Hormone-directed Transport of Assimilates in Decapitated Internodes of Phaseolus vulgaris L.

Application of ethylene, indole-3yl-acetic acid (IAA), 6-(benzylamino)-9-(2tetrahydropyranyl)-9-Hpurine (SD8339), or mixtures of IAA, gibberellic acid (GA),and cytokinins, increased the accumulation of ¹⁴C-activity indecapitated internodes of Phaseolus vulgaris seedlings. Differencesbetween treated and untreated tissues with respect to importof labelled assimilate were detected 3 h after application ofa mixture of IAA, GA, and SD8₃₃₉. In longer-term experimentseffects of the growth-regulator mixture on translocation oflabel were greater than those of IAA alone. Inhibitory effectsof abscisic acid on import of assimilate were counteracted bySD8₃₃₉. The ability of internode tissues to import ¹⁴C-photosynthatedeclines with time from decapitation, and a decrease in incorporationof ¹⁴C-leucine into protein was detected after 24 h. There wasan increase in protein and RNA synthesis in internodal tissuesfollowing a 2.5-h pre-treatment of decapitated internodes withIAA, GA, and SD8₃₃₉. Concentrations of 2, 3, 5-triiodobenzoicacid which inhibit ¹⁴C-IAA translocation stimulate protein synthesisin decapitated internodes, and augment the IAA-effect on importof ¹⁴C-photosynthate. ‘Hormone-directed’ assimilatetransport is discussed in relation to confounding effects ofgrowth responses and differential senescence of treated anduntreated tissues. It is suggested that accumulation of labelledassimilate in treated tissues results from effects of growthregulators on synthetic activities at the point of application.     

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.     

Transport 14C-markierter Assimilate im Phloem von Pelargonium zonale und Phaseolus vulgaris

Zusammenfassung 6–10 min nach Beginn der ¹⁴CO₂-Assimilation befindet sich ¹⁴C-Aktivität im Stiel des ¹⁴CO₂-exponierten Blattes belichteter Pflanzen von Pelargonium zonale und Phaseolus vulgaris. Die Verteilungsrichtung der Assimilate im Sproß scheint vor allem durch das Alter des ¹⁴C-assimilierenden Blattes bestimmt, jedoch nicht einseitig festgelegt zu sein; geringe, aber faßbare Mengen an ¹⁴C-Saccharose wereden innerhalb von 20 min (bei Phaseolus) und 180 min (bei Pelargonium) auch aus relativ jüngeren in ältere Blätter transportiert.Neben ¹⁴C-Saccharose wurden im Blattstiel-und Stengelgewebe stets markierte Zuckerphosphate, Hexosen und organische Säuren nachgewiesen. Stärke war nur zu einem verschwindend geringen Anteil an der Gesamtmarkierung der analysierten Transportstrecken beteiligt.

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Translocation of ¹⁴C-labelled assimilates in the phloem of Pelargonium zonale and Phaseolus vulgaris

Summary After the laminae of leaves of intact plants had been exposed to ¹⁴CO₂ the translocation of ¹⁴C-labelled assimilates across the petioles starts very quickly: 6 to 10 min later ¹⁴C-activity could be detected in the basal part of the petioles. The way of distribution within the plant seems to be influenced mainly by the age of the ¹⁴CO₂-assimilating leaf, however, but not in the sense of an unidirectional movement; little but distinct amounts of ¹⁴C were carried also from younger yet full expanded leaves down to older leaves, within 20 min (in Phaseolus) or 180 min (in Pelargonium). Besides sucrose, which was shown by paper chromatography to be the main form of assimilates translocated in these species, we identified sugar phosphates, hexoses, and some organic acids in the petiole and stem tissue as being radioactive also. In our experiments, the petiole segments did not contain any remarkable amount of ¹⁴C-labelled starch.

     

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     

Auxin-promoted Transport of Metabolites in Stems of Phaseolus vulgaris L.: SOME CHARACTERISTICS OF THE EXPERIMENTAL TRANSPORT SYSTEMS

Indol-3yl-acetic acid (IAA) applied to sterns of Phaseolus vulgarisseedlings, decapitated above primary leaves, enhanced the mobilizationof ¹⁴C-metabolites to the treated stumps and this effect wasapparent within 3–6 h of applying the hormone. More than90 per cent of the total ¹⁴C-activity transported to the stumpswas detected in the alcohol-soluble extracts. In all treatments,less than 5 per cent of the ¹⁴C-photosynthate exported fromthe primary leaves was translocated upwards. Accumulation of¹⁴C-activity was also increased when the IAA was applied laterallyto intact internodes. This effect was obtained when ¹⁴C wassupplied either above or below the point of hormone application.By selective heat girdling, it was shown that the auxin affected¹⁴C transport when either the root ‘sink’ was removedor transpiratory flow of water through the treated internodewas maintained. Decapitated stems treated with plain lanolinfor 3 d were found to retain their responsiveness to auxin interms of enhanced metabolite transport. Heat-girdling experimentsand estimates of ¹⁴C transport velocity suggested that mostof the ¹⁴C movement was restricted to the phloem of treatedstumps. Similar effects of IAA on a transport in excised stemsegments of Phaseolus vulgaris were observed.     

The Effect of IAA on Sugar Accumulation and Basipetal Transport of 14C-labelled Assimilates in Relation to Root Formation in Phaseolus vulgaris Cuttings

The effect of indol-3yl-acetic acid on root formation, accumulation of 80% ethanol-soluble sugars and basipetal transport of ¹⁴C-labelled assimilates has been investigated in Phaseolus vulgaris (cv. Canadian Wonder) hypocotyl cuttings. The removal of leaves reduced root formation in the hypocotyl, while excision of the apical bud was less detrimental. The expression of the IAA effect in inducing more roots was dependent on the area of leaves, and was found to be better when all leaves were present. Sugars accumulated slowly at the base of cuttings during a four-day period after excision, and IAA greatly enhanced this accumulation. By comparing sugar content at the base of green and starved cuttings it was established that IAA greatly increased it concurrently with root formation. IAA applied in solution to the hypocotyl greatly enhanced the basipetal transport of ¹⁴C-labelled assimilates and their accumulation at the hypocotyl during a 24-h period. The IAA-induced accumulation was found to be connected with a greater mobilization of labelled assimilates from upper parts of the cutting. Experiments involving pretreatment with IAA and transport in cuttings already possessing root primordia, suggest a dual effect of IAA: (I) a direct effect on transport, and (2) an increase in the root-“sink”. It is concluded that both may be operating in inducing basipetal accumulation of labelled assimilates. It is suggested that one of the roles of IAA in promoting rooting of cuttings is to increase sugar availability at the site of root formation.     

Auxin-Promoted Transport of Metabolites in Stems of Phaseolus vulgaris L.: EFFECTS REMOTE FROM THE SITE OF HORMONE APPLICATION

Phloem transport in stems of Phaseolus vulgaris was found tobe sensitive to treatment with the auxin transport inhibitor,2,3,5-triidobenzoic acid (TIBA). The response was dependenton the concentration of TIBA applied. A concentration of TIBA(0?5% in lanolin) which did not interfere with normal phloemtransport proved inhibitory to both basipetal transport of IAAand the acropetal component of IAA-promoted metabolite transport.In contrast, both acropetal IAA transport and basipetal IAA-promotedmetabolite transport were unaffected by TIBA treatment. Theinhibitory effect of TIBA on acropetal IAA-promoted transportwas overcome by providing IAA below the point of TIBA application.Both acropetal and basipetal IAA-promoted transport in stemsegments were unaccompanied by any corresponding changes inthe accumulation of [¹⁴C]sucrose by the segments.     

Methylammonium Transport in Phaseolus vulgaris Leaf Slices

Methylammonium (as a nonmetabolized analog of ammonium) transport was studied in leaf slices of Phaseolus vulgaris L. var. `Hawkesbury Wonder.' The relationship of influx to external pH (6.0-10.5) shows that the influx at low external pH is a larger fraction of that at high external pH than would be expected from the pK_α of methylammonium and the assumption that only CH₃NH₂ is entering the cells. The relationship between methylammonium influx and external methylammonium concentration shows some evidence of saturation; this is a function of the transport system rather than of the (limited) methylammonium metabolism in the cells. The “equilibrium” concentration ratio for methylammonium between leaf slices and bathing medium is far higher than can be explained by the transport of CH₃NH₂ alone and the pH of the compartments involved. These three lines of evidence strongly suggest that there is an influx of CH₃NH₃⁺, possibly by a uniporter driven by the electrical potential of the cytoplasm with respect to the medium, as has been shown for other plant cells. Competitive inhibition of methylammonium influx by ammonium suggests that there is also an ammonium transport system. The significance of this for the recycling of N within the plant and for exchange of gaseous NH₃ between leaves and the atmosphere is discussed.     

Auxin-promoted Transport of Metabolites in Stems of Phaseolus vulgaris L: EFFECTS AT THE SITE OF HORMONE APPLICATION

The hypothesis that indol-3yl-acetic acid (IAA) stimulates solutemobilization in stems by increasing metabolite utilization (i.e.sink strength) and/or sieve tube unloading mechanisms was investigatedusing seedlings of Phaseolus vulgaris L. Sink strength was assessedby obtaining estimates of rates of growth, ¹⁴C incorporationinto protein, sucrose metabolism, and sucrose uptake. The dataobtained suggest that, whilst enhancing assimilate mobilization,IAA had no short term effect on the sink strength of the treatedstumps. In several experiments involving long distance transportof ¹⁴C-assimilates, the magnitude of auxin-promoted transportwas found to be insensitive to potential changes in sink strength.Furthermore, ¹⁴C transport profiles demonstrated that the siteof hormone action was not confined to its point of application.     

The Pathway of Radial Transfer of Photosynthate in Decapitated Stems of Phaseolus vulgaris L.

[¹⁴C]Sucrose was found to be the predominant component of the¹⁴C-photosynthates that accumulated in the free space of decapitatedstems of P. vulgaris plants. The ¹⁴C-photosynthates appearedto occupy the entire free-space volume of the stems at totalsugar concentrations in the range of 3–12 mM. The free-spacesugar levels were found to rapidly decline once photosynthatetransfer to the stems was halted. Moreover, it was found thatestimates of the rate of in vitro sucrose uptake by the stemscould account fully for the decline in free-space sugar levels.Overall, the evidence indicated that at least part of the radialpathway of photosynthate transfer in bean stems involved thestem apoplast. It is tentatively proposed that, based on celland tissue distribution of ¹⁴C-photosynthates, the apoplasticpathway extends from the membrane boundary of the sieve element/companion-cellcomplex to all other cells of the stem. Apoplast, Phaseolus vulgaris L., bean, phloem unloading, photosynthates, symplast     

Cytokinin Effects on Leaf Architecture in Phaseolus vulgaris L.

Treatment of expanding primary leaves of bean plants (Phaseolnsvulgaris L. cv. Limburgse vroege) with benzyladenine (BA) orkinetin at 0.5 mM for five consecutive days resulted in thickerleaves showing a significant decrease in intercellular air spacevolume. Compared with control plants, exposed mesophyll cellsurface area was lower per unit tissue volume, but unchangedwhen expressed per unit leaf surface area. Stomata of treatedplants were not fully closed in the dark and they did not openas wide as controls in the middle of the light period, suggestingthat the treatment resulted in impaired stomatal action. Allthe effects mentioned were more pronounced after treatment withBA, compared to kinetin. In spite of their magnitude, the observedchanges in leaf structure and function did not seem to havean important effect on total leaf diffusion resistance to carbondioxide during the course of the light period. Key words: Cytokinins, Leaf architecture     

Auxin-Promoted Transport of Metabolites in Stems of Phaseolus vulgaris L.: FURTHER STUDIES ON EFFECTS REMOTE FROM THE SITE OF HORMONE APPLICATION

The proposal that indol-3yl-acetic acid (IAA) regulates acropetaltransport in stems by acting along the transport channel wasfurther investigated using decapitated seedlings of Phaseolusvulgaris. Concentrations of two inhibitors of auxin transport,which did not interfere with IAA-promoted basipetal transport,were found to decrease the IAA-promoted component of acropetalmetabolite movement. This latter inhibition was relieved bytreating the stems with a supplementary supply of IAA belowthe point of inhibitor application. These observations, togetherwith the finding that the response time of transport to hormoneaction was strongly dependent on the distance over which IAAneeded to move to be present throughout the length of the transportchannel, provide support for the above proposed mode of IAAaction.     

菜豆茎韧皮部卸出的细胞途径以及激素的促进作用(英文)

通过缩小叶面积和去茎尖改变源库比率,以调节韧皮部卸出的途径,证明了韧皮部卸出的共质体与质外体途径的季节变化,和由对氯高汞苯磺酸所诱发的从质外体向共质体途径的转变,是与光合产物的输入有关。缩小叶面积而降低源库比率,能增加夏季生长植株茎韧皮部的质外体卸出,但对冬季生长植株无影响。去尖而增加源库比率,则促进共质体卸出。赤霉酸和激动素能促进共质体的横向转运,但对质外体转运无作用。当质外体为主要运输途径时,赤霉酸和激动素开启共质体途径。赤霉酸和激动素刺激光合产物,通过共质体从筛管一伴胞复合体向韧皮部薄壁纽胞输送,并可能在韧皮部薄壁细胞被动扩散到自由空间。由此可进一步说明蔗糖在激素处理部位自由空间的增加。     

Abscisic Acid Accumulation in Developing Seeds of Phaseolus vulgaris L

Free and bound abscisic acid (ABA) in the pod, seed coat, and embryo were determined separately throughout seed development of Phaseolus vulgaris L. cv. `Taylor's Horticultural.' An internal standard method of gas-liquid chromatography was used for ABA quantification. In the embryo, two peaks of free ABA occurred at days 22 (1.18 micrograms per gram or 5.5 micromolar) and 28 (1.74 micrograms per gram or 12 micromolar); and a single peak of bound ABA at day 30. In the seed coat, there was one peak of free ABA at day 22 and only small amounts of bound ABA. Very small amounts of ABA were detected in the pod at any stage of development. In cv. PI 226895, in which seed development is more rapid than in `Taylor's Horticultural,' the embryo ABA peaks occur on days 20 and 26. The timing of the ABA peak in the embryo, and the concentration attained, are consistent with previous reports on the natural pattern of RNA synthesis and with ABA inhibition of RNA synthesis in developing bean fruit.     

Temperature Effects on Mitochondrial Respiration in Phaseolus acutifolius A. Gray and Phaseolus vulgaris L

Electron transport, using succinate as a substrate, was measured polarographically in mitochondria isolated from Phaseolus vulgaris and P. acutifolius plants at 25°C and 32°C. Mitochondria isolated from P. vulgaris plants grown at 32°C had reduced electron transport and were substantially uncoupled. Growth at 32°C had no effect on electron transport or oxidative phosphorylation in P. acutifolius compared to 25°C grown plants. Mitochondria isolated from 25°C grown P. vulgaris plants measured at 42°C were completely uncoupled. Similarly treated P. acutifolius mitochondria remained coupled. The uncoupling of P. vulgaris was due to increased proton permeability of inner mitochondrial membrane. The alternative pathway was more sensitive to heat than the regular cytochrome pathway. At 42°C, no alternative pathway activity was detected. The substantially greater heat tolerance of P. acutifollus compared to P. vulgaris mitochondrial electron transport suggests that mitochondrial sensitivity to elevated temperatures is a major limitation to growth of P. vulgaris at high temperatures and is an important characteristic conveying tolerance in P. acutifolius.     

Respiration of 14C-labelled Assimilates in Stems of Willow

Willow cuttings were allowed to assimilate ¹⁴CO₂, and the changein the specific activity of phloem sap, collected as aphid honeydew,was compared with the change in the specific activity of the¹⁴CO₂ given off from the respiration of the labelled translocates.With young shoots (3–5 weeks old), the acceleration inthe specific activities of honeydew and respiratory CO₂ werevery similar. With 2–4-year-old mature stems, however,there was a considerable difference between the accelerationof the two specific activities, that of the honeydew alwaysbeing greater than respiratory CO₂. Studies have also been made on the rate of breakdown of ¹⁴C-labelledtranslocates in isolated and intact young shoots and maturestems. No differences between the isolated and intact stemswere apparent. The results are discussed in relation to possible translocationmechanisms, and the results of other workers in this field ofexperimentation.     

Effects of high temperature on nodulation and nitrogen fixation by Phaseolus vulgaris L.

Screening of Rhizobium leguminosarum bv. phaseoli strains showed some that were able to nodulate common beans (Phaseolus vulgaris L.) at high temperatures (35 and 38°C/8 h/day). The nodulation ability was not related to the capability to grow or produce melanin-like pigment in culture media at high temperatures. However, nodules formed at high temperatures were ineffective and plants did not accumulate N in shoots. Two thermal shocks of 40°C/8 h/day at flowering time drastically decreased nitrogenase activity and nodule relative efficiency of plants otherwise grown at 28°C. Recovery of nitrogenase activity began only after seven days, when new nodules formed; total incorporation of N in tops did not recover for 2 weeks. Non-inoculated beans receiving mineral N were not affected by the thermal shock, and when growing continuously at 35 or 38°C had total N accumulated in shoots reduced by only 18%.     

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.     

Diurnal Rb+ Transport from Roots to the Laminar Pulvinus in Phaseolus vulgaris L.

The primary leaves of kidney bean (Phaseolus vulgaris L.) openunder light and close in the dark by the deformation of thepulvinus resulting from diurnal distribution changes of K⁺,Cl^–, organic acid (or H⁺) and NO₃^–. When Rb⁺ was added as a tracer of K⁺ to the seedlings throughtheir roots, it was transported to the pulvinus cells duringthe light period but not during the dark period. Transpirationoccurred vigorously in the light but almost stopped in the dark.We concluded that Rb⁺ absorbed by the roots was carried to thepulvinus by the transpiration stream. Phaseolus vulgaris L., pulvinus, Rb⁺, diurnal transport transpiration stream