Development of the Vascular System in the Ear of Barley

In the mature rachis internodes of a two-row barley ear therewere two large lateral vascular bundles and a number of smallermedian and outer lateral vascular bundles. These bundles rannearly the full length of the rachis with no cross connectionsbetween them. The lateral and the outer lateral bundles branchedat every node while the median bundles branched at every othernode. The vascular bundles to each spikelet passed through acomplex region in which transfer cells occurred. Development of the vascular system of the young main shoot earstarted at the triple mound stage when the procambium of lateralbundles was initiated. Initiation of the median bundles andthe outer lateral bundles followed in sequence with some differentiationof protophloem and protoxylem. At awn initial stage of the earthe vascular connections to the spikelets were established withdifferentiation of the almost complete procambium proceedingthroughout the ear elongation phase. The progress of vascularisation in the young ear is discussedwith reference to spikelet initiation, ear relative growth rateand death of terminal spikelets. It is proposed that the changesin the relative growth rate of the ear and death of the terminalspikelets may be related to vascular differentiation     

Effect of Temperature on Ear Abnormalities in Uniculm Barley

Field experiments with a uniculm mutant of Proctor spring barleyshowed that abnormal ear development often resulted from latesowing. The ear abnormalities were twin floret, supernumeraryparts, abnormal rachilla, opposite spikelets, one-ranked spikelets,branched rachis, collar -like and bare nodes, aborted apex,and tubular leaf. The degree of abnormality was unaffected byphotoperiod. In both uniculm Proctor and uniculm Kindred, nodenumber relative to normal genotype was decreased by high-temperaturetreatment and the proportion of abnormal rachis nodes and theseverity of the abnormality were increased. The transfer ofplants from high to low temperature and vice versa at differentstages of development showed that high temperature had an almostimmediate effect, inducing abnormal development, but that transferto low temperatures allowed the resumption of more normal development. The abnormalities closely resemble those induced by 2, 4.D andit may be that the effect of the mutant gene is in some wayto change the metabolism of auxin.     

2,4-D Resistance in a Tobacco Cell Culture Variant II. Effects of 2,4-D on Nucleic Acid and Protein Synthesis and Cell Respiration

The effects of 2,4-D on nucleic acid and protein synthesis andcell respiration were compared between a 2,4-D-resistant variantand its wild-type cell lines of tobacco (Nicotiana tabacum L.).The variant continued cell division and growth in the presenceof 100 µM 2,4-D which was strongly inhibitory to the wild-typecell lines. Among the macromolecular syntheses studied, DNAsynthesis was the most sensitive and protein synthesis was theleast sensitive to inhibitory concentrations of 2,4-D. The variantdisplayed threefold higher resistance to 2,4-D than the wild-typecell line based on the 50% inhibitory concentrations of 2,4-Don DNA synthesis. No significant differences which could explainthe 2,4-D resistance were found between the variant and thewild-type cell lines in 2,4-D concentrations required to inhibitRNA and protein synthesis. The effect of 2,4-D on cell respirationwas detectable without a noticeable lag. The resistance of thevariant based on the effect on cell respiration also was apparentimmediately after 2,4-D addition. According to the 50% inhibitoryconcentrations of 2,4-D on cell respiration, the variant showeda level of resistance similar to that estimated by DNA synthesis.These results indicate that the resistance of the variant isdue to a modification which reduces the cellular sensitivityto phyto-toxic concentrations of 2,4-D with respect to, at least,DNA synthesis and respiration. (Received August 6, 1985; Accepted November 27, 1985)     

Differences between Effects of Undissociated and Anionic 2,4-Dinitrophenol on Permeability of Barley Roots

Effects of 2,4-dinitrophenol (DNP) and several other substituted phenols on permeability of barley roots (Hordeum vulgare var. Trebi) to ions were assayed as a function of pH and phenol concentration. Solutions containing 0.1 micromolar undissociated DNP increase the permeability of barley root cells to small ions such as K⁺, Na⁺, Ca²⁺, and Cl⁻ with no inhibition of respiration. Undissociated forms of the other phenols increase permeability also, but they are less effective than DNP. Only the undissociated DNP is effective. Anionic DNP does not increase permeability or inhibit ion uptake, although it is the major species accumulated by the roots, both at pH 5 and pH 7. At pH 7, in contrast to pH 5, 10 micromolar DNP has no effect on ion permeability of barley roots yet it uncouples oxidative phosphorylation of barley root mitochondria. This indicates that the all too common use of DNP as a test for active transport or involvement of ATP synthesis can be misleading.     

Effects of 2,4-D and its metabolite 2,4-dichlorophenol on antioxidant enzymes and level of glutathione in human erythrocytes

The effects of in vitro exposure of human erythrocytes to different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and its metabolite 2,4-dichlorophenol (2,4-DCP) were studied. The activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and the level of reduced glutathione (GSH) were determined. The activity of erythrocyte superoxide dismutase SOD decreased with increasing dose of 2,4-D and 2,4-DCP, while glutathione peroxidase activity increased. 2,4-D (500 ppm) decreased the level of reduced glutathione in erythrocytes by 18% and 2,4-DCP (250 ppm) by 32%, respectively, in comparison with the controls. These results lead to the conclusion that in vitro administration of herbicide-2,4-D and its metabolite 2,4-DCP causes a decrease in the level of reduced glutathione in erythrocytes and significant changes in antioxidant enzyme activities. Comparison of the toxicity of 2,4-D and 2,4-DCP revealed that the most prominent changes occurred in human erythrocytes incubated with 2,4-DCP.     

The Control of Leaf and Ear Size in Barley

The relative growth rates, growth rates, and final size of tillersand main-shoot leaves, internodes, and ear of a freely tilleringspring barley genotype were measured and compared with thoseof a non-tillering single-gene mutant. Leaf and internode growthand final size were greater in the non-tillering mutant. Thedifferences, it is proposed, arise because of changes in internalcompetition for assimilates brought about by the absence oftillers. There was little difference in ear growth or size,possibly because of abnormalities of ear development, whichresulted in fewer spikelets in the non-tillering genotype.     

Metabolism of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Soybean Root Callus : EVIDENCE FOR THE CONVERSION OF 2,4-D AMINO ACID CONJUGATES TO FREE 2,4-D

An auxin-requiring soybean root callus metabolized [1-¹⁴C]-2,4-dichlorophenoxyacetic acid (2,4-D) to diethyl ether-soluble amino acid conjugates and water-soluble metabolites. The uptake in tissue varied with incubation time, concentration, and amount of tissue. Uptake was essentially complete (80%) after a 24-hour incubation and the percentage of free 2,4-D in the tissue fell to its lowest point at this time. At later times, the percentage of free 2,4-D increased and the percentage of amino acid conjugates decreased, whereas the percentage of water-soluble metabolites increased only slightly. Similar trends were seen if the tissue was incubated for 24 hours in radioactive 2,4-D, followed by incubation in media without 2,4-D for 24 hours. Inclusion of nonlabeled 2,4-D during the 24-hour chase period did not reduce amino acid conjugate disappearance but did reduce the percentage of free [1-¹⁴C]2,4-D. Thus, an external supply of 2,4-D does not directly prevent amino acid conjugate metabolism in this tissue. It is concluded that 2,4-D amino acid conjugates were actively metabolized by this tissue to free 2,4-D and water-soluble metabolites.     

Effects of pH Changes on Ion and 2,4-D Uptake of Wheat Roots

The quantitative relationships between pH-dependent ion and 2,4-D uptake in winter wheat seedlings (Triticum aestivum L. cv. Yubileynaya 50) have been investigated. The movement of various ions (potassium, phosphate, nitrate and ammonium) and 2,4-D across the root membranes was monitored with radioactive and stable isotope tracer methods. It was found that the H₊ ion concentration of the absorption solution strongly influences the 2,4-D uptake of the roots. Simultaneously, the 2,4-D uptake stimulates secretion of H⁺ into the absorption solution, that is, a H⁺ efflux can accompany the uptake of 2,4-D. This finding is consistent with the acid secretion theory of auxin and fusicoccin action. At pH 4 the 2,4-D uptake was much higher than at pH 6, thereby inhibiting the ion uptake and increasing the phytotoxicity in the plant. The results indicate that 2,4-D enters the root cells rapidly at the lower pH, mostly as undissociated molecules. With reference to the 2,4-D concentration in the roots at pH 4, a possible transport mechanism of the auxin herbicide is briefly discussed.     

Effects of the herbicide 2,4-D on the growth of nine aquatic macrophytes

A study was conducted to determine the effect of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on nine submersed macrophyte species. The first objective of the study was to investigate the sensitivity of various endpoints in macrophyte toxicity tests. A second objective was to investigate the implications of hormesis in the risk assessment of 2,4-D. 2,4-D was applied in concentrations ranging from 10 to 3000 μg L⁻¹. Endpoints determined 4 weeks after the start of the treatment were based on shoot and root growth in water. The EC₅₀s were calculated using models excluding and including a parameter describing hormesis. Results indicated that the total length of the roots can be regarded as a sensitive endpoint for the response of a macrophyte to 2,4-D. For the tested rooted macrophyte species, the EC₅₀ values for the length and number of the roots ranged from 92 to 997 and from 112 to 1807 μg L⁻¹, respectively. At low concentrations (10 and 30 μg L⁻¹), stimulation of some of the endpoints (hormesis) was found for several of the species. Although hormesis may have ecological implications, its importance for the ecological risk assessment of 2,4-D in this study was limited.     

Impacts of 2,4-D application on soil microbial community structure and on populations associated with 2,4-D degradation

The effect of 2,4-dichlorophenoxyacetic acid (2,4-D) application rate on microbial community structure and on the diversity of dominant 2,4-D degrading bacteria in an agricultural soil was examined using cultivation-independent molecular techniques coupled with traditional isolation and enumeration methods. Fingerprints of microbial communities established under increasing concentrations of 2,4-D (0-500 mg kg-1) in batch soil microcosms were obtained using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene segments. While a 2,4-D concentration of at least 100 mg kg-1 was required to obtain an apparent change in the community structure as visualized by DGGE, the greatest impact of 2,4-D concentration occurred in the 500 mg kg-1 treatment, resulting in significantly reduced diversity of the dominant populations and enrichment by Burkholderia-like populations. The greatest diversity of 2,4-D degrading isolates was cultivated from the 10 mg kg-1 treatment, indicating that under these conditions, cultivation was more sensitive than DGGE for detecting changes in community structure. Most of these isolates harbored homologs of Ralstonia eutrophus JMP134 and Burkholderia cepacia tfdA catabolic genes. Results from this study revealed that agriculturally relevant application rates of 2,4-D may provide a temporary selective advantage for organisms capable of utilizing 2,4-D as a carbon and energy source.     

Effects of 2,4-D butyl vapour on the growth of six crop species

Six species of crop plants (tomato, lettuce, clover, cabbage, sunflower and field bean) were exposed to concentrations of 2,4-D butyl in the range 3–50 ng/litre, for 3.5 h, using an air-flow system. Symptoms of phytotoxicity were recorded during the following 4 wk, after which the plants were harvested. Sunflower and field bean were found to be most sensitive, with tomato, lettuce and cabbage less affected and clover least sensitive, on the basis of weight. Small tomato plants were more sensitive than ones approximately twice the weight. A 50% reduction in dry weight was caused by a 3.5h exposure to less than 3 ng/litre 2,4-D butyl for sunflower, compared with over 50 ng/litre for clover. The ranking of sensitivities did not agree with reports based on liquid doses of 2,4-D, especially for field bean, which was found to be more sensitive than previously thought.     

Effects of light conditions and 2,4-D concentration in soybean anther culture

The morphogenic response of anther walls and connective tissue is the greatest obstacle to androgenesis in soybean anther culture. Whereas induction to microspore embryogenesis occurs in the dark in almost all plant species, soybean anthers have been cultured under light. In an attempt to establish culture conditions that simultaneously stimulate microspore embryogenesis and inhibit epidermal and connective cell proliferation, the effect of light and two 2,4-dichlorophenoxyacetic acid (2,4-D) concentrations (2 and 10 mg l^–1) on the induction process was investigated. Higher 2,4-D concentration speeded up microspore plasmolysis and did not improve androgenesis. Callogenesis and embryogenesis induction from sporophytic cells were significantly lower in the dark, and some microspores showed major alterations in the sporoderm. Auxin 2,4-D and induction under light contributed to the morphogenic response of the anther walls and connective tissue under the conditions previously recommended to trigger microspore embryogenesis.     

In vivo Nitrate Reductase Activity in Barley (Hordeum vulgare L.) during Ear Development

Experiments were conducted during the 1974–75 and 1975–76winter season with the barley (Hordeum vulgare L.) cultivarJyoti. From amongst the various plant parts, the flag leaf bladehad higher in vivo nitrate reductase (NR) activity than thelower two leaf blades, glumes, and grains. However, the potentialof a plant part to reduce NO₃^– is a function of its freshweight and the NR per unit fresh weight. On this basis, thesecond and third leaf blades could reduce more NO₃^– thanthe flag leaf blade. N fertilizer application resulted in enhancementof the activity of the leaf blades alone. N fertilizer appliedduring the reproductive phase was taken up and assimilated bythe various plant parts. The studies suggest that, even whenthe fertilizer is applied at optimum levels for obtaining maximumyields, the upper leaf blades have sub-optimal NR activity andthat there is a likelihood of either a preferential flow ofNO₃^– to the leaf blades or transnational barriers to NO₃^–movement to the ear.     

2,4-D impact on bacterial communities, and the activity and genetic potential of 2,4-D degrading communities in soil

The key role of telluric microorganisms in pesticide degradation is well recognized but the possible relationships between the biodiversity of soil microbial communities and their functions still remain poorly documented. If microorganisms influence the fate of pesticides, pesticide application may reciprocally affect soil microorganisms. The objective of our work was to estimate the impact of 2,4-D application on the genetic structure of bacterial communities and the 2,4-D-degrading genetic potential in relation to 2,4-D mineralization. Experiments combined isotope measurements with molecular analyses. The impact of 2,4-D on soil bacterial populations was followed with ribosomal intergenic spacer analysis. The 2,4-D degrading genetic potential was estimated by real-time PCR targeted on tfdA sequences coding an enzyme specifically involved in 2,4-D mineralization. The genetic structure of bacterial communities was significantly modified in response to 2,4-D application, but only during the intense phase of 2,4-D biodegradation. This effect disappeared 7 days after the treatment. The 2,4-D degrading genetic potential increased rapidly following 2,4-D application. There was a concomitant increase between the tfdA copy number and the 14C microbial biomass. The maximum of tfdA sequences corresponded to the maximum rate of 2,4-D mineralization. In this soil, 2,4-D degrading microbial communities seem preferentially to use the tfd pathway to degrade 2,4-D.     

Effect of Dissemination of 2,4-Dichlorophenoxyacetic Acid (2,4-D) Degradation Plasmids on 2,4-D Degradation and on Bacterial Community Structure in Two Different Soil Horizons

Transfer of the 2,4-dichlorophenoxyacetic acid (2,4-D) degradation plasmids pEMT1 and pJP4 from an introduced donor strain, Pseudomonas putida UWC3, to the indigenous bacteria of two different horizons (A horizon, depth of 0 to 30 cm; B horizon, depth of 30 to 60 cm) of a 2,4-D-contaminated soil was investigated as a means of bioaugmentation. When the soil was amended with nutrients, plasmid transfer and enhanced degradation of 2,4-D were observed. These findings were most striking in the B horizon, where the indigenous bacteria were unable to degrade any of the 2,4-D (100 mg/kg of soil) during at least 22 days but where inoculation with either of the two plasmid donors resulted in complete 2,4-D degradation within 14 days. In contrast, in soils not amended with nutrients, inoculation of donors in the A horizon and subsequent formation of transconjugants (10⁵ CFU/g of soil) could not increase the 2,4-D degradation rate compared to that of the noninoculated soil. However, donor inoculation in the nonamended B-horizon soil resulted in complete degradation of 2,4-D within 19 days, while no degradation at all was observed in noninoculated soil during 89 days. With plasmid pEMT1, this enhanced degradation seemed to be due only to transconjugants (10⁵ CFU/g of soil), since the donor was already undetectable when degradation started. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes showed that inoculation of the donors was followed by a shift in the microbial community structure of the nonamended B-horizon soils. The new 16S rRNA gene fragments in the DGGE profile corresponded with the 16S rRNA genes of 2,4-D-degrading transconjugant colonies isolated on agar plates. This result indicates that the observed change in the community was due to proliferation of transconjugants formed in soil. Overall, this work clearly demonstrates that bioaugmentation can constitute an effective strategy for cleanup of soils which are poor in nutrients and microbial activity, such as those of the B horizon.     

Effect of dissemination of 2,4-dichlorophenoxyacetic acid (2,4-D) degradation plasmids on 2,4-D degradation and on bacterial community structure in two different soil horizons

Transfer of the 2,4-dichlorophenoxyacetic acid (2,4-D) degradation plasmids pEMT1 and pJP4 from an introduced donor strain, Pseudomonas putida UWC3, to the indigenous bacteria of two different horizons (A horizon, depth of 0 to 30 cm; B horizon, depth of 30 to 60 cm) of a 2,4-D-contaminated soil was investigated as a means of bioaugmentation. When the soil was amended with nutrients, plasmid transfer and enhanced degradation of 2,4-D were observed. These findings were most striking in the B horizon, where the indigenous bacteria were unable to degrade any of the 2,4-D (100 mg/kg of soil) during at least 22 days but where inoculation with either of the two plasmid donors resulted in complete 2,4-D degradation within 14 days. In contrast, in soils not amended with nutrients, inoculation of donors in the A horizon and subsequent formation of transconjugants (10(5) CFU/g of soil) could not increase the 2,4-D degradation rate compared to that of the noninoculated soil. However, donor inoculation in the nonamended B-horizon soil resulted in complete degradation of 2,4-D within 19 days, while no degradation at all was observed in noninoculated soil during 89 days. With plasmid pEMT1, this enhanced degradation seemed to be due only to transconjugants (10(5) CFU/g of soil), since the donor was already undetectable when degradation started. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes showed that inoculation of the donors was followed by a shift in the microbial community structure of the nonamended B-horizon soils. The new 16S rRNA gene fragments in the DGGE profile corresponded with the 16S rRNA genes of 2,4-D-degrading transconjugant colonies isolated on agar plates. This result indicates that the observed change in the community was due to proliferation of transconjugants formed in soil. Overall, this work clearly demonstrates that bioaugmentation can constitute an effective strategy for cleanup of soils which are poor in nutrients and microbial activity, such as those of the B horizon.     

Early Growth of the Developing Ear of Spring Barley

The change in fresh weight of the developing ear and of groupsof spikelets of Maris Mink spring barley was measured for plantsgrown under three different conditions. Growth was closely describedby a third order polynomial equation. Instantaneous values ofrelative growth rate derived from these equations showed a declineto a minimum value, which was dependent on the growing conditionsand on position along the spike, followed by a rapid rise. Theminimum value was reached about 5 d before spikelet initiationceased and the subsequent rise in relative growth rate coincidedwith the period of rapid elongation of the rachis. Within thecar there was a tendency for younger spikelets to have a slightlyhigher relative growth rate than those initiated earlier. Possiblereasons for these growth changes are discussed in relation tospikelet differentiation, vascularization of the ear and nutrientavailability. Hordeum vulgare L., Barley, shoot apex, spikelets, ear, initiation, growth rate     

2,4-D和NAA在拟南芥细胞分裂和伸长中的作用分析

以拟南芥悬浮细胞体系为实验材料,研究了人工合成生长素NAA和2,4-D外源处理对细胞形态、细胞鲜重、细胞分裂指数等指标的影响.结果表明:2μmol/L 2,4-D可有效促进细胞分裂但不影响细胞伸长;同样浓度的NAA主要诱导细胞的伸长;细胞伸长和细胞分裂是2个不相偶联的过程;在2,4-D所诱导的细胞分裂过程中异三聚体G-蛋白α-亚基GPA1强表达.