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     

Comparison Between the Effect of the Fruit and of Exogenous GA3-Applications on Source-Sink Relationships in Citrus Sprouts

Inflorescence leaves of citrus (Citrus sinensis L. Osbeck) accumulatecarbohydrate reserves at the beginning of the fruit set period.This effect is mimicked by exogenous GA₃ applications in deflorateinflorescences. The effect of the hormone on two processes thatcould result in carbohydrate accumulation, i.e. increased ribulosebisphosphate carboxylase (RuBPCase) activity and changes inthe import/export balance of assimilates in the sprouts, wasstudied. Neither RuBPCase activity nor respiration rates were affectedby the hormonal treatment. On the other hand, blocking of thephloem connections with the rest of the plant induced an increasein carbohydrate contents in the leaves that was proportionallylower in GA₃-treated sprouts than in control deflorate inflorescences.This increase was minimal in leaves from inflorescences at laterstages of fruit development. This was in spite of a lower fruitgrowth rate that, in turn, brought about a decrease in totaldry weight of the sprout. In contrast, total dry weight washigher in girdled deflorate inflorescences, whether or not theywere treated with the hormone. The presence of the fruit induceda thickening of the stems of intact inflorescences that wasalso seen in ungirdled GA₂-treated sprouts. This increase indry weight per unit length, however, had a different chemicalbasis depending upon whether it was caused by the fruit or thehormone. From these data, the possible causes for the enhancement ofcarbohydrate accumulation in inflorescence leaves, and the involvementof gibberellin in the effect of fruit on the sprouts is discussed. Carbohydrates, Citrus sinensis L. Osbeck, gibberellic acid, girdling, orange, ribulose bisphosphate carboxylase, source-sink     

Retardation of Leaf Senescence by Ascorbic Acid

Leaf discs of Solatium melongena were floated on various concentrationsof ascorbic acid (AA), gibberellic acid (GA₃), and kinetin inorder to study their effect on senescence. AA was highly effectivein retarding senescence as shown by the arrest of the fall inlevels of chlorophyll, DNA, RNA, and proteins. AA was effectiveat a lower concentration than that of GA₃ or kinetin.     

The Effect of Gibberellic Acid on Starch Breakdown in Sprouting Tubers of Solanum tuberosum L.

The treatment of potato tubers with 150 µmol dm^–3gibberellic acid (GA₃) stimulated starch breakdown and hexoseaccumulation in tuber tissues and the transfer of dry matterto stems. These effects could not be accounted for by enhancedactivities of starch phosphorylase, amylase and acid invertase.Indeed enzyme activities either declined or remained relativelyconstant as starch degradation and hexose accumulation proceeded.Changes in the rate of starch depletion were related to changesin sink strength and sink type, the onset of tuber initiationin controls causing the rate of starch degradation to exceedthat in GA₃-treated tissues, in which tuberization was inhibited. Solanum tuberosum L., gibberellic acid, starch breakdown     

The Transport of Sugars in Developing Fruits of Satsuma Mandarin

Transport of sugars to the juice sacs of developing satsumamandarin (Citrus unshui Marc) has been studied in attached fruitsand in isolated fruit pieces. ¹⁴CO₂ fed to the leaves resultedin [¹⁴C]sugar accumulation in the juice sacs, mainly as [¹⁴C]sucrose.Uptake of sucrose and glucose by the excised fruit pieces proceededlinearly with time. Sucrose uptake was linearly related to sucroseconcentration over the range 25–300 mM, with no indicationof saturation. This uptake was insensitive to pH (5, 7 or 9),Ca²⁺(3 mM), PCMBS (2.5 mM), DNP (1 mM) or vanadate (0.1 mM)but was slightly reduced by erythrosin (21 % by 0–1 mM;27 % by 1 mM). No competitive effect of glucose (up to 100 mM)was detectable on sucrose uptake from 100 mM solution. Mostof the [¹⁴C]sucrose uptake observed was reversible, althoughconsiderable hydrolysis and metabolic conversion were evidenced.A vanadate-sensitive ATPase was demonstrated by EM localizationon the plasma membrane of the juice sac cells. These resultsare interpreted in relation to the accumulation of assimilatesby the developing fruit. Transport: sugar, satsuma mandarin, juice sacs     

Inhibition of Gibberellic Acid-Induced Elongation-Growth of Pea Epicotyls by Xyloglucan Oligosaccharides

The biological activity of a cell wall-derived xyloglucan nonasaccharide(XG9) was investigated using a bioassay with entire pea epicotyls(Pisum sativum cv. Progress). The xyloglucan fragment was foundto inhibit gibberellic acid-induced elongation of etiolatedpea epicotyls with maximum inhibition at concentrations rangingfrom 10^–11 to 10^–9M. Growth of etiolated epicotylsin the absence of exogenously applied GA₃ was also inhibitedby XG9 in the same concentration range. A cell wall-derivedheptasaccharide (XG7) lacking the fucosyl-galactosyl-side chainshowed no inhibitory effect in the pea epicotyl bioassay withand without exogenous GA₃. Furthermore, the biological activityof a synthetic pentasaccharide (XG5), containing the fucosylgalactosyl-sidechain which is necessary for the biological activity was investigatedin the same bioassay. Compared to XG9 the pentasaccharide hada similar inhibitory activity on GA₃-promoted elongation aswell as on the endogenous growth in the absence of exogenouslyapplied GA₃, but did not exhibit a distinct concentration optimum. Key words: Elongation-growth, gibberellic acid (GA₃), oligosaccharides, pea, XG9     

Effects of Plant Growth Regulators on Grain-filling and Yield of Rice

Effects of three phytohormones (IAA₁, GA₃ and kinetin) on grain-fillingand the pattern of ³²P translocation from individual leavesto grains were studied at intervals of 7 days during the progressof reproductive development of rice (Oryza saliva L. cv. Jaya).The plants were sprayed with 100 µg ml^–1 aqueoussolutions of the hormones at 100 days, when the plants wereentering the reproductive stage. Kinetin produced a pronouncedeffect on grain-filling as well as on ³²P mobilization fromindividual leaf to grains and increased yield, possibly by increasingleaf longevity. GA₃ and IAA also increased the grain-fillingand ³²P mobilization significantly over control but the effectswere less marked than those of kinetin. Oryza sativa L., rice, grain yield, translocation, growth regulators, gibberellic acid, indol-3-yl acetic acid, kinetin     

Specificity of Gibberellin and Sucrose-promoted Flower Bud Growth in Gladiolus

A critical stage in flower bud growth in the spike of Gladioluswhich is initiated by gibberellic acid (GA₃) and sustained bysucrose has been identified. This corresponds to the stage atwhich separation of the outer bract occurs. In buds at differentdevelopmental stages isolated and held in water, it is the samebud stage that first shows increased growth. Buds not inducedby light were shown to respond more significantly to GA₃ andsucrose than those induced by light. Since the separation ofthe outer bract results in light-induced amylase productionand starch hydrolysis leading to petal growth, it is proposedthat growth promotion by GA₃ is related to light-induced petalgrowth at this specific stage. flower bud growth, Gladiolus natalensis, gibberellic acid, sucrose     

The Pattern and Control of Phospholipid Metabolism in Wheat Aleurone Tissue

Phospholipid synthesis in wheat aleurone tissue was found tobe induced by imbibition. Radiotracer experiments using [Me-¹⁴C]cholineprecursor showed that the synthesized phospholipid was locatedin the microsomal fraction of the tissue. The most active periodof phospholipid synthesis was during the first day of germinationbefore gibberellic acid (GA₃) responses were evident. GA₃ was,in fact, without effect upon the rate of phospholipid synthesis,but evidence is presented which indicates that the hormone increasedthe rate of phospholipid breakdown. Abscisic acid (ABA) alsoinduced phospholipid breakdown, and ABA did not inhibit theGA₃-induced breakdown. The relationship of phospholipid synthesisand membrane formation to the induction of hydrolase productionby GA₃ is discussed.     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

Stimulation of Rooting of Citrus Embryoids by Gibberellic Acid and Adenine Sulphate

Embryoids obtained from subcultured ovular callus of the Shamoutiorange (Citrus sinensis) were grown on Murashige and Tuckernutrient medium (BM) in the presence and absence of gibberellicacid (GA₂), adenine sulphate (ADS) and combinations of these.Both GA₂ and ADS stimulated significantly the rooting of smallembryoids with unorganized tissue, and larger embryoids withpartially developed root zones. Only large embryoids with fullydeveloped root zones rooted well on BM but better on BM+GA₂+ADS.Rooting was best on media containing 1 to 5 mg per 1 ADS, andthese two combined. The optimum sucrose concentrations were5 to 6 per cent. Shoot formation on embryoids prior to rootingcompletely inhibited rooting which is otherwise enhanced byGA₂+ADS. Filter-sterilized and autoclaved GA₂, showed similaractivity in rooting.     

Gibberellic Acid Controls the Secretion of Acid Phosphatase in Aleurone Layers and Isolated Aleurone Protoplasts of Avena fatua

The role of gibberellic acid (GA₃) in controlling the secretion(across the plasma membrane) and release (through the cell wall)of acid phosphatase (E.C. 3.1.3.2 [EC] .) from Avena aleurone layershas been investigated. Evidence from this comparative studywith intact aleurone layers and isolated aleurone protoplastsreveals that the secretion of acid phosphatase is under GA₃control. The mechanism underlying secretion and release of theenzyme from aleurone cells is discussed. Key words: Avena fatua, Acid phosphatase, Aleurone protoplasts, Gibberellic acid, Secretion     

Stabilization and Transport Capacity of Cowpea and Barley Vacuoles

Subjecting either cowpea or barley protoplasts to a combinedosmotic and pH shock provides the optimum conditions for theisolation of cowpea and barley vacuoles. Incubation of vacuolesin a defined medium resulted in 50% lysis after 30 min (cowpea)and 20 min (barley). The addition of 1 mM EDTA resulted in increasedstability of vacuoles with 50% lysis occurring after 50 min(cowpea) and 120 min (barley). Other compounds were tested fortheir effects on the stability of vacuoles. The longer life of vacuoles in the presence of EDTA allowedtransport studies to be carried out using radiolabeled tracers.The uptake of [¹⁴C]sucrose (10 mM) by cowpea vacuoles was stimulatedapproximately two-fold by the presence of MgATP (10 mM); theK_m for [¹⁴G]sucrose uptake by cowpea vacuoles was 12.5 mM. Uptakeof [³H]GA₁ ([³H]gibberellin A₁) by cowpea vacuoles was alsostimulated two-to-four fold in the presence of 10 mM MgATP comparedto untreated vacuoles. No MgATP stimulation of [³H]GA₁ or [¹⁴C]sucroseuptake could be observed in barley vacuoles. The effect of pHon uptake of [³H]GA₁ was studied in both cowpea and barley vacuoles.Uptake was optimal at about neutral pH which also coincidedwith the optimum pH for maximum stability of vacuoles. ¹ Dedicated to the memory of Prof. J. Ashida. ² Present address: International Plant Research Institute, 853Industrial Road, San Carlos, CA 94070, U.S.A. ³ Present address: Institute de Agroquimica y Tecnológiade Alimentos, Jaíme Roig, 11, Valencia 10, Spain. (Received December 11, 1982; Accepted February 24, 1983)     

Influence of Chloride and Transpiration on Net15NO3-Uptake Rate byCitrus Roots

Three-month-old Carrizo citrange (hybrid of Citrus sinensisL. OsbeckxPoncirus trifoliata Blanco) seedlings were grown incontrolled environment chambers in pots of fine sand. Plantswere irrigated with either non-saline or saline solutions overa 3-week period. After these treatments, plants were transferredto vessels containing a 5 m M¹⁵NO₃K (96% atom excess¹⁵N) solution,and transpiration as well as concentration of¹⁵N and Cl^-in roots,stem and leaves were measured after 24 h. Transpiration and¹⁵NO₃^-uptakerates were inhibited after exposure to NaCl and the concentrationof salt pre-treatment determined the intensity of this inhibitoryeffect. To determine the effect of transpiration on NO₃^-absorption,net¹⁵NO₃^-uptake rate was measured in salt stressed and non-stressedplants exposed to different light intensities or relative humiditiesand also in detached roots. Reduction in NO₃^-uptake was moreclosely related to Cl^-antagonism from salt stress than to reducedtranspiration rate. Copyright 1999 Annals of Botany Company Nitrate, absorption, inhibition transport system, salt, light and humidity.     

Effects of a Plant-Growth Regulator, Prohexadione, on the Biosynthesis of Gibberellins in Cell-Free Systems Derived from Immature Seeds

Inhibition of the biosynthesis of gibberellins by prohexadione,3,5-dioxo-4-propionylcyclo-hexanecarboxylic acid, was studiedwith cell-free systems derived from immature seeds of Cucur-bitamaxima, Phaseolus vulgaris and Pisum sativum. Prohexadione,at a concentration of 10–⁴ M, inhibited C-7 oxidationof GA₁₂-aldehyde, C-20 oxidation of GA₁₅, conversion of C₂₀-gib-berellinsto C₁₉-gibberellins, 3ß-hydroxylation, 2,3-dehydrogenationof GA²⁰, 2,3-epoxidation of GA₅ and 2ß-hydroxylationof GA₉ and GA₂₀. The 3ß-hydroxylase activity appearedto be more sensitive to prohexadione than were the C-20 oxygenaseand the 2ß-hydroxylase activities. The conversionof mevalonic acid to GA₁₂-aldehyde and the 13-hydroxylationof GA₁₂ were not affected by prohexadione at a concentrationof 3 ? 10^–4 M. All of the steps inhibited by prohexadioneare oxidation steps catalyzed by soluble enzymes that require2-oxoglutarate, Fe²⁺ and oxygen, and all of them occur distalto the synthesis of GA₁₂-aldehyde in the biosynthesis of gibberellins. (Received April 4, 1990; Accepted September 14, 1990)     

Influence of Gibberellic Acid and the Rht3 Gene on Choline and Phospholipid Metabolism in Wheat Aleurone Tissue

The effect of gibberellic acid (GA3) on phospholipid metabolismand -amylase production was studied in aleurone tissue of twonear-isogenic lines of wheat (Triticum aesuvum L.). Incubationof embryoectomized seeds from a GA-responsive line (rht3, tall)with GA₃ caused the induction of -amylase activity after a lagphase of 30 h. In the case of embryoectomized seeds from a ‘GA-insensitive’line (Rh13, dwarf), however, the lag phase was extended up to50 h. During the first 14 h following imbibition, GA₃ inhibitedcholine uptake and its subsequent incorporation into phosphatidylcholine in the Rhr3 line but not in the rht3 line. GA₃ promotedphospholipid breakdown in both the lines during this period,however. GA₃ also terminated independent turnover of the cholineN-methyl groups in phosphatidyl choline and promoted turnoverof the whole choline headgroup. These results are discussedin relation to the possibility that phosphatidyl choline turnoveris an integral part of the GA₃ signal-transduction mechanismin aleurone tissue. Key words: GA3, Rht3 gene, choline, phospholipid     

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     

NaCl-and Gibberellic Acid-induced Changes in the Content of Auxin and the Activities of Cellulase and Pectin Lyase During Leaf Growth in Rice (Oryza sativa)

The interactive effect of NaCl salinity and gibberellic acidin the activities of cellulase and pectin lyase, and on thecontent of auxin and chlorophyll, has been determined duringleaf growth (fifth from base) in rice. The linear growth, chlorophyllcontent, activity of cellulase, and the auxin level of leaveswere markedly decreased when plants were exposed to salt stress(12 dS m^–1). However pectin lyase activity did not registerany significant alteration in the leaves of salt-stressed plantscompared with the control. Treatment of plants with gibberellicacid (GA₃) (10 ppm) increased the leaf growth and chlorophyllcontent with a concomitant rise in the activity of cellulaseunder stressed as well as non-stressed conditions. A markedincrease in the content of auxin was discernible in the leavesof salt-stressed plants treated with GA₃ compared with non-treatedsalinized ones. An appreciable increment in the activity ofpectin lyase in response to GA₃ administration was detectedonly in the leaves of non-stressed plants. These results indicatethat enhancement of cellulase activity and the augmentationof endogenous auxin content may be involved in the stimulationof rice leaf growth by GA₃ under saline conditions. Oryza sativa, rice, leaf growth, NaCl salinity, gibberellic acid, cellulase, pectin lyase, auxin     

Ammonia Induces Starch Degradation in Chlorella Cells

When ammonia was added to cells of Chlorella which had fixed¹⁴CO₂ photo synthetically, ¹⁴C which had been incorporated intostarch was greatly decreased. A similar effect was observedwhen potassium nitrate and sodium nitrite were added. The ammonia-induceddecrease in ¹⁴C-starch was observed in all species of Chlorellatested. With cells of C. vulgaris 11h, most of the radioactivityin starch was recovered in sucrose, indicating that ammoniainduces the conversion of starch into sucrose. The percent of¹⁴C recovered in sucrose differed from species to species andpractically no recovery in sucrose was observed in C. pyrenoidosa.In most species tested, the enhancing effects of blue lightand ammonia on O₂ uptake as well as the ammonia effect on starchdegradation were greater in cells which had been starved inphosphate medium in the dark than in non-starved cells. In contrast,the enhancing effect of ammonia on dark CO₂ fixation was muchgreater in non-starved cells. C. pyrenoidosa was unique in thatblue light did not show any effect on its O₂ uptake. (Received August 15, 1984; Accepted November 16, 1984)     

Effect of ABA and GA3 on tuberization and some chemical constituents of potato

The effects of abscisic acid (ABA) and gibberellic acid (GA₃)on the chemical composition of and tuberization in the potatowere studied. GA₃ at 10^–6 M inhibited and ABA at an equimolarconcentration promoted tuberization. The inhibitory effect ofGA₃ was relieved by the addition of ABA. The fresh weight ofthe shoot, chlorophyll content and the total glycoalkaloidslevel were increased by GA₃ treatment, but decreased by ABAtreatment. In contrast, total proteins were increased by ABA,but decreased by GA₃ treatment. ¹This work was supported by a PL-480 research grant (FG-Pa-262)from the United States Department of Agriculture widi co-ordinationby the Agriculture Research Council, Pakistan. (Received August 29, 1980; )