Effect of Gibberellic Acid and Cycocel on Tryptophan Metabolism and Auxin Destruction in the Sunflower Seedling

A comparative study of tryptophan conversion in different regions of the sunflower seedling indicates that the regions most active in converting tryptophan on a pathway to auxin are the root apical segments and young leaves; next highest in activity is the cotyledonary tissue. The stem apex proper with leaf primordia is less active than the above regions in converting the auxin precursor. Hypocotyl tissue was observed to be least active. Pre-treatment of the apical bud region of the stem with gibberellic acid (GA) gives rise to tryptophan conversion rates which are 2.1 times those in untreated seedlings. The enhanced tryptophan conversion in the apical bud is followed by an increased elongation rate of the 1st internode which is 2.2 times that in the 1st internode of untreated seedlings. Treatment of the seedlings with Cycocel [(2-chloroethyl)trimethylamnionium chloride] does not reduce tryptophan conversion in the apical bud region of the seedling although elongation of the stem is greatly retarded. Indoleacetic acid (IAA) destruction in cell free preparations as well as in whole sections of the elongating region of the seedling stem was studied. IAA-1-¹⁴C destruction rates with the release of ¹⁴CO₂ in whole sections of 1st internode tissue were approximately 3 times those in cell free preparations of the same region. No significant changes in IAA destruction rates in seedlings pre-treated with GA or Cycocel were observed.     

Effect of Auxin and Gibberellin on Sporulation in Yeast

Effect of auxin and gibberellic acid on sporulation of a yeast, Saccharomyces ellipsoideus, was studied. When added to the sporulation media, gibberellic acid promoted sporulation. The sporulation rate was higher in the medium SGV with vitamins than in the vitamin-free SG, but the effect of gibberellic acid was more pronounced in the latter. Auxin (IAA, 2,4-D, and NAA) inhibited sporulation in SGV, but promoted it in SG. This sporulation-promoting effect of IAA was reversed by an antiauxin, 2,4,6-T. Preculturing in the presence of added IAA increased sporulation. Added to the preculture medium, gibberellic acid alone showed little effect on sporulation, but in combination with IAA it enhanced sporulation conspicuously. IAA and gibberellic acid were effective in sporulation promotion only when added before the nuclear enlargement occurred in sporulation culture.     

Effect of Protein Synthesis Inhibitors, Auxin, and Gibberellic Acid on Abscission

Chloramphenicol, actinomycin D, and other inhibitors of protein synthesis promote abscission in several plant genera. Abscission is accelerated in species where an abscission layer is present, as well as in tissue where no abscission layer develops prior to abscission. The inhibitors promote abscission in species where cell division is reported to precede the separation processes as well as in tissues where no cell division is associated with the initiation of abscission. Indoleacetic acid (IAA) or auxin precursors, when applied with chloramphenicol and aclinomycin D, overcome the promotive effects of the inhibitors on abscission. These inhibitors apparently do not promote abscission through their effects on auxin precursor conversion, IAA transport, and IAA destruction in the petiole. IAA increases the incorporation of leucine-1-¹⁴C into a trichloroacetic acid precipitable fraction of the abscission zone under conditions where abscission is retarded. A low concentration of IAA which accelerates abscission, decreases incorporation of leucine into protein. Other promoters of abscission — chloramphenicol, d-aspartic acid, and gibberellic acid —also decrease the incorporation of leucine into the protein of the abscission zone. The data indicate that enzymes required for the degradative processes associated with abscission are already present in the abscission zone whereas a continuous synthesis of protein is required for the retention of the leaf.     

Effect of Treatments with Growth Retardant Chemicals on Petiole Abscission in Coleus

A bscission of debladed petioles of Coleus was observed following spray applications of growth retardant chemicals and particularly of Phosfon D to the foliage. Sprays were applied to some branches, which were left intact (inducing branches), or to adjacent branches the leaves of which were later debladed (induced branches). In all experiments two applications of growth retardant chemicals were made, after which the induced branches were debladed. Treatments on induced branches accelerated the petiole abscission relative to the controls. Treatments on inducing branches, instead, decreased abscission speed of debladed petioles. The evidence suggests that phosfon D affects abscission by interfering with the indoleacetic acid mechanism.     

Abscission in Coleus: Light and Phytohormone Control

Light control of leaf abscission in Coleus (Coleus blumei Benthcv. Ball 2719 Red) appears to be regulated by the quantity ofendogenous auxin transported from the leaf blade to the abscissionzone. Gas chromatographic—mass spectrophotometric analysisindicated that diffusate collected from leaf tissue treatedwith red light contained significantly higher levels of auxinthan dark and far-red light-treated leaf tissue. In addition,diffusate from red light-treated tissue inhibited abscissionof leafless petioles while diffusate from far-red light-treatedtissue promoted abcission when compared with diffusate fromdark-treated tissue. The effect of red light on abscission couldbe mimicked by IAA, but not by other phytohormones. An auxintransport inhibitor, 2, 3, 5-triiodobenzoic acid (TIBA), appliedeither as a lanolin ring around the petiole or vacuum infiltratedinto tissue, could completely eliminate any red light effecton abscission. The data are consistent with a phytochrome-mediatedlight regulation of endogenous auxin level in the leaf whichthen controls abscission. Key words: Abscission, Coleus, IAA, plant hormones, red (far-red) light, TIBA     

Abscisic Acid, Auxin, and Ethylene in Explant Abscission

Experiments with explants of Phaseolus vulgaris L., cv. CanadianWonder, show that abscission and the associated rise in oarboxymethyl-cellulaseactivity in the separation zone are initiated by a peak in ethyleneproduction during senescence of pulvinar tissue distal to thezone. Distal applications of abscisic acid (ABA) induce an earlierpeak in ethylene production, increase cellulase activity, andpromote abscission. ABA is more effective in these ways if treatmentis delayed from 0 to 24 h after excision. With increasing concentrations of ABA the maximum rate of ethylene production is achievedsooner. Indol-3yl-acetic acid (IAA) and ABA are antagonisticin this system and have opposing effects. IAA retards the timeof peak ethylene-production and delays abscission. Explantsmay be retained for long periods without abscinding if incubatedin an ethylene-free atmosphere: the addition of ethylene forany one 24-h period (except the first 24 h after excision) willinduce abscission. The initial period of insensitivity to ethyleneis extended by distal applications of IAA. Ethylene-inducedabscission can be inhibited by IAA applied up to 72 h afterexcision provided the ethylene is not applied first. It is proposedthat abscission in the explant is controlled at two levels:(1) an auxin-dependent stage determining the duration of insensitivityto ethylene; (2) the timing of a rise in ethylene productionin senescing tissue distal to the separation zone. An auxin-ethylenebalance-mechanism at the separation zone is discussed.     

Mercury-induced Ethylene Formation and Abscission in Citrus and Coleus Explants

Mercury vapor induces ethylene formation and abscission in Citrus and Coleus explants. Both responses are markedly greater in the absence of CO₂. The stimulation of these metabolically complex processes indicates that the action of mercury vapor is not consistent with the more popular conception of mercury toxicity. This was manifested in its complete failure to disturb respiratory gas exchange, and in the total absence of any necrosis. Accordingly, the effect of mercury appears to be highly specific. The overall significance of these findings is discussed with respect to physiological, environmental, and methodological aspects.     

The Role of Auxin and Gibberellin in Controlling Lignin Formation in Primary Phloem Fibers and in Xylem of Coleus blumei Stems

The hypothesis that auxin (IAA) and gibberellic acid (GA₃) control the formation of lignin is confirmed for the primary phloem fibers and for the secondary xylem in the stem of Coleus blumel Benth. Indoleacetic acid alone, or a combination of high IAA/low GA₃ (w/w), induced short phloem fibers with thick secondary walls, that contained lignin rich in syringyl units (high ratio of syringyl/guaiacyl). On the other hand, a combination of high GA₃/low IAA (w/w), which promoted the differentiation of long phloem fibers with thin walls, decreased the relative content of the syringyl units (low syringyl/guaiacyl ratio). In the secondary xylem, these hormonal treatments yielded only slight changes in the noncondensed monomeric guaiacyl units, confirming the relative stability of the guaiacyl lignification pattern in this tissue. In the xylem, indoleacetic acid alone, or a combination of high IAA/low GA₃ induced lignin poor in syringyl units (low syringyl/guaiacyl ratio). A combination of high GA₃/low IAA promoted a relatively slight increase in syringyl yield, indicating greater responsiveness of the syringyl lignification pattern to growth regulators. The possible functional and technological significance of our results is discussed.     

The Effect of Kinetin on the Occurrence of Acid Auxin in Coleus blumei

Excised shoots and potted plants of Coleus blumei Benth, were subjected to different treatments with kinetin solutions. Control treatments were made with water. Free and bound auxin were extracted with ether. The acid fractions were purified by electrophoresis to remove all traces of kinetin, and were then analyzed with the Avena straight-growth test. As compared with the controls, kinetin treatment increases the bound auxin, whereas the corresponding free auxin is unchanged. Also methanol extracts of treated stems contain more acid auxin than corresponding extracts of water-treated stems. This indicates that on methanol extraction not only free auxin but also some bound auxin is obtained. The extracted auxin behaves like indoleacetic acid in paper chromatography with four different solvent systems, as well as in gel filtration through Sephadex. New formation or decreased breakdown of auxin seem the most likely explanations for the observed effects of kinetin.     

Auxin, Gibberellin, Cytokinin and Abscisic Acid Production in Some Bacteria

Summary In this study, auxin (indole-3-acetic acid), gibberellin, cytokinin (zeatin) and abscisic acid production were investigated in the culture medium of the bacteria Proteus mirabilis, P. vulgaris, Klebsiella pneumoniae, Bacillus megaterium, B. cereus, Escherichia coli. To determine the levels of these plant growth regulators, high performance liquid chromatography (HPLC) technique was used. Our findings show that the bacteria used in this study synthesized the plant growth regulators, auxin, gibberellin, cytokinin and abscisic acid.     

The Effect of Gibberellin on Tryptophan Conversion and Elongation of the Avena Coleoptile

Gibberellic acid (GA₃) enhanced directly the release of ¹⁴CO₂ from tryptophan-1-^l4C by cell free preparations of Avena coleoptile tips. The rate of tryptophan metabolism in the presence of GA₃ was increased by approximately 100 per cent. The addition of auxin synthesis inhibitors to incubation flasks nullified the enhancement effect of GA₃ on elongation of the coleoptile tips. These studies implicate tryptamine as an intermediate in the formation of auxin from tryptophan. The possibility of GA₃-IAA interaction in the elongation processes was also investigated. Combination treatments of these growth-promoting substances did not induce a synergistic growth response by the coleoptile tissue.     

Regulation of Auxin Levels in Coleus blumei by Ethylene

An investigation of the effects of ethylene pretreatment on several facets of auxin metabolism in Coleus blumei Benth “Scarlet Rainbow” revealed a number of changes presumably induced by the gas. Transport of indoleacetic acid-1-¹⁴C in excised segments of the uppermost internode was inhibited by about 50%. Decarboxylation of indoleacetic acid-1-¹⁴C by enzyme breis was not affected by the pretreatment. Levels of extractable native auxin in upper leaf and apical bud tissue of the pretreated plants were approximately one-half of those present in untreated plants. The rate of formation of auxin from tryptophan by enzyme breis from pretreated plants was approximately one-half that occurring in incubation mixtures containing the enzyme system from untreated plants. The conjugation of indoleacetic acid-1-¹⁴C in a form characterized chromatographically as indoleacetylaspartic acid was increased 2-fold in the upper stem region of plants pretreated with ethylene.     

Effect of Gibberellin and Auxin on Parthenocarpic Fruit Growth Induction in the cv Micro-Tom of Tomato

The effect of applied gibberellin (GA) and auxin on fruit-set and growth has been investigated in tomato (Solanum lycopersicum L.) cv Micro-Tom. It was found that to prevent competition between developing fruits only one fruit per truss should be left on the plant. Unpollinated ovaries responded to GA₃ and to different auxins [indol-3-acetic acid, naphthaleneacetic acid, and 2,4-dichlorophenoxyacetic acid (2,4-D)], 2,4-D being the most efficient. GA₃- and 2,4-D-induced fruits had different internal morphology, with poor locular tissue development in the case of GA, and pseudoembryos development in the case of 2,4-D. Also, GA₃ produced larger cells in the internal region of the mesocarp (IM) associated with higher mean C values, whereas 2,4-D produced more cell layers in the pericarp than pollinated fruits. The smaller size of GA₃- compared with 2,4-D-induced fruits was due to them having fewer cells, only partially compensated by the larger size of IM cells. Simultaneous application of GA₃ and 2,4-D produced parthenocarpic fruits similar to pollinated fruits, but for the absence of seeds, suggesting that both kinds of hormones are involved in the induction of fruit development upon pollination. It is concluded that Micro-Tom constitutes a convenient model system, compared to tall cultivars, to investigate the hormonal regulation of fruit development in tomato.     

Effect of Auxin and Gibberellin on Conidial Germination in Neurospora crassa II. "Conidial Density Effect" and Auxin

Conidial germination in liquid shake culture of Neurospora crassawas affected by the number of conidia in the medium (conidialdensity effect) with the optimum density being around 2?10⁶conidia/ml. The conidial density effect at 2?10⁴ and 2?10⁵ conidia/mlwas eliminated by the addition of auxin, IAA or 2,4-D with theoptimum concentrations of IAA and 2,4-D being around 10^–6M. IAA and 2,4-D had no effect on the effect at 2?10⁷ conidia/ml.An active substance(s) for conidial germination which was relatedto the conidial density effect was detected in the cell-freefiltrate of the germination medium, and was found to be non-dialyzableand thermolabile. At the early stage of germination, the concentrationof active substance(s) in the medium increased in proportionto the conidial density and reached a supraoptimum amount forgermination at 2?10⁷ conidia/ml. IAA (10^–6M) enhancedthe concentration. Endogenous auxin concentrations in filtratesof the germination media containing 2?10⁵, 2?10⁶ and 2?10⁷ conidia/mlwere 5.8?10^–12, 4.6?10^–11 and 1.7?10^–10M IAAequivalent, respectively. The conclusion reached was that auxinmay control conidial germination with mediation by the activesubstance(s). (Received June 8, 1982; Accepted September 27, 1982)     

Seasonal Changes in Abscission Responses to Auxin in Debladed Petioles

The abscission of debladed petioles of various ages in Ervatamiaand Coleus has been followed throughout the year. In general,the retention times for the two species were found to be maximalin the summer and minimal in the winter months. In both speciesolder petioles tended to abscise earlier. The occurrences ofan auxin-inhibitable stage-I and an auxin-promotable stage-IIwere clearly established. The sensitivity to auxin in both stagesdeclined with increase in age, particularly in the two-nodeand three-node twigs of Ervatamia and in the four-node twigsof Coleus. The durations of stage-I and stage-II were foundto be characteristically different in different seasons. Ingeneral, stage-I lasted longer both in younger petioles andduring the summer months. Auxin sensitivity in both stages wasgreater in summer than in winter. Intermediate results wereobtained in the other two seasons. In both the species the auxin-promotablestage-II weakened with time, as shown by a smaller promotionwith delayed auxin application.