Effect of auxin on mesocotyl elongation of dark-grown maize under different seeding depths

In order to elucidate the physiological mechanism of maize mesocotyl elongation induced by auxin under different seeding depths, seeds of five maize inbred lines, including 3681-4 line tolerant to deep seeding, were treated with IAA and triiodobenzoic acid (TIBA) under seeding depths of 20 or 2 cm. Under deep seeding conditions, maize mesocotyls grew by 1.5–2.0 times faster than under shallow seeding conditions. IAA (10⁻⁶ to 10⁻⁴ M) applied to roots stimulated mesocotyl elongation only of 3681-4 line and only under deep seeding conditions. TIBA (10⁻⁵ and 10⁻⁴ M) applied to roots inhibited mesocotyl elongation in all lines, but only 3681-4 was sensitive to 10⁻⁶ M TIBA. IAA promoted only cell elongation, and TIBA inhibited both cell elongation and cell division. After IAA and TIBA treatments, endogenous IAA content changed in parallel with the mesocotyl growth rate under different seeding depths. Furthermore, ABP1 gene expression changed in parallel with the mesocotyl growth rate under deep seeding conditions. Therefore, deep seeding tolerance of 3681-4 line was achieved due to auxin-regulated rapid mesocotyl elongation.     

Inhibitory action of red light on the growth of the maize mesocotyl: evaluation of the auxin hypothesis

Brief irradiation of 3-d-old maize (Zea mays L.) seedlings with red light (R; 180 J m^-2) inhibits elongation of the mesocotyl (70–80% inhibition in 8 h) and reduces its indole-3-acetic acid (IAA) content. The reduction in IAA content, apparent within a few hours, is the result of a reduction in the supply of IAA from the coleoptile unit (which includes the shoot apex and primary leaves). The fluence-response relationship for the inhibition of mesocotyl growth by R and far-red light closely resemble those for the reduction of the IAA supply from the coleoptile. The relationship between the concentration of IAA (1–10 M) supplied to the cut surface of the mesocotyl of seedlings with their coleoptile removed and the growth increment of the mesocotyl, measured after 4 h, is linear. The hypothesis that R inhibits mesocotyl growth mainly by reducing the IAA supply from the coleoptile is supported. However, mesocotyl growth in seedlings from which the coleoptiles have been removed is also inhibited by R (about 25% inhibition in 8 h). This inhibition is not related to changes in the IAA level, and not relieved by applied IAA. In intact seedlings, this effect may also participate in the inhibition of mesocotyl growth by R. Inhibition of cell division by R, whose mechanism is not known, will also result in reduced mesocotyl elongation especially in the long term (e.g. 24 h).Abbreviations FR far-red light - IAA indole-3-acetic acid - P_fr phytochrome in the far-red-absorbing form - P_r phytochrome in the red-absorbing form - R red light     

EFFECT OF LIGHT ON AUXIN TRANSPORT AND ELONGATION OF AVENA MESOCOTYL

The present work was undertaken to find if there are relations between light and auxin action on elongation of coleoptilar node and mesocotyl with Avena seedlings. Red light inhibited the elongation of mesocotyl and simultaneously decreased the rate of transport of diffusible auxin through the node. Red light also inhibited the transport of exogenously given IAA through the nodal region. The light inhibition of IAA transport was closely related to the increase of IAA immobilization. As the age proceeds, the ability of IAA immobilization increased with the decrease in the rate of mesocotyl elongation, even if the seedling was grown in complete darkness. The nature of radioactive substances found in the IAA-C¹⁴ treated tissue was examined by paper chromatography. The above results strongly suggested that the increase of IAA immobilization might result in the inhibition of mesocotyl elongation.     

Gibberellin-induced ethylene production and its effect on cowpea epicotyl elongation

The effect of gibberellin A₁ (GA₁) on production of ethylene by cowpea (Vigna sinensis cv Blackeye pea no. 5) epicotyl explants and its relationship to epicotyl elongation was investigated. The explants were placed upright in water and incubated in sealed culture tubes or in large jars. GA, and IAA in ethanol solution were injected into the subapical tissues of the decapitated epicotyls. Cowpea epicotyl explants elongated after GA but not after IAA treatment, and they were very sensitive to exogenous ethylene. As little as 0.14 1/1 ethylene reduced significantly GA₁-induced epicotyl elongation.Treatment with GA₁ induced the production of ethylene which began 10 h after GA application, showed a peak at about 22 h and then declined. The yield of ethylene was proportional to the amount of GA, injected. The inhibition of epicotyl elongation in closed tubes was avoided by absorbing ethylene released with Hg(Cl0₄)₂ , or by adding AVG to the incubation solution to inhibit ethylene production. Treatment with IAA elicited a rapid production of ethylene which ceased about 10 h after application. The effects of IAA and GA₁ on ethylene production were additive.Abbreviations AVG aminoethoxyvinylglycine 2-amino-4-(2-aminoethoxy)-trans-3butenoic acid - ACC 1-aminocyclopropane-1-carboxylic acid - GA gibberellin - IAA indole-3-acetic acid     

Involvement of Abscisic Acid in Mesocotyl Growth in Etiolated Seedlings of a Foxtail Millet Dwarf Mutant

Etiolated seedlings of foxtail millet (Setaria italica Beauv.) dwarf mutant CH84113 were treated with various concentrations of abscisic acid (ABA), mefluidide, mannitol, or polyethylene glycol (PEG) 6000. It was found that these chemicals, at suitable concentrations, could increase mesocotyl length significantly, whereas these chemicals at higher concentrations had an inhibitory effect. Endogenous levels of ABA in mesocotyl were measured by enzyme-linked immunosorbent assay. It was found that endogenous ABA increased progressively in a chemical (ABA, mefluidide, mannitol, or PEG 6000) concentration-dependent manner, indicating that the effects of these chemicals on mesocotyl growth may be mediated by increased endogenous ABA levels. On the other hand, S-3307, an inhibitor of the oxidative reactions in gibberellin (GA) biosynthesis, inhibited the elongation of mesocotyl significantly. When ABA and GA₃ were applied simultaneously, the effect on mesocotyl growth was additive. These results imply that ABA and GA may control different processes in the regulation of mesocotyl growth. Received October 27, 1997; accepted May 11, 1998     

Comparative Effects of Indoleacetic Acid and Gibberellic Acid on Growth of Decapitated Etiolated Epicotyls of Pisum sativum cv. Alaska

Measurements were made of the growthof the sub-apical region of decapitated, etiolated epicotyls of Pisum sativum L. cv. Alaska after treatments with indoleacetic acid (IAA), gibberellic acid (GA) and triiodobenzoic acid (TIBA). Growth was measured either at the end of a 2-day period, at short intervals during growth, or was monitored continuously for 2–3 h using a position-sensing transducer. In experiments measuring growth after 2 days, high levels (0.1–10 μg/plnat) of IAA caused expansion, whereas similar levels of GA caused elongation. When both hormones were applied together, the effects of IAA were dominant and expansion ensued, even when GA was present at 100 times the amount of IAA. Very low amounts of IAA (0.5–5 ng/plant), however, caused elongation. The elongation elicited by high GA or low IAa was inhibited to a similar extent by TIBA and this inhibition of elongation was associated with an increased expansion at the extreme tip. When application of the hormones was delayed, GA-induced elongation was reduced considerably, IAA-induced elongation was lessened somewhat and IAA-induced expansion was partially converted into elongation. In experiments measuring elongation at short intervals, high levels of IAA caused rapid elongation followed after 3 to 6 h by expnasion. Both GA and low levels of IAA extended the duration of elongation with little apparent effect on the rate of growth. In fast-growth experiments, low, intermediate and high levels of IAA doubled the rate of elongation with a lag period of about 20 min, whereas GA had at most a very slight stimulatory effect on the growth rate. It is concluded that the main role of GA in this system is to maintain physiological levels of IAA in the growing zone and that the level of IAA present determines whether elongation or expansion will take place.     

Die Wirkung von Gibberellinsäure und Indolylessigsäure auf die Wurzelbildung von Tomatenstecklingen

Summary Root formation of tomato cuttings was always inhibited by GA, never promoted. The number of roots was reduced and the roots appeared later, so that at the end of the experiment (13 days later) a reduced dry weight resulted. The effect depended on the concentration of GA, the lowest effective concentration being 10^-3 mg/l. Root formation decreased up to 1000 mg/l GA. An effect on the shoot was noted at concentrations above 10 mg/l. Counts of root primordias after 3–5 days showed the same diminution of root formation. The growth of existing primordias seemed not to be influenced by GA.Short-time treatments with GA had a smaller effect, but a 3-day absorption-period resulted in the same decrease as a treatment during the whole experiment. When GA was given after the experiment had started, the first 3 days of treatment were again the most effective. This result shows that the induction of root primordias is inhibited or at least retarded.CCC had no effect on root formation nor was it able to alter the inhibition by GA. IAA alone did not promote the rooting process. In combination with GA (concentration range for both 10^-3–1 mg/l) IAA never reduced the inhibition by GA. On the contrary, 1 mg/l IAA+GA was somewhat more inhibitive than GA alone.     

Sources of Free IAA in the Mesocotyl of Etiolated Maize Seedlings

Sources of free indole-3-acetic acid (IAA) for the mesocotyl of intact etiolized maize ((Zea mays L.) seedlings are evaluated. The coleoptile unit, which includes the primary leaves and the coleoptilar node, is the main source of free IAA for the mesocotyl. The seed and the roots are not immediate sources of IAA supply. Dependence of the apical growing region of the mesocotyl on the coleoptile unit as a source of free IAA is almost total. One-half or more of the supply of IAA comes from the coleoptile tip, the rest mainly from the primary leaves. Removal of the coleoptile tip results in inhibition of mesocotyl elongation. The hypothesis that growth of the mesocotyl is regulated by auxin supplied by the coleoptile is supported. Conjugated forms of IAA appear to play little part in regulating the levels of free IAA in the shoot.     

Changes in peroxidase and IAA oxidase activities during cell elongation in Phaseolus hypocotyls

Cytoplasmic and salt-extracted peroxidase and IAA oxidase activities were studied in Phaseolus vulgaris hypocotyls treated with gibberellic acid (GA, 200 μM), naphthyl acetic acid (NAA, 100 μM) and distilled water control (DW). Peroxidase activity was assayed with four hydrogen donors during the initial phase of hypocotyl elongation. Though peroxidase activity showed a decreasing trend with time in all the hydrogen donors studied; considerable variation with different hydrogen donors was observed. NAA had maximum peroxidase activity as compared to DW or GA treatment. The activity showed a clear inverse correlation with hypocotyl growth. IAA oxidase activity showed a similar trend with growth as peroxidase activity. A highly significant correlation was observed between peroxidase and IAA oxidase activities and high molecular weight xyloglucan content (P<0.001). Finally, the possible role of peroxidase and IAA oxidase activities in hypocotyl elongation growth is discussed.     

CONTROL OF IN VITRO SEPAL DEVELOPMENT OF EXCISED FLORAL BUDS OF AQUILEGIA (RANUNCULACEAE)

Excised floral buds of Aquilegia formosa Fisch. were grown on a coconut-milk medium containing the minerals and vitamins of Murashige and Skoog, sucrose, and kinetin. The plant growth regulators indoleacetic acid (IAA, 0.5 mg/liter) and gibberellic acid (GA, 2.0 mg/liter) were added singly and in combinations; both were omitted from the control medium. The addition of GA to the basal medium was required to support sepal development on flowers at all phases of development. The formation of stomatal complexes in the epidermis of the sepals occurred only in the presence of GA. Sepals grown in the presence of GA also contained trichoblasts and developing trichomes, while none were formed in the absence of GA. The role of IAA in the development of these idioblasts was not clear but it appeared to have no effect. The hormones GA and IAA had different effects on the growth of the sepals. In the presence of GA the sepals increase in length until comparable with sepals grown in vivo. However, the sepals remained small when GA was omitted from the medium. Upon closer examination of this effect, it was determined that there was a direct proportionality between an increase in cell number in the epidermis and an increase in sepal length. The role of the two hormones in increasing epidermal cell length in sepals was distinct and separate. Exogenous IAA had no effect upon cell division but was required for cell elongation, while GA was required for cell division and had no effect on cell elongation. The GA effect in promoting cell division in the sepals was substantiated by use of autoradiography. If the buds were grown on media with GA, twice as many epidermal cells along the central file incorporated significant amounts of tritiated thymidine. The cell cycle of the epidermal cells of the GA-treated sepals was ca. 8.7 hr in duration and ca. 13.0 hr if GA was deleted from the medium.     

Micropropagation of meadowfoam (Limnanthes spp.)

Summary A rapid micropropagation system was developed for meadowfoam (Limnanthes spp. Brown) using four genotypes of three species. Murashige and Skoog (MS) medium supplemented with N⁶ benzyladenine (BA) and indole-3-acetic acid (IAA) at 0, 0.1, 0.5, 1.0 and 2.0 mg/l was tested for multiplication, shoot elongation and rooting. Expiants were taken from pot-grown plants. The most useful level for shoot growth and multiplication of both floral induced and non-induced plants was 0.5 mg/l BA. IAA failed to affect shoot growth or multiplication. Expiants from non-induced plants multiplied at moderate to high rates on 0.5 mg/l BA, while those from induced plants multiplied slowly and tended to elongate and flower. Non-induced plants on 2 mg/l BA produced large numbers of tiny shoots; induced plants did not respond. Shoots of all genotypes rooted on MS medium without hormones and all plants grew normally after transplanting to soil. This system provides a new tool for the development of meadowfoam as a crop plant.Abbreviations (BA) N ⁶ -benzyladenine - (IAA) indole-3-acetic acid - (MS) Murashige and Skoog medium, 1962     

Promotion of mesocotyl growth in etiolated rice seedlings by 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione

4-Ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione (TA) promoted mesocotyl growth in dark-grown rice (Oryza sativa L.) seedlings. In cultivars of the japonica type TA alone showed a small promotive effect and TA+gibberellic acid(GA₃) had a marked synergistic effect, while in other cultivars, mostly of the indica type, TA alone showed a great promotive effect and TA+GA₃ had only an additive effect. In cv. Nato, a typical representative of cultivars showing the second type of response, the concentration of TA giving the greatest growth promotion was around 0.1–0.2 mM. In Nato seedlings treated with TA at 0.1 mM, the mesocotyls continued to elongate for 6 days and reached about 75 mm in length, while the mesocotyls of control seedlings grew to a maximum of about 10 mm and growth was limited to the first 3 days after planting. The TA-induced mesocotyl elongation was mainly the consequence of increased cell multiplication in the meristematic area immediately below the coleoptilar node. GA₃, abscisic acid (ABA) and ethylene also stimulated mesocotyl growth in dark-grown Nato seedlings but their effects were much smaller than those of TA. ABA, like GA₃, had an additive effect with TA, but ethylene suppressed the effect of TA and resulted in increased lateral expansion in the upper region of the mesocotyls of TA-treated seedlings.Abbreviations ABA abscisic acid - GA(s) gibberellin(s) - GA₃ gibberellic acid - TA 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione Part 5 in the series Plant Growth-regulating Activities of Isourea Derivatives and Related Compounds; Part 4=Ogawa et al. (1978)     

Diferulic acid as a component of cell walls of Lolium multiflorum

Trans,trans-, cis,trans- and cis,cis-diferulic acids were released from cell walls of Lolium multiflorum by treatment with sodium hydroxide. The isomers were apparently bound via ester links to the structural carbohydrates of the cell walls. Sodium hydroxide treatment gave, per g of wall, 0.18 mg trans,trans-diferulic, 0.02 mg cis,trans-diferulic and a trace of cis,cis-diferulic acids compared with 5.3 mg trans-ferulic, 1.2 mg cis-ferulic, 0.78 mg trans-p-coumaric and 0.12 mg cis-p-coumaric acids. The significance of these acids in lignin biosynthesis is discussed. The effect of UV light on the trans,trans isomer and its fully silylated trimethylsilyl either derivative was also investigated.     

The role of GA,IAA and BAP in the regulation of <Emphasis Type="Italic">in vitro</Emphasis> shoot growth and microtuberization in potato

The effect of auxin, GA and BAP on potato shoot growth and tuberization was investigated under in vitro condition. The shoot length of potato explants increased with the increasing of concentrations (0.5 – 10 mg dm⁻³) of IAA treatment especially with the addition of GA₃ (0.5 mg dm⁻³), but was inhibited by BAP (5 mg dm⁻³). The root number and root fresh weight of potato explants increased with the increasing of IAA levels either in the presence of GA₃ (treatment IAA+GA) or not (IAA alone). However, no root was observed in the treatment IAA+BAP, instead there were brown swollen calli formed around the basal cut surface of the explants. The addition of GA₃ remarkably increased the fresh weight and diameter of calli. Microtubers were formed in the treatments of IAA+BAP and IAA + GA + BAP but not observed in the treatments of IAA alone or IAA + GA. IAA of higher concentrations (2.5 – 10 mg dm⁻³) was helpful to form sessile tubers. With the increasing of IAA levels, the fresh weight and diameter of microtubers increased progressively. At 10 mg/L IAA, the fresh weight and diameter of microtubers in the treatment of IAA + GA + BAP were 409.6 % and 184.4 % of that in the treatment of IAA + BAP respectively, indicating the interaction effect of GA and IAA in potato microtuberization.     

The effect of plant growth regulators on biomass formation and lobeline production of Lobelia inflata L. hairy root cultures

We have studied the biomass and alkaloid production of geneticallytransformed hairy root cultures of Lobelia inflata L. Thehairy root clone 8009/h7 transformed with Agrobacteriumrhizogenes strain R 1601 was cultivated on B5 solid media containingdifferent amounts of the growth regulators KIN, IAA or NAA. KIN significantlydecreased growth and lobeline production and strongly inhibited biomassformation at 5 mg/l. IAA and NAA had characteristic morphologicaleffects on growth, in increasing the number of the lateral roots. However theyrestricted linear growth. Addition of IAA or NAA into the culture mediumincreased the biomass formation and lobeline production of hairy roots. It wasfound that the greatest amount of lobeline was obtained at the 0.2mg/l IAA concentration, similar to the effect of NAA.     

影响辣椒离体再生芽伸长因素研究

以辣椒子叶为外植体,比较不同浓度BA和IAA激素组合对辣椒再生芽诱导的差异,利用筛选出的高效芽诱导培养基为基础,研究了赤霉素、芽诱导时间、培养基有机成分、不同激素组合和品种等因素对辣椒不定芽伸长的影响。结果表明:不同基因型辣椒子叶再生能力不同,BA3.0mg.L-1 IAA0.5mg.L-1的激素配比对不定芽诱导频率最高;不定芽的伸长百分率随着GA3浓度的增加而增加,GA3的适合浓度为1.0～2.0mg.L-1;不定芽诱导时间对不定芽的伸长有一定的影响,诱导21d的不定芽,其伸长频率明显高于诱导14d的不定芽;B5有机成分在辣椒不定芽的伸长中效果优于MS有机成分;激素组合对不定芽伸长有一定的影响,Zeatin GA3激素组合对伸长效果最好,BA IAA GA3伸长效果较好,BA PAA(苯乙酸,phenylaceticacid) GA3伸长效果次之;不同品种辣椒不定芽的伸长能力有一定差异,楚风和苏椒五号再生芽伸长能力最佳。与IAA和NAA相比,IBA对再生芽生根效果较好。     

Plant regeneration from meristem-derived callus protoplasts of apple (Malus3domestica cv. `Fuji')

A procedure has been established for regeneration from meristem-derived callus protoplasts of scion cultivars of apple that have been difficult to regenerate from leaf protoplasts. Calli were induced from the meristem of apples, Malus×domestica cvs `Fuji' and `Jonagold' and Malus prunifolia var `ringo Asami Mo84-A', cultured on MS medium (2 mg/l 2,4-D, 1 mg/l BA, 0.8% agar) and subcultured in a liquid medium. The ability to regenerate plants from suspension calli was studied under eight different combinations with respect to IAA, ABA, and TDZ concentrations. With the materials studied here, two combinations, one with 0.1 mg/l IAA, 0.1 mg/l ABA, and 2.0 mg/l TDZ and another with 0.1 mg/l IAA, 1.0 mg/l ABA, and 2.0 mg/l TDZ, were effective for plant regeneration. Protoplasts were isolated from the above suspension cultures and then cultured in KM8P medium containing IBA (2 mg/l), BA (1 mg/l), 2,4-D (0.4 mg/l), and MES (5 mM, pH 5.7). Shoot formation of protoplast-derived calli was studied in the above-mentioned regeneration media. The high concentration of Gelrite (0.5% and 0.7%) was also shown to be important for shoot formation of protoplast-derived calli. Shoot primordia were formed in the medium containing IAA (0.1 mg/l), ABA (1.0 mg/l), and TDZ (2.0 mg/l). Ultimately, five regenerants of `Fuji' protoplasts were obtained from 200 protoplast-derived calli. Received: 19 June 1998 / Revision received: 9 October 1998 / Accepted: 27 October 1998     

Boron and blue light reduce responsiveness of <Emphasis Type="Italic">Arabidopsis</Emphasis> hypocotyls to exogenous auxins

We reported earlier that boron stimulates hypocotyl growth in several Arabidopsis ecotypes but not in the boron-deficient mutant bor1-1. Others have shown that boron influences the metabolism and transport of the plant hormone auxin. We investigated how boron, in interaction with light, influences Arabidopsis hypocotyl growth responses to the exogenous auxins 1-NAA, 2,4-D and IAA. In either light condition, 1-NAA similarly inhibited hypocotyl growth in bor1-1 and the corresponding WT (Col-0), while in both genotypes, boron did not essentially affect the extent of the inhibition. Whatever the light conditions and in the absence of boron, 2,4-D inhibited hypocotyl elongation in WT, while in BL seedlings, high responsiveness to 2,4-D vanished when boron was added to the culture medium. Hypocotyl of bor1-1 seedlings in all boron concentrations tested and grown in the dark or RL responded to the auxin similar to WT plants. In BL, the mutant hypocotyls retained full sensitivity to 2,4-D at 0.1 mM H₃BO₃ but lost that sensitivity by 2 mM. In both genotypes tested, in the dark or RL, IAA inhibited hypocotyl growth. Conversely, IAA stimulated hypocotyl elongation in both genotypes developed in BL at 0.1 mM H₃BO₃. That stimulation disappeared when the boron supply increased to 2 mM. Our results suggest that specifically in BL, boron reduces hypocotyl responsiveness to auxins 2,4-D or IAA via the functional transporter BOR1. Our results lead to a discussion of how BL and BOR1 influence the mechanisms of auxin transport into and out of the cell.