The Role of Gibberellins in Early Growth and Development of Sugar Beet

Two gibberellin(GA)-like compounds were found in both rootsand shoots of sugar beet plants using the barley endosperm bioassay.One had chromatographic properties similar to GA₃ and GA₁; theother was highly non-polar, relatively inactive in the endospermassay, and may be a new gibberellin. Presence of the GA_3/1-likecompound was confirmed with the dwarf rice bio-assay. The quantityof this GA was relatively high in the root compared with theshoot at the 3–4 leaf stage when the first supernumerarycambia are being formed in the root. As plants developed throughthe 8–9 leaf stage and the 15–16 leaf stage thequantity of GA per unit fresh weight of material decreased. Application of gibberellic acid (GA₃) to the roots of youngsugar beet plants caused a significant increase in root dryweight shortly after treatment and the rate at which supernumerarycambia were produced was increased. Application of GA₃ to asingle petiole caused a significant increase in both root andshoot dry weight. GA₃ applied to either root or shoot causeda reduction in the rate of leaf formation although total leafarea per plant and shoot dry weight were unaffected. The probablerole of GA-like substances in controlling the growth and developmentof young sugar beet plants is discussed.     

Mode of Action of IAA and GA3 on Root and Shoot Growth of Epiphyllous Buds of Bryophyllum tubiflorum

Darkness and GA₃ stimulate the elongation of the first internodebut inhibit the production of roots while IAA inhibits internodalelongation but promotes the production of roots on epiphyllousbuds of Bryophylhum tubiflorum. Cycloheximide inhibits both,implicating the synthesis of proteins in the growth of bothroot and shoot. Even pre-treatment of buds with cycloheximidefor 4 h inhibits rooting as well as internodal elongation whenthese are subsequently transferred to IAA or GA₃. On the otherhand, pre-treatment with IAA or GA₃ even for 8 h does not alleviatethe inhibitory effect of cycloheximide suggesting that thereis a lag period between the application of these regulatorsand the synthesis of proteins caused by them.     

Does Cytokinin Transport from Root-To-Shoot in the Xylem Sap Regulate Leaf Responses to Root Hypoxia?

We have examined the hypothesis that cytokinins transportedfrom roots to shoots affects leaf growth, stomatal conductance,and cytokinin concentration of leaves of Phaseolus and a hybridpoplar (Populus trichocarpa x Populus deltoides) with hypoxicroots. Because cytokinins may interact with other substances,potassium and calcium concentrations were determined in xylemsap of Populus plants with hypoxic and aerated roots while gibberellin(GA) concentrations were measured in shoot tissues. Root hypoxiadecreased leaf growth and closed stomata in both species. Inboth species, fluxes of cytokinins out of the roots were reduced,but no differences in bulk leaf concentrations were measuredbetween the hypoxic and aerated plants. Shoots with aeratedroots contained slightly higher concentrations of GA₁ and GA₃than shoots from hypoxic plants. There were no differences incalcium or potassium concentrations in xylem sap between aerationtreatments. Exogenously applied cytokinins did not alleviatethe growth or stomatal responses caused by root hypoxia. Informationon the site(s) and mechanism(s) of cytokinin action and theways in which cytokinins are compartmentalized within plantcells will be required to understand the physiological significanceof cytokinin transport in the transpirational stream. Key words: Cytokinins, hypoxia, Populus, Phaseolus     

Growth and Nitrogen Accumulation in Young Tomato Plants Treated with Gibberellic Acid

The effects of foliar sprays of gibberellic acid (GA) on thegrowth of tomato plants cv. Potentate were studied in growthrooms and a glasshouse. Four sprays of GA (5 ppm) increasedleaf area and whole plant weight relative to water controlsgrown at constant temperatures (7, 17, 22, and 27 °C) for12 days, the largest plants being obtained with 5 ppm. Experimentsmade at four photoperiods (5, 10, 15, and 20 h) and at two lightintensities (7000 and 10 750 lx) showed that GA increased leafand whole plant weight at 15 h, leaf area at 10 and 15 h andstem height at all photoperiods; area, height, and weight increaseswere obtained at both light intensities, leaf growth being increasedmore by GA at 7000 lx and stem growth more at 10 750 lx. Four foliar sprays of GA (5 ppm) were combined with N supplementsapplied via leaf and/or root to plants in sand culture. Withlow supply to the roots (20 ppm N) GA failed to increase growth,but increased it at higher levels. Total N in leaf and stemwas increased by GA or by NH₄NO₃ (10 sprays 280 ppm N) at alllevels of N supplied to roots, but when applied together theeffect on total leaf N was more than additive except at thehighest level (540 ppm) GA increased the concentration of N(as per cent dry matter) in leaf and stem at all levels of Nsupplied to roots. GA and NH₄NO₃ together resulted in a greateramount and a higher concentration of N in the shoots (and usuallyalso in roots) than did NH₄NO₃ alone. Leaf thickness (as freshweight/unit area) could only be increased appreciably by sprayingwith a complete nutrient solution which reduced leaf area butnot dry weight. Growth increases induced by GA were detectable 43 days afterthe first of four sprays in the glasshouse and after 30 daysin the growth room. The persistence of GA effects was comparedwith those induced by sprays of NH₄NO₃.     

Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indole-3yl-acetic acid(IAA) were applied to roots of Phaseolus vulgaris under twodifferent light intensities and when either young or old leaveswere removed In all cases GA₃, promoted stem and lateral growth,especially when light intensity was reduced. Promotion by GA₃,of stem growth under reduced light was reduced if IAA and kinetinwere present; promotion of lateral growth under reduced lightwas reduced if IAA was added and eliminated if kinetin or kinetinplus IAA were added to GA₃. Removal of young and mature leavesreduced main stem growth; removal of young leaves promoted,and of mature leaves reduced, lateral shoot growth. We suggestthat shoot growth and apical dominance are governed by the balanceof hormones present in elongating internodes. There may be twoways of modifying this balance; firstly by altering light, temperature,or nutrients, or by applying hormones generally to the plant.Secondly, local modifications can be made by removing apicesor young leaves, or applying hormones in lanolin to specificareas. Knowledge of both the general and local conditions maybe necessary for a complete understanding of apical dominance.     

Mechanical Stress and Gibberellin: Regulation of Hollowing Induction in the Stem of a Bean Plant, Phaseolus vulgaris L.

In pole bean plants, mechanical stress (MS) inhibited stem elongationand induced radial thickening of the stem. Application of uniconazole,an inhibitor of gibberellin biosynthesis, also reduced stemgrowth but had no effect on stem diameter. Both MS and uniconazolesignificantly reduced hollowing of the first internodes, butonly the former increased ethylene evolution from the firstinternode. Application of GA₃ increased the length of the firstinternode and decreased its diameter in bush bean plants; thiswas accompanied by a significant promotion of stem hollowing.Aminooxyacetic acid (AOA) decreased ethylene evolution fromthe GA₃-treated internodes, though it did not reduce the GA₃-inducedhollowing of the first internodes. Application of GA₃ affectedneither ethylene evolution nor cellulase activity in the firstinternodes of bush bean plants. Application of GA₃ stimulatedmuch greater cell elongation in the center of pith tissue thanin the outer surrounding tissues, suggesting a possible physicalbreakage of the inner cells, which leads the hollowing of beanstems. These results suggest that gibberellin is a factor responsiblefor stem hollowing in bean plants. Because MS is known to reducegibberellin content in bean plants [Suge (1978) Plant Cell Physiol.21: 303] MS may inhibit stem hollowing by reducing the amountof endogenous gibberellin. (Received July 1, 1994; Accepted November 8, 1994)     

Gibberellins and Stem Growth as Related to Photoperiod in Silene armeria L

Stem growth and flowering in the long-day plant Silene armeria L. are induced by exposure to a minimum of 3 to 6 long days (LD). Stem growth continues in subsequent short days (SD), albeit at a reduced rate. The growth retardant tetcyclacis inhibited stem elongation induced by LD, but had no effect on flowering. This indicates that photoperiodic control of stem growth in Silene is mediated by gibberellins (GA). The objective of this study was to analyze the effects of photoperiod on the levels and distribution of endogenous GAs in Silene and to determine the nature of the photoperiodic after-effect on stem growth in this plant. The GAs identified in extracts from Silene by full-scan combined gas chromatography-mass spectrometry (GC-MS), GA₁₂, GA₅₃, GA₄₄, GA₁₇, GA₁₉, GA₂₀, GA₁, GA₂₉, and GA₈, are members of the early 13-hydroxylation pathway. All of these GAs were present in plants under SD as well as under LD conditions. The GA₅₃ level was highest in plants in SD, and decreased in plants transferred to LD conditions. By contrast, GA₁₉, GA₂₀, and GA₁ initially increased in plants transferred to LD, and then declined. Likewise, when Silene plants were returned from LD to SD, there was an increase in GA₅₃, and a decrease in GA₁₉, GA₂₀, and GA₁ which ultimately reached levels similar to those found in plants kept in SD. Thus, measurements of GA levels in whole shoots of Silene as well as in individual parts of the plant suggest that the photoperiod modulates GA metabolism mainly through the rate of conversion of GA₅₃. As a result of LD induction, GA₁ accumulates at its highest level in shoot tips which, in turn, results in stem elongation. In addition, LD also appear to increase the sensitivity of the tissue to GA, and this effect is presumably responsible for the photoperiodic after-effect on stem elongation in Silene.     

Effects of a Plant-Growth Regulat or, Prohexadione-Calcium (BX-112), on the Endogenous Levels of Gibberellins in Rice

The effects of the plant-growth regulator, prohexadione-calcium,on the levels of the endogenous gibberellins in rice shootswere measured by GC-SIM using ²H-labeled gibberellins as internalstandards. The compound was applied at the 4-leaf stage andshoots were harvested 5 and 12 days after treatment. Plant lengthwas reduced to 78% and 66%, respectively, relative to controlby application of the compound at 1 and 30 mg m^–2, whenplant length was measured 12 days after treatment. The levelof GA, was reduced to 36% and 18%, respectively, relative tocontrol in the treated plants. The levels of GA₁₉and GA₂₀ increasedbut that of GA₄₄ was reduced in the treated plants. The levelof GA₅₃ was unchanged. These results suggest that primary modeof action of the compound in vivo is the inhibition of the 3ß-hydroxylationof GA₂₀ to GA₁ and further support the hypothesis that GA₁ notGA₁₉ nor GA₂₀ is active in promoting shoot elongation in rice. ³Present address: Frontier Research Program, RIKEN, Wakoshi,Saitama, 351-01 Japan.     

Evidence that Daminozide, but not Two Other Growth Retardants, Modifies the Fate of Applied Gibberellin A9 in Chrysanthemum morifolium Ramat

Interactions between three growth retardants and gibberellinA₉ (GA₉) in Chrysanthemum morifolium Ramat. cv. Bright GoldenAnne grown in short days have revealed that the particular retardantemployed modifies the response to this gibberellin. When plants were given a foliar spray of daminozide (a substitutedsuccinamic acid), the effects of a subsequent application ofGA₉ to each lateral shoot, on both stem length and the rateof inflorescence development, were relatively small. However,GA₉ was highly active on plants previously sprayed with piproctanylbromide (a quaternary ammonium, piperidinium compound) or onthose given a compost drench of chlorphonium chloride (a quaternaryphosphonium retardant). In the absence of GA₉ all three retardantsreduced stem length and delayed flowering. Irrespective of the extent of the responses to various dosesof GA₉ (1–50 µg per shoot), a close relationshipwas maintained between internode extension and earliness offlowering, as in previous studies with retardants and othergibberellins. On plants which had received chlorphonium chlorideGA₃ and GA₁₃ were highly active and poorly active, respectively. The data suggest that daminozide could act as a retardant notonly by blocking the biosynthesis of gibberellins but also,wholly or partly, by restricting the metabolism or action ofendogenous gibberellins.     

Effects of Gibberellin on Shoot Development in the dgt Mutant of Tomato

The morphological effects of gibberellin A₃ (GA₃) on the dgtmutant of tomato were investigated. The mutant effectively showedthe normal range of responses, including a promotion of stemlength due to an increased number of longer internodes, a dramaticincrease in apical dominance, and effects on leaf shape andcolour. In the case of stem elongation, the quantitative responseof the mutant was greater than normal. The morphological abnormalitiescharacteristic of the dgt mutant, such as horizontal growth,a thin stem and hyponastic leaves, were not normalized by GA₃. It is concluded that the demonstrated lack of response to auxinof the dgt mutant does not impair its gibberellin responses. Tomato, gibberellin, auxin, mutant, shoot development     

An Analysis of the Effects of Gibberellic Acid on Tomato Leaf Growth

The effects of four consecutive daily sprays of gibberellicacid (GA₃) on the growth of leaves of young tomato plants cv.Potentate were studied. Total leaf weight and area were increasedby GA₃. The percentage changes were larger in the younger leavesthan in the older but the absolute increases of the middlleleaves accounted for most of the total response. Chlorophyllcontent, both total and per unit weight, was reduced by GA inthe older leaves and increased in the younger; on an area basisit was reduced in all but the youngest leaves. Palisade cell length and palisade cell number per unit sectionlength were reduced by GA₃ in the oldest leaves and increasedin the youngest. There were larger intercellular spaces in bothmesophyll layers and a larger transectional area of the mid-ribsof the oldest and two youngest leaves in GA₃ plants. The ‘surfaceareas’ of epidermal cells were also increased by GA₃ treatment.Leaf fresh weight per unit area was only a true index of laminathickness in the two oldest leaves.     

The Role of Roots in Control of Bean Shoot Growth

Restriction of root growth by growing bean plants (Phaseolusvulgaris L.) in very small pots led to the development of dwarfplants. The leaves of those plants were smaller and their internodesshorter than those of control plants which were grown in largerpots and had developed a more extensive root system. A largequantity of starch—much more than in control plants —accumulated in the leaves and shoots of the dwarf plants. Increasingthe amount of minerals which was supplied to the roots, enhancedleaf growth of the control plants but failed to affect the dwarfones, in spite of the fact that in both cases the treatmentincreased the content of N, P and K in all the plant organs.The leaf water content was similar in both treatments, but theleaf water potential was higher in the dwarf plants. Exogenousapplication of gibberellic acid (GA₃) to the dwarf plants overcamethe reduction of stem growth completely, and that of the leavespartially. Application of the cytokinin, benzyladenine (BA)did not affect stem growth, but increased that of the primaryleaves. A combined supply of GA₂ + BA restored completely thegrowth of the stem and the primary leaves, and partially thatof the trifoliate leaves. It is concluded that a limited rootsystem restricts shoot growth through an hormonal system inwhich at least gibberellins and cytokinins are involved, andthat the dwarfing is not a consequence of mineral or assimilatedeficiency, or due to water stress. Phaseolus vulgaris L., leaf growth, stem growth, root restriction, gibberellic acid, benzyladenine, cytokinin     

The roles and interactions of ethylene with gibberellins in the far-red enriched light-mediated growth of <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> seedlings

Wild type (WT) tomato seedlings responded to a low red to far-red (R/FR) ratio with increased stem elongation, similar leaflet area expansion and lower shoot ethylene levels. The levels of endogenous growth-active GA₁ and its immediate precursor GA₂₀ were decreased by low R/FR ratio, whereas the levels of GA₁ catabolite, GA₈, increased. To examine the interaction of ethylene with GAs in regulating tomato shoot growth under low R/FR ratio, transgenic (T) seedlings bearing Le-ACS2 and Le-ACS4 antisense mRNA were utilized. Low R/FR ratio increased stem elongation and decreased ethylene levels in T tomato shoots, as it did in WT shoots. However, T stems were significantly taller than the WT stems under low R/FR ratio. Leaflet areas were significantly larger for T, than WT seedlings under both R/FR ratios. Low R/FR ratio did not decrease endogenous levels of GA₁ and GA₂₀ in T shoots, but did increase GA₈ levels, which were higher than in WT shoots. These results, and hormone/inhibitor application studies, showed that in tomato shoots subjected to low R/FR ratio, GAs play a growth-promotive role in stem elongation, whereas ethylene is growth-inhibitory. Further, these results may imply that decreasing ethylene production under low R/FR ratio causes increases in stem elongation and GA levels.     

Gibberellin Metabolism and Transport During Germination and Young Seedling Growth of Pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.)

The role of gibberellins (GAs) during germination and early seedling growth is examined by following the metabolism and transport of radiolabeled GAs in cotyledon, shoot, and root tissues of pea (Pisum sativum L.) using an aseptic culture system. Mature pea seeds have significant endogenous GA₂₀ levels that fall during germination and early seedling growth, a period when the seedling develops the capacity to transport GA₂₀ from the cotyledon to the shoot and root of the seedling. Even though cotyledons at 0–2 days after imbibition have appreciable amounts of GA₂₀, the cotyledons retain the ability to metabolize labeled GA₁₉ to GA₂₀ and express significant levels of PsGA20ox2 message (which encodes a GA biosynthesis enzyme, GA 20-oxidase). The large pool of cotyledonary GA₂₀ likely provides substrate for GA₁ synthesis in the cotyledons during germination, as well as for shoots and roots during early seedling growth. The shoots and roots express GA metabolism genes (PsGA3ox genes which encode GA 3-oxidases for synthesis of bioactive GA₁, and PsGA2ox genes which encode GA 2-oxidases for deactivation of GAs to GA₂₉ and GA₈), and they develop the capacity to metabolize GAs as necessary for seedling establishment. Auxins also show an interesting pattern during early seedling growth, with higher levels of 4-chloro-indole-3-acetic acid (4-Cl-IAA) in mature seeds and higher levels of indole-3-acetic acid (IAA) in young root and shoot tissues. This suggests a changing role for auxins during early seedling development.     

Gibberellic-Acid-Promoted Transport of Assimilates in Stems of Phaseolus vulgaris. Effects on Assimilate Accumulation by the Sink

Under conditions of apoplastic unloading from the sieve element-companioncell (se-cc) complexes in fully-elongated stems of Phaseolusvulgaris plants, gjbberellic acid (GA₃ stimulated in vitro uptakeof [¹⁴C]sucrose by the stem tissues. The GA₃, response dependedupon the incubate containing calcium ions and being bufferedat pH 6. The GA₃ action could be accounted for by a reductionin the Michaelis-Menten constant of the uptake process. Promotedtransport by GA₃ in the decapitated stems resulted in all thetissues accumulating higher levels of [¹⁴C]photosynthates. Comparisonof this response with that for in vitro uptake of [¹⁴C]sucroseindicated that GA₃ stimulation of the sucrose uptake processcontributed significantly to the accumulation of photosynthatesby the pith alone. The bulk of enhanced photosynthate accumulationby the remaining stem tissues can be accounted for by a GA,-inducedelevation of the apoplast sucrose concentration. In terms ofonset and change in rate, the time-course kinetics of GA₃ stimulationof [¹⁴C]photosynthate transport and of in vitro [¹⁴CJsucroseuptake were found to be similar. It is proposed that GA₃ promotionof photosynthate accumulation by the pith tissues is a minorcontributing factor to GA₃ regulation of phloem translocation Phaseolus vulgaris L., french bean, stem, assimilate transport, gibberellic acid, rink accumulation     

Gibberellin physiology of safflower: endogenous gibberellins and response to gibberellic acid

Endogenous gibberellins (GAs) were extracted from safflower (Carthamus tinctorius L.) stems and detected by capillary gas chromatography-mass spectrometry from which GA₁, GA₃, GA₁₉,, GA₂₀, GA₂₉, and probably, GA₄₄ were detected. The detection of these GAs suggests that the early 13-OH biosynthetic pathway is prevalent in safflower shoots. Deuterated GAs were used as internal standards and GA concentrations were determined in stems harvested at weekly intervals. GA₁ and GA₁₉ levels per stem increased but concentrations per gram dry weight decreased over time. GA₂₀ was only detected in young stem tissue.Gibberellic acid (GA₃) was also applied in field trials and both GA₃ and the GA biosynthetic inhibitor, paclobutrazol, were applied in growth chamber tests. GA₃ increased epidermal cell size, internode length, and increased internode cell number causing stem elongation. Conversely, paclobutrazol reduced stem height, internode and cell size, cell number and overall shoot weight. In field tests, GA₃ increased total stem weight, but decreased leaf weight, flower bud number and seed yield. Thus, GA₃ promoted vegetative growth at the expense of reproductive commitment. These studies collectively indicate a promotory role of GAs in the control of shoot growth in safflower, and are generally consistent with gibberellin studies of related crop plants. Author for correspondence     

Effects of a New Plant Growth Regulator Prohexadione Calcium (BX-112) on Shoot Elongation Caused by Exogenously Applied Gibberellins in Rice (Oryza sativa L.) Seedlings

The effects of a novel plant growth regulator (PGR) prohexadionecalcium (BX-112; calcium 3,5-dioxo-4-propionylcyclohexanecarboxylate)on shoot elongation caused by exogenously applied GA₁, GA₃,GA₄₎ GA₁₉ and GA₂₀ were investigated in rice (Oryza sativa L.cv. Nihonbare and cv. Tan-ginbozu) seedling test. Dependingon the dose, BX-112 reduced shoot elongation in both cultivarscaused by GA₁₉ and GA₂₀, but not by GA₁. When a high dose ofBX-112 (e.g. 250 ng/plant and over) was applied with GA₁, orGA₄, shoot elongation was even promoted. This promotive effect,however, was not observed with GA₃. These results suggest thatBX-112 inhibits gibberellin (GA) biosynthesis in the rice plantat the 3ß- and 2ß-hydroxylation of GAs,namely steps of activation and inactivation, respectively. (Received September 6, 1989; Accepted November 27, 1989)     

Gibberellins and the Growth of Excised Tomato Roots: Comparison of gib-1 Mutant and Wild Type and Responses to Applied GA3 and 2S, 3S Paclobutrazol

Clones of excised roots of wild type tomato (Lycopersicon esculentum,Mill., cv. Moneymaker) and a near-isogenic GA-deficient mutant(gib-1/gib-1) were cultured in modified White's medium containing1.5% w/v sucrose. The linear elongation rate of the main axisof the gib-1 mutant was 40% less than that of the wild type.In addition, the main axis of the gib-1 mutant was thicker thanthat of the wild type but main axis volume growth was the samein both genotypes, indicating that the gib-1 allele was affectingthe orientation of root expansion. There was no evidence tosuggest that the gib-1 allele affected either the pattern ofemergence or the density of lateral roots. Elongation rate andthickness of gib-1 mutant roots were restored to those of thewild type by the addition of low concentrations (0.1–1.0µM) of gibberellic acid (GA3). These concentrations ofGA3 caused a slight reduction in extension growth of wild typeroots, indicating that endogenous GAs were not limiting elongationof normal roots in culture. The GA biosynthesis inhibitor, 2S,3S paclobutrazol, at 0.1 µM, significantly reduced elongationof wild type roots and this inhibition was counteracted by 0.1µM GA₃. It is concluded that the difference in growthbetween the gib-1 mutant and the wild type represented GA-dependentgrowth. Low concentrations of 2S, 3S paclobutrazol caused onlya small (5%) reduction in growth of the gib-1 mutant and thisgrowth inhibition was not reversed by GA₃. This observation,and the fact that gib-1 mutant roots grow in the absence ofadded GA₃, suggested that part of root growth was GA-independent.However, the possibilities that the gib-1 mutant is ‘leaky’and that paclobutrazol does not inhibit GA biosynthesis completelycannot be excluded. Key words: gib-1 mutant, gibberellic acid, Lycopersicon esculentum, 2S, 3S paclobutrazol, root growth     

Shoot Inversion-induced Ethylene Production in the Diageotropica Tomato Mutant

Shoot inversion was found to inhibit shoot elongation over 24h in the diageotropica (dgt) mutant tomato and its isogenicparent, VNF8, by 55% and 51%, respectively. Previous studieswith normal tomato and other species would suggest that gravitystress-induced ethylene production in the inverted shoot retardselongation. Since exposure of the diageotropic shoot of thedgt mutant tomato to ethylene restores normal upward growth,it might appear that dgt is defective in its capacity to produceethylene. That shoot inversion did stimulate some ethylene productionand that the ethylene action inhibitor, AgNO₃, largely negatedthe inhibiting effect of shoot inversion on elongation in dgtstrongly suggest that the ethylene produced in the invertedshoot was responsible for its retardation of growth. Althoughethylene production in the slower growing dgt was much lessthan that in the faster-growing VNF8, the dgt shoot was foundto be much more sensitive to ethylene. Shoot inversion, ethylene, shoot elongation, diageotropica (dgt), auxin