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.     

Apical Dominance in the 'Rogue' Tomato

The rogue tomato exhibits less apical dominance than the normalplant though the degree of correlative inhibition varies considerablybetween winter- and summer-sown plants. An examination of thelevel of endogenous hormones in both rogue and normal plantsat both times of year indicates that the degree of branchingis strongly associated with the levels of auxin in the tissue.It is suggested that this hormone has an effect on apical dominanceby virtue of its role in hormone-directed transport and by itseffect on the formation of abscisic acid in the region of thelateral buds. The results are discussed in relation to currenthypotheses of the mechanism of apical dominance.     

Apical Dominance in Vicia faba

Apical dominance phenomena have been studied in seedlings ofVicia faba particularly in relation to the movement about theplant of uracil-2-¹⁴C applied to the cotyledons. Decapitationjust below the second node releases the growth of the lowermostlateral bud and inhibition is completely reimposed by applicationof indole-3-acetic acid (IAA) to the cut surface. Uracil-2-¹⁴Capplied in solution to the cotyledons is distributed in thestems of all experimental seedlings with no consistent differencesdue to decapitation or IAA application. On the other hand, decapitationresults in a rapid increase in uracil-2-¹⁴C content in the lateralbuds which far exceeds their promoted growth. This uptake iscompletely suppressed by IAA application. A ring of tri-iodobenzoicacid (TIBA)-lanolin paste around the stem above the bud suppressesIAA action both in bud growth and on uracil-2-¹⁴C uptake, andalso on the movement of IAA-1-¹⁴C down the stem. TIBA-application to the base of the bud does not prevent IAAaction on bud growth, but also does not prevent the movementof IAA-1-¹⁴C (or a water soluble product of its metabolism)into the bud. Direct application of kinetin to the lateral bud of intact plantscauses a short-lived release of growth. Gibberellic acid producesa smaller and scarcely significant increase which is additiveto the kinetin effect. Neither has any effect on uracil-2-¹⁴Cmovement into the bud. The implications of these findings are discussed in relationto various existing theories of the mode of auxin action inapical dominance and it is concluded that their strongest supportis for a mechanism involving the suppression of phloem differentiationin the vascular supply to the bud.     

植物腋芽生长与顶端优势

文章介绍植物腋芽生长与顶端优势的研究进展。     

Light Effects on Apical Dominance

Reducing light intensity from 18·0 klx to 5·4klx promoted main-stem growth in Phaseolus vulgaris but leftlateral extension unaffected. Shading individual laterals orapices of main stems promoted elongation of the shaded portion.Increasing day length from 8 to 16 or 24 h did not greatly affectplant growth if full-intensity and full-spectrum light was used.If, however, the additional light was supplied by incandescenttubes containing a high proportion of infra-red light, growthof main stems but not laterals was induced in proportion tothe length of the additional light period. It is suggested thatthe increased growth of the main stem in response to infra-redlight prevented the equivalent response of the laterals becauseof the enhanced ability of the main stem to suppress lateralelongation.     

Apical Dominance in Phaseolus vulgaris L.

Although determinations of the ABA content of lateral buds ofPhaseolus vulgaris revealed no difference between decapitatedand intact control plants in the first 12 h following decapitation,a relative decrease in the ABA content of lateral buds of decapitatedplants was detectable 24 h following decapitation. Shoot decapitationwas also observed to result in a decrease in the ABA contentof stem tissue. The application of IAA to the stem of decapitatedplants prevented these changes and increased the ABA contentof stem tissue relative to that of intact plants. The levelsof IAA and ABA were also determined in the stem tissue fromthe nodes of intact bean plants. The possible interdependenceof these two plant hormones was further investigated by a studyof [2_–14ClABA metabolism. The results are discussed inrelation to the possible role of these hormones in apical dominance. Key words: Apical dominance, Abscisic acid, Indole-3-acetic acid     

The Mechanism of Apical Dominance in Coleus

The development of lateral buds in isolated stems of Coleus blumei is inhibited by low concentrations of indoleacetic acid or other auxins, just as in other plants. The inhibition can be fully reversed by kinetin, about 3 times as much kinetin as IAA being needed. However, the outgrowth of the same lateral buds on intact Coleus plants is sensitive to environmental conditions, well-nourished plants in full daylight often showing little inhibition by applied auxin. It is shown that (a) the solvent used for IAA, (b) the light intensity and (c) the nitrogen and phosphorus nutrition, all control the sensitivity of the buds to auxin inhibition. Using water instead of lanolin, lowering the light intensity or decreasing the supply of either nitrogen or phosphorus all increase the degree of apical dominance.     

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.     

乙烯在豌豆植株顶端优势中的作用

用人工合成细胞分裂素BAP和CPPU处理豌豆植株叶腋可诱导处理部位侧芽的生长,同时伴有大量乙烯产生;用乙烯合成抑制剂AVG处理或植株去顶同样可导致创芽生长,但乙烯释放量却明显少于对照,表明侧芽的生长与乙烯释放量的多少无关。而3种物质处理后诱导产生的侧芽的数目、长度及其鲜重与处理部位内源IAA含量的增加则呈正相关。     

Senescence of Inhibited Shoots of Peas and Apical Dominance

When peas of the cultivar Radio have their epicotyl removedand are selected to have two unequal shoots, the smaller ofthese shoots is inhibited and starts senescing when the plantsare about 17 days old. This senescence is a correlative phenomenon:removal of the dominant shoot prevents it in every case. Indole-3-acetic acid partially replaces the dominant shoot incausing the senescence of the inhibited shoot. Kinetin, whenapplied to the inhibited shoot, prevents its senescence andcauses renewed growth. The control of this senescence, therefore, resembles the inhibitionof lateral growth. It differs from it in occurring only whenthe plants have reached a definite age. The age at which senescencestarts is the same under very different conditions; it doesnot depend on a lack of nutrients or the maturation of the leaves.It might be associated with the development of flowers.     

Some Observations on Factors Controlling Apical Dominance in the 'Rogue' Tomato

The rogue tomato differs from the normal plant in that it exhibitsa lesser degree of apical dominance. Grafting techniques andmeasurements of the endogenous levels of growth substances inthe two types have been used in order to establish whether thisdifference is due to an altered hormonal balance in the roguetype. The results suggest that root-produced cytokinins play no rolein the control of apical dominance in the tomato plant, andthat lateral bud out-growth is influenced by a balance betweenapically-produced auxin, abscisic acid produced at the sitesof bud development and cytokinins synthesized within the budsthemselves. Lycopersicon esculentum L., tomato, apical dominance, abscisic acid, auxins, cytokinins, growth regulation     

Endogenous Cytokinins and the Breaking of Dormancy and Apical Dominance in Potato Tubers

Cytokinins are present in all parts of potato tubers, and areequally distributed between the apical, lateral, and internodaltissue when dormant. However, the breaking of dormancy coincidedwith a rapid increase in the free base cytokinin levels in theapical buds and the tissue adjacent to it. These high levelsof cytokinin in the apical tissue were maintained while apicaldominance was displayed. Once apical dominance was overcomethe cytokinin levels in the lateral buds and the tissue adjacentto them were similar to the levels in the apical regions. Thepresent evidence suggests that cytokinin glucosides are transportedto the meristematic regions of the tubers where they are hydrolysedto their free bases. Amounts of free bases in excess of thoserequired for growth are apparently again converted to storageforms (particularly zeatin glucoside) in the meristematic regionsof the tubers and in the sprouts.     

Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

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

植物的顶端优势和水分上升机理新说

植物体有一个能量系统,由植物顶端、由植物顶端、形成层及其初生韧皮部和木质部、传递细胞等组成。这些细胞含线粒体量多质好,摘顶等刺激这些地方ＡＴＰ复合酶能产生大量能量,通过胞间连丝引起连锁反应并刺激和激活激素、营养物质等而产生生命活动、项端优势等。植物细胞的原生质是一种液晶,只需极少能量便能产生很大的作用。除去顶芽,刺激线粒体能产生大量能量供给侧芽,激活侧芽激素等而使侧芽生长,由于能量作功,逐渐减少,     

Cytokinin/Auxin Control of Apical Dominance in Ipomoea nil

Although the concept of apical dominance control by the ratioof cytokinin to auxin is not new, recent experimentation withtransgenic plants has given this concept renewed attention.In the present study, it has been demonstrated that cytokinintreatments can partially reverse the inhibitory effect of auxinon lateral bud outgrowth in intact shoots of Ipomoea nil. Althoughless conclusive, this also appeared to occur in buds of isolatednodes. Auxin inhibited lateral bud outgrowth when applied eitherto the top of the stump of the decapitated shoot or directlyto the bud itself. However, the fact that cytokinin promotiveeffects on bud outgrowth are known to occur when cytokinin isapplied directly to the bud suggests different transport tissuesand/or sites of action for the two hormones. Cytokinin antagonistswere shown in some experiments to have a synergistic effectwith benzyladenine on the promotion of bud outgrowth. If theratio of cytokinin to auxin does control apical dominance, thenthe next critical question is how do these hormones interactin this correlative process? The hypothesis that shoot-derivedauxin inhibits lateral bud outgrowth indirectly by depletingcytokinin content in the shoots via inhibition of its productionin the roots was not supported in the present study which demonstratedthat the repressibility of lateral bud outgrowth by auxin treatmentsat various positions on the shoot was not correlated with proximityto the roots but rather with proximity to the buds. Resultsalso suggested that auxin in subtending mature leaves as wellas that in the shoot apex and adjacent small leaves may contributeto the apical dominance of a shoot. (Received September 24, 1996; Accepted March 16, 1997)     

Light and Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

Gibberellic acid (GA₂), kinetin, and indole-3yl-acetic acid(IAA) each at four concentrations (0, 0.5, 5, and 50 µM)were applied alone and in all possible combinations to rootsof Phaseolus vulgaris L. grown under four different light regimes(7000, 14 000, 21 000, and 28 000 lx). GA₃ increased growthof main stem and laterals but reduced apical dominance, especiallyin the absence of, or at low kinetin concentrations. A highlevel of kinetin lowered GA₃ induced growth of main stems and,to a lesser extent, laterals. Kinetin greatly reduced apicaldominance, especially in the absence of, or at low GA₃ concentrations.IAA slightly reduced growth of main stems and laterals and slightlyincreased apical dominance. Generally the magnitude of the IAAeffects were less than those of GA₃ or kinetin and there wereless interaction between IAA and other factors than betweenGA₃ or kinetin and other factors. Light affected growth of bothmain stem and laterals but the effect was dependent on GA₃ andkinetin levels and the interactions were complex. Generallya hormone balance seems to be operative with gibberellin-promotinggrowth of main stem and laterals and cytokinins and possiblyauxins preventing excessive elongation. Differential responsesbetween main stem and lateral may be due to different localhormone concentrations and over-all responses may be temperedby light intensity.     

Apical Dominance and the Utilization of Carbo-hydrates During Storage of Potato Tubers

Although carbohydrates are metabolized throughout potato tubersduring storage, it would nevertheless appear as if there isenhanced carbohydrate metabolism in the region of the apicalbud. Soluble sugars are higher in this region of the tuber duringthe whole period of storage and growth. In the sprouts themselvesglucose accumulates to extremely high levels. It is postulatedthat this glucose is pooled and is eventually used for the synthesisof starch, especially during the development of ‘littlepotatoes’ which occurs during prolonged storage at lowtemperature in the dark.     

Catabolism of Cyanogenic Glycosides by Purified Vicianin Hydrolase from Squirrel's Foot Fern (Davallia Trichomanoides Blume)

Vicianin hydrolase, which catalyzes the hydrolysis of vicianin (K_m, 4.9 millimolar) to (R)-mandelonitrile and vicianose at an optimum pH of 5.5, was extensively purified from the young fronds and fiddleheads of the squirrel's foot fern (Davallia trichomanoides Blume) using DEAE-cellulose and Ultrogel HA chromatography. The native molecular weight of the enzyme was 340,000, and the isoelectric point was 4.6 to 4.7. SDS-PAGE analysis yielded three polypeptides with molecular weights of 56,000, 49,000, and 32,500. The enzyme hydrolyzed only a narrow range of glycosides and, among cyanogenic glycosides, exhibited a strict requirement for (R)-epimers and a preference for disaccharides over monosaccharides. (R)-Amygdalin, (R)-prunasin and p-nitrophenyl-β-d-glucoside were hydrolyzed at 27, 14, and 3%, respectively, of the rate of vicianin hydrolysis. Mixed substrate studies showed that (R)-vicianin, (R)-prunasin, and p-nitrophenyl-β-d-glucoside competed for the same active site. The enzyme was significantly inhibited by castanospermine, δ-gluconolactone, and p-chloromercuriphenylsulfonate. Failure to recognize concanavalin A-Sepharose 4B and to stain with periodic acid-Schiff reagent indicated that the enzyme was not a glycoprotein.