Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

Pattern and Control of Distribution of 14C-assimilates in Reproductive Plants of Lolium multiflorum Lam. var. Westerwoldicum

The distribution of ¹⁴C-assimilates was examined in reproductiveplants of Lolium multiflorum Lam. var. Westerwoldicum (cv. Tama)from which all emerged tillers had been removed, leaving themain tiller with two expanding leaves, one of them the flagleaf, and two expanded leaves. Export of ¹⁴C from the lowerexpanded leaf was mainly to the tiller in its axil, the steminternode below its node and the roots, whereas the upper expandedleaf supplied predominantly the expanding leaves, the ear, steminternodes, roots and the tiller bud in the axil of the lowerleaf. Defoliation and root-pruning showed that expanding leaveswere able to compete successfully for assimilates, probablythrough the production of substances capable of mobilizing supply.Local application of 1-naphthaleneacetic acid (NAA), gibberellicacid (GA₃) and 6-benzylaminopurine (BAP) to small tiller budsshowed that GA³ and BAP promoted bud growth and ¹⁴C accumulation,but that addition of NAA reduced these effects.     

Kinetin Transport to Axillary Buds of Dwarf Pea (Pisum sativum L.)

Decapitation resulted in the transport of significant amountsof ¹⁴C to the axillary buds from either point of application,but pretreatment of the cut internode surface of decapitatedplants with IAA (alone or in combination with unlabelled kinetin)inhibited the transport of label to the axillary buds and resultedin its accumulation in the IAA-treated region of the stem. Inintact plants to which labelled kinetin was applied to the apicalbud there was little movement of ¹⁴C beyond the internode subtendingthis bud; when labelled kinetin was applied to the roots ofintact plants, ¹⁴C accumulated in the stem and apical bud butwas not transported to the axillary buds. A considerable proportionof the applied radioactivity became incorporated into ethanol-insoluble/NaOH-solublecompounds in the apical bud of intact plants, in internodestreated with IAA, and in axillary buds released from dominanceby removal of the apical bud. The results are discussed in relation to the possible role ofhormone-directed transport of cytokinins m the regulation ofaxillary bud growth.     

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.     

Abscisic acid and apical dominance in Phaseolus coccineus L.

Abscisic acid (ABA) in lanolin, applied to the internode of decapitated runner bean plants enhances the outgrowth of lateral buds. The optimum concentration of the paste is 10^-5 M. The effect of ABA is counteracted by indoleacetic acid (IAA) but not by gibberellic acid (GA₃). There is no effect when ABA is applied to the apical bud or lateral buds of intact plants. However, 13.2 ng given to the lateral buds of decapitated plants stimulate their growth, whereas higher concentrations are inhibitory. Consequently, ABA enhances growth of lateral buds directly, but only when apical dominance is already weakened. The growth of the decapitated 2^nd internode was not affected by ABA. Radioactivity from [2-¹⁴C] ABA, applied to nonelongating 2^nd internode stumps of decapitated runner bean plants moves to the lateral buds, whereas [1-¹⁴C]IAA-and [³H]GA₁-translocation is much weaker. ABA transport is inhibited if IAA or [³H]GA₁ is applied simultaneously. In elongating internodes [¹⁴C]ABA is almost completely immobile. [¹⁴C]IAA-and [³H]GA₁-translocation is not affected by ABA. The amount of radioactivity from labelled ABA, translocated to the lateral buds, is highest during the early stages of bud outgrowth.Abbreviations ABA 2,4-cis, trans-(+)-abscisic acid - GA gibberellic acid - IAA indoleacetic acid - p.l. plain lanolin     

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 Distribution and Identity of Assimilates in Tomato with Special Reference to Stem Reserves

Much of the work on the distribution of ¹⁴C-labelled assimilatesin tomato has been done in winter under low light intensities,and consequently the reported distribution patterns of ¹⁴C maynot be representative of plants growing in high light. Further,there are several somewhat conflicting reports on patterns ofdistribution of ¹⁴C-assimilates in young tomato plants. We soughtto clarify the situation by studying the distribution of ¹⁴C-assimilatesin tomato plants of various ages grown in summer when the lightintensity was high. In addition, the role of the stem as a storageorgan for carbon was assessed by (a) identifying the chemicalfractions in the stem internode below a fed leaf and monitoring¹⁴ C activity in these fractions over a period of 49 d, and(b) measuring concentrations of unlabelled carbohydrates inthe stem over the life of the plant. The patterns of distribution of ¹⁴C-assimilates we found fortomato grown under high light intensity confirmed some of thosedescribed for plants grown under low light, but export of ¹⁴Cby fed leaves was generally higher than reported for much ofthe earlier work. Lower leaves of young plants exported over50% of the ¹⁴C they fixed, although export fell sharply as theplants aged. Initially, the roots and apical tuft were strongsinks for assimilates, but they had declined in importance bythe time plants reached the nine-leaf stage. On the other hand,the stem became progressively more important as a sink for ¹⁴C-assimilates.Older, lower leaves exported more of their ¹⁴C-assimilates tothe upper part of the plant than to the roots, whereas youngleaves near the top of the plant exported more of their assimilatesto the roots. The stem internode immediately below a fed leafhad about twice the ¹⁴C activity of the internode above theleaf. Mature leaves above and below a fed leaf rarely importedmuch ¹⁴C, even when in the correct phyllotactic relationshipto the fed leaf. In the first 3 d after feeding leaf 5 of nine-leaf plants, theorganic and amino acid pools and the neutral fraction of theinternode below the fed leaf had most of the ¹⁴C activity, butby 49 d after feeding, the ethanolic-insoluble, starch and lipidfractions had most of the ¹⁴C activity. Glucose, fructose andsucrose were the main sugars in the stem. Although concentrationsof these sugars and starch declined in the stem as the plantsmatured, there was little evidence to indicate their use infruit production. Stems of plants defoliated at the 44-leafstage had lower concentrations of sugars and starch at maturity,and produced less fruit than the controls. It was concludedthat tomato is sink rather than source limited with respectto carbon assimilates, and that the storage of carbon in thestem for a long period is possibly a residual perennial traitin tomato.Copyright 1994, 1999 Academic Press Lycopersicon esculentum, tomato, assimilate distribution, ¹⁴C, internode storage, sink-source relationships, starch, stem reserves, sugars     

Nitrogen, Phosphorus, and Potassium Distribution in Relation to Apical Dominance in Dwarf Bean (Phaseolus vulgaris, c.v. Canadian Wonder)

The levels and distributions of nitrogen, phosphorus, and potassiumwere followed in the axillary buds and internodes of dwarf beanplants subsequent to decapitation and application of eitherlanolin or lanolin/IAA to the cut surface of the stem. Nitrogencontinued to accumulate in decapitated internodes supplied withIAA for at least 15 days, whereas decapitated internodes nottreated with auxin showed only a slight accumulation of nitrogen.The lanolin/IAA preparation also maintained correlative inhibitionof the axillary buds for at least 15 days. However, enhancedaccumulation of N, P, and K in an IAA-treated internode didnot appear to be sufficient to deprive the axillary buds ofan adequate supply of these nutrients, for approximate balancesheets showed that more total NPK was accumulated in the internodeand axillary buds, taken together, in plants treated with plainlanolin than in those treated with IAA. Furthermore, the totalN, P, and K content per unit dry weight of the apical 5 mm ofaxillary buds was higher in the inhibited buds of IAA-treatedplants than in the elongating buds of lanolin-treated plants.Nevertheless, in dwarf bean it was found that an adequate nitrogensupply to the roots favoured lateral bud growth. From theseresults it would appear that this effect of nitrogen is an indirectone, perhaps influencing the production of substances, suchas cytokinins, stimulatory to lateral bud growth.     

Development of shoot inHydrangea macrophylla I. Terminal and axillary buds

The structure of shoots, in particular of winter buds, ofHydrangea macrophylla was examined. The non-flower-bearing shoot is usually composed of a lower and an upper part, between which a boundary is discernible by means of a distinctly short internode. This internode is the lowermost of the upper part, and it is usually shorter than the internodes immediately above and below, although the internodes tend to shorten successively from the proximal to the distal part of the shoot. Variations exist in the following characters among the terminal bud, the axillary bud on the lower part of the shoot and the axillary bud on the upper part: (1) length of bud; (2) character of the outermost pair of leaf primordia; (3) degree of development of secondary buds in the winter bud; and (4) the number of leaf primordia. Usually, the terminal bud contains several pairs of foliage leaf primordia with a primordial inflorescence at the terminal of the bud, but the axiallary bud contains only the primordia of foliage leaves in addition to a pair of bud scales.     

Effects of external ABA,GA<Subscript>3</Subscript> and NAA on the tiller bud outgrowth of rice is related to changes in endogenous hormones

Hormones play an important role in regulating the growth of rice tiller buds. However, little is known about the hormonal changes that occur during tiller bud growth and the mechanism of hormonal regulation of tiller bud growth. Here, two rice cultivars, Yangdao 6 (Indica) and Nanjing 44 (Japonica), were used to investigate the changes in plant hormones during tiller bud growth and the mechanism that underlies the hormonal regulation of tiller bud growth. In the present study, panicles were removed after heading to stimulate the growth of dormant tiller buds located at the elongated upper internodes. At the same time, external abscisic acid (ABA), gibberellic acid (GA₃) and α-naphthalene acetic acid (NAA) were applied. The results demonstrated that auxin and cytokinin (CTK) play important and different roles in the regulation of tiller bud growth. Auxin in the nodes inhibits tiller bud growth, while CTK is transferred to the tiller buds to promote growth. The inhibitory effects of GA₃ and NAA on tiller bud growth are mainly due to the control of the indole-3-acetic acid (IAA) or CTK contents in plants. As opposed to auxin and CTK, the ABA contents in nodes and tiller buds remained unchanged before tiller bud growth after panicle removal. Meanwhile, external ABA application only slightly slowed the growth of the tiller buds, suggesting that ABA may not be a key regulator of tiller bud growth. These results indicate that auxin, CTK and ABA together likely play roles in the regulation of tiller bud growth.     

Factors Influencing the Distribution of Growth Between Stem and Axillary Buds in Decapitated Bean Plants

Phaseolus multiflorus plants at three stages of developmentwere decapitated either immediately below the apical bud orlower down at a point 1 cm above the insertion of the primaryleaves. Growth regulators in lanolin were applied to the cutstem surface. IAA always inhibited axillary bud elongation anddry-matter accumulation, and enhanced internode dry weight butnot elongation. GA₃ applied below the apical bud greatly increasedinternode elongation and dry weight, but simultaneously reducedbud elongation and dry-weight increase. Application of GA₃ 1cm above the buds had no effect on bud elongation in the youngestplants, but enhanced their elongation in the two older groups.IAA always antagonized GA₃-enhancement of internode extensiongrowth, whereas its effects on GA₃-enhanced dry-matter accumulationdepended on the stage of internode development. Bud elongationwas greater in plants treated with GA₃+IAA than in plants treatedonly with IAA, except in the youngest plants decapitated immediatelybelow the apical bud, where GA₃ caused a slight increase inIAA-induced bud inhibition. GA₃ increased inhibition of buddry weight by IAA in the two youngest groups of plants, butslightly reduced it in the oldest plants. No simple compensatorygrowth relationship existed between internode and buds. It wasconcluded that, (1) auxin appears to be the principal growthhormone concerned in correlative inhibition, and (2) availabilityof gibberellin to internode and buds is of importance as a modifyingfactor in auxin-regulated apical dominance by virtue of itslocal effects on growth in the internode and in the buds.     

Role of Cytokinin in Vessel Regeneration in Wounded Coleus Internodes

Cytokinin was found to be a controlling or limiting factor invessel regeneration around a wound in internodes of Coleus blumeiBenth. in which the endogenous cytokinin level was minimized.The cytokinin was applied in aqueous solution to the base ofexcised, mature internodes that had an active vascular cambium.Each internode also received IAA in lanolin at its apical end.Under low (0.1 %, w/w) or high (10%, w/w) auxin concentrations,the control internodes (without exogenous cytokinin) exhibitedsmall amounts of vessel regeneration. At appropriate concentrationszeatin, kinetin and 6-benzylamino-purine (BAP) induced a significantincrease in vessel regeneration around the wound. The threecytokinins also induced novel patterns of supplementary regenerationfurther from the wound surface. Kinetin and BAP showed the strongestpromoting effect at 5 and 10 µg ml^–1, while zeatinwas most effective at 20 µg ml^–1. At a low (0.1%) auxin level zeatin was the most effective cytokinin, whereaskinetin was the most effective one at high (1 %) auxin. An inhibitoryeffect on vessel regeneration was observed at the highest kinetinconcentration tested (50 µg ml^–1). The regenerationof vessels induced by cytokinin was very polar. Many more regeneratedvessel members differentiated below the wound than above it,and the regeneration process proceeded acropetally from thebase of the internode to its upper parts. Our results implya basipetal polar increase in cambium responsiveness along thestem axis from internode 5 to 7. The possible significance ofsuch a basipetal increase in cambium sensitivity in wood formationin trees is discussed. Auxin, Coleus blumei, cytokinin, vascular differentiation, vessel regeneration, wound xylem     

Epicormic Bud Development in Quercus robur L. Studies of Endogenous IAA, ABA, IAA Polar Transport and Water Potential in Cambial Tissues10

Seasonal measurements of IAA,³ made using GC-MS, ⁴ indicatedthat in Q. robur the spring initiation of cambial activity andonset of visible bud outgrowth in the canopy is preceded byan increase in cambial region IAA. The effects of notch-girdlescut into the bole indicated that IAA in the cambial region laterwas present in separate physiological pools, with only the polar-transportedfraction affecting epicormic bud outgrowth. The stage in thespring when the epicormic buds grew out coincided with an increaseboth in cambial region IAA and in the capacity of cambial explantsfor IAA polar transport. Thus the stimulus needed by the epicormicbuds to overcome inhibition by polar-transported IAA appearedto be self-generated. The observed effects of exogenous hormoneson epicormic bud outgrowth from stem explants indicated thatthis stimulus might be cytokinin. The seasonal changes detectedin cambial region ABA³ were consistent with a role for stress-inducedABA in the induction of epicormic bud dormancy after canopydevelopment during the summer. No consistent effects of standthinning on cambial region IAA, ABA, water potentials or watercontents were detected, although polar transport of exogenousIAA by cambial region explants removed in the spring was reducedby thinning. Key words: Epicormic buds, cambium, hormones     

Distribution of 14C-labelled sucrose in seedlings of Pisum sativum L. Treated with indoleacetic acid and kinetin

Summary The influence of decapitation and treatment with IAA and/or kinetin on the pattern of distribution of ¹⁴C-labelled sucrose applied to the third leaf of 14-day old dwarf pea seedlings was investigated. Decapitation resulted in a diversion of the labelled metabolites to the lateral buds, and greatly increased the radioactivity present in the root system indicating that in these seedlings the roots and apex actively competed for translocates from the third leaf. Application of IAA to the decapitated internode prevented the growth of the lateral buds for the duration of the experiment and restored the pattern of distribution of labelled metabolites found in the intact plant. Application of kinetin alone resulted in a marked accumulation of labelled materials in the lateral buds, but when kinetin was applied with IAA metabolites were once again diverted from the lateral buds to the treated internode. Neither of these treatments had any influence on the proportion of the translocated materials which accumulated in the root system when compared with intact plants. The results are discussed in relation to current concepts of hormone-directed transport of nutrients in plants.     

The Extent of Starch Turnover in Mature Pepper Leaves in the Light

The extent of starch turnover in pepper leaves in the lighthas been estimated. After leaves were labelled with ¹⁴CO₂ atconstant specific activity for 4–7 h, the irradiance wasreduced to a level which caused no net change in the starchcontent of the leaf, and the supply of ¹⁴CO₂ was removed. Therewas no significant change in specific activity of starch overthe following 6–10 h, thus there was no exchange of ¹⁴C-starchwith ¹²C-assimilates entering the chloroplasts. Starch, turnover, ¹⁴C-labelling, pepper, Capsicum annuum L.     

Intercellular Transport and Photosynthetic Differentiation in Chara corallina

Intercellular transport of ¹⁴C-labelled photoassimilates, bothin isolated upper shoots and in isolated internode-branchletcomplexes of Chara corallina, was measured. The isolated uppershoots were composed of a primary apex, two mature internodes,and three branchlet whorls. A 10 min loading of the isolatedupper shoot with H¹⁴CO₃^– resulted in a greater accumulationof ¹⁴C in the apical complex and branchlets than in the internodes,while a subsequent 50 min chase with unlabelled solution inthe light resulted in a greater accumulation of ¹⁴C in internodesthan in other parts of the shoot. In the isolated internode-branchlet complex, when the apex wasnot detached, the amount of ¹⁴C transported from branchletsto internodes was about fives times that transported from internodesto branchlets. Removal of the apex resulted in a decrease intransport from branchlets to internodes and an increase in transportin the opposite direction. In an attempt to explain the mechanism of the polar transportof photosynthetically fixed carbon between branchlets and internodes,photosynthetic activities of both types of cells were investigated.Detached branchlets have higher photosynthetic ¹⁴C-fixationactivities than those of internodes. Chlorophyll contents, measuredin terms of surface area, in internodes and branchlets werealmost identical. The ribulose-l,5-bisphosphate carboxylase(RuBPCase) activity of branchlets was 1.6 times that of internodes,and the rate of ferricyanide-dependent evolution of oxygen inbranchlets was 1.4 times that in internodes. Key words: Chara, internode, branchlet, polar transport, photosynthesis     

Effects of Plant Growth Regulators and Nutrient Supply on Tiller Bud Outgrowth in Barley (Hordeum distichum L.)

Seedlings of spring barley were raised in 100 and 20% nutrientsolution and treated with a foliar application of Terpal, Cerone,TIBA, GA₃ or BAP. The growth of individual tiller buds and tillers,the main shoot and the root system was recorded over the following15 d. Terpal and Cerone stimulated tiller bud elongation within5 d at both nutrient levels and after 15 d the number of emergedtillers was increased at the higher nutrient level. Terpal characteristicallypromoted the growth of secondary tiller buds whereas Ceronepromoted the emergence of the coleoptile tiller; both thesePGRs also retarded the development of the main shoot. TIBA increasedthe number of elongating tiller buds but this did not resultin greater tillering. GA₃ reduced the number of elongating tillerbuds and restricted their growth, especially in the high nutrientregime; this was accompanied by an increase in main shoot elongation.The growth and development of tiller buds was reduced by BAPand the number of emerged tillers was reduced at 15 d in bothnutrient levels; main shoot dry weight and root elongation werealso reduced. The results are considered in relation to theoverall influence of hormonal factors and mineral supply ontiller bud outgrowth. Hordeum distichum, spring barley, tiller bud outgrowth, plant growth regulators, Terpal, Cerone, GA₃, BAP, nutrient supply, apical dominance, TIBA     

The Morphogenesis of Regeneration Buds in Hordeum bulbosum L.--A Perennial Grass

The tillering phase in Hordeum bulbosum L. is terminated whenthe newly-formed axillary buds no longer emerge as tillers,but differentiate into dormant regeneration buds. The patternof development of the axillary buds differs during the tilleringphase and the post-tillering phase. During the former, accumulationof leaf primordia corresponds to the age of the bud, i.e., leafnumber per bud increases basipetally along the shoot. Duringthe post-tillering phase, leaf number per bud decreases basipetallyfrom the base of the future bulb internode. This transitionis brought about by an acceleration in the rate of accumulationof leaf primordia which is more sustained in the buds situatedcloser to the base of the bulb internode. These positional differencesin the morphogenesis of the regeneration buds are reflectedin their physiological responses during the relaxation of dormancyand activation of the buds.     

The Cellular Pathway of Short-distance Transfer of Photosynthates and Potassium in the Elongating Stem ofPhaseolus vulgarisL. A Physiological Assessment

Plasmolytic disruption of plasmodesmata interconnecting metaphloemsieve element-companion cell complexes with small and largephloem parenchyma cells in the elongating region of internode2 ofPhaseolus vulgarisL. seedlings did not affect accumulationof phloem-imported¹⁴C-photosynthates and⁸⁶rubidium. The membrane-impermeantdye, 5(6) carboxyfluorescein, loaded into leaf phloem as themembrane-permeant diacetate ester, was found not to move radiallyout of the importing sieve elements in the internode elongationregion. In contrast, the apoplasmic tracer, Calcuofluor White,rapidly moved laterally throughout all tissues of the elongationzone. Hexoses, sucrose and potassium were identified as themain osmotica in internode apoplasmic sap. Label asymmetry in[¹⁴C](fructosyl)sucrose was retained on accumulation by excisedstem segments. Uptake of [¹⁴C]sucrose and⁸⁶rubidium by stemsegments exhibited saturation kinetics. Sucrose uptake was inhibitedby the slowly penetrating sulphydryl reagent, para-chloromercuribenzenesulphonicacid.In vitrorates of sucrose uptake, at apoplasmic concentrations,corresponded to its predictedin vivorate of delivery to thestem ground tissues from mature sieve elements when respiratorylosses were assumed to be confined to the stem phloem. For potassium,the total delivery rate could be accounted for by itsin vitrorateof uptake. Overall, it was concluded that radial transport,in the elongation zone of internode 2 ofPhaseolus vulgarisL.seedlings, follows an apoplasmic route from mature sieve elementsto stem ground tissues.Copyright 1998 Annals of Botany Company PhaseoluLes vulgaris, apoplasm, elongating stem, French bean, photosynthates, potassium, radial transfer, symplasm.     

The Export and Distribution of 14C-labelled Assimilates from each Leaf on the Shoot of Lolium temulentum during Reproductive and Vegetative Growth

In both reproductive and vegetative plants of Lolium temulentumL., the export of ¹⁴C-labelled assimilates from each healthyleaf on the main shoot to terminal meristem, stem, tillers,and roots was measured each time a new leaf was expanded, fora period of 5 to 6 weeks. Some labelled assimilates moved fromeach leaf on the main shoot to every meristem in the same shoot,as well as to the tops and roots of adjacent organically attachedtillers. The terminal meristem of the reproductive shoot, which includedthe developing inflorescence, received 70–80 per centof the carbon assimilated by the emerged portion of the growingleaf, 15–25 per cent of the carbon assimilated by thetwo youngest expanded leaves, and 5–10 per cent of thatfrom each of the older leaves. A similar pattern of carbon supplyto the terminal meristem was found in vegetative shoots, exceptthat older leaves on young vegetative shoots supplied even lessof their carbon to the terminal meristem. The general conclusionis that developing leaves at the tip of the shoot receive aboutthe same proportion of carbon from each leaf as does a developinginflorescence. Young expanded leaves provided most labelled assimilates forstem growth; during both reproductive and vegetative growth,expanded leaves increased their export of labelled carbon tostem, and exported less of their ¹⁴C to roots and sometimesto tillers. In these reproductive and vegetative shoots, grown in a constantexternal environment, the major changes in the pattern of distributionof labelled assimilates appeared to be the result of increasedmeristematic activity in stem internodes; the development ofan inflorescence had no obvious direct effect on the carboneconomy of shoots.