Effect of Reduction of Sink Strength in Developing Seeds on Vein Loading Patterns of Photoassimilate in Source Leaves of Pisum sativum L

The effect of sink strength reduction in developing seeds onvein loading of photoassimilate has been studied in Pisum sativumL. The sink strength was manipulated by means of the ‘openseed coat technique’. Sink strength of the operated ovuleswas controlled by the osmolality of a substitute medium replacingthe embryo. A high osmolality of the medium (400 mM mannitol)or a low osmolality of the medium (without mannitol) was usedto maintain a high or low sink strength, respectively. To studythe effect of sink strength reduction on vein loading, macro-autoradiographywas used. After applying ¹⁴CO₂ to the source leaf for 10 to20min autoradiographs of plants with different sink strengthshowed differences in distribution of ¹⁴C-photoassimilate overthe mesophyll and the veins. Under low sink strength conditionsvein loading of ¹⁴C-photoassimilate was reduced. After longertime spans (40 to 60 min) no clear differences in vein loadingwere visible in the autoradiographs. However, measurement of¹⁴C in plant parts along the path of transport from source tosink showed a decrease of the rate of export of ¹⁴C from thesource leaf under low sink strength conditions. Apparently,accumulation of ¹⁴C-photoassimilate into the phloem and exporttowards sink regions can be reduced by lowering the sink strength.A signal must have been transferred from sink all the way tothe source regions. The mechanism of such a signal is discussed. Key words: Pisum sativum, phloem loading, photoassimilate transport, seed development, sink-source interactions     

Photosynthetic carbon metabolism in wild, primitive and cultivated forms of wheat at three levels of ploidy: Role of the glycolate pathway

¹⁴CO₂ assimilation was studied with diploid, tetraploid, hexaploidspecies of the genera Triticum and their wild relatives Aegilops.Attached mature leaves of 3–4 weekold plants were allowedto undergo photosynthesis under air at ambient temperature.The pattern of distribution of ¹⁴C was notably similar in Triticumand Aegilops species whatever the level of ploidy. Sucrose wasthe sink for photosynthetic carbon. ¹⁴C for sucrose synthesis was supplied either through the glycolatepathway by glycolate, the product of the photorespiration orby the Calvin cycle intermediates exported into the cytoplasm.Depending on the species, the glycolate pathway provided 40to 75%of the sucrose ¹⁴C. The higher labeling of sucrose was associated with the greaterparticipation of the glycolate pathway in the wild diploid (DD)A. squarrosa and in the cultivated hexaploid (AABBDD) T. aestivum.The results suggest that the expression of the male D genomeis dominant over the female AB genome in T. aestivum. In T. aestivum under ambient conditions lowering (low temperature)or hindering (1% O₂ ) photorespiration, sucrose labeling decreased,but serine and glycine labeling was favoured. We propose thatin wheat leaves, the role of photorespiration is to drain artof the carbon exported from the chloroplast as glycolate, towardssucrose synthesis. (Received March 16, 1979; )     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: II. RELATIONSHIP BETWEEN GROWTH RATE, CARBOHYDRATE CONCENTRATION AND 14C-PARTITIONING WITHIN TUBERS

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. The growth rates of individualtubers were closely reflected by their ¹⁴C-content 20 h after¹⁴CO₂ had been applied to the aerial parts of the shoot for4 h. The ¹⁴C-content of the tuber (sink strength) was significantlycorrelated to the ¹⁴C-concentration of the tuber tissue (¹⁴Cg^–1 fr. wt.=sink activity). The sink activity, which differedbetween individual tubers by up to a factor of 10, was alsoclosely related to the conversion rates of ¹⁴C into the starchand the remainder as well as to the ¹⁴C-content in the ethanolsoluble fraction. This indicates the simultaneous use of photosynthatefor growth and storage in the growing tubers. No preferenceof photosynthate utilization for either of these processes couldbe detected in relation to the sink activity of the tubers.Tubers with high sink activity imported ¹⁴C-labelled photosynthateat higher rates although their tissue contained higher concentrationsof reducing sugars and sucrose than the tissue of tubers withlow sink activity. Despite the close relationship between sinkactivity and the rate of starch synthesis (¹⁴C-conversion intostarch), no significant correlation was found between sink activityand the actual starch concentration of the tissue. The applicationof zeatin riboside directly onto individual tubers increasedtheir growth rates in comparison to non-treated tubers of thesame plant. The results indicate the importance of both growthand storage processes for the regulation of sink activity inyoung potato tubers. Key words: Potato tuber, ¹⁴C-photosynthate partitioning, zeatin riboside application     

Translocation of Assimilates Within and Between Potato Stems

Three aspects of translocation in potato were examined: (i)translocation within stems (ii) translocation between individualstems of a plant (iii) translocation between tubers followinginjection of ¹⁴C sucrose into a single daughter tuber. Assimilatesexported from single leaves of evenly illuminated potato stemsremained confined to the same side of the stem as the sourceleaf in a pattern consistent with the internal arrangement ofvascular bundles in the stem, and tubers borne on stolons verticallybelow the source leaf contained higher concentrations of ¹⁴Cthan those on the opposite side. Consequently ¹⁴C import intothe tubers bore little relationship to tuber growth rates. However,alteration of source/sink relations by pruning stems to a singlesouce leaf resulted in an even distribution of ¹⁴C throughoutthe vascular bundles of the stem and ¹⁴C import into the tubersbore a stronger relationship to tuber growth rates than to thephyllotactic relationship of the tubers with the source leaf. Labelling one stem of a potato plant resulted in little or nomovement of ¹⁴C into tubers on other unlabelled stems. However,removal of the unlabelled stems at ground level induced a significantmovement of ¹⁴C from the labelled stem to the tubers on unlabelledstems, this movement occurring via the mother tuber. Shadingthe unlabelled stems had less effect than stem removal. ¹⁴C sucrose injected into single daughter tubers was translocatedto other tubers on the same stem and also to tubers on a secondstem at the opposite end of the mother tuber. The sucrose wasconverted to starch in these tubers. The results favour the view that each potato stem functionsas an independent unit with potential for assimilate redistributionwithin a stem but with little or no carbon exchange occurringbetween stems, unless under severely altered source/sink patterns. Assimilates, ¹⁴C, autoradiography, potato (Solanum tuberosum L.), tuber growth     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: III. RELATIONSHIP BETWEEN GROWTH RATE OF INDIVIDUAL TUBERS, TUBER WEIGHT AND STOLON GROWTH PRIOR TO TUBER INITIATION

Potato plants (Solanum tuberosum L.) were grown in water culture.About 14 d after tuber initiation no significant differenceswere found between apical and basal tuber parts in ¹⁴C-uptakeand partitioning into various fractions from ¹⁴C-labelled photosynthate.Thus, the fresh weight of these tubers could be used as a parameterfor the sink size. The ¹⁴C-content per tuber (sink strength)20 h after ¹⁴CO₂-supply to the foliage was significantly correlatedwith the tuber fresh weight. No correlation was found betweenthe ¹⁴C-concentration of the tuber (sink activity; ct. min^–g^– fr. wt.) and tuber fresh weight. Consequently, tuberfresh weight (sink size) per se must have been a factor whichinfluenced sink strength. Stolon parameters characterizing theirgrowth prior to tuber initiation (e.g. stolon volume) and theircapacity for photosynthate transport (diameter, length) weremeasured at the time of tuber initiation. Significant correlationswere found between these stolon parameters and subsequent growthof individual tubers. Anatomical studies on the proportion ofvarious tissues in the cross sectional area of stolons supportthe idea of a negative relation between growth of individualtubers and transport resistance in the phloem of the stolons.It is concluded that in the initial phase of tuber growth, mainlyfactors outside of the tuber determine its growth rate. In laterstages of tuber growth, when the sink strength increases, thecompeting strength of individual tubers for photosynthate isdominated mainly by factors within the tuber itself, such astheir sink size and sink activity. Key words: Potato tuber, sink size, tuber initiation, transport resistance     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.     

Effects of Inhibitors of Protein Synthesis on Transmembrane Auxin Transport in Cucurbita pepo L. Hypocotyl Segments

Pretreatment of 2?0 mm segments of etiolated zucchini (Cucurbitapepo L.) hypocotyl with cycloheximide (CH) or 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide(MDMP) eliminated the stimulation by N-1-naphthylphthalamicacid (NPA) of net uptake of [1-¹⁴C]indol-3yl-acetic acid ([1-¹⁴C]IAA),but had relatively little effect on the net uptake of IAA inthe absence of NPA. The efflux of [1-¹⁴C]IAA from preloadedsegments was not substantially affected by inhibitor pretreatmentin the absence of NPA, but CH pretreatment significantly inhibitedthe reduction of efflux caused by NPA. Pretreatment with CHor MDMP did not affect net uptake by segments of the pH probe[2-¹⁴C]5,5-dimethyl-oxazolidine-2,4-dione ([2-¹⁴C]DMO), or thenet uptake of [¹⁴C]-labelled 3-O-methylglucose ([¹⁴C]3-0-MeGlu),suggesting that neither inhibitor affected intracellular pHor the general function of proton symporters in the plasma membrane.Both compounds reduced the incorporation of label from [³⁵S]methionineinto trichloroacetic acid (TCA)-insoluble fractions of zucchinitissue, confirming their inhibitory effect on protein synthesis. The steady-state association of [³H]IAA with microsomal vesiclesprepared from zucchini hypocotyl tissue was enhanced by theinclusion of NPA in the uptake medium. The stimulation by NPAof [³H]IAA association with microsomes was substantially reducedwhen the tissue was pretreated with CH. However, CH pretreatmentdid not affect the level of high affinity NPA binding to themembranes indicating that treatments did not result in lossof NPA receptors. It is suggested that the auxin transport site on the effluxcarrier system and the receptor site for NPA may reside on separateproteins linked by a third, rapidly turned-over, transducingprotein. Key words: Auxin carriers, auxin efflux, Cucurbita pepo, phytotropin receptors     

Quantitative Analysis of Intercellularly-Transported Photoassimilates in Chara corallina

Using a thin-layer chromatographic technique, we have identifiedthe photoassimilates that are transported intercellularly frombranchlets to internodes in Chara corallina. An internode-branchletcomplex having a primary apex was used in these experiments.After feeding 1 mol m³ NaH¹⁴CO₃ to a branchlet for 10 min, the¹⁴C-labelled photoassimilates (¹⁴C-photoassimilates) found inthe sol endoplasm of the branchlet were composed of sucrose,amino acids, malate, and sugarphosphates. The composition ofthe ¹⁴C-photoassimilates transported from the source branchletto the sink internode in 10 min was the same as that in thesol endoplasm of the source branchlet. From the proportion ofeach ¹⁴C-photoassimilate in both the source branchlet and thesink internode, it was deduced that the main photoassimilatesinvolved in the intercellular transport were sucrose and aminoacids. We found previously that polar transport of photoassimilatesoccurs from a branchlet to an internode with an apex. Determinationof the amount of sucrose, amino acids, glucose-6-phosphate,and malate in both branchlet and internode with or without anapex revealed that there were gradients in the concentrationsof sucrose, serine, and glutamic acid between the sol endoplasmof the two cells. The levels were higher in the branchlet andlower in the internode and the gradients decreased when theapex was detached. Therefore, it is concluded that sucrose andthese amino acids are the compounds involved in the polar intercellulartransport. Key words: Chara corallina, intercellular transport, photoassimilates, ¹⁴C     

Tracheary Element Differentiation Induced in Isolated Cylinders of Lettuce Pith: a Bipolar Gradient Technique

To study the influence of morphogenetic gradients on vasculardifferentiation patterns, a new technique was developed whichallows different substances to be applied at opposite ends ofa tissue block. It yielded information on the mobility of particularmorphogens and on the dependence of callus formation and trachearyelement differentiation on their presence. Application of indol-3ylacetic acid (1AA) (10 mg l^–1), zeatin (0.1 mg l^–1)and sucrose (3 per cent, w/v) in various combinations to theends of cylindrical explants of lettuce pith (Lactuca sativaL.) showed that (a) callus formation was stimulated by IAA,whereas induction of tracheary elements required both IAA andzeatin; (b) callus was confined to a few millimetres at theends of the explants, and tracheary elements occurred mainlywithin the callus; (c) sucrose or its metabolic products diffusedthe 10 mm length of the explants, while IAA and zeatin wereeffective only close to the application site; and (d) some callusand tracheary elements formed when no sucrose was applied, butboth increased with sucrose application, though inhibition oftracheary elements formation occurred with high sucrose concentrations. differentiation, pith explant, tissue culture, xylogenesis, indol-3yl acetic acid, sucrose, zeatin, lettuce, Lactuca sativa     

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.     

Effect of indoleacetic acid on the penetration of leucine and glucose through epidermal tissue of onion bulb

The penetration of leucine-(U)-¹⁴C and glucose-(U)-¹⁴C throughthe bulb epidermal tissue of Allium cepa was examined in thepresence of indoleacetic acid (IAA). Not only the uptake ofleucine-¹⁴C and glucose-¹⁴C in epidermal tissue but also theirtranscellular penetration were accelerated by IAA treatment.N-Ethylmaleimide (NEM) inhibited their uptake and transcellularpenetration, and the inhibitory effect was relieved by additionalIAA. In the presence of IAA, leucine-¹⁴C and glucose-¹⁴C weremore penetrable by adaxial than abaxial application, but inthe absence almost no difference due to application side wasobserved. IAA appears to promote permeability of the epidermaltissue only to substances applied adaxially. N,N'-Dicyclohexylcarbodiimide(DCCD) showed a little inhibitory effect on the IAA-inducedpromotion of the uptake and penetration of leucine-¹⁴C appliedadaxially. Leucine-¹⁴C and glucose-¹⁴C penetrated more easilythrough killed than fresh tissue, with little difference betweenabaxial and adaxial applications. ¹ Present address: Department of Biology, Faculty of Science,Kochi University, Kochi 780, Japan. ² Present address: Department of Medical Zoology, Medical School,Mie University, Tsu 514, Japan. (Received October 13, 1977; )     

Unsaponifiable Lipid Biosynthesis in the Seedling of Euphorbia lathyris L.: A Bypass via Alcoholic Fermentation

[1-¹⁴C]-ethanol supplied to the cotyledons of 9-d-old Euphorbialathyris seedlings was rapidly incorporated into unsaponifiablelipids, particularly into sterols, latex triterpenols and intothe triterpene ketones of the epicuticular wax. The [¹⁴C]-triterpenoidproduction from ethanol was hardly affected by sucrose in theexternal medium when sucrose uptake rates were low, but whenthe uptake rate was higher the [¹⁴C]-triterpenoid productionfrom [¹⁴C]-ethanol was greatly reduced. This observation isconsistent with the proposition that at high sucrose uptakerates, some sucrose is converted into ethanol, so that the incorporationof [¹⁴C]-ethanol into triterpenoids is reduced by competitionwith endogenously formed ethanol. A calculation based on theputative daily ethanol production in the cotyledons and thedaily triterpenoid production of seedlings indicates that about10 % of the triterpenoid synthesis in vivo may be from ethanol. Ethanol, Euphorbia lathyris, fermentation, seedling, triterpenoid biosynthesis     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18 °C). With a temperatureregime of 35 °C day, 25 °C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35 °C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves     

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     

Ammonia Induces Starch Degradation in Chlorella Cells

When ammonia was added to cells of Chlorella which had fixed¹⁴CO₂ photo synthetically, ¹⁴C which had been incorporated intostarch was greatly decreased. A similar effect was observedwhen potassium nitrate and sodium nitrite were added. The ammonia-induceddecrease in ¹⁴C-starch was observed in all species of Chlorellatested. With cells of C. vulgaris 11h, most of the radioactivityin starch was recovered in sucrose, indicating that ammoniainduces the conversion of starch into sucrose. The percent of¹⁴C recovered in sucrose differed from species to species andpractically no recovery in sucrose was observed in C. pyrenoidosa.In most species tested, the enhancing effects of blue lightand ammonia on O₂ uptake as well as the ammonia effect on starchdegradation were greater in cells which had been starved inphosphate medium in the dark than in non-starved cells. In contrast,the enhancing effect of ammonia on dark CO₂ fixation was muchgreater in non-starved cells. C. pyrenoidosa was unique in thatblue light did not show any effect on its O₂ uptake. (Received August 15, 1984; Accepted November 16, 1984)     

Effect of Temperature on Starch Degradation in Chlorella vulgaris 11h Cells

Analysis of products formed in Chlorella vulgaris 11 h cellsduring photosynthesis in air containing 3,000 ppm ¹⁴CO₂ at varioustemperatures revealed that the level of ¹⁴C-starch was maximumaround 20–24?C and decreased with further rise in temperatureuntil 40?C, while ¹⁴C-sucrose greatly increased at temperaturesabove about 28?C. Elevating the temperature from 20 to 38?Cduring photosynthetic ¹⁴CO₂ fixation resulted in a remarkabledecrease in ¹⁴C in starch and a concomitant increase in ¹⁴Cin sucrose. This conversion of starch to sucrose when shiftingthe temperature from 20 to 38?C proceeded even in the dark.Hydrolysis of sucrose by rß-fructosidase showed that,irrespective of the experimental conditions, the radioactivitiesin sucrose were equally distributed between glucose and fructose.The enhancement of starch degradation with temperature risewas more remarkable than that of the activity of ribulose bisphosphatecarboxylase from the same cells. When Chlorella cells whichhad been preloaded with ¹⁴C-starch after photosynthesis for30 min at 20?C were incubated in the dark for an additional30 min at 20?C, ¹⁴C-starch was degraded by only about 4%. However,the values after 30-min dark incubation at 28, 32, 36 and 40?Cwere increased by about 10, 19, 36 and 50%, respectively. Duringthe temperature-dependent conversion of starch to sucrose, nosignificant amount of radioactivity accumulated in free glucoseand maltose. (Received October 27, 1981; Accepted January 9, 1982)     

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.     

Biosynthesis of Indole-3-Acetic Acid from L-Tryptophan in Coleoptile Tips of Maize (Zea mays L.)

Coleoptile tips (about 2.5 mm in length) were excised from 3-day-olddark-adapted maize (Zea mays L.) seedlings and incubated indarkness in potassium phosphate buffer that contained ¹⁴C-L-tryptophan(Trp). Subsequent analysis by gas chromatography-mass spectrometryindicated that a significant portion of endogenous indole-3-aceticacid (IAA) had been labeled with ¹⁴C. About 8% of the IAA thatdiffused from the tissue into the medium during incubation from0.5 to 2 h was labeled, and 12% of the IAA extracted from thetissue after a 2-h incubation was labeled. On the other hand,30% of the Trp extracted from the tissue after a 2-h incubationwas ¹⁴C-Trp, which was more than those determined for IAA. Sincethe experiments were carried out under the non-steady-stateconditions in which the tissue content of ¹⁴C-Trp increasedwith time, and since the extracted Trp included the ¹⁴C-Trpin the apoplastic space, it seemed that synthesis de novo fromTrp was the major means by which IAA was produced in the coleoptiletip. The conversion of Trp to IAA was not detected in sub-apicalsegments (5–7.5 mm from the top) that were incubated similarly,an indication that synthesis of IAA occurs specifically in thetip region. When intact seedlings were irradiated with a pulseof red light 2 h before excision of tips and the applicationof ¹⁴C-Trp, the amounts of extractable and diffusible IAA werereduced by 40–60% without a change in the rate of ¹⁴Cincorporation. This result indicated that the production ofIAA from Trp is controlled by a red-light signal. (Received May 15, 1995; Accepted September 1, 1995)     

Effect of some Metabolic Inhibitors on Rooting Cuttings of Phaseolus mungo under Varying Light Conditions and its Relationship with Auxin and Nutrition

Water and 1 mg1^–1 each of IAA and IBA completely inhibitedon the cuttings of Phaseolus mungo obtained from the seedlingsraised under far-red light but rooting took place in the darkand under white and red lights. Sucrose, however, caused rootingunder far-red light and its effectiveness increased with theaddition of IAA and IBA to the sucrose medium IBA being moreeffective. Culturing in 1 and 5 mg 1^–1 each of FudR, actinomycin-D,cycloheximide and chloramphenicol after pre-treatment with water,IAA, IBA, sucrose and IAA/IBA + sucrose inhibited rooting. Theeffect increased with the concentration of each inhibitor. Incontrast to this, the culturing in water, IAA, IBA, sucroseand IAA/IBA + sucrose after pre-treatment with these metabolicinhibitors produced varying effects. While the inhibition persistedin water, IAA and IBA and even in 5 mg 1^–1 of each inhibitorthat in sucrose stimulated rooting and the effect increasedwith the addition of IAA and IBA to sucrose, the effect of IBA+ sucrose being more pronounced. This stimulation was irrespectiveof the inhibitor and light condition except that 1 mg 1^–1actinomycin-D inhibited rooting in the dark and under far-redlight.