot and leaf 4, respectively. The slope of the relationship between nitrate and [N]_i indicated that in all tissues nitrate accounted for 50–55% of the extra N accumulated above the threshold [N]_i. All growth requirements for N were satisfied before nitrate accumulated.     

Endogenous gibberellins in young seedlings of wheat (Triticum aestivum) cultivars

Gibberellins A₁, A₃, A₄ and A₇ were identified by combined gas chromatography mass spectrometry (GC-MS) in leaf and stem tissues of 17-day-old seedlings of wheat ( Triticum aestivum L. ), cvs Siete Cerros (semi-dwarf, Rht1) and Møystad (tall), of F₁, hybrids from the cross Møystad × Siete Cerros and of 2 selected lines from the cross Møystad x Sonora 64 (Rht1 and Rht2). GA, and GA, were identified by full scan mass spectra separately in all 5 extracts, GA₄ and GA₇, were identified by selected ion monitoring in a bulked fraction. About 90% of the biological activity (Tan-ginbozu dwarf rice bioassay) in all 5 extracts was due to the GA₁/GA₃-fraction.     

Accelerated production of transgenic wheat (Triticum aestivum L.) plants

We have developed a method for the accelerated production of fertile transgenic wheat (Triticum aestivum L.) that yields rooted plants ready for transfer to soil in 8–9 weeks (56–66 days) after the initiation of cultures. This was made possible by improvements in the procedures used for culture, bombardment, and selection. Cultured immature embryos were given a 4–6 h pre-and 16 h post-bombardment osmotic treatment. The most consistent and satisfactory results were obtained with 30 g of gold particles/bombardment. No clear correlation was found between the frequencies of transient expression and stable transformation. The highest rates of regeneration and transformation were obtained when callus formation after bombardment was limited to two weeks in the dark, with or without selection, followed by selection during regeneration under light. Selection with bialaphos, and not phosphinothricin, yielded more vigorously growing transformed plantlets. The elongation of dark green plantlets in the presence of 4–5 mg/l bialaphos was found to be reliable for identifying transformed plants. Eighty independent transgenic wheat lines were produced in this study. Under optimum conditions, 32 transformed wheat plants were obtained from 2100 immature embryos in 56–66 days, making it possible to obtain R3 homozygous plants in less than a year.