玉米幼苗根系分泌物对芘污染的响应

根际袋土培试验研究了玉米幼苗根系分泌物中的可溶性糖、低分子量有机酸和氨基酸对不同芘污染水平(50、200、800mgkg-1,记为T1、T2、T3)的响应差异,探讨芘胁迫下植物根系的生理生态效应。结果表明,较低浓度芘可适当地刺激玉米的生长,高浓度芘处理抑制了玉米的生长,并且抑制作用随芘处理浓度的提高而增强;芘对玉米根系的影响要大于对茎叶的影响。芘胁迫下促进了根系分泌可溶性糖、低分子量有机酸和氨基酸增多。T1、T2和T3处理根系分泌物中可溶性糖、低分子量有机酸、氨基酸含量分别是T0处理的1.14、1.81、1.35倍,1.24、4.31、2.94倍,1.58、5.56、5.40倍。不同芘污染水平下,乙酸分泌量表现为T2T3T1,酒石酸和柠檬酸分泌量表现为T3T2T1,草酸分泌量表现为T3≈T2T1。芘处理对根系分泌氨基酸种类的影响不大,而对各氨基酸分泌量的变化幅度影响较大;芘胁迫处理对于18种常见氨基酸组分的分泌量的影响各不相同。不同芘污染水平下,天门冬氨酸、丝氨酸和丙氨酸分泌量表现为T3T2T1,苏氨酸、谷氨酸、脯氨酸、甘氨酸、胱氨酸、缬氨酸、甲硫氨酸、异亮氨酸、亮氨酸、酪氨酸、苯丙氨酸、赖氨酸、组氨酸、γ-氨基丁酸、鸟氨酸分泌量表现为T2T3T1。     

Manifestation of heterosis during early maize (Zea mays L.) root development

Heterosis is typically detected in adult hybrid plants as increased yield or vigor compared to their parental inbred lines. Only little is known about the manifestation of heterosis during early postembryonic development. Objective of this study was to identify heterotic traits during early maize root development. Four German inbred lines of the flint (UH002 and UH005) and dent (UH250 and UH301) pool and the 12 reciprocal hybrids generated from these inbred lines were subjected to a morphological and histological analysis during early root development. Primary root length and width were measured daily in a time course between 3 and 7 days after germination (DAG) and displayed average midparent heterosis (MPH) of 17–25% and 1–7%, respectively. Longitudinal size of cortical cells in primary roots was determined 5 DAG and displayed on average 24% MPH thus demonstrating that enlarged primary roots of hybrids can mainly be attributed to elongated cortical cells. The number of seminal roots determined 14 DAG showed on average 18% MPH. Lateral root density of all tested hybrids was determined 5 DAG. This root trait showed the highest degree of heterosis with an average MPH value of 51%. This study demonstrated that heterosis is already manifesting during the very early stages of root development a few days after germination. The young root system is therefore a suitable model for subsequent molecular studies of the early stages of heterosis manifestation during seedling development.     

Epistasis in maize (Zea mays L.)

Summary Three flint and three dent maize (Zea mays L.) inbred lines, their possible F₁ crosses, F₂ and backcross progenies, and all possible three-way crosses were evaluated in a three-year experiment for yield, ear moisture, and plant height. The purpose was to estimate genetic parameters in European breeding materials from (i) generation means analysis, (ii) diallel analysis of generation means, and (iii) analysis of F₁ and three-way cross hybrids. Method (i) was based on the F-metric model and methods (ii) and (iii) on the Eberhart-Gardner (1966) genetic model; both models extended for heterotic maternal effects.Differences among generation means for yield and plant height were mainly attributable to dominance effects. Epistatic effects were significantly different from zero in a few crosses and considerably reduced heterosis in both traits. Additive x additive and domiance x dominance effects for yield were consistently positive and negative, respectively. Significant maternal effects were established to the advantage of generations with a heterozygous seed parent. In the diallel analysis, mean squares for dominance effects were greater than for additive effects for yield and plant height but smaller for ear moisture. Though significant for yield and plant height, epistatic variation was small compared to additive and dominance variation. Estimates of additive x additive epistasis for yield were significantly negative in 11 of 15 crosses, suggesting that advantageous gene combinations in the lines had been disrupted by recombination in the segregating generations. The analysis of hybrids supported the above findings regarding the analysis of variance. However, the estimates of additive x additive epistasis for yield were considerably smaller and only minimally correlated with those from the diallel analysis. Use of noninbred materials as opposed to materials with different levels of inbreeding is considered the main reason for the discrepancies in the results.     

Proteomic analysis of shoot-borne root initiation in maize (Zea mays L.)

Postembryonically formed shoot-borne roots make up the major backbone of the adult maize root stock. In this study the abundant soluble proteins of the first node (coleoptilar node) of wild-type and mutant rtcs seedlings, which do not initiate crown roots, were compared at two early stages of crown root formation. In Coomassie Bluestained 2-D gels, representing soluble proteins of coleoptilar nodes 5 and 10 days after germination, 146 and 203 proteins were detected, respectively. Five differentially accumulated proteins (> two-fold change; t-test: 95% significance) were identified in 5-day-old and 14 differentially accumulated proteins in 10-day-old coleoptilar nodes of wild-type versus rtcs. All 19 differentially accumulated proteins were identified via ESI MS/MS mass spectrometry. Five differentially accumulated proteins, including a regulatory G-protein and a putative auxin-binding protein, were further analyzed at the RNA expression level. These experiments confirmed differential gene expression and revealed subtle developmental regulation of these genes during early coleoptilar node development. This study represents the first proteomic analysis of shoot-borne root initiation in cereals and will contribute to a better understanding of the molecular basis of this developmental process unique to cereals.     

Genomic prediction of seedling root length in maize (Zea mays L.)

Genotypes with extreme phenotypes are valuable for studying ‘difficult’ quantitative traits. Genomic prediction (GP) might allow the identification of such extremes by phenotyping a training population of limited size and predicting genotypes with extreme phenotypes in large sequences of germplasm collections. We tested this approach employing seedling root traits in maize and the extensively genotyped Ames Panel. A training population made up of 384 inbred lines from the Ames Panel was phenotyped by extracting root traits from images using the software program aria . A ridge regression best linear unbiased prediction strategy was used to train a GP model. Genomic estimated breeding values for the trait ‘total root length’ (TRL) were predicted for 2431 inbred lines, which had previously been genotyped by sequencing. Selections were made for 100 extreme TRL lines and those with the predicted longest or shortest TRL were validated for TRL and other root traits. The two predicted extreme groups with regard to TRL were significantly different (P = 0.0001). The difference in predicted means for TRL between groups was 145.1 cm and 118.7 cm for observed means, which were significantly different (P = 0.001). The accuracy of predicting the rank between 1 and 200 of the validation population based on TRL (longest to shortest) was determined using a Spearman correlation to be ρ = 0.55. Taken together, our results support the idea that GP may be a useful approach for identifying the most informative genotypes in sequenced germplasm collections to facilitate experiments for quantitative inherited traits.     

Assimilate transport in maize (Zea mays L.) seedlings at vertical low temperature gradients in the root zone

Even moderate chilling temperatures may cause important modifications in assimilate movement in maize seedlings from the shoot to the roots, but there is no information on long-distance transport of assimilates in plants subjected to vertical gradients of moderately low temperatures in the root zone. Seedlings of a chilling-tolerant (KW1074) and a chilling-sensitive inbred line (CM109) of maize were grown in a system that allowed the maintenance of temperature gradients between the topsoil (0-10 cm) and the subsoil (10-50 cm). After pregrowth at 24C until the third-leaf stage, plants were subjected to chilling-stress regimes for 6 d (17/17/17C, 17/17/12°C, 12/12/12°C, 12/12/17°C, air/topsoil/subsoil). The time taken for the assimilates to enter the phloem from the second leaf increased at low temperatures for both lines, but to a much greater extent in CM109. Although mainly influenced by air and topsoil temperature, low temperature in the subsoil also affected this trait in CM109. The speed of assimilate transport between the second leaf and the mesocotyl in KW1074 was strongly reduced by cool temperatures in the shoot and topsoil as well as by 12°C in the subsoil in CM109, because the latter line had a larger portion of its root system in the subsoil as compared to KW1074. The portion of assimilates allocated to the root decreased at low temperatures in both lines, but to a greater extent in CM109, and was controlled mostly by the subsoil temperature. After rewarming, values of all measured parameters of assimilate transport returned to near pregrowth levels within a few days.Keywords: Assimilate transport, low temperature stress, root growth, vertical soil temperature gradients, Zea mays L.      

Genome-wide association analysis of seedling root development in maize (Zea mays L.)

Background

Plants rely on the root system for anchorage to the ground and the acquisition and absorption of nutrients critical to sustaining productivity. A genome wide association analysis enables one to analyze allelic diversity of complex traits and identify superior alleles. 384 inbred lines from the Ames panel were genotyped with 681,257 single nucleotide polymorphism markers using Genotyping-by-Sequencing technology and 22 seedling root architecture traits were phenotyped.

Results

Utilizing both a general linear model and mixed linear model, a GWAS study was conducted identifying 268 marker trait associations (p ≤ 5.3×10^-7). Analysis of significant SNP markers for multiple traits showed that several were located within gene models with some SNP markers localized within regions of previously identified root quantitative trait loci. Gene model GRMZM2G153722 located on chromosome 4 contained nine significant markers. This predicted gene is expressed in roots and shoots.

Conclusion

This study identifies putatively associated SNP markers associated with root traits at the seedling stage. Some SNPs were located within or near (<1 kb) gene models. These gene models identify possible candidate genes involved in root development at the seedling stage. These and respective linked or functional markers could be targets for breeders for marker assisted selection of seedling root traits.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1226-9) contains supplementary material, which is available to authorized users.     

Low-P tolerance by maize (Zea mays L.) genotypes: Significance of root growth,and organic acids and acid phosphatase root exudation

We investigated some mechanisms, which allow maize genotypes to adapt to soils which are low in available P. Dry matter production, root/shoot-ratio, root length and root exudation of organic acids and acid phosphatase were investigated in four maize genotypes grown under P-deficient and P-sufficient conditions in sterile hydroponic culture. A low-P tolerant, an acid-tolerant and a low-P susceptible genotype of maize were compared with a Swiss commercial cultivar. The study found increased root development and increased exudation of acid phosphatase under P-deficient conditions in all maize genotypes, except for the Swiss cultivar. Effects on root formation and acid phosphatase were greater for the low-P tolerant than for the low-P susceptible, and the acid soil tolerant genotypes. Organic acid contents in root tissues were increased under P deficiency and related to increased PEPC activity. However, the increase in contents was associated with an increase in exudation for the low-P tolerant genotype only. The low-P susceptible genotype was characterized by high organic acid content in roots and low organic acid exudation. The organic acids content in the phloem exudates of shoots was related to root exudation under different P supply, to the difference between lines in organic acids root content, but not to the low-P tolerance or susceptibility of maize genotypes.     

Conserved and unique features of the maize (Zea mays L.) root hair proteome

Root hairs are unicellular extensions of specialized epidermis cells. Under limiting conditions, they significantly increase the water and nutrient uptake capacity of plants by enlarging their root surface. Thus far, little is known about the initiation and growth of root hairs in the monocot model species maize. To gain a first insight into the protein composition of these specialized cells, the 2573 most abundant proteins of maize root hairs attached to four-day-old primary roots of the inbred line B73 were identified by combining 1DE with nanoLC-MS/MS in a shotgun proteomic experiment. Among the identified proteins, homologues of 252 proteins have been previously associated with root hair formation and development in other species. Comparison of the root hair reference proteome of the monocot species maize with the previously published root hair proteome of the dicot species soybean revealed conserved, but also unique, protein functions in root hairs of these two major groups of flowering plants.     

Biochemical composition of maize (Zea mays L.) pollen

Summary Mean percentages of sugars, water-soluble polysaccharides, starch, total carbohydrates and lipids were 40.1, 7.4, 28.6, 76.1, and 1.8 respectively. Differences among the mutants were found only for water-soluble polysaccharides with both wx and sh ₂ decreasing the percentage a small but significant amount. In terms of the various carbohydrates measured, no correlation was found between the expression of these mutants in the pollen and the kernel.

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Zusammenfassung Die Untersuchung des Kohlenhydrat- und Lipid-Gehaltes im Pollen der Endosperm-Mutanten waxy, shrunken und sugary vom Mais ergab einen gemittelten Gehalt an Zucker von 40,1%, wasserlöslichen Polysacchariden 7,4%, Stärke 28,6, Gesamtkohlenhydraten 76,1% und Lipiden 1,8%.Unterschiede zwischen den Mutanten wurden lediglich hinsichtlich der wasserlöslichen Polysaccharide gefunden, und zwar bei wx und sh ₂, die einen signifikant niedrigeren Gehalt aufwiesen.Hinsichtlich der verschiedenen analysierten Kohlenhydrate wurde keine Korrelation zwischen der Expression der Mutanten im Pollen und in den Karyopsen gefunden.

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Herrn Professor Dr. J. Straub (Köln-Vogelsang) zu seinem 60. Geburtstag gewidmet.

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Journal Series Paper No. 3621, Florida Agricultural Experiment Station.     

RFLP mapping of quantitative trait loci controlling abscisic acid concentration in leaves of drought-stressed maize (Zea mays L.)

 Abscisic acid (ABA) concentration in leaves of drought-stressed plants is a quantitatively inherited trait. In order to identify quantitative trait loci (QTLs) controlling leaf ABA concentration (L-ABA) in maize, leaf samples were collected from 80 F_3:4 families of the cross Os420 (high L-ABA)×IABO78 (low L-ABA) tested under drought conditions in field trials conducted over 2 years. In each year, leaf samples were collected at stem elongation and near anthesis. The genetic map obtained with 106 restriction fragment length polymorphism (RFLP) loci covered 1370 cM, which represented approximately 85% of the UMC maize map. Sixteen different QTLs with a LOD>2.0 were revealed in at least one sampling. Across samplings, only four QTLs significantly influenced L-ABA, accounting for 66% of the phenotypic variation and 76% of the genetic variation among families. At these QTLs, the alleles which increased L-ABA were contributed by Os420. The two most important QTLs were mapped on chromosome 2 near csu133 and csu109a. The effects associated with the QTL near csu133 were more pronounced near anthesis. The support intervals of the four primary QTLs for L-ABA did not overlap the presumed map position of mutants impaired in ABA biosynthesis. Received: 27 January 1998 / Accepted: 22 April 1998     

Biochemical composition of maize (Zea mays L.) pollen

Summary Pollen grains containing either the Wx, wx, Su ₁, su ₁, Sh ₂ or sh ₂ alleles were stored at 0, 1, 2, 3, 4 and 5 days at 2 °C. After each storage period, a portion of pollen from each genotype was analyzed for free amino acid content. Over all genotypes, storage significantly altered the content of all 16 amino acids measured. With increasing storage, a relatively consistent increase in aspartic acid, isoleucine, leucine, phenylalanine, ethanolanine, aminobutyric acid, NH₃ and lysine was found. A relatively consistent decrease in glutamic acid, proline, glycine and alanine occurred with increasing storage. No consistent response to storage was obtained with threonine-serine, valine, histidine and the unknown. Apparently, storage or stage of viability loss has a pronounced effect on amino acid metabolism in maize pollen grains. The experiment was designed so that comparisons free of genetic background effects could be made between alleles at each locus. Significant allele X storage interactions at each locus were found as follows: at the waxy locus, aspartic acid, glycine, alanine and ethanolanine; at the sugary locus, aspartic acid, alanine, ethanolanine and aminobutyric acid; and at the shrunken locus, aspartic acid, alanine, valine, leucine and ethanolanine. Amino acid metabolism is apparently influenced by the action of the alleles at these loci. The differences between the loci in the amino acids affected indicate the different areas of amino acid metabolism are influenced by each locus.Journal Series Paper No. 4425, Florida Agricultural Experiment Station.     

Biochemical composition of maize (Zea mays L.) pollen

Summary Proline was the most abundant amino acid with a mean value of 186.28 moles/mg dry pollen. The other amino acids tested were below 33 moles/mg dry pollen. The mutant wx significantly increased aspartic acid, valine, histidine and an unknown but significantly decreased aminobutyric acid. The mutant sh ₂ significantly increased glutamic acid, proline, lysine, histidine and an unknown but significantly decreased aspartic acid and aminobutyric acid. The effect of su ₁ was altered by the genetic background involved. In one genetic background, su ₁ did not significantly increase any amino acid but significantly decreased alanine and aminobutyric acid. However, in a distinctly different background, su ₁ significantly increased aminobutyric acid but significantly decreased aspartic acid and glutamic acid. Apparently the genetic background is capable of producing major shifts in the amino acid pattern in addition to the action of these mutants.The fatty acids, palmitic and linolenic were the most common with percentages of 54.1 and 34.4 respectively. The mutants tested did not affect the fatty acid distribution.

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Zusammenfassung Prolin war die am reichlichsten vorkommende Aminosäure mit einem mittleren Gehalt von 186,28 Mikromol per mg trockenen Pollen. Die anderen Aminosäuren erreichten weniger als 33 Mikrogramm per mg trockenen Pollen.Die Mutante wx zeigte einen signifikant erhöhten Gehalt an Asparaginsäure, Valin, Histidin, sowie einer nicht identifizierten Komponente, während der Gehalt an -Aminobuttersäure signifikant erniedrigt war. Die Mutante sh ₂ ist gekennzeichnet durch einen signifikant erhöhten Gehalt an Glutaminsäure, Prolin, Lysin, Histidin, sowie einer unbekannten Fraktion; der Gehalt an Asparaginsäure und -Aminobuttersäure war dagegen signifikant erniedrigt. Die Wirkung des mutierten Gens su ₁ wurde durch das übrige Genom, in dem es sich befand, geändert. In dem einen genetischen Milieu verursachte su ₁ keine signifikante Erhöhung des Gehaltes irgend einer Aminosäure, während der Gehalt an Alanin und -Aminobuttersäure signifikant erniedrigt war. In einem anderen genetischen Milieu jedoch zeigte su ₁ eine signifikante Erhöhung der -Aminobuttersäure; Asparaginsäure und Glutaminsäure waren signifikant erniedrigt.Offensichtlich ist das übrige Genom zusätzlich zu der Wirkung der genannten Mutanten in der Lage, wesentliche Verschiebungen im Verteilungsmuster der Aminosäuren zu verursachen.Von den Fettsäuren wurden am häufigsten Palmitin- und Linolen-Säure mit einem Gehalt von 54,1 bzw. 34,4% gefunden. Die untersuchten Endosperm-Mutanten zeigten keinen Einfluß auf die Fettsäureverteilung im Pollen.

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Journal Series Paper No. 3468, Florida Agricultural Experiment Station.     

Spatial distribution and phenotypic variation in root cortical aerenchyma of maize (Zea mays L.)

Background and aims

Previous research has suggested that root cortical aerenchyma (RCA) can enhance soil exploration and crop performance by decreasing root respiration. This trait is a potential breeding target for adaptation to abiotic stresses such as drought and low nutrient availability. However, little is known of phenotypic variation in aerenchyma or its distribution among root classes.

Methods

The spatial distribution of RCA was evaluated in freehand sections from 13 sites in the root systems of 11 recombinant inbred and commercial lines of maize (Zea mays). RCA variation was evaluated in 583 recombinant inbred lines of maize at one sampling position.

Results

RCA varied significantly among root classes and axial positions. Genotypic differences were observed for the amount of RCA at corresponding sampling locations and for the mean amount of RCA across all sampling locations, but genotypes did not differ in the proportional distribution of RCA within the whole root system. The amount of RCA in a cross-section was independent of several other anatomical traits.

Conclusions

There is substantial genetic variation for RCA, and this variation is independent of other anatomical traits. RCA can be phenotyped in greenhouse-grown plants by sampling the middle parts of second- or third-whorl crown roots.     

Thiols in cadmium- and copper-treated maize (Zea mays L.)

Maize plants (Zea mays L. cv. Honeycomb F-1) were grown on quartz sand containing amounts of Cd or Cu which resulted in comparable internal contents in the roots. Fresh and dry weights and the content of Cd or Cu were measured in roots and shoots after eight weeks. In addition, cysteine, γ-glutamylcysteine (γEC), glutathione (GSH) and the thiols in heavy-metal-binding peptides (HMBPs) were determined in the roots. At low internal contents, Cd and Cu inhibited root growth to the same extent. Inhibition by Cu was enhanced, however, at high internal contents, indicating that Cu was more toxic than Cd. Separation of extracts from roots of Cd- and Cutreated plants on a Sephadex G-50 column resulted in HMBP complexes with relative molecular masses (M_rs) of 6200 and 7300, respectively. Separation of these HMBP-complexes using HPLC resulted in a distinct pattern of thiol compounds for each heavy metal. The accumulation of HMBPs was linearly dependent on the content of Cd at all values examined. In Cu-treated roots, HMBP accumulation was linearly dependent on the internal Cu content only up to 7.1 μmol·g^?1 dry weight. At internal contents which caused an enhanced inhibition of root growth, no further significant increase in the HMBP content was detected. At these internal Cu contents an increased transport of Cu to the shoot was measured. This result indicates that HMBPs are involved in reducing heavy-metal transport from roots to shoots.