Change in Electrophoretic Pattern of Ribonuclease during Dormancy and Growth of Bird-cherry Buds

A morphactin formulation containing methyl-2-chloro-9-hydroxyfluorene-9-carboxylate as the major component caused abnormal stem growth in Pinus radiata D. Don seedlings when applied as a bark band. The banded region swelled due to increased cell division in the periderm and cambium. The abnormal stem development in treated trees did not cause a localized girdling effect. The morphactin treatment inhibited shoot elongation and root growth. Treated trees exposed to ¹⁴CO₂ translocated significantly less assimilate to the roots than did control trees although fixation of ¹⁴CO₂ by the shoots was not reduced. Label from a bark band of ¹⁴C-morphactin was rapidly translocated to the roots indicating that direct inhibition of root growth by the inhibitor probably occurred.     

Morphactin transport and metabolism in tree bark tissues: comparative studies in vitro

Bark banding of morphaction is an effective means of controling stem elongation in Pinus radiata D. Don (Monterey pine) but not Juglans regia L. (English walnut). Diffusion coefficients of ¹⁴C-labeled morphactin across excised disks of tree bark, measured in specially designed diffusion chambers, were 11 to 85 fold greater in pine than walnut. In seedlings of comparable age, the suberin layer of walnut bark is much thicker than that of pine; if the layer is removed, diffusion of ¹⁴C-morphactin is enhanced 39-fold in pine and 285-fold in walnut. Morphactin applied to the bark as an ester is rapidly hydrolyzed to its carboxylic acid derivative in both pine and walnut. This conversion occurs rapidly in the bark of both species and does not appear to limit the rate of morphactin movement across the bark. These results suggest that diffusion across the suberin layer and not metabolism limits morphactin transport across the bark.     

A New Laboratory Method Used for Investigating the Uptake, Translocation and Metabolism of Bark Banded Morphactin by Trees

Cut twigs of Monterey pine(Pinus radiata D.Don) were banded with a ¹⁴C labelled morphactin formulation and the lower half of the twig placed in a Scholander type pressure bomb. Water was pumped through the twig from a reservoir inside the bomb and exudate collected from the protruding end of the twig. Using this method it was possible to determine that the slowest step in the translocation of morphactin was the passage across the outer layer of bark. Subsequent passage through the twig was not affected by girdling the bark suggesting that morphactin was translocated upwards via the xylem. The ¹⁴C compound in the exudate from live twigs differed from morphactin and was tentatively identified as the carboxylic acid derivative of the morphactin ester. The cut twig system facilitated studies on the uptake, metabolism and translocation of morphactin and should prove useful for studying the uptake and fate of other chemicals considered for bark application to trees.     

Mode of Dinitroaniline Herbicide Action: II. CHARACTERIZATION OF [C]ORYZALIN UPTAKE AND BINDING

The intracellular binding of dinitroaniline herbicides was studied in order to analyze the mechanism of their colchicine-like action. When corn root apices (5 millimeters) are incubated in [¹⁴C]oryzalin (a dinitroaniline herbicide), the ¹⁴C is taken up rapidly, reaching a plateau in about 4 hours, which corresponds to the minimum incubation time in oryzalin required to get maximum inhibition of elongation. At 4 hours, the [¹⁴C]oryzalin concentration inside the roots is 35 times higher than that in the incubation medium. Since this accumulation of [¹⁴C]oryzalin is not affected by 1 millimolar sodium azide and there is no metabolism of [¹⁴C]oryzalin under these conditions, the [¹⁴C]oryzalin must be accumulated (bound) in corn root apices by a process not requiring metabolic energy.     

UV-B-induced Inhibition of Stem Elongation and Leaf Expansion in Pea Depends on Modulation of Gibberellin Metabolism and Intact Gibberellin Signalling

Information on the involvement of elongation-controlling hormones, particularly gibberellin (GA), in UV-B modulation of stem elongation and leaf growth, is limited. We aimed to study the effect of UV-B on levels of GA and indole-3-acetic acid (IAA) as well as involvement of GA in UV-B inhibition of stem elongation and leaf expansion in pea. Reduced shoot elongation (13%) and leaf area (37%) in pea in response to a 6-h daily UV-B (0.45 W m^?2) exposure in the middle of the light period for 10 days were associated with decreased levels of the bioactive GA₁ in apical stem tissue (59%) and young leaves (69%). UV-B also reduced the content of IAA in young leaves (35%). The importance of modulation of GA metabolism for inhibition of stem elongation in pea by UV-B was confirmed by the lack of effect of UV-B in the le GA biosynthesis mutant. No UV-B effect on stem elongation in the la cry-s (della) pea mutant demonstrates that intact GA signalling is required. In conclusion, UV-B inhibition of shoot elongation and leaf expansion in pea depends on UV-B modulation of GA metabolism in shoot apices and young leaves and GA signalling through DELLA proteins. UV-B also affects the IAA content in pea leaves.     

Distribution of labelled assimilates within a young apple tree after supplying14CO2to a leaf or shoot

Labelled carbon dioxide was supplied for 22 hrs to a leaf of the leader or to the lateral shoot in two-year-old apple seedlings. The distribution of radioactive assimilates within the plant following this treatment was investigated by using radioautography. The transport of labelled assimilates from the young leaf of the leader was very meagre and affected only parts of the stem and the leaves situated in the close vicinity of the treated leaf. The¹⁴C-labelled assimilates from the mature leaf of the leader were transported in a considerable amount to the apex and to the other leaves of the leader. They were also found in an appreciable amount in the stem and the roots, as well as in some lateral shoots. After supplying¹⁴CO₂ to the lateral shoot remarkable transport of labelled assimilates was observed. Radioactivity was detected in the tip and in the youngest leaves of the leader, as well as in the roots. Their path in the stem was studied by dissecting the plant and examining the cross section from each internode. This method revealed that the assimilates from the treated leaf or shoot were transported downward only on one side of the stem in a helical pattern. The lateral shoots situated on the radioactive side of the stem were also labelled, whereas those situated on the opposite (non-radioactive) side were not labelled.     

Effect of Transverse Gravity Stimulation, Gibberellin and Indoleacetie Acid upon Polar Transport of IAAC14 in the Stem of Helianthus annuus

Using IAA^C14, polar transport has been studied in Helianthus annuus shoots in which stem elongation was inhibited by a transverse gravity stimulus induced by horizontal orientation of the plant with daily rotation. Marked inhibition of polar transport of IAA ^C14 occurred in the treated plants. A similar degree of inhibition occurred in the upper and lower halves of non-rotated horizontally trained shoots. Horizontal orientation of stem segments during the transport test had no consistent effect upon IAA transport. Pretreatment of erect plants with gibberellin greatly enhanced IAA^C14 transport and also reduced the inhibitory effect of horizontal orientation. Pretreatment of erect plants with non-radioactive IAA or ethylene inhibited transport of IAA ^C14 and induced the same symptoms in the shoot as the transverse gravity stimulus. The similarities between the response of the auxin transport system to gravity stimulation, IAA and ethylene are discussed.     

RNA AND PROTEIN METABOLISM IN SENESCENT SHOOT APICES OF ‘ALASKA’ PEAS

Senescence of shoot apices of Pisum sativum L. ‘Alaska’ as measured by cessation of stem elongation was delayed by removal of flowers. Analyses of total RNA, nitrogen, protein and inorganic phosphorus in shoot tips of deflowered and control (flower- and fruit-bearing) plants throughout ontogeny revealed that the levels of all these metabolites declined during senescence. Also throughout ontogeny shoot tips of control and deflowered plants were compared with respect to their ability to enzymically degrade RNA and to take up and incorporate P³²-orthophosphate into RNA. The specific activity of ribonuclease increased as senescence progressed while the absolute activity appeared to decrease in correlation with a decrease in total nitrogen content. Compared with nonsenescing shoot tips, senescing shoot tips accumulated less P³² but exhibited an apparent enhancement of P³² incorporation into RNA, which was attributed to a reduction in the endogenous phosphorus pool causing a smaller dilution of the accumulated P³². It is concluded that decreases in the levels of RNA, protein and inorganic phosphorus and in the tran-spirational uptake of nutrients are factors correlated with senescence of the shoot apex.     

Effect of Morphactin, Gibberellic Acid and Auxin and on Growth and Development of Bryophyllum tubiflorum

six month old LD- and SD- grown plants of Bryophyllum tubiflorum were treated with morphactin (n-buty1-9-hydroxy-fluorene-(9)-carboxylate), singly and in combination with GA₃ and IAA. Morphactin and IAA decreased stem elongation and number of leaves, the effect increasing with concentration concentation. Morphactin also caused lateral buds to develop into branches and the fusion of upper leaves to form structures of different shapes. GA₃ enhanced stem elongation, increased leaf number and induced floral buds under SD conditions. It reversed the inhibitory effect of morphactin on stem elongation, leaf number and leaf fusion and also restored apical dominance when applied simultaneously with morphactin. The stimulaneous application of IAA also reversed the morphactin effects on leaf fusion and on apical dominance. The results have been discussed in the light of literature available on the subject.     

Root Growth Activity of Barban in Relation to Auxin and Other Growth Factors

The effect of barban (4-Cl-2-butynyl-N-3-Cl-phenylcarbamate) on the growth of roots of wheat seedlings has been studied. In concentrations of 10^?7 to 5 · 10^?7M barban causes rapid inhibitions of cytokineses and cell elongation, the effects of which are spontaneously reversible. The reversion of the meristem inhibition is enhanced by thymidylic acid and indole-3-acetic acid (IAA). Initiation of cell elongation is slowed down or ceases during cytostasis; its reversal, on the other hand, is promoted by IAA and kinetin but inhibited by Fe. The final cell elongation attained is strongly reduced by barban and reversed under transient aberrant elongation. This inhibition and the recovery appear both to be additive to cell elongation actions of auxin and antiauxin but reversed by nucleic acid components. The inhibition of elongation is increased by Fe. The following explanation for this phenomenon is suggested: the primary effect of barban is known to be the blocking of metaphases under anaesthesis; this blocking then leads to reduced activation of IAA, kinetin and other metabolites. Auxin is required for cell divisions and initiation of elongation: the apical root growth equals in this respect that of shoot apices and lateral meristems. Initiation of cell elongation is closely dependent upon metabolites produced in dividing meristematic cells, whereas the limitation of cell stretching is independent of the meristem activity. No explanation is offered for the role of Fe.     

Transport of exogenous auxin in two-branched dwarf pea seedlings (Pisum sativum L.)

Dwarf pea plants bearing two cotyledonary shoots were obtained by removing the epicotyl shortly after germination, and the patterns of distribution of ¹⁴C in these plants was investigated following the application of [¹⁴C]IAA to the apex of one shoot. Basipetal transport to the root system occurred, but in none of the experiments was ¹⁴C ever detected in the unlabelled shoot even after transport periods of up to 48 h. This was true both of plants with two equal growing shoots and of plants in which one shoot had become correlatively inhibited by the other, and in the latter case applied whether the dominant or subordinate shoot was labelled. In contrast, when [¹⁴C]IAA was applied to a mature foliage leaf of one shoot transfer of ¹⁴C to the other shoot took place, although the amount transported was always low. Transport of ¹⁴C from the apex of a subordinate shoot on plants bearing one growing and one inhibited shoot was severely restricted compared with the transport from the dominant shoot apex, and in some individual plants no transport at all was detected. Removal of the dominant shoot apex rapidly restored the capacity of the subordinate shoot to transport apically-applied [¹⁴C]IAA, and at the same time led to rapid cambial development and secondary vascular differentiation in the previously inhibited shoot. Applications of 1% unlabelled IAA in lanolin to the decapitated dominant shoot maintained the inhibition of cambial development in the subordinate shoot and its reduced capacity for auxin transport. These results are discussed in relation to the polarity of auxin transport in intact plants and the mechanism of correlative inhibition.Abbreviations IAA Indol-3-yl-acetic acid - TIBA 2,3,5-triiodobenzoic acid - 2,4D 2,4-dichlorophenoxyacetic acid - IAAsp Indol-3-yl-acetyl aspartic acid     

Phytotoxic effects,regrowth, and 14C-sucrose translocation in Canada thistle treated with mefluidide,flurprimidol, and systemic herbicides

Foliar applications of the plant growth regulators (PGRs) flurprimidol and mefluidide suppressed shoot elongation and regrowth and enhanced shoot injury caused by selected herbicides in Canada thistle (Cirsium arvense L.). Flurprimidol stimulated movement of ¹⁴C-sucrose from leaves to roots. However, the stimulation was nullified when glyphosate, chlorsulfuron, or clopyralid was applied to foliage 1 week after application of the PGR. Herbicide-induced root injury was not enhanced by PGR application but these PGRs may be useful in decreasing weed competition among crops not similarly inhibited.     

Mode of dinitroaniline herbicide action I. Analysis of the colchicine-like effects of dinitroaniline herbicides

Colchicine and a variety of dinitroaniline herbicides (DNHs)produce a similar pattern of inhibition of elongation, inductionof swelling in the elongation zone, depolarization of cell enlargement,and induction of multiple nuclei in corn seedling roots. However,a 1000-fold higher concentration of colchicine is needed toproduce effects quantitatively similar to those of oryzalin.Both colchicine- and DNH-inhibition of elongation start at about3 hr. Since these compounds cause swelling and inhibition ofelongation in -seedling roots, segments from the root elongationzone and intact roots in the presence of cell division inhibitors(all growing without cell division), it appears that the inhibitionof root elongation is caused in part by their effect on cellelongation independent of their effect on cell division. Sincethe growth (increase in fresh weight) of -seedling roots andexcised root segments is not inhibited by these compounds, theireffect on the polarity of cell enlargement must be fairly specific.Unlike colchicine, oryzalin applied to the roots did not causeany significant, visible effect on shoot (mesocotyl and coleoptile)growth. These organs are not resistant to oryzalin, for theIAA-induced elongation of coleoptile segments is inhibited whenthey are floated in oryzalin solutions. As expected, when coleoptilesegments are incubated in ¹⁴C-oryzalin, it is taken up rapidlyand not degraded. The failure of root-applied oryzalin to affectseedling shoot growth is due to lack of transport to the shoots. (Received June 14, 1977; )     

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.     

Effect of morphactin on stem growth in relation to auxin in precooled rooted tulip bulbs

Effect of morphactin IT 3456, an auxin transport inhibitor, on tulip stem elongation induced by indole-3-acetic acid (IAA) was investigated. Tulip stem growth induced by IAA 0.1 % in lanolin paste applied on the top internode after excision of flower bud and removal of all leaves was greatly inhibited by 0.2 % morphactin IT 3456 applied on the 4th, 3rd, 2nd and 1st internode. The inhibitory effect of the morphactin on tulips stem growth promoted by IAA was restored by additional application of IAA below the morphactin treatment place. Morphactin inhibited also the growth of all internodes induced by flower bud in the absence of leaves. These results suggest a crucial role of auxin in the control growth of all internodes in tulip stem.     

The transport and metabolism of 14C-labelled indoleacetic acid in intact pea seedlings

Summary Part of the IAA-I- or IAA-2-¹⁴C applied at low concentrations to the apices of intact, light-grown dwarf pea seedling was transported unchanged to the root system The calculated velocity of transport in the stem was 11 mm per hour. In the root the label accumulated in the developing lateral root primordia.A large proportion of the applied IAA was converted by tissues of the apical bud, stem and root to indole-3-acetyl-aspartic acid (IAAsp). This compound was not transported. In addition evidence was obtained for the formation of IAA-protein complexes in the apex and roots, but not in the fully-expanded internodes.Large quantities of a decarboxylation product of IAA, tentatively indentified as indole-3-aldehyde (IAld), and several minor metabolites of IAA, were detected in extracts of the roots and first internodes, but not in the above-ground organs exposed to light. These compounds were readily transported through stem and root tissues. Together, the decarboxylation of IAA and the formation of IAAsp operated to maintain a relatively constant level of free IAA-¹⁴C in the root system.     

Translocation of Shoot-Applied Indolylacetic Acid into the Roots of Populus tremula

Application of 10 to 100 μg indol-3-ylacetic acid to the leaves of rooted cuttings of aspen caused inhibition of root growth after three hours. Root growth recovered within 24 hours after IAA treatment. Swelling of the root tips occurred during the period of inhibition. The roots responded in the same way if IAA was applied in solution to the cut stem surface above the mature leaves. IAA-1-¹⁴C applied through a cut stem surface or to mature leaves was translocated downwards in the plants and labelled IAA could be isolated from the roots 3 to 24 hours after application. The ethanol-soluble activity decreased rapidly indicating a rapid metabolism or binding of IAA. IAA-1-¹⁴C applied to growing leaves was not translocated. From the rapid response of root growth it was concluded that IAA was translocated into the roots at a rate of about 7 cm per hour. This rate of translocation indicates that the sieve tubes are involved in the translocation. Implications of the results for the translocation of endogenous auxin into the roots are discussed.     

Source—sink characteristics of carbon transport in Chara hispida

Abstract Rates of uptake of ¹⁴C-labelled inorganic carbon were measured for whole Chara hispida plants, detached parts of the shoot and isolated (split-chamber technique) apices, lateral branchlets and rhizoid—node complexes. The rates of inorganic carbon uptake by the rhizoid—node complex expressed per gram fresh weight whole plant were three to four orders of magnitude less than the uptake for the whole plant. Up to 70% of the carbon taken up by the rhizoid—node complex was translocated to the shoot. After 12 h exposure to ¹⁴C-labelled inorganic carbon the concentration of ¹⁴C was greater in apices than in uppermost or central internodal cells and in all lateral branchlets, regardless of whether label was supplied to the whole plant or isolated rhizoid—node complexes. Measurement of inorganic carbon uptake by detached internodal cells and detached and isolated apices and lateral branchlets showed that lateral branchlets had the greatest rates of inorganic carbon uptake. During 12 h exposure to ¹⁴C, isolated lateral branchlets translocated to the attached shoot 55% of the labelled carbon taken up; for isolated apices this value was only 13%. It is concluded that it is highly unlikely that the rhizoid of Chara hispida could acquire a significant fraction of the whole plant requirement for inorganic carbon and that apices are sink regions for photosynthate while lateral branchlets are source regions.     

Accumulation of 14C from exogenous labelled auxin in lateral root primordia of intact pea seedlings (Pisum sativum L.)

When [¹⁴C]indol-3yl-acetic acid was applied to the apical bud of 5-day old dwarf pea seedlings which possessed unbranched primary roots, a small amount of ¹⁴C was transported into the root system at a velocity of 11–14 mm h^-1. Most of the ¹⁴C which entered the primary root accumulated in the young lateral root primordia, including the smallest detectable (20–30 mm from the primary root tip). In older (8-d old) seedlings in which the primary root bore well-developed lateral roots, ¹⁴C also accumulated in the tertiary root primordia. In contrast, little ¹⁴C was detected in the apical region of the primary root or, in older plants, in the apices of the lateral roots.Abbreviations IAA indol-3yl-acetic acid     

The differential effects of C-16,17-dihydro gibberellins and related compounds on stem elongation and flowering in Lolium temulentum

Plants of Lolium temulentum L. cv. Ceres grown under short days (SDs) can be induced to initiate inflorescences either by exposure to one long day (LD) or by single applications of some gibberellins (GAs), which also enhance the flowering response to one LD. Single doses of up to 25 μg per plant of C-16, 17-dihydro-GA₅ were about as effective as GA₅ for promoting flowering after one LD but inhibited stem elongation by up to 40% over three weeks. The promotion of flowering but not the inhibition of elongation by 16, 17-dihydro-GA₅ was reduced in SDs or in LDs low in far-red (FR) radiation. With shoot apices cultured in vitro, 16, 17-dihydro-GA₅ was more florigenic than GA₃ for apices excised after one LD of 14 h or more, but less florigenic for apices excised from plants in shorter days. 16, 17-Dihydro-GA₅ was ineffective compared with GA₁, GA₃ and GA₅ for α-amylase production by half-seeds of Lolium, a response concordant with its effect on stem elongation. As with GA₅, 16, 17-dihydro derivatives of GA₁, GA₃, GA₂₀ and several other GAs were more effective for flowering and less effective for stem elongation than the GAs from which they were derived. Hydroxylation at C-17 and/or C-16 generally reduced the effectiveness of 16, 17-dihydro-GA₅ for flowering. These results extend the known features of GA structure which favour flowering relative to stem elongation in L. temulentum. Moreover, C-16, 17-dihydro-GA₅ mimics, in its daylength- and wavelength-dependence and lack of stem elongation, characteristics of the LD stimulus in L. temulentum.