The Effect of 2,4-Dichlorophenoxyacetic Acid and Related Compounds on the Fine Structure of the Primary Leaves of Phaseolus vulgaris

The epidermal cuticle of the abaxial surface of the primaryleaves of Phaseolus vulgaris used for these experiments is notmore than 0.15 µm thick except on the walls of basal cellsof epidermal hairs. The cuticle apparently has no internal structure;neither channels or canals can be seen passing through it. An examination of the fine structure of leaf tissue 24 h afterthe application of 1.6 x 10^–3 M solutions of 2-chlorophenoxyaceticacid (2-CPA), 4-chlorophenoxyacetic acid (4-CPA), 2,6-dichlorophenoxyaceticacid (2,6-D), and 2,4-dichlorophenoxyacetic acid (2,4-D) hasshown that 2,4-D alone, and then only in the light, induceschanges in the morphology and internal structure of the chloroplast.As early as 4 h after application, there is an apparent breakdownin the structure of the membrane systems of the cells of theepidermis, palisade, and mesophyll. After 8 h the chloroplastsare distorted and contain electron-dense granules, and the cellsappear to be plasmolysed. Subsequently these changes becomemore pronounced. It is possible that the specific disturbancesbrought about by 2,4-D reflect its phytotoxic properties.     

Blue-light-dependent osmoregulation in protoplasts of Phaseolus vulgaris Pulvini.

Blue light was found to induce shrinkage of the protoplasts isolated from first-leaf lamina pulvini of 18-day-old Phaseolus vulgaris. The response was transient following pulse stimulation, while it was sustainable during continuous stimulation. No apparent difference was found between flexor and extensor protoplasts. Protoplasts of the petiolar segment located close to the pulvinus showed no detectable response. In the plants used, the pulvinus was fully matured and the petiole was ceasing its elongation growth. When younger, 12-day-old, plants were used, however, the petiolar protoplasts did respond to blue light. The pulse-induced response was similar to that in pulvinar protoplasts, although the response to continuous stimulation was transient and differed from that in pulvinar protoplasts. No shrinkage was induced in pulvinar protoplasts when the far-red-light-absorbing form of phytochrome was absent for a period before blue-light stimulation, indicating that the blue-light responsiveness is strictly controlled by phytochrome. Inhibitors of anion channels and H(+)-ATPase abolished the shrinking response, supporting the view that protoplasts shrink by extruding ions. The response of pulvinar protoplasts is probably involved in the blue-light-induced, turgor-based movement of pulvini. The blue-light responding system in pulvini is suggested to have evolved from that functioning in other growing organs.     

Transport and Degradation of Auxin in Relation to Geotropism in Roots of Phaseolus vulgaris

The movement of auxin in Phaseolus vulgaris roots has been examined after injection of IAA^?3H into the basal root/hypocotyl region of intact, dark-grown seedlings. Only a portion of the applied IAA^?3H was transported unchanged to the root tip. The major part of the chromatographed, labelled compounds translocated to the roots was indole-3-acetylaspartic acid (IAAsp) and an unidentified compound running near the front in isopropanol, ammonia, water. The velocity of the auxin transport (7.2 mm per hour) was calculated from scintillation countings of methanol extracts from serial sections of the root. An accumulation of radioactive compounds in the extreme root tip, was observed 5 h after the injection of IAA. The influence of exogenous IAA on the geotropical behaviour of the bean seedling roots was examined. Pretreated roots were stimulated for 5 min in the horizontal position and then rotated parallel to the horizontal axis of the klinostat for 60 or 90 min. The resulting geotropic curvature of IAA-injected and control roots showed significantly different patterns of development. When the stimulation was started 5 h after application of the auxin, the geotropic curvature became larger in roots of the injected plants than in the controls. If, however, the translocation period was extended to 20 h the geotropic curvature was significantly smaller in the roots of the injected plants. The auxin injection did not significally affect the rate of root elongation. The change in geotropical behaviour of the roots is interpreted as a result of the influence of the conversion products of the applied IAA on the geotropical responsiveness.     

Auxin-Promoted Transport of Metabolites in Stems of Phaseolus vulgaris L.: Auxin Dose-Response Curves and Effects of Inhibitors of Polar Auxin Transport

Transport of ¹⁴C-photosynthate in decapitated stems of Phaseolusvulgaris explants was dependent on the concentration of indole-3-aceticacid (IAA) applied to the cut surfaces of the stem stumps. Thephysiological age of the stem influenced the nature of the transportresponse to IAA with stems that had ceased elongation exhibitinga more pronounced response with a distinct optimum. Increasednutrient status of the explants had little influence on theshape of the IAA dose-response curve but increased, by two ordersof magnitude, the IAA concentration that elicited the optimalresponse. Applications of the inhibitor of polar auxin transport,1-(2-carboxyphenyl)-3-phenylpropane-1, 3-dione (CPD), affectedIAA-promoted transport of ¹⁴C-photosynthates. At sub-optimalIAA concentrations, CPD inhibited transport, whereas at supra-optimalIAA concentrations, ¹⁴C-photosynthate transport was marginallystimulated by CPD. Treatment with CPD resulted in a significantreduction in stem levels of [¹⁴C]IAA below the site of inhibitorapplication, while above this point, levels of [¹⁴C]1AA remainedunaltered. The divergent responses of auxin-promoted transportto CPD treatment are most consistent with a remote action ofIAA on photosynthate transport in the decapitated stems. Key words: Auxin, photosynthate, transport     

Root Formation on Petioles of Detached Primary Leaves of Dwarf Bean (Phaseolus vulgaris) Pretreated with Gibberellic Acid, Triiodobenzoic Acid, and Cytokinins

Rooting experiments carried out with isolated primary leavesof dwarf bean demonstrated the effect of GA on increasing theIAA level and IAA synthesis. Pretreatment of the lamina of isolatedleaves with GA, especially when tryptophane was added at thesame time, strikingly increased the rooting of petioles. Enhancedroot formation on the petiole of GA-pretreated leaves can beattributed to increase of IAA level by GA in the lamina, i.e.in IAA biosynthesis the utilization of tryptophane releasedfrom the proteins of isolated leaves is promoted by GA. Application of TIBA on the upper part of petiole suppressedthe stimulatory effect of GA on root initiation presumably becauseTIBA inhibits the transport of IAA into the petiole, which resultsin failure of rooting. Pretreatment of the leaves with cytokinins also results in failureof root production. These substances retard protein decompositionin isolated leaves so that the quantity of TPP available forauxin synthesis is less. Simultaneously, this treatment increasesthe cytokinin concentration in the leaf tissues so that theauxin/cytokinin ratio alters and mainly callus forms on thebase of the petioles and differentiation of root primordia cannottake place.     

2,4-二氯苯氧乙酸的研究进展

2,4-二氯苯氧乙酸经常作为除草剂和植物生长调节剂使用,在农林业中发挥了重大作用,尤其在水果(如柑橘)保鲜中应用广泛,但其毒性问题也受到广泛关注,因此了解2,4-D的生理作用、在生物及环境中的代谢降解、残留毒性和提取鉴定等的研究进展很有必要.     

Growth Rates of a Pseudomonad on 2,4-Dichlorophenoxyacetic Acid and 2,4-Dichlorophenol

The growth of a pseudomonad on 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4-DCP (2,4-dichlorophenol) was studied in batch and continuous culture. The optimum growth rate using 2,4-D was 0.14/h at 25 C in a pH range from 6.2 to 6.9. Highest specific growth rate using 2,4-DCP was 0.12/h at 25 C in a pH range from 7.1 to 7.8. Growth was strongly inhibited by 2,4-DCP above a concentration of 25 mg/liter whereas no appreciable inhibition was observed with 2,4-D at concentrations up to 2,000 mg per liter. Growth on 2,4-DCP was described by Monod kinetics at subinhibitory concentrations but the inhibition by 2,4-DCP exhibited an unusual linear response to substrate concentration, and did not fit a model based on noncompetitive inhibition. The lag phase of batch cultures was found to depend on both 2,4-DCP concentration and prior adaptation of the inoculum. A study such as this on the kinetics of growth on related substrates may be useful as a method of finding the rate-limiting step in a metabolic sequence.     

Uptake of 2,4-Dichlorophenoxyacetic Acid by Pseudomonas fluorescens

Factors influencing the uptake of the sodium salt of 2,4-dichlorophenoxyacetic acid (2,4-D), under conditions in which no net metabolism occurred, were investigated in an effort to determine both the significance of "non-metabolic" uptake as a potential agent in reducing pesticide levels and the mechanisms involved. Uptake of 2,4-D was affected by pH, temperature, and the presence of other organic and inorganic compounds. Uptake was more pronounced at pH values less than 6, which implies that there may be some interaction between charged groups on the cell and the ionized carboxyl group of 2,4-D. Active transport, carrier-mediated diffusion, passive diffusion, and adsorption were considered as possible mechanisms. Though uptake was inhibited by glucose, sodium azide, and fluorodinitrobenzene (but not by uranyl ion), 2,4-D was not accumulated against a concentration gradient, a necessary consequence of an active transport system, nor was isotope counterflow found to occur. Thus, carrier-mediated diffusion was finally precluded, implying that uptake probably occurs by a two-step process: sorption onto the cell wall followed by passive diffusion into the cytoplasm.     

Auxin Physiology of Decapitated Stems of Phaseolus vulgaris L. Treated with Indol-3yl-acetic Acid

Physiological amounts of indol-3yl-acetic acid (IAA) were accumulatedby decapitated stems of Phaseolus vulgaris L. seedlings fromlanolin pastes, containing 0.1 per cent IAA, applied to thecut surfaces of the stumps. Both the levels and gradients ofextractable and diffusable IAA detected in the treated stumpscompared favourably with those reported for the whole plants.A considerable portion of IAA that entered the tissue was metabolizedto a compound that had chromatographic properties similar toindol-3yl-acetylaspartic acid. Two other metabolities were tentativelyidentified as indol-3yl-acetylaspartic acid indol-3yl-acetylglucose.The accumulated IAA appears to be transported as indol-3yl-aceticacid at an apparent velocity of 28 mm/h down the decapitatedinternodes.     

Effects of Ca on Amino Acid Transport and Accumulation in Roots of Phaseolus vulgaris

Ca²⁺ stimulates the uptake of α-aminoisobutyric acid (AIB) into excised or intact Phaseolus vulgaris L. roots by a factor of two. In roots depleted of Ca²⁺ by preincubation with ethylenediaminetetraacetate, ethyleneglycol-bis(β-aminoethyl ether)-N,N′-tetraacetic acid, or streptomycin, the stimulatory effect is 7- to 10-fold. In the presence of Ca²⁺, roots accumulate AIB more than 100-fold; Ca²⁺-depleted roots only equilibrate with AIB. Radioautography shows [¹⁴C]AIB to be present in all cells after 90 min. Although Ca²⁺-depleted roots lose accumulated [¹⁴C]AIB about 10 times faster than roots supplied with Ca²⁺, this increased efflux is not the main cause for the decrease in net uptake observed. The latter is rather due to a less negative membrane potential Δψ in Ca²⁺ depleted roots (−120 mV → −50 mV). The basic feature explaining all the results of Ca²⁺ deficiency is an increase in general membrane permeability. No indication of a specific regulatory function of Ca²⁺ in membrane transport of roots has been obtained.     

Diurnal Changes in the Malic Acid Concentration in Phaseolus coccineus L. Pulvini

Concentration of malic acid was determined in pulvini and petiolesand in isolated parts of the pulvinus, i.e. extensor and flexorregions, in Phaseolus coccineus. In the light period of thecircadian cycle, the concentration of malic acid in whole pulvinireached the highest value of 35.1 mmole CW while in the darkphase the respective value was 21.0 mmole CW. In the petiole,the highest concentration of malic acid was only 15.3% of themaximum concentration in the whole pulvinus. In isolated regions of motor cells, a cyclic alternation inthe concentration of malic acid was observed. In the light phase,the maximum acid concentration of 43.7 mmole CW in the extensorzone corresponds with the lowest concentration of 15.5 mmoleCW in the flexor region. The lowest value of acid concentrationof 30.8 mmole CW in the extensor part corresponds with the highestacid concentration of 31.1 mmole CW in the flexor part in thedark phase. About 22% of the total concentration of malic acid was transportedbetween the two opposite parts of the pulvinus as dependingupon the phases of leaf movement. (Received February 28, 1986; Accepted May 23, 1986)     

Auxin Regulation of the Response of Phaseolus vulgaris to a Fungal Elicitor

The effect of IAA and 2,4-D on the response of Phaseolus vulgaristo limiting concentrations of cell wall elicitors of Colletotrichumlindemuthianum was investigated in attached leaves of both thesusceptible, Pinto, and resistant, Kievit, cultivars. Low concentrationsof the plant hormones augmented the response, as measured bychanges in the activity of enzymes of the flavanoid pathway(phenylalanine ammonia-lyase (PAL) and -coumaric acid coenzyme-Aligase (-CL)) and phytoalexin concentration, both cultivars.This contrasts to a previous study with ethylene, where augmentationwas observed in leaves of cv. Kievit only; however, in the absenceof elicitor neither auxin nor ethylene have any effect. It wasalso observed that IAA promoted the synthesis of ethylene inthe leaves of cv. Kievit; inhibition of ethylene synthesis demonstratedthat the hormone could, nevertheless, act independently of ethyleneto enhance phytoalexin synthesis. The effect of auxin was particularly pronounced on PAL—hithertoidentified as a key regulatory enzyme on the flavanoid pathwaywhich, it is proposed, could be under the dual regulation ofboth auxin and ethylene. Similarly, the mode of action of auxinwas shown to resemble that of ethylene in that its effect isbrought about, partially if not entirely, as a result of itsregulation of the synthesis of enzymes of the flavanoid pathway. ¹Present address: School of Chemistry, Molecular and BiologicalSciences, University of Sussex, Brighton, U.K. (Received February 7, 1990; Accepted May 8, 1990)