Growth Regulators and the Phytochrome-Mediated Dormancy of Celery Seeds

Seeds of five celery (Apium graveolens L.) cultivars germinated at 15°C in the light or dark but at 22°C only in the light. This light requirement was overcome by treatment with a mixture of the gibberellins GA₄ and GA₇ (GA_4/7) but interactions of cytokinins, daminozide, ethephon, EDTA and N-phenyl-N′-4-pyridylurea (NC5392) with GA_4/7 were observed. Varietal differences in response to GA_4/7 concentration and the requirement for cytokinins were related to the upper temperature limits for germination of the different cultivars. Seeds of cultivars responding to low concentrations of GA_4/7 appeared to contain less natural inhibitor than those requiring either high concentrations of GA_4/7 or cytokinin in addition to low GA_4/7. The cytokinin requirement for germination was partially removed by leaching the seeds with water. Interaction studies with applied hormones indicated that in seeds incubated in the light inhibition by abscisic acid was partially alleviated by N⁶-benzyladenine but not by GA_4/7 application. The implications of these results are discussed in relation to the involvement of natural plant hormones in the dormancy mechanism of celery seeds.     

外源赤霉素对紫斑牡丹种子萌发的影响

以紫斑牡丹种子为试验材料,研究不同浓度的赤霉素(GA_3)处理对种子生根以及生根过程中营养物质、酶活性和内源激素水平变化的影响,为探讨紫斑牡丹种子萌发机制提供依据。结果表明:(1)GA_3处理能够促进种子生根,并以300 mg/L GA_3处理对种子生根效果最好,与对照相比可提前14.67 d生根,生根率可达71.00%。(2)与对照相比,GA_3处理可以在0～15 d时促进种子淀粉水解和可溶性糖的积累,并加速可溶性蛋白的消耗,在0～30 d促进过氧化物酶(POD)活性的提高,从而促进种子萌发生根。(3)在种子沙藏生根过程中,种子脱落酸(ABA)含量呈下降趋势,赤霉素(GA)、玉米素核苷(ZR)和吲哚乙酸(IAA)含量均表现出先上升后下降的趋势,与对照相比,GA_3处理可使种子GA、ZR和IAA的含量在沙藏前期明显上升,以解除种子休眠。研究发现,外源GA_3处理可以调控紫斑牡丹种子内源激素含量和POD活性的变化,促进营养物质转化,从而提前解除种子休眠使其萌发。     

Heavy metal-hormone interactions in rice plants: Effects on growth,net photosynthesis,and carbohydrate distribution

The effect of external applications of gibberellins (GA₃) and abscisic acid (ABA) on the growth, carbohydrate content, and net photosynthesis of heavy metal-stressed rice plants (Oryza sativa cv. Bahía) was investigated. Treatment with cadmium (0.1 mm) and nickel (0.5 mm) inhibited rice growth and stimulated carbohydrate accumulation, especially in seeds from which seedlings were developing, stems, and first leaves. The addition of GA₃ (14 m) to the rice culture solution together with Cd or Ni partially reversed the effects of heavy metals, stimulating growth as well as mobilization of carbohydrate reserves in seeds from which seedlings had developed. GA₃ increased the sugar content in roots and second and third leaves and also modified the carbohydrate distribution pattern compared with heavy metal-treated plants. In contrast to GA₃, ABA (19 m) supplied to rice cultures potentiated the effect of heavy metals, inhibiting the growth of young leaves and the translocation of storage products from source to sink organs. In addition, sugars were accumulated in roots and second leaf but not in the third leaf, the extension in length of which was also inhibited by the treatment. Net photosynthesis rates recovered transitorily in Cd-treated plants after the addition of hormones. The possible relationship between growth and carbohydrate distribution, as well as the involvement of hormones, in the response of plant to heavy metal stress is discussed.Abbreviations 5DT 5 days after treatment - 10DT 10 days after treatment - ABA abscisic acid - GA₃ gibberellic acid - TMC total metabolizable carbohydrates     

Induced parthenocarpy—a way of changing the levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 1. Extractable hormones

Ethylene, indol-3-acetic acid (IAA), gibberellin-like substances (GAs) and abscisic acid (ABA) were analysed in extracts from normal, seed-containing and parthenocarpic tomato fruits throughout fruit development. Parthenocarpic fruit growth was induced with an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃) and compared with that of pollinated control fruits. Fruit growth was only affected by the treatment with GA₃, decreasing size and fresh weight by 60%. The peak sequence of hormones during fruit development was ethylene-GAs-IAA-ABA. Seeded fruits contained the highest levels of IAA and ABA but the lowest levels of GAs. Also, in seeded fruits, a high proportion of IAA and ABA was found in the seeds whereas this was not the case for GAs.Hormone levels of tomato fruits may be successfully, easily and reproducibly altered by inducing parthenocarpic fruit growth and thus eliminating development of seeds which are a major source of hormone synthesis. In spite of markedly changed hormone levels, there was no obvious relationship between fruit growth and extractable hormones per se. However, the results indicate that a high ratio of GAs: auxins is unfavourable for growth of tomato fruits.     

Dormancy of <Emphasis Type="Italic">Nicotiana benthamiana</Emphasis> seeds can be broken by different compounds

The influence of after-ripening, sodium nitroprusside, potassium ferricyanide, cyanide, paclobutrazol and nitrite on germination of seeds of Nicotiana benthamiana was investigated as well as the influence of plant hormones such as gibberellins and abscisic acid. Dormancy of N. benthamiana seeds was broken by all treatments except treatments with abscisic acid, paclobutrazol and gibberellic acid (GA₃). Gibberellins had an interesting effect on dormancy breakage of studied seeds which was dependent on use of particular gibberellin: GA₃ or GA₄₊₇. Unlike GA₃, GA₄₊₇ had broken seed dormancy.     

Hormonal Regulation of Expression of Two Cysteine Endopeptidase Genes in Rice Seedlings

Two cDNA probes (pRP60 and pRP80) were used to examine the hormonalregulation of expression of two cysteine endopeptidase genesin germinated whole seeds and de-embryonated seeds of rice.The pRP60 protein is a major rice cysteine endopeptidase namedREP-1 that digests rice glutelin, the main seed storage protein.The pRP80 protein has features of a cysteine endopeptidase buthas not yet been confirmed to be one. Neither mRNA was detectablein dry seeds, and the levels per seed increased sharply uponimbibition, reached peaks at d 6 to d 9, and then decreased.Both mRNAs were expressed in a seed-specific manner, but theaccumulation of pRP60 mRNA was about ten times greater thanthe other. When seeds were de-embryonated and incubated, theamounts of both mRNAs were reduced to very low levels, but inthe presence of 0.01 to 1 µM. gibberellic acid (GA₃) bothagain reached high levels. Addition of abscisic acid (ABA) oruniconazole, an inhibitor of gibberellin biosynthesis, partlyeliminated the effect of GA₃. Protein immunoblot analysis showedthat the accumulation of the REP-1 protein in seeds was regulatedby GA₃ and ABA similarly to that of pRP60 mRNA, but the changein pRP60 mRNA with time after the onset of imbibition precededthat of the REP-1 protein. (Received May 28, 1997; Accepted September 8, 1997)     

Identification of gibberellins A17, A25, A45, abscisic acid,phaseic acid,and dihydrophaseic acid in seeds of Pyrus communis

Gibberellin A₁₇, abscisic acid, and 4′-dihydrophaseic acid were identified by GC-MS of derivatized extracts from both immature and mature seeds of pear. Immature seeds also contained phaseic acid, gibberellins A₂₅ and A₄₅, and two presumed mono-hydroxylated derivatives of GA₄₅, one of which was tentatively identified as 3β-hydroxy-GA₄₅. Several presumed metabolites of abscisic acid were detected in both mature and immature seeds.     

Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance

The physiological characteristics of seed dormancy in Nicotiana plumbaginifolia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to germination) under favourable environmental conditions. A wild-type line shows a clear primary dormancy, which is suppressed by afterripening, whereas an abscisic acid (ABA)-deficient mutant shows a non-dormant phenotype. We have investigated the role of ABA and gibberellic acid (GA₃) in the control of dormancy maintenance or breakage during imbibition in suitable conditions. It was found that fluridone, a carotenoid biosynthesis inhibitor, is almost as efficient as GA₃ in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, fluridone and exogenous GA₃ inhibited the accumulation of ABA in imbibed dormant seeds. This reveals an important role for ABA synthesis in dormancy maintenance in imbibed seeds. Received: 31 December 1998 / Accepted: 9 July 1999     

Estimation of endogenous contents of phytohormones during internode development in <Emphasis Type="Italic">Merremia emarginata</Emphasis>

During the entire period of internode growth of Merremia emarginata contents of gibberellic acid (GA₃), phenyl-acetic acid (PAA), indole-3-acetic acid (IAA, free and conjugated) and abscisic acid (ABA, free and conjugated) were estimated by ELISA using polyclonal antibodies raised against each hormones. At the time of internode elongation free auxin content was low and increased with the decrease in the rate of elongation. In contrast, conjugated IAA showed declining trend where free IAA content was remarkably high, suggesting thereby that conjugated IAA might have mobilized during the later phase of internode development. The endogenous GA₃ contents were high as compared to other hormones; however, no significant role of GA₃ was discernible in elongation growth. Conjugated ABA contents remained very low during the elongation growth and increased thereafter.     

Pollen tube growth is affected by exogenous hormones and correlated with hormone changes in styles in <Emphasis Type="Italic">Torenia fournieri</Emphasis> L.

In the present report, we described the effects of indole-3-acetic acid (IAA), zeatin (ZT), gibberellin (GA₃), and abscisic acid (ABA) on in vitro pollen germination and pollen tube growth in Torenia fournieri L. The results showed that IAA and GA₃ stimulated in vitro pollen tube growth, ABA inhibited pollen tube growth, and ZT had no significant effect on the process. The stimulating effect of exogenous IAA was particularly distinct, and led to synchronous growth of straighter and more slender pollen tubes compared with the controls. However, no significant changes were found in the germination of the treated pollen. The auxin efflux inhibitor, 10 μM 1-N-naphthylphthalamic acid (NPA), was also found to stimulate pollen tube growth. We measured the content of hormones (free IAA, ZT, GA₃, and ABA) in the stigmas and styles before and after pollination. The hormone contents of stigmas measured 0.5 h after pollination (0.5 HAP) showed that ABA content decreased, whereas the content of IAA, ZT, or GA₃ did not change significantly. The hormone level in pollinated styles (4 HAP) when pollen tubes had grown into the middle part of style was characterized by an increase in free IAA and GA₃ and a decrease in ABA, which was in agreement with the results that IAA and GA₃ promoted but ABA inhibited pollen tube growth in vitro. Furthermore, the change of IAA level in styles was most notable, which was accordant to the fact that auxin stimulated significantly pollen tube growth in vitro. Using immunoenzyme and immunogold labeling techniques and an anti-IAA monoclonal antibody, we confirmed that free IAA was present throughout style tissues, and distributed in the nucleus and cytoplasm of style cells. All these results suggested that hormones, especially IAA, play important roles in pollen tube growth of T. fournieri. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

宁夏枸杞果实内源激素的变化及其与细胞壁成分和相关酶的关系

采用高效液相色谱技术, 研究了不同发育时期宁杞1号和宁杞5号枸杞(Lycium barbarum)果皮和种子内源激素(玉米素(ZT)、赤霉素(GA₃)、生长素(IAA)和脱落酶(ABA))含量与果实生长发育的关系。结果表明, 宁杞5号果实横纵径和单粒重均大于宁杞1号, 果实发育前期, 尤其是缓慢生长期, 是宁杞5号果实大小和重量积累的关键时期。宁杞1号种子中的生长素含量与果实横径和果实单粒重均呈极显著正相关, 与果实纵径呈显著正相关。宁杞5号果皮中玉米素含量与果实横径和单粒重均呈显著正相关, 种子中生长素含量与果实横径和单粒重均呈显著正相关。玉米素促进细胞的分裂, 而细胞数目比细胞体积对决定果实大小的作用更大; 在缓慢生长期(开花后8–25天), 宁杞5号果皮和种子中的脱落酸含量均显著小于宁杞1号。以上两点可能是宁杞5号的横纵径和单粒重均大于宁杞1号的主要原因。宁杞1号果皮中的GA₃与半纤维素酶(Cx)活性的变化相反, 说明宁杞1号果实发育前期和中期果皮中高含量的GA₃对细胞壁中Cx活性有一定的抑制作用, 从而表现出果实膨大。宁杞5号果皮中的IAA与多聚半乳糖醛酸酶(PG)和果胶酯酶(PE), ZT与PE, ABA与Cx, 种子中的ZT与PE的变化均相反, 说明宁杞5号果实发育前期和中期果皮中高含量的IAA、ZT、ABA及种子中的ZT可促进果实的膨大。推测这可能是宁杞5号果实单粒重大于宁杞1号的主要原因之一。宁杞5号果皮中的ZT和种子中的IAA可以增强Cx的活性; 宁杞1号果皮中的ABA可以增强PE的活性, 进而促进果实的成熟。     

Hormonal changes associated with fruit set and development in mandarins differing in their parthenocarpic ability

Satsuma [Citrus unshiu (Mak) Marc.] and Clementine [Citrus reticulata (Hort.) Ex. Tanaka, cv. Oroval] are two related species of seedless mandarins which differ in their tendency to set parthenocarpic fruits. Satsuma fruits naturally set parthenocarpically whereas Clementine mandarins show very low ability to set fruit in the absence of cross-pollination. The endogenous levels of gibberellins (GAs) and free and conjugated indole-acetic acid (IAA) and abscisic acid (ABA) throughout early stages of fruit development were investigated in seedless cultivars of both species. Analyses performed by full-scan combined gas chromatography-mass spectrometry (GC-MS) of extracts from ovaries at anthesis demonstrated the presence of GA₁₉, GA₂₀, GA₂₉, GA₁, GA₈, GA₃ and iso-GA₃ in Satsuma mandarin, whereas only GA₂₉, GA₃ and trace levels of GA₈ were detected in Clementine. At this developmental stage GA-like substances, as estimated by bioassay, reached their highest levels in Satsuma, while Clementine mandarins contained relatively lower levels. In both species the highest levels of free IAA were found at petal-fall stage at which time free ABA levels also peaked. Developing fruits of Clementine had higher amounts of both free IAA and ABA. In Satsuma, levels of conjugated IAA remained low throughout reproductive development whereas in Clementine they increased as the free form declined. In contrast, conjugated ABA was at low levels in Clementine but reached higher concentrations in Satsuma. These results suggest that in these mandarins the potential for setting parthenocarpic fruits is mainly influenced by the hormonal status of the fruit during the later stages of cell division and early stages of cell enlargement. Thus, the condition of low ability to set parthenocarpic fruits appears to be associated with lower levels of active GAs, lower capability to catabolize ABA to conjugated ABA and higher ability to conjugate IAA during this period.     

Identification and characterization of a gibberellin-regulated protein,which is ASR5, in the basal region of rice leaf sheaths

Gibberellins (GAs) regulate growth and development in higher plants. To identify GA-regulated proteins during rice leaf sheath elongation, a proteomic approach was used. Proteins from the basal region of leaf sheath in rice seedling treated with GA₃ were analyzed by fluorescence two-dimensional difference gel electrophoresis. The levels of abscisic acid-stress-ripening-inducible 5 protein (ASR5), elongation factor-1 beta, translationally controlled tumor protein, fructose-bisphosphate aldolase and a novel protein increased; whereas the level of RuBisCO subunit binding-protein decreased by GA₃ treatment. ASR5 out of these six proteins was significantly regulated by GA₃ at the protein level but not at the mRNA level in the basal region of leaf sheaths. Since this protein is regulated not only by abscisic acid but also by GA₃, these results indicate that ASR5 might be involved in plant growth in addition to stress in the basal regions of leaf sheaths.     

Auxin-gibberellin interaction in apical dominance: Experiments with tall and dwarf varieties of pea and bean

Summary Seedlings of dwarf and tall varieties of pea and bean, growing in John Innes Compost No. 2, were studied in relation to the effects of decapitation, indole-3-acetic acid (IAA), and gibberellic acid (GA₃) on axillary bud growth. In all varieties, GA₃ antagonized the inhibitory influence of IAA on bud growth when both hormones were applied to the upper cut end of the stem. Thus, GA₃ caused a reduction in IAA-induced correlative bud inhibition in tall, as well as in dwarf, plants. These results agree with those obtained by several workers, but contrast with some recent reports of increased apical dominance in a tall pea variety when seedlings were treated with GA₃ in addition to IAA. An attempt was made to identify the cause of opposite results being obtained by different workers, and it is considered that possibly the most important factor is mineral nutrition.     

Physiological characteristics and related gene expression of after‐ripening on seed dormancy release in rice

After‐ripening is a common method used for dormancy release in rice. In this study, the rice variety Jiucaiqing (Oryza sativa L. subsp. japonica) was used to determine dormancy release following different after‐ripening times (1, 2 and 3 months). Germination speed, germination percentage and seedling emergence increased with after‐ripening; more than 95% germination and 85% seedling emergence were observed following 1 month of after‐ripening within 10 days of imbibition, compared with <45% germination and 20% seedling emergence in freshly harvested seed. Hence, 3 months of after‐ripening could be considered a suitable treatment period for rice dormancy release. Dormancy release by after‐ripening is mainly correlated with a rapid decline in ABA content and increase in IAA content during imbibition. Subsequently, GA₁/ABA, GA₇/ABA, GA₁₂/ABA, GA₂₀/ABA and IAA/ABA ratios significantly increased, while GA₃/ABA, GA₄/ABA and GAs/IAA ratio significantly decreased in imbibed seeds following 3 months of after‐ripening, thereby altering α‐amylase activity during seed germination. Peak α‐amylase activity occurred at an earlier germination stage in after‐ripened seeds than in freshly harvested seeds. Expression of ABA, GA and IAA metabolism genes and dormancy‐related genes was regulated by after‐ripening time upon imbibition. Expression of OsCYP707A5, OsGA2ox1, OsGA2ox2, OsGA2ox3, OsILR1, OsGH3‐2, qLTG3‐1 and OsVP1 increased, while expression of Sdr4 decreased in imbibed seeds following 3 months of after‐ripening. Dormancy release through after‐ripening might be involved in weakening tissues covering the embryo via qLTG3‐1 and decreased ABA signalling and sensitivity via Sdr4 and OsVP1.     

Response of Amaranthus retroflexus L. seeds to gibberellic acid, ethylene and abscisic acid depending on duration of stratification and burial

Freshly harvested, dormant seeds of Amaranthus retroflexus were unable to germinate at 25 and 35 °C. To release their dormancy at the above temperatures, the seeds were stratified at a constant temperature (4 °C) under laboratory conditions or at fluctuating temperatures in soil or by outdoor burial in soil. Fully dormant, or seeds stratified or buried (2006/2007 and 2007/2008) for various periods were treated with exogenous gibberellic acid (GA₃), ethephon and abscisic acid (ABA). Likewise, the effects of these regulators, applied during stratification, on seed germination were determined. The results indicate that A. retroflexus seed dormancy can be released either by stratification or by autumn–winter burial. The effect of GA₃ and ethylene, liberated from ethephon, applied after various periods of stratification or during stratification, depends on dormancy level. GA₃ did not affect or only slightly stimulated the germination of non-stratified, fully dormant seeds at 25 and 35 °C respectively. Ethylene increased germination at both temperatures. Seed response to GA₃ and ethylene at 25 °C was increased when dormancy was partially removed by stratification at constant or fluctuating temperatures or autumn–winter burial. The response to GA₃ and ethylene increased with increasing time of stratification. The presence of GA₃ and ethephon during stratification may stimulate germination at 35 °C. Thus, both GA₃ and ethylene can partially substitute the requirement for stratification or autumn–winter burial. Both hormones may also stimulate germination of secondary dormant seeds, exhumed in September. The response to ABA decreased in parallel with an increasing time of stratification and burial up to May 2007 or March 2008. Endogenous GA_n, ethylene and ABA may be involved in the control of dormancy state and germination of A. retroflexus. It is possible that releasing dormancy by stratification or partial burial is associated with changes in ABA/GA and ethylene balance and/or sensitivity to these hormones.     

Interaction of jasmonic acid with some plant growth regulators in the control of apple (Malus domestica) embryo germination

Embryos isolated from dormant apple seeds were treated with jasmonic acid (JA), gibberellin A₃ (GA₃), abscisic acid (ABA) and hydrogen cyanide in darkness and in light. The chemicals were present in the culture medium continuously and simultaneously or applied for 2 days and in different sequences. All treatments stimulated embryo germination except ABA, which was strongly inhibitory. Additive effects of JA with light and with GA₃ on embryo germination were observed, whereas ABA interacted synergically with JA, HCN and light. ABA and GA₃ were most effective when applied early during embryo incubation, but the late JA treatment was more stimulatory. It is concluded that JA does not act on the regulatory pathway that is initiated by light and which leads to embryo germination through gibberellin accumulation and alkaline lipase activation. ABA and HCN appear to be involved in the control of this pathway. JA and ABA may be involved in the control of alkaline lipase activity, independently of this regulatory chain.Abbreviations ABA abscisic acid - GA₃ gibberellin A₃ - JA jasmonic acid     

Lettuce seed germination: modulation of pregermination protein synthesis by gibberellic Acid, abscisic Acid, and cytokinin

Protein synthesis in gibberellin-treated lettuce (Lactuca sativa) seeds has been studied during the lag phase between the beginning of imbibition and the first signs of radicle protrusion. When compared to the water-imbibed controls, both polyribosome populations and radioactive leucine incorporation into protein increase in the embryos of GA₃- induced seeds early in the imbibition period. Since these results are contradictory to previously published studies, the reasons for the differences are outlined and various alternative possibilities eliminated. The protocol for protein extraction, particularly the speed at which the supernatant from the seed homogenate is cleared, is important for demonstrating the GA₃-mediated changes. Embryos maintained in the dormant state by abscisic acid still conduct considerable amounts of protein synthesis, and this is enhanced by concentrations of 6-benzylaminopurine which also promote germination. Therefore, the actions of GA₃, abscisic acid, and cytokinin on lettuce seed germination are mediated, directly or indirectly, via protein synthesis.     

Hormones-induced modifications in the response of wheat flag leaf to NaCl

A field experiment was carried out to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in 33 or 66 mM NaCl and indolyl-3-acetic acid (IAA at 50 g m⁻³), gibberellic acid (GA₃ at 100 g m⁻³) or kinetin (100 g m⁻³) on some tolerance criteria in wheat flag leaf at different stages of development. At various stages of flag leaf development pretreatment with 33 or 66 mM NaCl decreased degree of succulence (particularly 66 mM), relative growth rate, net assimilation rate, relative water content, K⁺ content and K⁺/Na⁺ ratio and at the same time induced accumulation of abscisic acid and Na⁺. In the majority of cases grain pretreatment with GA₃ or kinetin and to a lesser extent with IAA alleviated either partially or completely the deleterious effect of salinity on the above mentioned parameters.     

Hormonal regulation of cotton ovule and fiber growth: Effects of bromodeoxyuridine,AMO-1618 and p-chlorophenoxyisobutyric acid

The effects of 5-bromo-2-deoxyuridine (BUdR, thymidine analogue), AMO-1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride), a growth retardant, and p-chlorophenoxyisobutyric acid (PCIB, an antiauxin) on growth (dry weight increase) and fiber development in unfertilized cotton (Gossypium hirsutum L.) ovules grown in vitro have been studied. BUdR (5 M) causes about 70% inhibition of fiber production, with little effect on ovule growth, if applied during the first 6 d of culture in the presence of GA₃ and IAA. AMO-1618, when used with GA₃ alone, causes only a small reduction in both dry weight and fiber production, but when used with IAA alone reduces both fiber production and dry weight, the effect on the latter being predominant. In the presence of both IAA and GA₃, AMO-1618 causes a small decrease in fiber production but a major decrease in dry weight. PCIB completely inhibits fiber growth but has little effect on dry weight, especially when GA₃ is present. These results indicate that GA₃ mainly promotes ovule growth while IAA is largerly responsible for fiber growth.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride - BUdR 5-bromo-2-deoxyuridine - GA₃ gibberellic acid - IAA indole-3-acetic acid - PCIB p-chlorophenoxyisobutyric acid - TFU total fiber units