Seminal Roots Of Wheat Research Articles

Histone acetylation modification affects cell wall degradation and aerenchyma formation in wheat seminal roots under waterlogging

Recent studies have shown that histone acetylation, which is an important epigenetic modification, plays a key role in abiotic stress responses in plants. Programmed cell death and aerenchyma formation occur in cortical cells of wheat seminal roots under waterlogging stress. To explore the role of histone acetylation in aerenchyma formation of cortical cells under waterlogging, the seminal roots of two wheat cultivars, namely, Huamai 8 (waterlogging-tolerant) and Huamai 9 (waterlogging-sensitive) were investigated with waterlogging and simultaneous treatment with an acetylation inhibitor. In this study, the immunefluorescence technique and Western blotting were used to determine the histone acetylation levels in wheat seminal roots under waterlogging stress. Cell wall degradation-related enzymes (cellulase and pectinase) were observed using the method of ultracytochemical localization. We also tested the expression of related genes, such as histone acetyltransferase (HAT1), histone deacetylase (HD3), endoglucanase (CEL), polygalacturonase (PG), and xyloglucan endotransglucosylase (XET). The results indicated that histone acetylation is involved in eliciting responses to waterlogging stress as well as in the aerenchyma formation by affecting cell wall degradation of cortical cells in wheat seminal roots. We also present a model of waterlogging-induced aerenchyma formation in cortical cells of wheat seminal roots based on our experimental results and the findings of previous studies.

Early response of wheat seminal roots growing under copper excess

Growth reduction caused by copper excess during plant photoautotrophic metabolism has been widely investigated, but information regarding early responses of root apical meristem (RAM) to toxic concentrations of this metal at the initial heterotrophic stage is certainly scarce. We analysed some determinants of seminal root growth in developing wheat seedlings germinated in the presence of 1, 5 and 10 μM CuCl2, focussing on oxidative damage to cell membrane and to proteins, and investigated the expression patterns of some genes relevant to cell cycle progression and cell expansion. The proliferation zone of the RAM was shorter under 5 and 10 μM CuCl2. Cyclin D and CDKA levels remained unchanged in the root apexes of wheat seedlings grown under these Cu2+ concentrations, but more carbonylated levels of both proteins and less ubiquitinated-cyclin D was detected under 10 μM CuCl2. Increased levels of ROS were revealed by fluorescent probes at this Cu2+ dose, and severe cell membrane damage took place at 5 and 10 μM CuCl2. Several genes related to retinoblastome phosphorylation and therefore involved in the transition from G1 to S cell cycle stage were found to be downregulated at 10 μM CuCl2, while most expansin genes here analysed were upregulated, even at a non-toxic concentration of 1 μM.These results together with previous findings suggest that a “common” signal which involves oxidative posttranslational modifications of specific cell cycle proteins may be necessary to induce root growth arrest under Cd2+ and Cu2+ stress.

Characterization of a wheat pathogenesis-related protein, TaBWPR-1.2, in seminal roots in response to waterlogging stress

We examined the role of pathogenesis-related protein TaBWPR-1.2 in the context of molecular and physiological responses of wheat (Triticum aestivum) seminal roots under waterlogging stress. Two cDNAs corresponding to the TaBWPR-1.2 gene, TaBWPR-1.2#2 and TaBWPR-1.2#13 were cloned from seminal roots. These cDNAs were predicted to encode proteins of 173 and 172 amino acids, respectively. In a time-course experiment, TaBWPR-1.2 gene expression was highest in whole seminal roots after 1 day of waterlogging treatment and higher than the control for at least 10 days; significantly increased protein abundance was observed after 7 days of waterlogging. Drought, another abiotic stress, did not influence TaBWPR-1.2 gene expression in wheat seminal roots at 5-d-old seedlings. Tissue-specific studies revealed that the highest TaBWPR-1.2 gene expression and protein levels were in the aerenchymatous root zone. TaBWPR-1.2 expression in seminal roots was also increased by the signalling molecules 1-aminocyclopropane-1-carboxylic acid (ACC; an ethylene precursor), H2O2, jasmonic acid (JA), and nitric oxide (NO); however, treatment with abscisic acid (ABA), salicylic acid (SA), and ethanol did not alter its expression. Interestingly, aerenchyma formation in the seminal root cortex was induced only by ACC and H2O2. Taken together, these results indicate that TaBWPR-1.2 is a waterlogging-responsive gene that might be associated with root cortex tissue alteration in wheat plants through ACC and/or H2O2 regulatory mechanisms.

Process of aerenchyma formation and reactive oxygen species induced by waterlogging in wheat seminal roots

The development and regulation of aerenchyma in waterlogged conditions were studied in the seminal roots of wheat. Evans blue staining and the first cell death position indicated that the cortical cell death began at the root mid-cortex cells in flooding conditions. Continuous waterlogging treatment caused the spread of cell death from the mid-cortex to the neighboring cells and well-developed aerenchyma was formed after 72 h. Meanwhile, the formation of radial oxygen loss barrier was observed in the exodermis owing to the induction of Casparian bands and lignin deposition. Analysis of aerenchyma along the wheat root revealed that aerenchyma formed at 10 mm from the root tip, significantly increased toward the center of the roots, and decreased toward the basal region of the root. In situ detection of radial oxygen species (ROS) showed that ROS accumulation started in the mid-cortex cells, where cell death began indicating that cell death was probably accompanied by ROS production. Further waterlogging treatments resulted in the accumulation of ROS in the cortical cells, which were the zone for aerenchyma development. Accumulation and distribution of H₂O₂ at the subcellular level were revealed by ultracytochemical localization, which further verified the involvement of ROS in the cortical cell death process (i.e., aerenchyma formation). Furthermore, gene expression analysis indicated that ROS production might be the result of up-regulation of genes encoding for ROS-producing enzymes and the down-regulation of genes encoding for ROS-detoxifying enzymes. These results suggest that aerenchyma development in wheat roots starts in the mid-cortex cells and its formation is regulated by ROS.

Ion transport in seminal and adventitious roots of cereals during O2 deficiency

O(2) deficiency during soil waterlogging inhibits respiration in roots, resulting in severe energy deficits. Decreased root-to-shoot ratio and suboptimal functioning of the roots, result in nutrient deficiencies in the shoots. In N(2)-flushed nutrient solutions, wheat seminal roots cease growth, while newly formed adventitious roots develop aerenchyma, and grow, albeit to a restricted length. When reliant on an internal O(2) supply from the shoot, nutrient uptake by adventitious roots was inhibited less than in seminal roots. Epidermal and cortical cells are likely to receive sufficient O(2) for oxidative phosphorylation and ion transport. By contrast, stelar hypoxia-anoxia can develop so that H(+)-ATPases in the xylem parenchyma would be inhibited; the diminished H(+) gradients and depolarized membranes inhibit secondary energy-dependent ion transport and channel conductances. Thus, the presence of two transport steps, one in the epidermis and cortex to accumulate ions from the solution and another in the stele to load ions into the xylem, is important for understanding the inhibitory effects of root zone hypoxia on nutrient acquisition and xylem transport, as well as the regulation of delivery to the shoots of unwanted ions, such as Na(+). Improvement of waterlogging tolerance in wheat will require an increased capacity for root growth, and more efficient root functioning, when in anaerobic media.

Lateral root development, including responses to soil drying, of maize (Zea mays) and wheat (Triticum aestivum) seminal roots

The spatial distribution of lateral roots in the soil is an important factor influencing water and nutrient absorption. However, lateral root development has rarely been studied in detail, especially concerning morphological variations, mainly because such examinations are both time‐consuming and laborious. We measured the number and length of all first‐order lateral roots on the seminal roots of maize (Zea mays L.) and wheat (Triticum aestivum L.) to investigate variations in linear frequency and length. This was conducted with reference to species, root types, and positions on their parental roots. Although the linear frequency of first‐order lateral roots varied along the root axis in maize, the variation was not as great as in wheat. Variations were found in the length of lateral roots among plant species, root types, and positions on their parental root axes. Such variations in the length of lateral roots along the root axes were caused by differences in the elongation period of lateral roots rather than those in the elongation rate. Additionally, we examined the effects of soil drying on lateral root development. As a response to soil drying, the length of lateral roots varied depending on the period they were placed under the stressed condition. Moderate soil drying could also accelerate the elongation of some lateral roots. Variations in the length of first‐order lateral roots and their responses to soil drying could help distribute their tips thoroughly throughout the soil. This might be adaptive for water absorption for root system development when resources are limited.

Impact of water deficit intensity on durum wheat seminal roots

Experiments were performed under controlled conditions to study seminal roots traits of durum wheat genotypes grown under four water conditions. Seminal root length, root-to-shoot dry matters ratio and piliferous layer cell size were measured. Root volume was assessed at three soil depths. Water stress has affected significantly root traits and piliferous layer cell size and this impact depends on its intensity. Severe water stress reduced markedly root traits. Water treatment by genotype interaction was observed. Middle-East genotypes responded differently from Algerian ones. Our results and those obtained elsewhere on the same genotypes for other physiological traits are discussed. To cite this article: A. Adda et al., C. R. Biologies 328 (2005).

Intermittent anoxia induces oxidative stress in wheat seminal roots: assessment of the antioxidant defence system, lipid peroxidation and tissue solutes.

The effects of continuous and intermittent anoxia on components of the antioxidant defence system were evaluated in the expanded zones of wheat seedling roots. Intermittent anoxia caused oxidative stress (measured by the proportion of reduced glutathione) after three cycles of anoxia-aeration. The concentration of glutathione and activities of glutathione reductase (GR) and catalase (CAT) were decreased by 50% under both continuous and intermittent anoxia. Ascorbate peroxidase (APX) activity was unaffected by anoxia but stimulated almost 2-fold during the aerated periods of intermittent anoxia. Superoxide dismutase activity was decreased by 20% under continuous anoxia but ultimately returned to aerated activities under intermittent anoxia. Membrane damage appeared to be negligible or reversible, as K+ concentrations recovered to original levels under intermittent anoxia and there was no increase in terminal lipid peroxidation products. Addition of 5 mm exogenous ascorbate to intermittently anoxic roots prevented oxidative stress and avoided the decreases in glutathione, GR and CAT. Therefore, it is likely that the oxidative stress resulted from inadequate levels of, or damage to, these two enzymes.

Site, Scale and Time-course for Adjustments in Lateral Root Initiation in Wheat Following Changes in C and N Supply

The pattern of lateral root initiation in seminal roots of wheat (Triticum aestivumL. cv. Alexandria) and the location, scale and time-course for adjustments in initiation were studied after changes in C and N supply. Macroscopically visible primordia appeared in a non-acropetal sequence with the frequency (number per unit length) increasing with distance behind the main root apex to a maximum at 40–50 mm behind the root tip. Pruning the root system to a single seminal axis increased the primordia frequency by 23% within 15 h. After longer periods, the effect of root-pruning was greater. The enhanced primordia frequency was first observed in tissue located 0–10 mm behind the apex at the start of treatment. Feeding glucose (50 mM) also increased primordia frequency within 15 h, but to a greater extent, and here additional primordia were initiated in tissue located 0–10and10–20 mm behind the apex at the start of treatment. Withdrawing NO3−from one part of a split-root system, whilst maintaining the supply to the other, reduced primordia frequency in the non-fed roots and, in some cases, a compensatory increase in the NO3−-fed roots was observed. The location and scale of the adjustments were similar to those found with root-pruning and glucose-feeding, but were slightly slower to appear. In spite of some differences in detail, there was a broad similarity in site, scale and time-course for adjustments in lateral root initiation with these treatments, which is consistent with the operation of a common mechanism. Whenever an increase in primordia frequency was observed, it was associated with an increase in the ethanol-soluble sugar content of the tissue. However, the reduction in frequency in NO3−-deprived roots was also accompanied by an increase in sugar content. There was no consistent relationship between total N content of the tissue and primordia frequency, but there was between primordia frequency and the rate of net NO3−uptake. The possible mechanisms controlling lateral root initiation are discussed.

Modelling of early infection of cereal roots by the take-all fungus: a detailed mechanistic simulator.

A stochastic model is constructed to simulate the spatial and temporal spread of infection of the take-all fungus, Gaeumannomyces graminis var. tritici (Sacc.) Arx & Olivier var. tritici Walker on seminal roots of wheat. The model is designed to synthesize information on the dynamics and spatial orientation of the growth of main seminal root axes of wheat and the dynamics of primary and secondary infection of the pathogen. Primary infection is initiated by the soil inoculum. Three types of secondary infection by runner hyphal growth are distinguished; re-infection of the same root, infection of another root on the same plant via the crown, and cross-infection between roots on different plants. There are nine pathogen parameters, 14 host parameters, as well as four system parameters in addition to the location and orientation of seedlings. The pathogen parameters comprise estimates for the size and density of inoculum, the rate of growth of the fungus on roots, and the mean distances and probability of occurrence for primary and secondary infection. The host parameters concern orientation, density, emergence, rates of growth and size of roots. The principal output variables are total and infected root length, numbers of infections, proportion of infected roots and the numbers of primary and cross infections. Results of sensitivity analysis of the output variables to selected input parameters are presented. The model is tested against independent data-sets from inoculum-density experiments for different soil temperatures and ranges of inoculum density. Statistical methods of response curve analysis are used to compare the behaviour of inoculum density-disease response curves for the simulated and experimental data. The model fitted the data satisfactorily for the majority of host and infection variables. Inclusion of secondary infection in the model improved the goodness-of-fit but the density of secondary infections was small relative to primary infections. Practical and conceptual problems in the validation of complex simulation models for fungal infection are discussed. The advantages and limitations of this and related models are critically assessed.

The dynamics of infection by the take-all fungus on seminal roots of wheat: sensitivity analysis of a stochastic simulation model.

The effects and interactions of inoculum density (Iρ), rate of fungal growth (kf) and the maximum distances for primary (wp ) and secondary (cross) (ws ) infection on the temporal progress of infection of the take-all fungus, Gaeumannomyces graminis, in small populations of contiguous wheat plants are examined in factorial combination using a stochastic simulation model. The effects are analyzed in relation to infection progress curves for the percentage infected roots, the total length of infected root, the density of separate infection and the mean length of separate infections as well as the densities of primary and cross infections. Linear models are used to analyze the effects of changing parameter values on components of the infection progress curves. Non-linear, logistic models are used to summarize infection progress curves and to map the effects of changing simulation model parameters onto the parameters of the simpler, growth curve function. The proportion of infected roots was most influenced by Iρ and wp with a negligible effect due to ws . The density and length of infections on roots was principally controlled by kf. Changes in infection length were non-monotonic. The average length of infections increased towards a temporary maximum, following the first wave of primary infections, dipped as infections overlapped and then increased rapidly as root colonization progressed. The first wave of cross infection occurred 7 d after the initiation of primary infection. The density of primary infections was controlled principally by Iρ and wp . The density of cross infections was controlled not only by kf and ws , which are directly involved in cross infection, but also by kf and wp which affect the amount of infected and susceptible tissue. The asymptotic parameter of the logistic model for the infection progress curves was the most frequently affected parameter, followed by the delay parameter, with relatively few changes affecting the rate parameter. Some problems in the use of complex, stochastic simulation models to simulate experimental conditions are discussed.

The contribution of different regions of the seminal roots of wheat to uptake of nitrate from soil

The contribution of different regions of the seminal roots of wheat to uptake of nitrate from soil

Prospective companion cells differentiate into abnormal sieve elements in colchicine-treated roots ofTriticum aestivum

Companion cells (CCs) of seminal roots of wheat (Triticum aestivum L.) flank protophloem sieve elements (PSEs) on their inner side. In roots growing in the presence of 2 mM colchicine prospective CCs are induced to differentiate into abnormal sieve elements. The most convincing evidence that they deviate from their programmed developmental sequence is the deposition of dense crystalloid inclusions within their plastids, a feature characterizing sieve elements of gramineous species. These plastids, however, are ultrastructurally different from those of normal and abnormal PSEs in that they contain only one kind of crystalloid inclusion, exceptionally dense stroma, swollen vesicular structures and plastoglobuli. Mitochondria accumulate in large groups and appear unusually swollen and deformed. Walls develop abnormal thickenings which are deposited irrespective of the position of plasmodesmata. Nuclei become polyploid and appear highly lobed, but degenerate similarly to those in normal sieve elements. Aggregates of paracrystalline material occur in the cytoplasm between the nucleus and cell wall. The end walls display features characterizing developing sieve plates, callose is deposited around plasmodesmata, but sieve pores are not formed. Aberrant CCs may reach “maturity” and co-exist with colchicine-affected PSEs. Their arrangement may be similar to or differ from that of normal phloem poles. Not all cells in CC files are induced to deviate into abnormal sieve elements, nor does their development occur in sequence. Because developmental changes also occur in polyploid cells, which result from colchicine blocked cell divisions, it is concluded that cell division is not a prerequisite for cell differentiation.

The gravitropic response of roots and the shaping of the root system in cereal plants

The spatial distribution of seminal and nodal roots in cereals varies according to species and genotype. This is due to the plagiogravitropic growth of the axes. The plagiogravitropic response of a nodal root depends on its diameter and the position of the internode from which it emerges. The response also changes in the course of root growth and the stage of shoot development. The growth angle of the axes is, therefore, programmed and controlled by genetic, physiological and environmental factors. With respect to the latter, the seminal roots of wheat are sensitive to the water environment which may modify the growth angle as a result of the effect of hormonal regulators such as abscisic acid (ABA). Concerning the gravitropic response of nodal roots in rice, physiological controls may operate through assimilates coming from the shoot. It is concluded that the gravitropic response of axes, which determines the shape of the root system, is primarily controlled by genetic factors but is also influenced by environmental conditions.

Behavior of lateral roots in winter wheat as affected by temperature

The experiment was conducted to evaluate the effects of temperature on growth of laterals on the seminal roots of wheat ( Triticum aestivum L.). Wheat seedling root growth was measured on alternate days for 28 days beginning at 4 days after planting. The length, number, time of emergence, and the distance apart of primary lateral roots and the length of the unbranched axis were determined on the plants under air temperatures of 10, 20, 25 and 30°C. The primary lateral roots (i) emerged earlier with increased temperature, and developed closer to the tip of the seminal axis at 20 and 30°C than at 10 and 25°C, (ii) were more closely spaced along the seminal axis at the higher temperatures, (iii)_increased in density along a segment of root within a period of time after planting that varied with temperature, indicating that lateral root emergence did not follow an acropetal sequence, (iv) had a distribution in length that was unaffected by temperature, (v) were fewest in number and least in length at 10°C, greatest in number and length at 25°C, and were intermediate in length and number at 20 and 30°C, and (vi) had lengths that accounted for about 46, 83, 85 and 72% of the total seminal root length at 10, 20, 25 and 30°C, respectively.

Inheritance of geotropic responses in wheat seminal roots.

The mode of inheritance of geotropic responses in wheat primary seminal roots was investigated in materials cultured on an agar medium. F1 and F2 plants frorn the cross between Norin 58, which shows large growth angles of inclination of the roots, and Chinese Spring, which shows small values, were examined. Means and standard deviations of growih angles of inclination of the roots for Norin 58, Chinese Spring and the F1 plants were 68±21°, 16±14°and 15±21°, respectively. The corresponding values of the F2 plants ranged from O' to 90°. The observed segregation of the F2 plants with small (0∼50°) and large (60∼90°) values fitted to the ratio of 3 : 1. Therefore, the limited geotropic response associated with a small growth angle of inclination of the root was considered to be controlled by a single dominant gene.

Effect of colonization by a sterile red fungus on viability of seed and growth and anatomy of wheat roots

Invasion patterns of the sterile red fungus (SRF) into tissues of seminal roots of wheat were examined 4, 8 and 10 d after inoculation. At 4 d, 2·7% of the cortical cells were free of the fungus (category A), 16·2% had 1–50% (category B) and 81·1%, 50–100% (category C) of the cell lumen filled by hyphae. The percentage of cortical cells in category C increased at 8 and 20 d, with a concurrent decrease in categories B and A. Most cells within the stele were free of the fungus, especially at 4 and 8 d. Even when they were found within stelar tissues they were only at low densities. The thickness of the walls of endodermis was not affected by the presence of the SRF. The SRF colonized wheat seeds without affecting their viability. The SRF was recovered at a greater proportion from seeds incubated with the fungus for 12 h than for 8 or 10 h, although some reduction in the viability was noted with seeds incubated for 12 h. Wheat seeds exposed to the SRF for 8, 10 and 12 h germinated more rapidly than untreated seeds, the seeds incubated for 10 h showing the best effect. Forty eight hours after planting there was no difference evident in the germination percentage among seeds inoculated for 8 h, 10 h and the control treatment. The SRF or its exudate increased the shoot and root weights and root length compared to the control. The SRF also increased the diameter of wheat roots which was not affected by the exudate. The root length, however, was greater in the exudate treatment than in the treatment receiving the fungus.

Influence of biopores on root growth, water uptake and grain yield of wheat (Triticum aestivum) based on predictions from a computer model

The use of vertical biopores by wheat (Triticum aestivum) seminal roots for easy access to the subsoil and the consequences for plant water supply and yield has been investigated by computer simulation. Parameters included were: biopore density and diameter, depth of cultivation and strength of the subsoil — all under a wide range of seasonal weather conditions. The model predicts that biopores add significantly to root penetration at depth, even at a density of 0.1% v/v of small, vertical pores, while 1.5% to 2.0% v/v can ensure maximum root penetration. When the growing season is shorter a larger number of biopores is needed to ensure timely root penetration to depth. With shallow tillage, biopores occur closer to the soil surface, and their importance is increased. Deeper root penetration invariably gives greater water uptake and transpiration, but may have a negative effect on grain yield, especially under the driest climatic conditions. An increase in early water use may result in less soil water being available during the grain-filling period. The effect of biopores on plant transpiration varies from year to year, depending on the amount of rain and its distribution in time, and on the amount of soil water stored at time of sowing.

Distribution of a Take-All Suppressive Strain of Pseudomonas fluorescens on Seminal Roots of Winter Wheat

An antibiotic-resistant strain of Pseudomonas fluorescens, that suppresses take-all of wheat, was used to study the distribution of the bacteria on seminal roots of wheat after being introduced onto seeds. Cells of P. fluorescens were isolated from the entire length of the root, and density of the introduced bacteria declined with the distance from the base of the root. Maximum populations of 10 to 10 CFU and 10 to 10 CFU per cm of root were detected on sections of roots near the seed and root tip, respectively. The introduced bacteria competed well with indigenous bacteria, comprising at least 25% of the fluorescent pseudomonads detected by plate counts for 48 days after planting.

Growth of Gaeumannomyces graminis var. tritici in soil in the presence and absence of wheat roots

The distance over which hyphae of Gaeumannomyces graminis var. tritici (Ggt) grow towards wheat roots in soil was examined by using an inoculum and a plant chamber. Gauze between the two chambers permitted hyphal growth from the inoculum chamber into the plant chamber but prevented roots growing into the inoculum chamber. In soil fumigated with methyl bromide, hyphae of Ggt from ground oat inoculum grew 6–9 mm in 15 days and 9–14 mm in 28 days to colonize seminal roots of wheat and cause lesions. In natural soil, hyphae from inocula up to 9–14 mm from roots colonized them in 15 days. Lesions were formed only from hyphae growing from inocula up to 8 mm from roots. At similar distances between roots and inocula, the hyphal density on roots in natural soil was less than in fumigated soil. In the absence of wheat roots, hyphae of Ggt grew up to 5 mm from inocula in fumigated soil and up to 2 mm in natural soil.