Abscisic acid and apical dominance in Phaseolus coccineus L.

Abscisic acid (ABA) in lanolin, applied to the internode of decapitated runner bean plants enhances the outgrowth of lateral buds. The optimum concentration of the paste is 10^-5 M. The effect of ABA is counteracted by indoleacetic acid (IAA) but not by gibberellic acid (GA₃). There is no effect when ABA is applied to the apical bud or lateral buds of intact plants. However, 13.2 ng given to the lateral buds of decapitated plants stimulate their growth, whereas higher concentrations are inhibitory. Consequently, ABA enhances growth of lateral buds directly, but only when apical dominance is already weakened. The growth of the decapitated 2^nd internode was not affected by ABA. Radioactivity from [2-¹⁴C] ABA, applied to nonelongating 2^nd internode stumps of decapitated runner bean plants moves to the lateral buds, whereas [1-¹⁴C]IAA-and [³H]GA₁-translocation is much weaker. ABA transport is inhibited if IAA or [³H]GA₁ is applied simultaneously. In elongating internodes [¹⁴C]ABA is almost completely immobile. [¹⁴C]IAA-and [³H]GA₁-translocation is not affected by ABA. The amount of radioactivity from labelled ABA, translocated to the lateral buds, is highest during the early stages of bud outgrowth.Abbreviations ABA 2,4-cis, trans-(+)-abscisic acid - GA gibberellic acid - IAA indoleacetic acid - p.l. plain lanolin     

Changes in abscisic acid and indole-3-acetic acid in axillary buds of Elytrigia repens released from apical dominance

Growth of axillary buds on the rhizomes of Elytrigia repens (L) Nevski is strongly dominated by the rhizome apex, by mechanisms which may involve endogenous hormones. We determined the distribution of indole-3-acetic acid (IAA) and abscisic acid (ABA) in rhizomes and measured (by gas-chromatography-mass spectrometry) their content in axillary buds after rhizomes were decapitated. The same measurements were also made in buds induced to sprout by removing their subtending scale leaves. The ABA content tended to be higher in the apical bud and in the axillary buds than in the adjacent internodes, and tended to decline basipetally in the internodes and scale leaves. IAA was similary distributed, except that there was less difference between the buds and other rhizome parts. After rhizomes were decapitated, the ABA content of the first axillary bud declined to 20% of that of control values within 24 h, while the IAA content showed no marked tendency to change. The ABA content also declined within 12 h in the first axillary bud after rhizomes were denuded, while the content of IAA tended to increase after 6 h. These changes occurred before the length of the first axillary bud increased 24–48 h after rhizomes were decapitated or denuded. We conclude that the release of axillary buds from apical dominance in E. repens does not require IAA content to be reduced, but is associated with reduced ABA content.     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L.--Influence of the Environment

The influence of various environmental factors upon main stemand lateral bud growth has beeninvestigated using Phaseolusvulgaris, with the object of discovering why there is variabilityin the response of lateral buds on decapitated plants to apically-appliedIAA. Light intensity, light quality and temperature had differentand specific effects on main stem and lateral bud growth inintact plants and on the effectiveness of IAA in inhibitingprimary leaf axillary bud growth in decapitated plants. Photoperiod,on the other hand, was apparently ineffective. It is concluded that environmental factors, as well as contributingto the normal regulation of apical dominance, could also partlyor wholly account for the variation in effectiveness of appliedIAA found by different workers. IAA was least effective whenthe temperature was lower at night than during the day.     

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.     

Correlative Inhibition of Lateral Bud Growth in Pisum sativum L. and Phaseolus vulgaris L.: Studies of the Role of Abscisic Acid

The possibility has been investigated that abscisic acid (ABA)might act as a correlative inhibitor of lateral bud growth inPisum sativum and Phaseolus vulgaris. Application of ABA insmall quantities (2µg) to axillary buds on decapitatedplants of P. sativum caused appreciable inhibition of theirgrowth, and induced a compensatory growth of the bud on an adjacentnode. Application of this same quantity of ABA to axillary budson decapitated plants of Phaseolus vulgaris was without effect,but a high concentration in lanolin (1 mg g^–1) did substantiallyreduce bud outgrowth. Endogenous ABA-like substances in Phaseolusvulgaris, detected by bioassay and electron capture g.l.c.,were present in similar concentrations in shoot tips, lateralbuds on intact plants and lateral buds on plants decapitated24 h earlier. The effects of applied ABA suggested that it might be involvedin the mechanism of correlative inhibition in Pisum sativum,but it was not possible to test this hypothesis by determiningendogenous ABA levels in axillary buds because of their smallsize. The evidence presented here suggests that ABA is not acorrelative inhibitor in Phaseolus vulgaris even though at highconcentration it can inhibit the growth of axillary buds.     

Correlative inhibition of lateral bud growth in Phaseolus vulgaris L. timing of bud growth following decapitation

Summary On intact, 3-week-old plants of Phaseolus the larger bud in the axils of the primary leaves shows slow, continuous elongation growth. Release from correlative inhibition can be detected within 30 min following decapitation. When 0.1% indoleacetic acid in lanolin is applied to the decapitated stem stump, the lateral bud shows slow growth during the first 7 h, then stops completely for a further 15 h but after 2 days a further gradual increase in length is observed.The movement of ¹⁴C-labelled assimilates from the subtending primary leaf into the lateral bud increases following removal of the shoot apex. When indole acetic acid is applied to decapitated plants the ability of the buds to import ¹⁴C increases for 5–7 h and then declines to a negligible amount. Little or no radioactivity from tritiated indoleacetic acid is transported into the lateral buds of decapitated plants during the first 48 h following removal of the apex and it appears that rapid metabolism of the compound occurs in the stem tissues.     

Role of indoleacetic Acid and abscisic Acid in the correlative control by fruits of axillary bud development and leaf senescence

When fully filled pods of bean plants were deseeded, the rate of axillary bud growth and the chlorophyll content of leaves were increased. Application of 0.1% indoleacetic acid (IAA) in lanolin on the deseeded pods caused abscission of axillary buds, inhibited growth of the remaining buds, and decreased leaf chlorophyll content. The response of bud development to fruit-applied IAA was concentration dependent between 0.001 and 0.1% IAA (representing from 2 to 200 micrograms IAA per fruit) resulting in greater growth inhibition at higher IAA concentrations.     

Changes after Decapitation in Concentrations of Indole-3-Acetic Acid and Abscisic Acid in the Larger Axillary Bud of Phaseolus vulgaris L. cv Tender Green

Early changes in the concentrations of indole-3-acetic acid (IAA) and abscisic acid (ABA) were investigated in the larger axillary bud of 2-week-old Phaseolus vulgaris L. cv Tender Green seedlings after removal of the dominant apical bud. Concentrations of these two hormones were measured at 4, 6, 8, 12 and 24 hours following decapitation of the apical bud and its subtending shoot. Quantitations were accomplished using either gas chromatography-mass spectrometry-selected ion monitoring (GS-MS-SIM) with [¹³C₆]-IAA or [²H₆]-ABA as quantitative internal standards, or by an indirect enzyme-linked immunosorbent assay, validated by GC-MS-SIM. Within 4 hours after decapitation the IAA concentration in the axillary bud had increased fivefold, remaining relatively constant thereafter. The concentration of ABA in axillary buds of decapitated plants was 30 to 70% lower than for buds of intact plants from 4 to 24 hours following decapitation. Fresh weight of buds on decapitated plants had increased by 8 hours after decapitation and this increase was even more prominent by 24 hours. Anatomical assessment of the larger axillary buds at 0, 8, and 24 hours following decapitation showed that most of the growth was due to cell expansion, especially in the intermodal region. Thus, IAA concentration in the axillary bud increases appreciably within a very few hours of decapitation. Coincidental with the rise in IAA concentration is a modest, but significant reduction in ABA concentration in these axillary buds after decapitation.     

Tiller Bud Suppression in Reproductive Plants of Lolium multiflorum Lam. Cv. Westerwoldicum

The control of tiller bud growth during reproductive developmentwas investigated in experimental plants ofLolium multiflorumLam. cv. Westerwoldicum that were reduced to a main axis havinga developing but unemerged ear, elongating stem internodes,a series of expanded leaves, slow-growing tiller buds and aroot system. Isolation of the ear by excision of its base, ordecapitation so as to remove the ear together with the upperleaves, promoted the movement of ¹⁴C-assimilates to tiller buds,decapitation being the more effective treatment. Applicationof 0.1 per cent indol–3yl-acetic acid (IAA) to cut tissuesof decapitated plants diverted ¹⁴C-assimilates to upper internodesbut did not reduce import by buds, whereas application of 1.0per cent IAA both diverted labelled assimilates to upper internodesand reduced bud import. Radioactivity from [¹⁴C] IAA appliedto the upper leaves or to the ear base was recovered from budsin very small amounts; larger amounts were recovered from budsfollowing the application of labelled IAA to an elongating internode,especially from the bud at the base of the treated internode.It is suggested that tiller bud suppression may be influencedby the movement of inhibitory levels of auxin into buds fromnearby elongating stem internodes, whose activity in turn maybe controlled by the developing inflorescence and upper leaves.     

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     

Lateral Bud Growth in Phaseolus vulgaris L. and the Levels of Ethylene in the Bud and Adjacent Tissue

Ethephon and the ethylene inhibitors Ag⁺ and aminoethoxyvinylglycine (AVG) inhibited outgrowth of the axillary bud of thefirst trifoliate leaf in decapitated plants of Phaseolus vulgaris.Endogenous ethylene levels decreased in the stem upon decapitationalthough it is not conclusive that a causal relationship existsbetween this decrease and the release of axillary buds frominhibition. The proposition that auxin-induced ethylene is responsiblefor the suppression of axillary bud growth in the decapitatedplant when the apical shoot is replaced by auxin is not borneout in this study. Application of IAA directly to the axillarybud of intact plants gave rise to a transient increase in budgrowth. This growth increment was annulled when AVG was suppliedwith IAA to the bud despite the fact that the dosage of AVGused did not affect the normal slow growth rate of the bud ofthe intact plant or bud outgrowth resulting from shoot decapitation.     

The Distribution of Hormones in Relation to Apical Dominance in Brussels Sprouts (Brassica oleracea var. gemmifera L.) Plants

The lateral buds of intact Brussels sprout plants containedless auxin and gibberellin than the main apex. When the apexwas removed the auxin content of the top lateral buds increasedwithin 2 days, but gibberellin activity did not increaseuntilshoot extension was apparent. Auxin application to the cut surfaceof decapitated plants caused lateral bud inhibition, but didnot completely prevent bud growth. Both auxin and gibberellinactivity in the plant apex decreased with increasing age, butonly gibberellin activity decreased in the lateral buds. Theauxin content of the lateral buds on intact plants increasedwith time. It is suggested that in Brussels sprouts, lateral bud inhibitionis due to sub-optimal auxin activity, and that decapitationinduces an auxin increase in these buds which then grow out.Lateral shoots are produced following decapitation of youngplants because the gibberellin content of the lateral buds isrelatively high. Only bud swelling occurs in decapitated olderplants because the gibberellin content of the buds is too lowto stimulate shoot extension. It is concluded that these results support the theory that hormone-inducednutrient diversion may control lateral bud development.     

Hormone Levels and Apical Dominance in the Aquatic Fern Marsilea drummondii A. Br

Terminal buds and successively subjacent lateral buds of the water fern, Marsilea drummondii, were examined to determine the pattern of hormone distribution in relation to apical dominance. Quantitative levels of indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin and zeatin riboside (Z and ZR), and isopentenyladenosine (iPA) were determined by a solid-phase immunoassay using polycional antihormone antibodies. Enzyme-linked immunosorbent assay was used following a one-step HPLC purification procedure to obtain the free hormones. Active shoot apices contained the most IAA and Z-type cytokinins and inhibited buds the least. No significant differences in ABA levels were found leading to the conclusion that ABA did not play any role in apical dominance. The normal precedence of the most rapid outgrowth of the youngest inhibited bud as observed previously in decapitated plants was well correlated with its very high level of iPA observed in this study. The same phenomenon was observed in the median buds but with a weaker amplitude. The presence of this storage form could indicate that a bud at its entry into quiescence eventually looses the ability to hydroxylate iPA to Z-type cytokinins when it is fully inhibited. IAA and Z + ZR are concluded to be essential for lateral bud growth.     

Effect of relative hormone concentration on auxin-gibberellin interaction in correlative inhibition of axillary buds

Summary Indole-3-acetic acid (IAA) applied to the fully elongated second internode of decapitated Phaseolus multiflorus plants always inhibited axillary bud elongation at concentrations down to 100 g/g lanolin, whereas gibberellic acid (GA₃) enhanced bud elongation at concentrations down to 1000 g/g lanolin. Lower concentrations than these of either IAA or GA₃ were without significant effect. All possible combinations of IAA and GA₃ within the concentration range 10¹ to 10⁵ g/g lanolin were antagonistic; IAA tending to inhibit, and GA₃ promote, axillary bud elongation growth. Treatment of an elongating internode with the hormones resulted in an increase in inhibition of bud growth by IAA in the presence of GA₃.     

Transport of benzyl-8-14C-adenine in pea seedlings in relation to stem apical dominance

In intact, decapitated and decapitated indole-3-acetic acid (IAA) treated pea seedlings the translocation of benzyl-8-^l4C-adenin (¹⁴C-BA) from the roots was studied with regard to the release of lateral buds from apex-induced inhibition. In intact plants (controls) a substantial part of the activity was found in the apical part of the epicotyl. Decapitation resulted in the initiation of growth of lateral buds. As early as 24 h after decapitation and application of¹⁴C-BA a significantly higher activity was found in growing lateral buds (cotylars) of decapitated plants than in inhibited ones of intact or IAA-treated decapitated plants. The accumulation of¹⁴C-activity in stump tops of decapitated plants treated with IAA was associated with the thickening growth.     

Enhancement of lateral bud growth in Coleus blumei BENTH. by (2-chloroethyl) trimethylammonium chloride (CCC)

The relationship of GA to apical dominance in Coleus was examinedby substituting 1 % IAA, in lanolin, for the shoot apex of CCC-treated,control and GA-treated plants containing, theoretically, hyponormal,normal and hypernormal GA levels, respectively. The greatestinhibition of lateral bud growth was obtained in the treatmentcombining 1 % IAA and 100 ppm GA, suggesting that GA may beimportant in the apical dominance of Coleus. CCC inhibited main axis growth, reduced the level of endogenousGA and caused a marked release of lateral buds from apical dominance. The significant stimulation of lateral bud growth by CCC couldnot be ascribed to reduced endogenous GA since it was not reversedby exogenous GA, or by GA plus IAA, whereas 100 ppm GA overcamethe inhibition of main axis growth by CCC. It was also shownthat the CCC stimulation was not a result of compensatory growth,that is, enhanced lateral bud growth resulting from reducedapical bud growth. The CCC effect on lateral buds was interpretedas involving a system independent of auxin and GA or else apossible immobilization of auxin in addition to inhibition ofGA biosynthesis. (Received December 5, 1967; )     

The Effect of Hadacidin on Bud Development and its Implications for Apical Dominance

Hadacidin, which is known to inhibit the enzyme adenylo-succinate synthetase, was applied locally to lateral buds on decapitated Pisum sativum L. plants. In controls the buds grew out normally, but the treated buds were almost completely inhibited. After a delay, the buds overcame the inhibition, and their subsequent outgrowth could be further hastened by the local application of a cytokinin. The inhibition, unlike that due to IAA, was not transported to a second bud, and it could be largely reversed by kinetin or dimethylallylaminopurine. Adenine itself produces little or no reversal, however. There was some reversal by aspartic acid, which is known to reverse, at least partially, the hadacidin inhibition of the isolated enzyme. It is deduced that lateral bud development is dependent on the synthesis of a cytokinin, which may take place by a biochemical route similar, but probably not identical, to that for adenine. It follows that this synthesis takes place locally in the bud itself.     

Isolation and identification of lateral bud growth inhibitor,indole-3-aldehyde,involved in apical dominance of pea seedlings

A lateral bud growth inhibitor was isolated from etiolated pea seedlings and identified as indole-3-aldehyde. The indole-3-aldehyde content was significantly higher in the diffusates from explants with apical bud and indole-3-acetic acid treated decapitated explants, in which apical dominance is maintained, than in those from decapitated ones releasing apical dominance. When the indole-3-aldehyde was applied to the cut surface of etiolated decapitated plants or directly to the lateral buds, it inhibited outgrowth of the latter. These results suggest that indole-3-aldehyde plays an important role as a lateral bud growth inhibitor in apical dominance of pea seedlings.     

Effect of Abscisic Acid and Other Plant Hormones on Growth of Apical and Lateral Buds of Seedlings

The effect of abscisic acid (AbA) on the growth of lateral and apical buds was studied in seedlings of Pisum sativum and some other species. The hormone was applied in three different ways: 1) directly to the lateral bud on the second node of decapitated pea seedlings as 5 μI droplets in an ethanolic solution; 2) to the cut surface of decapitated seedlings: 3) to the apical bud of intact plants. AbA directly applied in amounts of 5 to 0.1 μg to the lateral bud of the second node of decapitated seedlings had a strong inhibitory effect on the bud. Application to the cut surface of seedlings decapitated about 5 mm above the second node resulted in slight inhibition of the lateral bud on the second node and in growth promotion of the bud on the first node. When AbA at 10 to 0.1 μg was applied to the apical bud of intact seedlings, the growth of this bud was inhibited but the lateral buds grew out. It is concluded that the release of the lateral buds from apícal dominance is the result of the inhibitory effect of AbA on growth of the apical bud and of low transport of AbA. This conclusion is supported by application of GA₃ and IAA, individually and each combined with AbA.     

硼对吲哚乙酸在植物体内运输的影响

以绿豆为指示作物,研究缺硼对侧芽生长及³H-吲哚乙酸（IAA）在完整植株体内运输的影响.结果表明：缺硼诱导侧芽生长,导致³H-IAA移动峰靠近植株顶端,茎中³H-IAA的放射性活度也低于供硼充分的植株,说明缺硼抑制了³H-IAA在植株体内的极性运输;无论缺硼与否侧芽中均未检测到³H-IAA,所以侧芽的生长与³H-IAA在其中的积累没有关系,表明硼并不是通过调节IAA在侧芽中的积累,而是通过调节IAA在主茎的移动流调控侧芽生长;给缺硼植株供硼24 h能够恢复IAA在植株体内的极性运输能力.