The Effect of Gibberellins on Growth and Flowering of Fragaria and Duchesnea

In a series of experiments petiole lengths were increased, steminternode elongation induced, runner formation promoted, andflower initiation inhibited both in the perpetual-fruiting andthe seasonal-fruiting varieties of strawberry by applicationsof gibberellic acid. Runners were induced to form in Fragariavesca semper-florcns var. Baron Solemacher, which does not normallyrunner. Thus the physiological processes which lead to the morphologicaldifferences between perpetual and seasonal fruiting types wereoverruled by treatment with gibberellic acid. Gibberellins A₁, A₄, A₇, and A₉, like gibberellic acid (A₃),induced elongation of petioles (a normal photoperiodic response),elongation of internodes on the main stem, and inhibition offlower formation in Baron Solemacher (responses not inducedby photoperiod). When applied to the cut stump of a debladed petiole, gibberellicacid inhibited flower formation at the growing apex of the stem,thus substituting for the leaf blade, which in long photoperiodsinhibited flower formation. A morphological study suggested that in Duchesnea indica, arelated genus, flower initiation is not regulated by environmentalcircumstances, but is the inevitable consequence of growth.Although promoting increase in petiole length and in elongationof lateral growths as in strawberry, gibberellic acid did notinhibit flower initiation in this species, except in so faras it caused a retardation in the growth of certain axillarybuds, so that a lower proportion of them reached the stage offlower initiation within the duration of the experiment. These results are discussed in relation to the hypothesis thatflower formation is regulated by an inhibitory hormone in seasonal-fruitingstrawberries.     

ANATOMY OF GIBBERELLIN-INDUCED STEM ABSCISSION IN COTTON

In an investigation of the abscission responses of excised cotyledonary nodes (explants) of cotton to applications of gibberellic acid, applications to the petiole stumps accelerated petiole abscission only. Applications to stem stumps accelerated petiole abscission and induced stem abscission in approximately 30% of the explants. Following stem applications, petiole abscission always preceded stem abscission by at least 1 day. Morphologically, both the petiole and stem abscission zones, as well as the changes which took place within them during abscission, appeared identical.     

Ethylene-induced Tropism of Trifolium fragiferum L. Stolons

The hypothesis that ethylene regulates prostrate stem growth was investigated using stolons of strawberry clover (Trifolium fragiferum L. var. Salina). Stolons became erect when treated with ethylene or 2-chloroethylphosphonic acid. Curvature was visibly detectable 2 hours after ethylene treatment, and subsequent stem elongation was rapid. Indoleacetic acid application to prostrate stolons caused only a small transitory curvature persisting less than 48 hours. Indoleacetic acid-stimulated curvature was accompanied by an increase in ethylene evolution. When stolon curvature was induced by placing strawberry clover plants in darkness or by applying gibberellic acid, ethylene production did not parallel stolon curvature.     

Bacillus methylotrophicus M4-96 Stimulates the Growth of Strawberry (Fragaria × ananassa ‘Aromas’) Plants In Vitro and Slows Botrytis cinerea Infection by Two Different Methods of Interaction

Bacillus methylotrophicus M4-96 is a beneficial rhizobacterium that has been isolated from the rhizosphere of maize (Zea mays). In this study, we investigated its efficacy as a plant growth promoter for strawberry in vitro, as well as its ability to induce callose deposition in leaves to reduce the severity of Botrytis cinerea infection. Two methods of plant-bacterial interaction were used: inoculation near the root and emission of volatile compounds with no physical contact. Plant biomass increased under both treatments, but with developmental parameters of the plants differentially stimulated by each method. Root inoculation increased petiole number and root length, whereas bacterial volatiles increased petiole length and root number. A chemical analysis of the bacterial culture revealed the presence of indole acetic acid (0.21 μg L⁻¹) and gibberellic acid (6.16 μg L⁻¹). Acetoin was previously identified as the major volatile produced by the bacteria, and its application to strawberry explants increased their growth and development. Furthermore, when acetoin and both phytoregulators were added to the culture media, these positive effects were enhanced. The inoculation method also affected the size and quantity of callose deposits in the leaves. Treatment with volatiles increased callose deposition in the leaves by up to five-fold, which promoted a rapid defense reaction that inhibited the incidence of gray mold by reinforcing cell wall. Taken together, our results show that B. methylotrophicus M4-96 promotes growth and induces systemic resistance in strawberry plants.

     

Modification of growth habit of Majestic potato by growth regulators applied at different times

The effect of gibberellic acid, CCC (2-chloroethyltrimethylammonium chloride) and B 9 (N-dimethylaminosuccinamic acid) was studied on growth of potato plants in pots. Growth was analysed on four occasions and changes in habit defined in terms of internode lengths, leaf areas and growth of lateral branches. Soaking seed pieces for 1 hr. in GA solution caused six internodes to elongate greatly, an effect not prevented by CCC applied when the shoot emerged from the soil. The effects on internode extension were determined by the length of the interval between GA treatment and CCC treatment. Treatment at emergence with CCC shortened all internodes and more CCC applied 4 weeks later had no effect. Late application of CCC or B9 shortened the top two lateral branches, usually very long in untreated plants. The regulators affected leaf growth differently from internode growth: usually growth regulators had less effect on leaf growth. Effects on growth depended on when the regulators were applied. Treatment with GA alone inhibited bud development at higher nodes than in untreated plants; when followed by late treatment with CCC, lateral growth at higher nodes was also less. CCC retarded development of lateral branches especially when applied early. B9 had a similar effect to CCC applied late. When regulators retarded growth of lower laterals, upper laterals often grew more than in untreated plants. Treatments did not affect the number of leaves on the main stem at first but later GA hastened senescence. GA increased the number of leaves on lateral stems, and the effect was enhanced by CCC. CCC alone increased the number of first- and second-order lateral leaves. GA lengthened and CCC shortened stolons. The effect of CCC persisted throughout the life of the plant. CCC or B 9 shortened stolons whenever applied. CCC hastened tuber initiation but slowed tuber growth. CCC at first retarded formation of lateral tubers but had no effect on the ultimate numbers of lateral and terminal tubers. The value of E (net assimilation rate) did not alter with time. CCC applied at emergence increased E, probably because it hastened tuber initiation and temporarily increased sink capacity. Although tubers formed earlier with CCC, their growth was slower and their demand for carbohydrate was also less. The increase in second-order laterals in CCC-treated plants indicates that they utilize carbohydrate that would normally go to tubers. This experiment also demonstrates that crowding leaves by shortening stems did not diminish E, possibly because another over-riding process (bigger sinks) offsets the effect of shading.     

INHIBITION OF CELL PROLIFERATION AND EXPANSION IN VITRO BY THREE STEM GROWTH RETARDANTS

Three inhibitors of stem elongation, Amo, CCC, and Phosfon, inhibit cell division and expansion in tissues cultured in vitro. However, contrary to the case in intact plants, gibberellic acid does not prevent the retardant-induced inhibition in vitro. Supplementary auxin is also without effect in preventing the inhibition. Thus, the effect of the retardants cannot be simply that of inhibiting gibberellin or auxin synthesis. With respect to growth, carrot, chrysanthemum, and geranium tissues are equally sensitive to all 3 retardants, whereas tobacco tissues are considerably more resistant to Amo and apparently unaffected by CCC.     

In vitro propagation of cauliflower,Brassica oleracea var. botrytis for hybrid seed production

Methods for obtaining heterotic F₁ and maintaining purebred lines for breeding of Brassica oleracea are limited by absence of male sterile lines and occurrence of inbreeding depression, respectively. The use of vegetative (stem, petiole, leaf, leaf rib) and floral (peduncle, pedicel, flower bud, curd) explants of cauliflower to regenerate purebred lines for crossing were examined. Of four growth regulator treatments and explant types used, best results were obtained with curd explants on MS medium with 6-benzyladenine (cytokinin) and gibberellic acid. Although 6-benzyladenine alone promoted formation of shoots in floral explants, both 6-benzyladenine and α-napthaleneacetic acid were required for vegetative explants. Use of α-napthaleneacetic acid, however, often increased callus formation. These culture techniques to maintain purebred regenerated plants will complement newly-derived nuclear-based male sterile lines obtained by the introduction of antisense copies of the gene BcpI, which is required for pollen fertility. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of gibberellic Acid and sucrose on the growth of oat (Avena) stem segments

Gibberellic acid induced growth in Avena (oat) stem segments within 35 minutes after hormone application. The total elongation elicited by gibberellic acid was greater than 15 times the control growth. The sensitivity of the segments to low concentrations of gibberellic acid (1 pmole) and the specificity of the segments to the gibberellin class of hormones suggest that oat stem segments would be a valuable tool for gibberellin bioassays. Both gibberellic acid-induced growth and control growth are temperature-dependent and showed a Q₁₀ of two or greater. Although the most apparent effect of gibberellic acid was to promote the uptake of water into the internode, the hormone also promoted transport of endogenous substrate and the uptake of exogenous substrate into the growing region. The growth promotion was accomplished without an apparent increase in osmotic pressure.     

Runner Formation in Everbearing Strawberry as Influenced by Growth-Promoting and Inhibiting Substances

The interactive effects of gibberellic acid, abscisic acid,and benzyladenine were studied in relation to runner formationof the everbearing strawberry. In two of three cultivars studied,Ozark Beauty and Superfection, exogenous gibberellic acid stimulatedrunner formation and inhibited flowering. In the Geneva cultivar,a shy runner producer, gibberellic acid application as a foliarspray failed to induce runners. When applied in combinationwith benzyladenine, gibberellic acid greatly stimulated runnerformation Benzyladenine alone had no effect on runnering. Exogenous abscisic acid inhibited petiole length and runnerformation and had no influence on the number of inflorescencesinitiated. Response to exogenous gibberellic acid or abscisicacid varied according to the reproductive or vegetative stagethe plant exhibited at the time of treatment. Activity of endogenous gibberellin-like substances was not substantiallydifferent between flowering and non-flowering field-grown Genevaplants when sampled in long day lengths of August. Endogenousinhibitors were highly active in flowering Geneva plants andrelatively inactive in non-flowering plants The implications of these findings on hormonal balance in thestrawberry are discussed.     

Environmental control of growth and development of Scrophularia marilandica

Summary Seedlings of Scrophularia marilandica were grown at different combinations of day/night temperature and photoperiod under controlled conditions. The species flowered in long days. The stems of plants grown at low temperature and short photoperiod failed to elongate. Treatment with gibberellic acid (GA₃) simulated the effect of increasing temperature and photoperiod and caused stem elongation in plants which would otherwise not have elongated. Application of GA₃ to plants grown at high temperature and long photoperiod resulted in increased stem elongation and flowering. The growth retardant (2-chloroethyl)trimethylammonium chloride (CCC) had little effect on rosette plants grown at low temperature and short photoperiod. Application of CCC to +GA₃ plants grown at a higher temperature and long photoperiod gave a significant increase in stem height. The interaction between temperature and applied GA is described in an experiment using plants grown at high and low temperatures for varying periods of time.This work was supported by National Science Foundation Grant GB 17483.     

Some Effects of Daylength, Temperature and Exogenous Growth Regulator Application on the Growth of Actinidia chinensis Planch

The growth responses of Actinidia chinensis raised from cuttingswere compared in 8 h short days (SD) and 16 h long days (LD)at 15, 20 and 25 °C, as well as under varying day and nighttemperatures The data obtained reveal effects on stem elongation,apparent plastochrons, leaf area and shape, as well as dry matteraccumulation and water contents of different plant parts Theseinvestigations were supplemented by studies on the effects ofapplied GA₃ and ethephon Alternating day/night temperatures(thermoperiodicity) increased leaf area and d wt accumulationin LD Effects on sugar and starch contents, are described anddiscussed Unexpected effects such as very high petiole watercontents and their continuous growth, increased twisting ofthe climbing stem in SD and other findings are also reportedand discussed Actinidia chinensis, Kiwi fruit, gibberellic acid, ethephon, temperature, photoperiod, themoperiodicity     

Auxin-induced growth of tuber tissue of Jerusalem artichoke IV. Significance of gibberellin biosynthesis and basic proteins in chromatin in aging process

The role of endogenous gibberellin in the aging process preparatoryto auxin action of expanding cells was studied, using tissueslices excised from cold-stored Jerusalem artichoke tuber. CCC inhibited the auxin-induced expansion growth when addedto slices during the aging period. This inhibition was alleviatedby the simultaneous addition of gibberellic acid. The amountof gibberellin-like substances increased during the aging periodand this increase was suppressed by CCC. During the aging period, acid-soluble basic proteins in thechromatin fraction decreased in amount, and exogenous gibberellicacid enhanced the decrease. (Received October 30, 1967; )     

The effects of mechanically-induced stress in plants — a review

Mechanically-induced stress (MIS) occurs naturally in plants as the aerial parts are moved, usually by wind, but also by such agents as rain and animals. It can be induced indoors by various actions such as rubbing or bending the stem or shaking or brushing the entire shoot. The most noticeable effect of MIS is a reduction in stem, leaf or petiole length invariably resulting in plants which are smaller and more compact than unstressed controls. However, the response of other variables can often differ between species and there may be either increases or decreases in stem or petiole diameter, root: shoot weight ratio, chlorophyll content or drought resistance. Why species should differ in this way, and what is the endogenous control mechanism for MIS responses, are inanswered questions. Ethylene, which increases as a result of MIS in several species may cause some MIS responses such as increased stem diameter, epinasty or a change in sex expression. However, evidence suggests that MIS retardation of extension growth may equally be due to lower or supraoptimal auxin levels or lower gibberellin levels.The uses in the field of the growth promoter gibberellin or the growth retardant chlormequat chloride (CCC) appear to be examples of respectively reversing or stimulating MIS growth response. MIS may be applied indoors if short compact plants are needed, either for aesthetic purposes as with floral crops, or if hardier and more manageable plants are needed, such as seedlings for transplanting in the field. Much more research is needed to estimate the importance of MIS in the field and to assess how such knowledge may be used to improve crop yield.     

Cyclic Purine Mononucleotides: Induction of Gibberellin Biosynthesis in Barley Endosperm

The de novo synthesis of α-amylase in barley endosperm and isolated aleurone layers is induced by 3′,5′-cyclic purine mononucleotides and gibberellic acid. The induction of α-amylase by cyclic purine mononucleotides is prevented by 2,4-DNP, inhibitors of RNA and protein syntheses, CCC, AMO-1618 and phosfon. The induction of α-amylase formation by 3′,5′-cyclic purine mononucleotides, but not by gibberellic acid, is also blocked by inhibitors of DNA synthesis. Extracts from cyclic AMP-treated endosperm halves exhibit a characteristic gibberellin-like activity which is detectable within 12 hours from the addition of the cyclic AMP. On paper chromatograms this gibberellin-like activity is located at the Rf typical for GA₃. Its formation is prevented by inhibitors of DNA synthesis, CCC and AMO-1618. Glucose inhibits the formation of α-amylase induced by gibberellic acid. Glucose has no effect on the cAMP-induced gibberellin biosynthesis. The evidence shows that the cyclic purine mononucleotides induce DNA synthesis, which results in gibberellin biosynthesis, which in turn activates the synthesis of α-amylase.     

CONTROL OF FLOWER FORMATION BY GROWTH RETARDANTS AND GIBBERELLIN IN SAMOLUS PARVIFLORUS,A LONG-DAY PLANT

The growth retardants AMO–1618 and CCC inhibited flower formation and stem elongation in Samolus parviflorus, a long-day rosette plant, under inductive conditions. The vegetative growth of the plants, as measured by leaf formation, was affected only slightly, or not affected at all. Application of gibberellic acid (GA₃) reversed completely the inhibition both of flower formation and of stem elongation caused by AMO, but relatively larger amounts of GA were required to reverse the CCC inhibition of stem elongation than that of flower formation. When applied under short-day conditions, AMO had no effect on the level of applied GA required for flower induction. When applied following long-day treatment the retardant caused some reduction of flower formation after marginal numbers of long days, but had no effect when enough long days to cause 100% flower formation were given. Other evidence indicates that the growth retardants act by inhibiting the synthesis of endogenous gibberellin. In LD plants, at least part of the action of inductive environmental conditions consists in causing an increase of gibberellin synthesis, supporting the hypothesis that relatively high GA levels are necessary for the production of the floral stimulus in this group of plants, as in long-short-day plants. The experiments with CCC indicate that stem elongation and flower formation in Samolus can be separated, and that the effect of GA on flower formation is not necessarily dependent on its effect on stem elongation.     

Effect of gibberellic Acid on elongation and longevity of coleus petioles

The effects of gibberellic acid on the longevity and elongation of variously aged, debladed petioles of Coleus blumei were studied, with particular reference to the hypotheses 1) that auxin increases longevity by increasing growth, and 2) that gibberellic acid acts by increasing the endogenous levels of auxin.

Gibberellic acid, substituted for the leaf blades, significantly decreased longevity of younger petioles, as measured by days or hours to abscission. Gibberellic acid also decreased the longevity resulting from 0.1% indoleacetic acid. This is the opposite of the effect expected if it is increasing auxin levels in the petiole.

In its effect on elongation of younger petioles, however, gibberellic acid did act in the direction expected if it were increasing effective levels of auxin in the petiole. The elongation rate from 0.1% gibberellic acid plus 0.1% indoleacetic acid in lanolin was as large or larger than that for 1.0% indoleacetic acid.

Petioles which were 10 or more weeks old (i.e., at positions 5+ below the apical bud were not affected by 0.1% gibberellic acid in either longevity or rate of elongation, with or without 0.1% indoleacetic acid. Since 1.0% indoleacetic acid increases both longevity and elongation rate of these petioles over 0.1% indoleacetic acid, gibberellic acid is clearly not acting on older petioles as if it were increasing effective auxin levels).

     

The effects of mechanically-induced stress and plant growth regulators on the growth of lettuce,cauliflower and bean (Phaseolus vulgaris L.) plants

The plant growth regulators, gibberellic acid (GA₃), ethephon and chlormequat chloride (CCC) were sprayed on young lettuce, cauliflower and bean (Phaseolus vulgaris) plants, which had either been given or not been given a mechanically-induced stress (MIS) treatment. MIS was applied by brushing the plants with paper for 1.5 minutes each day. GA₃ increased extension growth of bean and leaf length of lettuce in unbrushed plants as much as in brushed ones. CCC and ethephon were less effective at reducing the height of brushed bean plants compared to unbrushed ones. The effects of CCC on the growth of cauliflower and lettuce plants was not influenced by brushing, whereas unbrushed plants responded more readily to ethephon than did brushed ones. The effects of CCC on growth were generally similar to those of MIS whereas the effects of ethephon were in many ways different to MIS.The results are discussed in relation to the use of PGR and MIS treatments for modifying plant growth.     

Role of Indole-3-acetic Acid and Gibberellin in the Control of Internodal Elongation in Avena Stem Segments: Long Term Growth Kinetics

Exogenous application of indoleacetic acid results in a significant suppression of the linear growth that is promoted by exogenous gibberellic acid in Avena stem segments in a fashion similar to that previously noted in Avena leaf base segments (van Overbeek and Dowding, 1961, Fourth International Conference Plant Growth Regulation). Treatment with the auxin transport inhibitors, methyl-2-chloro-9-hydroxyfluorene-(9)-carboxylate (CFM) or 2,3,5-triiodobenzoic acid (TIBA), alone promotes elongation growth of the stem segments over that of control growth. This effect is interpreted as being due to the interference in the transport of native indoleacetic acid by CFM and TIBA, thus removing the inhibitory effect of native indoleacetic acid on gibberellin-promoted growth in the internodal intercalary meristem. This results in a greater promotion of internodal growth by native gibberellins. In the presence of (2-chloroethyl) trimethylammonium chloride (CCC), the growth-promoting effects of CFM and TIBA are decreased, and the antiauxin, PCIB (4-chloro-phenoxyisobutyric acid), has no growth-promoting effects whatsoever. These results indicate that the CFM and TIBA-promoted growth require the continuous presence of gibberellins. They further support the view that native indoleacetic acid acts as a growth suppressor hormone in its regulation of gibberellin-promoted internodal extension in Avena shoots.     

Expansion growth of isolated leaf blades of Todea barbara

Summary Etiolation of Todea barbara sporophytes and the subsequent deetiolation of excised leaf blades have been studied. In etiolated plants leaf blade growth is arrested, petiole and stem growth is enhanced, and root growth is decreased. De-etiolation permits the resumption of leaf blade growth and differentiation, and the resulting de-etiolated blade appears comparable to its light-grown counterpart in every respect but cell number. Only two factors are required to attain maximum surface area growth in cultured leaf blades; these are light and sucrose. The addition of plant growth substances does not increase the final area attained. However, the inhibition of leaf blade growth with growth retardants and its partial reversal by exogenously supplied gibberellic acid demonstrates a role for gibberellins in leaf expansion in Todea.     

Effect of Growth Retardants on α-Amylase Production in Germinating Barley Seed

The effect of growth retarding compounds, (2-chloroethyl)trimethylammonium chloride (CCC), 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride (AMU-1618), tributyl-2,4-dichlorobenzylphosphonium chloride (Phosfon D) and N-dimethylamino succinamic acid (B-995) on α-amylase production in germinating barley seed was studied. Seeds were germinated in growth retardants in presence and absence of gibberellic acid (GA₃). CCC, AMO-1618 and Phosfon D inhibitedα-amylase production in germinating seed and the effect was reversed by GA₃ Phosfon D and AMO-1618 were stronger inhibitors of α-amylase production than CCC. CCC was by far the strongest inhibitor of all the other analogs tested. B-995 was comparatively only slightly inhibitory. The results reported here, when viewed in light of the results of other workers, provide good evidence that CCC, AMO-1618 and Phosfon D inhibit α-amylase production by inhibiting the synthesis of gibberellin or gibberellin-like hormone(s) during germination of barley seed. Consistent with other reports, B-995 possibly acts by other mechanism (s).