Lead phytotoxicity on wheat (Triticum aestivum L.) seed germination and seedlings growth

Lead (Pb) is an environmental pollutant extremely toxic to plants and other living organisms including humans. To assess Pb phytotoxicity, experiments focusing on germination of wheat seeds were germinated in a solution containing Pb (NO(3))(2) (0.05; 0.1; 0.5; 1g/L) during 6 days. Lead accumulation in seedlings was positively correlated with the external concentrations, and negatively correlated with morphological parameters of plant growth. Lead increased lipid peroxidation, enhanced soluble protein concentrations and induced a significant accumulation of proline in roots. Esterase activity was enhanced in the presence of lead, whereas α-amylase activity was significantly inhibited. Antioxidant enzymes activities, such as, ascorbate peroxidase, peroxidase, superoxide dismutase, catalase and glutathione S-transferase were generally significantly increased in the presence of lead in a dose-dependent manner. The present results thus provide a model system to screen for natural compounds able to counteract the deleterious effects of lead.     

The development of waterlogging damage in wheat seedlings (Triticum aestivum L.)

Summary Decreases in the concentrations of nitrogen, phosphorus, potassium, calcium and magnesium, in the shoots of wheat seedlings soon after the start of waterlogging were mainly attributed to an inhibition of ion uptake and transport by roots in the oxygen deficient soil. There was a small net accumulation of nitrogen, phosphorus and potassium by the aerial tissues, principally the tillers rather than the main shoot. By contrast, calcium and magnesium accumulated in both tillers and main shoot. With waterlogging, nitrogen, phosphorus and potassium were translocated from the older leaves to the younger growing leaves, and in the case of nitrogen this was associated with the onset of premature senescence. Calcium and magnesium were not translocated from the older leaves, the younger leaves acquiring these cations from the waterlogged soil. The promotion of leaf senescence by waterlogging was counteracted by applications of nitrate or ammonium to the soil surface, or by spraying the shoots with solutions of urea, but the beneficial effects on shoot growth were small.The role of mineral nutrition in relation to waterlogging damage to young cereal plants is discussed.     

Silicon absorption by wheat (Triticum aestivum L.)

Although silicon (Si) is a quantitatively major inorganic constituent of higher plants the element is not considered generally essential for them. Therefore it is not included in the formulation of any of the solution cultures widely used in plant physiological research. One consequence of this state of affairs is that the absorption and transport of Si have not been investigated nearly as much as those of the elements accorded 'essential' status. In this paper we report experiments showing that Si is rapidly absorbed by wheat (Triticum aestivum L.) plants from solution cultures initially containing Si at 0.5 mM, a concentration realistic in terms of the concentrations of the element in soil solutions. Nearly mature plants (headed out) 'preloaded' with Si absorbed it at virtually the same rate as did plants grown previously in solutions to which Si had not been added. The rate of Si absorption increased by more than an order of magnitude between the 2-leaf and the 7-8 leaf stage, with little change thereafter. This revised version was published online in June 2006 with corrections to the Cover Date.     

The development of waterlogging damage in wheat seedlings (Triticum aestivum L.)

Summary The effects of waterlogging on concentrations of gases and various solutes dissolved in the soil water were investigated in the laboratory, to determine whether the early disruption to the growth of wheat was most closely associated with depletion of dissolved oxygen, accumulation of toxins, or changes in concentrations of nutrient ions in the soil water. Waterlogging slowed shoot fresh weight accumulation, leaf extension and nodal root growth; it also caused death of the seminal root system and early senescence of the lower leaves. However, the shoot dry weight initially increased above that of the non-waterlogged controls, and thus was not a reliable indicator of the early restriction to plant growth and development. The symptoms of damage to shoots and roots were attributed to the fall in soil oxygen concentrations, rather than to any decrease in concentration of inorganic nutrients in the soil water, or to the accumulation of any other measured solutes to toxic concentrations.     

Mapping loci associated with milling yield in wheat (Triticum aestivum L.)

A partial genetic linkage map constructed using 150 single seed descent (SSD) lines generated from a cross between the hexaploid wheat varieties Schomburgk and Yarralinka was used to identify loci controlling milling yield. Milling yield data were obtained using seed collected from field trials conducted at different sites over two seasons. The estimated broad-sense heritability of milling yield in this population was calculated as 0.48. In the preliminary analysis, two regions were identified on chromosomes 3A and 7D, which were significantly associated with milling yield and accounted for 22% and 19% of the genetic variation, respectively. Bulked segregant analysis in combination with AFLP identified other markers linked to these loci, as well as an additional region on chromosome 5A, which accounted for 19% of the genetic variation. The applicability of these markers as selection tools for breeding purposes is discussed.     

Mapping loci associated with flour colour in wheat (Triticum aestivum L.)

 An RFLP map constructed using 150 single seed descent (SSD) lines from a cross between two hexaploid wheat varieties (‘Schomburgk’בYarralinka’) was used to identify loci controlling flour colour. Flour colour data were obtained from field trials conducted over two seasons at different sites. The estimated heritability of this trait was calculated as 0.67. Two regions identified in the preliminary analysis on chromosomes 3A and 7A, accounted for 13% and 60% of the genetic variation respectively. A detailed analysis of the major locus on 7A was conducted through fine mapping of AFLP markers identified using bulked segregant analysis (BSA). Seven additional markers were identified by the BSA and mapped to the region of the 7A locus. The applicability of these markers to identify wheat lines with enhanced flour colour is discussed. Received: 30 September 1997 / Accepted: 4 February 1998     

Influence of minerals on cytoplasmic streaming in root hairs of intact wheat seedlings (Triticum aestivum L.)

The calcium dependency of the cytoplasmic streaming of wheat root hairs was demonstrated by adding the Ca-Ionophore A 23187. Within three minutes the streaming velocity was decreased dramactically. The influence of ammonium on the cytoplasmic streaming is highly pH-dependent. While at a pH of 9.0 an inhibitory effect was observed even at low ammonium concentrations (0.5 mM) no effect could be measured at a pH of 6.5. Nitrate, independently of medium pH had no effect on the cytoplasmic streaming. The same is true for aluminium. It is suggested that at pH 9 ammonium permiates the plasmalemma as NH₃. Due to higher cytoplasmic pH ( 7.5), NH₃ is protonated leading to an increase in cytoplasmic pH. Ammonium may displace sorbed calcium leading to an increase in the free cytoplasmic calcium responsible for the cessation of the streaming. Alternative explanations are discussed.Abbreviations HEPES N-2-Hydroxyethylpiperazine-N-2-ethanesulfonic acid     

Enzyme activities associated with developing wheat(Triticum aestivum L.) grain amyloplasts

Intact amyloplasts from endosperm of developing wheat grains have been isolated by first preparing the protoplasts and then fractionating the lysate of the protoplasts on percoll and ficoll gradients, respectively. Amyloplasts isolated as above were functional and not contaminated by cytosol or by organelles likely to be involved in carbohydrate metabolism. The enzyme distribution studies indicated that ADP-glucose pyrophosphorylase and starch synthase were confined to amyloplasts, whereas invertase, sucrose synthase, UDP-glucose pyrophosphorylase, hexokinase, phosphofructokinase-2 and fructose-2,6-P₂ase were absent fro the amyloplast and mainly confined to the cytosol. Triose-P isomerase, glyceraldehyde-3-P dehydrogenase, phosphohexose isomerase, phosphoglucomutase, phosphofructokinase, aldolase, PPi-fructose-6-P-1 phosphotransferase, and fructose-l,6-P₂ase, though predominantly cytosolic, were also present in the amyloplast. Based on distribution of enzymes, a probable pathway for starch biosynthesis in amyloplasts of developing wheat grains has been proposed.     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The flag leaf of wheat was examined for changes in quantity and activity of ribulose-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39), in the proteolytic degradation of RuBPCase and other native proteins, and in the ultrastructure of the leaf cells during grain development. Proteolytic degradation of RuBPCase at pH 4.8 increased until 8–10 d after anthesis, then declined, and increased again 16–18 d after anthesis. The second peak coincided with the onset of a preferential loss of immunologically recognizable RuBPCase. The specific activity and number of active sites per molecule of RuBPCase did not change during senescence. Examination of ultrastructure with the electron microscope showed little change in the appearance of the mitochondria as the flag leaf aged. Prominent cristae were still evident 35 d after anthesis. In contrast, the chloroplasts showed a progressive disruption of the thylakoid structure and an increasing number of osmiophilic glubules. The double membrane envelope surrounding the chloroplast appeared intact until at least 20 d after anthesis. The tonoplast also appeared intact up to 20 d. At later stages of senescence of the leaf the outer membrane of the chloroplast adjacent to the tonoplast appeared to break but the inner membrane of the envelope appeared intact until at least 35 d after anthesis.Abbreviation RuBPCase ribulose-1,5-bisphosphate carboxylase (EC. 4.1.1.39) I=Waters et al. 1980     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The technique of EDTA-enhanced phloem exudation (King and Zeevaart, 1974: Plant Physiol. 53, 96–103) was evaluated with respect to the collection and identification of amino acids exported from senescing wheat leaves. Whilst the characteristics of the exudate collected conform with many of the accepted properties of phloem exudate, unexpectedly high molar proportions of phenylalanine and tyrosine were observed. By comparing exudation into a range chelator solutions with exudation into water, the increased exudation of phenylalanine and tyrosine relative to the other amino acids occurring when ethylene-diaminetetracetic acid was used, was considered to an artefact.In plants thought to be relying heavily on mobilisation of protein reserves to satisfy the nitrogen requirements of the grain, the major amino acids present in flag-leaf phloem exudate were glutamate, aspartate, serine, alanine and glycine. Only small proportions of amides were present until late in senescence when glutamine became the major amino acid in phloem exudate (25 molar-%). Glutamine was always the major amino acid in xylem sap (50 molar-%).The activities of glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.7.1), glutamate dehydrogenase (EC 1.4.1.3) and asparagine synthetase (EC 5.3.5.4) were measured in the flag leaf throughout the grain-filling period. Glutamine synthetase and glutamate-synthase activities declined during this period. Glutamate-dehydrogenase activity was markedly unchanged despite variation in the number of multiple forms visualised after gel electrophoresis. The activity of the enzyme reached a peak only very late in the course of senescence of the flag leaf. No asparagine-synthetase activity could be detected in the flag leaf during the grain-filling period.II. Peoples et al. (1980)     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The activity of a range of endo- and exopeptidase enzymes have been measured in the glumes, flag leaf and stem during the period of grain development in wheat. The enzymes show a sequential pattern of appearance with activity peaks occurring at a number of intervals from anthesis until just prior to the cessation of grain growth. Of the enzymes studied only the haemoglobin- and casein-degrading activity and alanylglycine-dipeptidase activity increased during the period of rapid protein loss, while aminopeptidase, carboxypeptidase and leucyltyrosine dipeptidase reached maximum activity prior to this period.     

Physiological traits associated with heat tolerance in bread wheat (Triticum aestivum L.)

Field experiments for evaluating heat tolerance-related physiological traits were conducted for two consecutive years using a mapping population of recombinant inbred lines (RILs) from the cross RAJ4014/WH730. Chlorophyll content (Chl) and chlorophyll fluorescence (CFL) were recorded under timely sown (TS) and late sown (LS) conditions. Late sowing exposes the terminal stage of plants to high temperature stress. Pooled analysis showed that CFL and Chl differed significantly under TS and LS conditions. The mean value of CFL (Fv/Fm) and Chl under both timely and late sown conditions were used as physiological traits for association with markers. Regression analysis revealed significant association of microsatellite markers viz., Xpsp3094 and Xgwm131 with coefficients of determination (R²) values for CFL (Fv/Fm) and Chl as 12 and 8 %, respectively. The correlation between thousand grain weight (TGW) with Chl and CFL were 14 and 7 % and correlation between grain wt./spike with Chl and CFL were 15 and 8 %, respectively. The genotypes showing tolerance to terminal heat stress as manifested by low heat susceptibility index (HSI = 0.43) for thousand grain weight, were also found having very low Chl, HSI (−0.52). These results suggest that these physiological traits may be used as a secondary character for screening heat-tolerant genotypes.     

Impaired electron transfer accounts for the photosynthesis inhibition in wheat seedlings (Triticum aestivum L.) subjected to ammonium stress

No single mechanism can provide an adequate explanation for the inhibition of photosynthesis when plants are supplied with ammonium (NH₄⁺) as the sole nitrogen (N) source. We performed a hydroponic experiment using two N sources [5 mM NH₄⁺ and 5 mM nitrate (NO₃^?)] to investigate the effects of NH₄⁺ stress on the photosynthetic capacities of two wheat cultivars (NH₄⁺‐sensitive AK58 and NH₄⁺‐tolerant XM25). NH₄⁺ significantly inhibited the growth and light‐saturated photosynthesis (A_sat) of both cultivars, but the extent of such inhibition was greater in the NH₄⁺‐sensitive AK58. The CO₂ concentration did not limit CO₂ assimilation under NH₄⁺ nutrition; though both stomatal and mesophyll conductance were significantly suppressed. Carboxylation efficiency (CE), light‐saturated potential rate of electron transport (J_max), the quantum efficiency of PSII (Φ_PSII), electron transport rate through PSII [Je(PSII)], and F_v/F_m were significantly reduced by NH₄⁺. As a result, NH₄⁺ nutrition resulted in a significant increase in the production of hydrogen peroxide (H₂O₂) and superoxide anion radicals (O₂^??), but these symptoms were less severe in the NH₄⁺‐tolerant XM25, which had a higher capacity of removing elevated reactive oxygen species (ROS). Thus, NH₄⁺ N sources might decreased electron transport efficiency and increased the production of ROS, exacerbating damage to the electron transport chain, leading to a reduced plant photosynthetic capacity.     

砷对小麦生长和光合作用特性的影响

研究了水培条件下砷对小麦根系和地上部分生长速率、光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(Tr)的影响.结果表明,随着营养液中砷浓度的提高,小麦根长生长量和地上部分生长量较对照减少;鲜重和砷的浓度呈显著负相关.在0～90mg/L 砷处理内,Pn、Gs、Tr都随砷的浓度的提高而降低;Ci呈先降低,后升高的变化.在As≤30 mg/L时Ci逐渐降低,气孔限制值Ls升高,使Pn下降,造成气孔性限制;而As>30 mg/L时,Ci升高,气孔限制值Ls下降,Pn降低,造成了非气孔性限制.叶片水分利用效率WUE和气孔限制值Ls在As≤30 mg/L时变化一致,都有所升高;但是当As>60 mg/L时,小麦趋于死亡,水分利用率降低.叶绿素含量在0～10mg/L As处理内,差异不显著,在较高砷浓度(As>30 mg/L)时叶绿素显著下降.这说明较低浓度的砷不会抑制小麦叶绿素的合成.砷主要是毒害小麦根系生长,造成植株体光合作用的气孔性限制和非气孔性限制出现,最终影响小麦的生长和发育.     

Interactive influence of arsenate and selenate on growth and nitrogen metabolism in wheat (Triticum aestivum L.) seedlings

The effect of arsenate and selenate, either alone or in combination, on plant growth and nitrogen metabolism was studied in wheat seedlings. The root-shoot elongation and the biomass production were significantly decreased with increasing arsenate concentrations. Arsenate toxicity severely affected activities of different antioxidant scavenging enzymes and oxidative stress markers in the test seedlings. The activities of nitrate and nitrite reductase were also affected resulting in reduced nitrate and nitrite contents. Glutamine synthetase and glutamate synthase activities were also reduced, whereas the glutamate dehydrogenase activity was substantially increased resulting in an increased accumulation of ammonium contents in the test seedlings. Arsenate treatments also adversely affected the levels of total and soluble nitrogen contents and free amino acid contents. Combined application of arsenate with selenate in the test seedlings showed significant alterations in all parameters tested under the purview of arsenate treatment alone leading to better growth and nitrogen metabolism.     

The HPLC profile of proteins of thermoprotection-acquired wheat (Triticum aestivum L.) seedlings

A pre-treatment of 40 °Cprovided thermoprotection to wheat seedlings against 43 °C, which was otherwise a lethal temperature. Due to temperature pretreatment, the rate of protein synthesis at 45 °C increased in both plumules and radicles. The HPLC profile of plumule and radicle proteins of thermoprotection-acquired seedlings was different from the plumules and radicles of non-treated seedlings.     

小麦根愈伤组织胚胎发育过程研究

实验通过对６个人工合成小麦品系和对照品种“中国春”种子根愈伤组织分化形成再生植株的过程进行形态和组织切片观察,发现分化初期有２种途径,一种是从愈伤组织先形成不定胚,然后再发育成不定芽和不定根,另一种途径是直接从愈伤组织中分化发育成不定根和不定芽;分化后期不定芽和不定根生长发育有３种类型：一种是不定芽发育先于不定根,一种是不定芽与不定期不定芽和不定根生长发育有种类型：一种是不一定芽发育先于不定根,一     

The wheat (Triticum aestivum L.) leaf proteome

The wheat leaf proteome was mapped and partially characterized to function as a comparative template for future wheat research. In total, 404 proteins were visualized, and 277 of these were selected for analysis based on reproducibility and relative quantity. Using a combination of protein and expressed sequence tag database searching, 142 proteins were putatively identified with an identification success rate of 51%. The identified proteins were grouped according to their functional annotations with the majority (40%) being involved in energy production, primary, or secondary metabolism. Only 8% of the protein identifications lacked ascertainable functional annotation. The 51% ratio of successful identification and the 8% unclear functional annotation rate are major improvements over most previous plant proteomic studies. This clearly indicates the advancement of the plant protein and nucleic acid sequence and annotation data available in the databases, and shows the enhanced feasibility of future wheat leaf proteome research.