Gibberellin-Induced Changes in Starch Content in Isolated Chloroplasts of Light-Grown Cucumber Hypocotyls

Gibberellin A₃ (GA₃) was found to reduce the starch contentin chloroplasts isolated from light-grown cucumber (cv. Aonagajibai)hypocotyls. Chloroplasts incubated with 50 mM sucrose showedan increase in starch content. The GA₃-induced reduction occurredboth in the presence and absence of exogenous sucrose. GA₃ hadno effect on the level of starch already formed from exogenoussucrose. (Received April 4, 1984; Accepted June 7, 1984)     

Auxin-gibberellin relationships in their effects on hypocotyl elongation of light-grown cucumber seedlings. Responses of sections to auxin, gibberellin and sucrose

The sensitivity of light-grown cucumber hypocotyl sections toIAA and GA₃ depends on the degree of aging of the tissue. Agreater response to GA₃ was obtained with young tissue, whilethat to IAA was obtained with relatively old tissue. The responseto IAA reached a maximum at about 15 hr of incubation; the youngerthe tissue the earlier the time of maximum response. The responseto GA₃ continued for more than 70 hr with a constant growthrate. Very young tissue started to respond to GA₃ without lagtime; the older the tissue the later the start of the response. Sucrose (2%) inhibited IAA-induced elongation, while there wasa distinct synergism between GA₃ and sucrose. The promotiveeffect of sucrose on GA₃-induced elongation was also obtainedwhen sections were pretreated with sucrose, then transferredto GA₃. Mannitol (1%) strongly inhibited IAA-induced elongation,but not GA₃-induced elongation. (Received December 6, 1972; )     

Gibberellin-Induced Suppression of Chloroplast Starch Formation from Exogenous Sucrose in Isolated Epidermis of Light-Grown Cucumber Hypocotyls

The effects of gibberellin A₃(GA₃) on chloroplast starch formationfrom exogenous sucrose in epidermal strips of light-grown cucumber(Cucumis sativus L. cv. Aonagajibai) hypocotyls were studied.Chloroplast starch formation was measured by counting microscopicallythe number of I₂KI stained chloroplasts. In the presence ofsucrose (1–50 mM) and in light, chloroplast starch formationoccurred rapidly for 5 hr and then the rate declined. GA₃ (100µM) simultaneously supplied with sucrose clearly suppressedboth the rate and the degree of starch formation. When the epidermiswas preincubated in the dark with sucrose in the presence orabsence of GA₃ and then post-incubated in light with bufferonly in the presence or absence of GA₃, starch formation wassuppressed to the same degree by GA₃ given either in the pre-or post-incubation period. When the epidermis was preincubatedin the dark with GA₃ alone and then transferred to light forpost-incubation with sucrose alone, GA₃ suppressed the initialrate of starch formation during the post-incubation period.The degradation of chloroplast starch formed in advance fromexogenous sucrose in light was not significantly affected byGA₃ These results are discussed in relation to the mechanismof the GA₃ action and also to the GA₃-induced decrease in theosmotic potential of the cell. (Received February 2, 1982; Accepted May 31, 1982)     

Effect of gibberellic acid on starch content of soybean (Glycine max L.) and its correlation with extension growth

This investigation was undertaken to study the effect of GA₃on extension growth of Glycine max L. and on starch contentof its individual internodes at maturity. The effect on hydrolyticactivity of the extract of different internodes was also studied.GA₃ stimulates the extension growth of stem by increasing theelongation of those internodes which are either in the processof elongation or being differentiated at the time of treatment.Starch content decreases with the position of the internode(from base upwards) on the intact plant. Corresponding internodeshave minimum starch content in 100 ppm GA₃-treated plants andmaximum in the controls. Internodes which show the maximum elongationdue to GA₃ treatment, show the least starch content and alsoshow maximum hydrolytic activity during the period of elongation.It is suggested that enhanced extension growth is brought aboutby enhanced mobilization of reserve food by GA₃. (Received November 21, 1967; )     

The role of gibberellins in the growth of floral organs of Pharbitis nil

Evidence that the synthesis of GA₃ is involved in the growthof floral orga'ns of Pharbitis nil is presented. GAs in floralorgans at different developmental stages were surveyed usingTLC followed by the bioassay with two dwarf rice seedlings,‘Tanginbozu’ and ‘Waito-C’. The amountof GAs in the petal and stamen increased rapidly after the petalemerged from calyx, reached a maximum 12 hr before anthesis,then declined markedly thereafter. The GA content in the calyxremained unchanged before and after anthesis, and that in thepistil increased after anthesis. Pharbitis flowers containedat least two active GAs, one of which was probably GA₃, theother appeared to be GA₁₉. GA₃ was detected in relatively largeamounts in both the petal and stamen during their rapid elongation.In the calyx, which showed little increase in fresh weight duringrapid flower growth, GA₉ was the dominant GA. Exogenously suppliedGA₃ promoted elongation of sections in excised young filaments.Sucrose was necessary for definite growth promotion by GA₃.GA₁₉ had little effect on filament elongation, and IAA was ratherinhibitive. (Received July 29, 1972; )     

Interaction of Gibberellin A3 and Ancymidol in the Growth and Cell-Wall Extensibility of Dwarf Pea Roots

Effects of ancymidol (Anc) and gibberellin A₃ (GA₃) on rootgrowth, osmotic concentration and cell-wall extensibility ofthe root were investigated in the gibberellin-sensitive cultivarof dwarf pea, Little Marvel. Anc strongly suppressed elongationof both shoots and roots in darkness. Although the elongationof shoots of this dwarf cultivar was severely retarded in thelight, it was repressed still further by Anc. GA₃ promoted elongationof shoots both in the presence and in the absence of Anc, whereasit reversed suppression of root elongation by Anc. The concentrationof GA₃ required for the recovery of root elongation was lowerthan that required for the promotion of shoot elongation. Treatmentwith Anc led to increased thickening of roots with increasednumbers of cells per cross section and lateral expansion ofcells in the cortex. GA₃ had little effect on the osmotic concentration of cell sapobtained from root segments. Anc-treated roots did not respondto acid solutions by elongation, whereas GA₃-treated roots respondednormally to such solutions. Anc suppressed but GA₃ enhancedthe cell-wall extensibility of roots as measured in vivo andin vitro. These results indicate that a low concentration of gibberellinplays a role in normal elongation of roots by maintaining theextensibility of the cell wall in this gibberellin-sensitivedwarf pea. (Received January 17, 1994; Accepted July 15, 1994)     

Mitotic Activities and Levels of Nuclear DNA in the Apical Meristem of Silene armeria (strain SI.2) Following Application of Gibberellin A3

Strain S1.2 of Silene armeria was grown under an 8h-photoperiodand treated with GA₃ every day for 20 days. This growth substancecaused stem elongation, but no flowering in this long-day plant.Changes in the mitotic index and DNA content of cells in thevarious zones of the apical meristem before, during and afterGA₃ treatment were described. Mitotic activity and increasein the proportion of nuclei at the 4C level (S+G₂ phase of thecell cycle) were strongly stimulated in the rib-meristem, andto a lesser extent in the lateral zone, but not in the axialzone. This stimulation of apical activity reached a peak aftertwo GA₃ treatments and then declined gradually, so that after20 days the activity in GA₃-treated meristems was lower thanthat in untreated controls; at this point most cells were inthe G₁ phase. When the GA₃ treatment was discontinued, there was a gradualincrease in the mitotic activity which ultimately reached thesame level as that in controls. Stem elongation ceased and leavesformed aerial rosettes. It is concluded that in vegetative plants of strain S1.2 ofSilene armeria GA₃ acts mainly on the rib-meristem cells whichresults in stem elongation. Lack of response in the axial cellsexplains why GA₃ fails to induce flowering in this strain ofSilene armeria. (Received June 18, 1983; Accepted August 3, 1983)     

Interaction of a Brassinosteroid with IAA and GA3 in the Elongation of Cucumber Hypocotyl Sections

A synthetic brassinosteroid, 22,23(S,S)-homobrassinolide (hBR),was examined for its interaction with IAA and GA₃ in the elongationof hypocotyl sections of light-grown cucumber (Cucumis salivusL. cv. Aonagajibai) seedlings. hBR alone was less active thanIAA. Its optimal concentration was around 10 µM and thelowest effective concentration between 10 and 100 µM,which is more than 100 times higher than that of brassinolide.hBR was more active in sections from younger seedlings. Itsgrowth-promoting effect was negated or greatly reduced by inhibitorsof auxin-induced elongation such as p-chlorophenoxyisobutyricacid and kinetin. hBR acted synergistically with IAA and 2,4-Dbut not with GA₃ showing only an additive effect. Sequentialtreatment of sections with hBR and then with IAA also resultedin synergistic enhancement of auxininduced elongation, but whenthe order of treatment was reversed, hBR was inactive. The synergisticeffect was obtained with 1 h pretreatment with hBR and couldbe reduced by subsequent washing with water. There was no sequentialinteraction between hBR and GA₃. The synergistic pretreatmenteffects of hBR and GA₃ were simply additive to each other. Amembrane-bound ATPase inhibitor, dicyclohexylcarbodiimide, inhibitedthe hBR-induced elongation, but did not affect GA₃-induced elongation.The findings led to the conclusion that brassinosteroids enhanceauxin action and possess growth-promoting activity which isindependent of that of gibberellin. (Received November 9, 1984; Accepted February 18, 1985)     

Factors Influencing the Distribution of Growth Between Stem and Axillary Buds in Decapitated Bean Plants

Phaseolus multiflorus plants at three stages of developmentwere decapitated either immediately below the apical bud orlower down at a point 1 cm above the insertion of the primaryleaves. Growth regulators in lanolin were applied to the cutstem surface. IAA always inhibited axillary bud elongation anddry-matter accumulation, and enhanced internode dry weight butnot elongation. GA₃ applied below the apical bud greatly increasedinternode elongation and dry weight, but simultaneously reducedbud elongation and dry-weight increase. Application of GA₃ 1cm above the buds had no effect on bud elongation in the youngestplants, but enhanced their elongation in the two older groups.IAA always antagonized GA₃-enhancement of internode extensiongrowth, whereas its effects on GA₃-enhanced dry-matter accumulationdepended on the stage of internode development. Bud elongationwas greater in plants treated with GA₃+IAA than in plants treatedonly with IAA, except in the youngest plants decapitated immediatelybelow the apical bud, where GA₃ caused a slight increase inIAA-induced bud inhibition. GA₃ increased inhibition of buddry weight by IAA in the two youngest groups of plants, butslightly reduced it in the oldest plants. No simple compensatorygrowth relationship existed between internode and buds. It wasconcluded that, (1) auxin appears to be the principal growthhormone concerned in correlative inhibition, and (2) availabilityof gibberellin to internode and buds is of importance as a modifyingfactor in auxin-regulated apical dominance by virtue of itslocal effects on growth in the internode and in the buds.     

Enhancement of Gibberellic Acid-stimulated Hypocotyl Elongation of Lettuce (Lactuca sativa L. cv. Grand Rapids) by Phlorizin and Light

The interaction of light, gibberellic acid (GA₃), and phlorizinin the growth of lettuce (Lactuca sativa L. cv. ‘GrandRapids’) hypocotyls was investigated. At all concentrationsof GA₃, phlorizin enhanced GA₃-induced growth at luminous intensitiesabove 50 ft-c (continuous light). Without GA₃, phlorizin hadno effect on hypocotyl growth in the light but it inhibitedgrowth in the dark. Both seedlings and hypocotyl sections respondedto phlorizin in the presence of GA₃. There was no iteractionbetween phlorizin and KCl. Water-growth was severly inhibitedby light. GA₃,-induced growth was slightly inhibited by light,and then only at luminous intensities above 50 ft-c. Thus, relativeto H₂O-growth, GA₃-induced growth increased with increasingluminous intensity up to 450 ft-c, where it reached saturation.It seems that a synergism may exist between light and GA₃ aswell as between phlorizin and GA₃. Lactuca sativa L, lettuce, hypocotyl elongation, gibberellic acid, phlorizin, light     

Embryo Water Status and Development of the Recalcitrant Species Quercus robur L: Determination of Water Relations Parameters by Pressure-Volume Analysis

The water status and water content of embryos of Quercus roburhave been determined during development. Using psychrometers,changes in osmotic potential at full imbibition and the proportionof water at zero reciprocal water potential, R₀, were estimatedfrom curves of embryo relative water content and reciprocalwater potential. The specific moisture content of embryos decreasedduring development, with a concomitant increase in the osmoticpotential. However, R₀ also increased such that, during thelast four weeks of development, there was little net changein the content of osmoticum per dry weight. Evidence is presentedthat starch stored in the cotyledon may be the major site ofmatrix-bound water, R₀. Isolated embryonic axes had a slightly higher osmotic potentialthan the whole embryo but the R₀ was much lower. The differencesbetween whole embryo and axis water relations parameters emphasizethe need to take account of R₀ when discussing seed water statusand survival. The results are considered in relation to currentmodels of seed water status and recalcitrant behaviour. Key words: Quercus robur L., embryo water relations, development, starch     

Auxin-gibberellin relationships in their effects on hypocotyl elongation of light-grown cucumber seedlings II. Effect of GA3-pretreatment on IAA-induced elongation

IAA-induced growth of light-grown cucumber hypocotyl sectionsis markedly enhanced by GA₃-pretreatment of the sections; thereis a distinct synergism between IAA and GA₃. Water pretreatmentalso enhances IAA-induced growth. On the other hand, IAA-pretreatedsections showed practically no further growth in response topost treatment with GA₃. The enhancing effect of GA₃ is obtainedwith only 30 min pretreatment, the maximum effect occuring with2 hr pretreatment. Pretreatment longer than 8 hr is less effective.This enhancing effect of GA₃ can be observed soon after posttreatment with IAA. The response of GA₃-pretreated sectionsto IAA is greater in pretreatment with higher concentrationsof GA₃, and higher degrees of synergism between IAA and GA₃are obtained at IAA concentrations less than 10^-4 M. This synergisticinteraction between GA₃ and IAA is more marked in aged hypocotylsections than in young sections. From these results we concludedthat gibberellin sensitizes hypocotyl cells to the subsequenteffect of auxin on cell elongation. (Received October 6, 1973; )     

Actinomycin D Inhibits the GA3-Induced Elongation of Azuki Bean Epicotyls and the Reorientation of Cortical Microtubules

Actinomycin D inhibited the elongation of epicotyl segmentsfrom azuki bean seedlings that was induced by simultaneous treatmentwith IAA and GA₃. The drug also inhibited the elongation ofthe segments that was caused by IAA alone when it was appliedtogether with IAA. When the segments were pretreated with GA₃and then incubated with IAA, GA₃ promoted the elongation causedby IAA and brought about a predominance of transverse corticalmicrotubules (MTs) in the epidermal cells of the segments. Thechange in the arrangement of MTs caused by pretreatment withGA₃ was evident 1 h after the start of subsequent incubationwith IAA when the effect of pretreatment with GA₃ on the elongationhad not yet become apparent. Pretreatment with GA₃ did not causeany change in the arrangement of MTs when GA₃-pretreated segmentswere not incubated subsequently with IAA. Although actinomycinD applied before treatment with IAA did not inhibit the IAA-inducedelongation, the drug diminished the promotion of the elongationcaused by pretreatment with GA₃ and prevented GA₃ from bringingabout a predominance of transverse MTs when the drug was appliedduring the pretreatment with GA₃. GA₃-induced synthesis of mRNA seems to be involved in the promotionby GA₃ of IAA-induced elongation and in the GA₃-induced rearrangementof cortical MTs. (Received June 15, 1993; Accepted August 16, 1993)     

Light-controlled sugar-starch interconversion in epidermal chloroplasts of light-grown cucumber hypocotyl sections and its relationship to cell elongation

Sugar-starch interconversion in epidermal chloroplasts of light-grown cucumber hypocotyl sections as a regulatory mechanism of the osmotic potential of the cell was studied in relation to cell elongation. The presence of chloroplasts in epidermal cells was confirmed by electron microscopy, and also the chloroplasts were shown to act as the site of sucrose-starch interconversion. Chloroplast starch formation was induced by light, which was more distinct in the presence of sucrose (50 mM). The starch formation was microscopically detectable even at 1 hr incubation in the light with sucrose. On the other hand, no starch formation was observed in the dark both in the presence and absence of sucrose. Red light was effective, but not blue light. A photosynthetic inhibitor, 3-(4-chlorophenyl)-1:1-dimethylurea, also inhibited starch formation. Thus, epidermal chloroplast starch formation was induced under conditions where cell elongation is small and the osmotic potential (Ψ ₀) of the epidermal cell is high. The sugar quantity (free sugar and reducing sugar) as the osmotica of the cell was larger in the dark than in the light, whereas the quantity of starch was greater in the light than in the dark. It is assumed from these results that one of the regulatory mechanisms of the osmotic potential of the epidermal cells in sugar-starch interconversion which occurs in epidermal chloroplasts.     

Gibberellin-colchicine interaction in elongation of azuki bean epicotyl sections

In azuki bean (Azukia angularis = Vigna angularis) epicotylsections, gibberellin A₃ (GA₃) enhanced the growth promotingeffect of indoleacetic acid (IAA), but showed no growth effectwhen applied alone. Sections showed practically no cell division.The promoting effect of GA₃ on section growth seems to be dueto its promoting effect on cell elongation. The diameters of sections treated with IAA increased, but thediameters of sections treated with GA₃ together with IAA remainedconstant. GA₃ seems to suppress cell expansion in a directiontransverse to the cell axis. Colchicine at a concentration with no inhibiting effect on IAA-inducedelongation almost completely reversed the effect of GA₃ On the basis of these results, the participation of wall microtubulesin GA₃-induced elongation is discussed. (Received October 22, 1971; )     

Effect of Hormones on Sucrose Uptake and on ATPase Activity of Citrus sinensis L. Osbeck Leaves

Carbohydrate accumulation in young, fully expanded leaves ofCitrus sinensis L. Osbeck is affected by the presence of thefruitlet on the shoot. Previous work gave evidence that gibberellinsmay be involved in this 'fruit effect'. In the present workwe have studied the effect of gibberellic acid (GA₃) on ¹⁴C-sucroseuptake by leaf discs and whether its action could be due toa modulation of the plasma membrane ATPase, which maintainsthe H⁺ gradient that drives H⁺/sucrose co-transport. The effect of GA₃ on ¹⁴C-sucrose uptake depended on the osmolarityof the assay medium. At 300 mOsm a reduction in the uptake ratewas observed. The inhibitory effect of the hormone disappearedafter preincubating the leaf discs with para-chloromercuri-phenylsulphonicacid (PCMPS), a sulphydril binding inhibitor. ATPase activityof isolated plasma membrane vesicles was inhibited by IAA treatments,while GA₃ or ABA did not affect this enzyme, even after a 3h preincubation period. However, in the absence of a surfactantin the assay medium, GA₃, together with turgor pressure, modulatedplasma membrane ATPase activity, possibly through modificationsof membrane permeability. The hormone effect on ¹⁴ C-sucroseuptake may involve action on the sucrose carrier.Copyright 1994,1999 Academic Press Abscisic acid, Citrus sinensis, gibberellic acid, indoleacetic acid, orange, osmotic pressure, plasma membrane ATPase, ¹⁴C-sucrose uptake     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)     

Gibberellin response in lettuce hypocotyl sections

Excised lettuce (Lactuca sativa L.) hypocotyl sections retain the ability to elongate in response to gibberellic acid (GA₃) addition. In 48 hr at 30 C a GA₃-treated segment more than doubles while a control segment elongates less than 50%. Auxin has no detectable effect on this system. Sensitivity to GA₃ is not decreased by apex or root removal. Of the experimental variables tested, temperature, sucrose, and preincubation in water affect growth both with and without GA₃. Blue and far red light inhibit growth without GA₃; this inhibition is reversed by GA₃. Potassium chloride stimulates growth of illuminated sections treated with GA₃ but has no effect on control growth. When sections are incubated in the dark, KCl has a promotive effect on elongation.     

Relationship between gibberellic acid and water amount in the cotton seed

The role of endogenous GA₃ and its application to seed development in two cotton genotypes Hybrid-6 (H-6) (big seeds) and Gujarat cotton 13 (G. Cot) (small seeds) was studied. Kernel and seed coat were subjected to growth analysis in terms of dry weight, water amount, and rates of dry matter accumulation and water uptake. H-6 kernel had manifold higher dry weight and water amount than G. Cot. Seed coat of both genotypes had similar dry weight at maturity, but the maximum rates of dry matter accumulation and water uptake were distinctly higher in H-6. According to growth analysis, development of seed kernel and coat was subdivided into four phases, i.e., cell division, cell elongation, dry matter accumulation and maturation. Endogenous GA₃ level was estimated in kernel and seed coat by indirect ELISA using antibodies raised against GA₃. GA₃ amount per seed components was higher in the seed kernel of H-6 than of G. Cot, except 33 and 36 days after anthesis in kernel. H-6 seed coat had the higher amount of GA₃ during cell division phase than that of G. Cot. Close correlation between in vivo GA₃ level and water amount was recorded in both seed components. With GA₃ or GA₃ + NAA treatments in ovule culture, higher promotion in dry weight, water amount and seed size was noted in G. Cot than in H-6 suggesting that G. Cot is more deficient in endogenous GA₃. The greatest stimulation of parameters studied was obtained in ovule culture with GA₃ + NAA. When GA₃ or GA₃ + NAA was applied, initial significant difference in water amount and seed size was nullified. Data presented in this study indicated that GA₃ regulates cell expansion through the water uptake by cotton seed.     

Changes in the Sugar Content of the Leaf Sheath of Dwarf Maize Seedlings Associated with Gibberellin-Induced Growth

Changes in the time in sugar and starch content of the firstleaf sheath were compared among normal, d₅, and GA₁-treated(1µg/plant) d₅ seedlings of Zea mays L., from which endospermshad been removed. The patterns of changes in the levels of thesecarbohydrates were more or less similar to one another amongthe three groups of seedlings. Generally, the levels decreasedtoward the time of maturation of the leaf sheath except forthe level of sucrose which showed a sharp increase followedby a decrease. There was an inverse relationship over time betweengrowth and levels of glucose and fructose. Although treatmentwith GA₁ resulted in a decrease in sucrose content, it had practicallyno significant effect on the levels of the other sugars. Inthe leaf sheath of d₅, growth is probably not limited by thelevels of these sugars, and GA-induced elongation does not seemto have any significant correlation with the changes in thelevels of sugars. ¹Present address: Department of Botany, Suri Vidyasagar College,Suri, Dt. Birbhum, West Bengal, India. (Received March 18, 1988; Accepted November 21, 1988)