Release Of Buds Research Articles

Morphology of potato (Solanum tuberosum L. cv. Sante) stem node cultures in relation to the level of endogenous cytokinins

Stem node culture of the potato (Solanum tuberosum) cv. Sante was used to examine the phenotypical alterations due to different levels of endogenous cytokinins. The altered phenotype, which dramatically deviates from the control phenotype, was induced after treatment of plantlets with 1 μm jasmonic acid. Plantlets grown on the medium supplemented with jasmonic acid were taller, with well developed root systems, expanded leaves, thickened stems, and they showed hyperhydric symptoms. Their cytokinin content was about half that of the control plantlets. Morphologic characteristics corresponding to transgenic plants that overproduce cytokinins, including release of axillary buds and inhibited rooting, correlated with the high cytokinin levels in control plants.

Branching in Pea (Action of Genes Rms3 and Rms4).

The nonallelic ramosus mutations rms3-2 and rms4 of pea (Pisum sativum L.) cause extensive release of vegetative axillary buds and lateral growth in comparison with wild-type (cv Torsdag) plants, in which axillary buds are not normally released under the conditions utilized. Grafting studies showed that the expression of the rms4 mutation in the shoot is independent of the genotype of the root-stock. In contrast, the length of the branches at certain nodes of rms3-2 plants was reduced by grafting to wild-type stocks, indicating that the wild-type Rms3 gene may control the level of a mobile substance produced in the root. This substance also appears to be produced in the shoot because Rms3 shoots did not branch when grafted to mutant rms3-2 rootstocks. However, the end product of the Rms3 gene appears to differ from that of the Rms2 gene (C.A. Beveridge, J.J. Ross, and I.C. Murfet [1994] Plant Physiol 104: 953-959) because reciprocal grafts between rms3-2 and rms2 seedlings produced mature shoots with apical dominance similar to that of rms3-2 and rms2 shoots grafted to wild-type stocks. Indole-3-acetic acid levels were not reduced in apical or nodal portions of rms4 plants and were actually elevated (up to 2-fold) in rms3-2 plants. It is suggested that further studies with these branching mutants may enable significant progress in understanding the normal control of apical dominance and the related communication between the root and shoot.

Dormancy release and chilling requirement of buds of latitudinal ecotypes of Betula pendula and B. pubescens.

Bud burst and dormancy release of latitudinal ecotypes of Betula pendula Roth and B. pubescens Ehrh. from Denmark ( approximately 56 degrees N), mid-Norway ( approximately 64 degrees N) and northern Norway ( approximately 69 degrees N) were studied in controlled environments. Dormant seedlings were chilled at 0, 5 or 10 degrees C from October 4 onward and then, at monthly intervals from mid-November to February, batches of seedlings were held at 15 degrees C in an 8-h (SD) or 24-h (LD) photoperiod to permit flushing. A decline in days to bud burst occurred with increasing chilling time in all ecotypes. In November, after 44 chilling days, time to bud burst was least in plants chilled at 0 and 5 degrees C. The difference diminished with increasing chilling time, and in February, after 136 chilling days, bud burst was earliest in plants chilled at 10 degrees C. Long photoperiods during flushing significantly reduced thermal time after short chilling periods (44 and 74 days), but had no effect when the chilling requirement was fully met after 105 or more chilling days. No significant difference in these responses was found between the two species. In both species, chilling requirement decreased significantly with increasing latitude of origin. Bud burst was normal in seedlings overwintered at 12 degrees C, but was erratic and delayed in seedlings overwintered at 15 and especially at 21 degrees C, indicating that the critical overwintering temperature is between 12 and 15 degrees C. We conclude that there is little risk of a chilling deficit in birch under Scandinavian winter conditions even with a climatic warming of 7-8 degrees C. The likely effects of a climatic warming include earlier bud burst, a longer growing season and increased risk of spring frost injury, especially in high latitude ecotypes.

Effect of apex excision and replacement by 1‐naphthylacetic acid on cytokinin concentration and apical dominance in pea plants

As known from literature lateral buds from pea (Pisum sativum) plants are released from apical dominance when repeatedly treated with exogenous cytokinins. Little is known, however, about the endogenous role of cytokinins in this process and whether they interact with basipolar transported IAA, generally regarded as the main signal controlling apical dominance. This paper presents evidence that such an interaction exists.The excision of the apex of pea plants resulted in the release of inhibited lateral buds from apical dominance (AD). This could be entirely prevented by applying 1‐naphthylacetic acid (NAA) to the cut end of the shoot. Removal of the apex also resulted in a rapid and rather large increase in the endogenous concentrations of zeatin riboside (ZR), isopentenyladenosine (iAdo) and an as yet unidentified polar zeatin derivative in the node and internode below the point of decapitation. This accumulation of ZR and iAdo, was strongly reduced by the application of NAA. The observed increase in cytokinin concentration preceded the elongation of the lateral buds, suggesting that endogenous cytokinins play a significant role in the release of lateral buds from AD. However, the effect of NAA on the concentration of cytokinins clearly demonstrated the dominant role of the polar basipetally transported auxin in AD. The results suggest a mutual interaction between the basipolar IAA transport system and cytokinins obviously produced in the roots and transported via the xylem into the stem of the pea plants.

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.

396 CALLA LILY VEGETATIVE & REPRODUCTIVE DEVELOPMENT PATTERNS

The release of latent buds (adaptive reiteration) and aerial shoot architecture of the rhizomatous calla lily plant has been researched for pot production. Rhizome mapping has explicitly shown vegetative and floral bud positioning in relation to tissue growth and expansion. Floral initiation normally occurred only on the mother portion of rhizomes. Gibberellic acid (GA3) application enhanced this phenomenon and caused initiation on daughter ramets. Bud excision performed at planting through Day 16 microscopically revealed lack of floral initiation in dissected meristems prior to planting, transition by Day 4, elongation beginning at Day 8 and `small to medium sized spadixes present by Day 12 and 16. Floral development was similar in treated and untreated primary buds, but delayed in secondary and tertiary buds with elongation occurring by Day 16. Pretreatment of GA3 prior to planting revealed spadix presence at Day 0. Floral development correlated with ramet size showed most flowers on largest ramets but formation on all sizes with GA3 treatment. GA3 also caused increased vegetative bud formation on rhizomes.

Does Auxin Play a Role in the Release of Apical Dominance by Shoot Inversion in Ipomoea nil?

According to the auxin-inhibition hypothesis of apical dominance, apically produced auxin moves down the stem and inhibits axillary bud outgrowth, either directly or indirectly. This hypothesis has been examined further by monitoring changes in basipetal auxin transport and endogenous auxin concentration in Ipomoea nil caused by shoot inversion, a stimulus that releases apical dominance. The results indicate that inversion reduces auxin transport in the main stem. In upright shoots of intact plants, a 16-h pretreatment with [3H]IAA 4 cm below the apex results in downward movement of label and accumulation in nodes, especially the cotyledonary node. Label does not accumulate in the lateral buds. GC-MS determinations of endogenous free auxin level in the fourth node, where a lateral bud grows out following inversion of the upper part of the shoot, show no changes at 3 and 8 h after inversion, the range of times for inversion-induced bud release, or at 24 h, when bud outgrowth is continuing. However, inversion did cause a just-detectable decrease (approx. 10%) in the IAA level of the shoot's elongation region. Although auxin transport in segments of the main stem is partially inhibited by inversion over a period shorter than the latent time of bud release, thus providing a means for the expected depletion of auxin in the fourth node, no depletion could be detected there. These results suggest that either a decrease in IAA level in the main stem is not causal of bud release or that the decreased IAA pool responsible for bud release is compartmented and cannot be measured in whole-tissue extracts.

Tall Fescue Sward Dynamics: II. Influence of Four Plant Growth Regulators

Very little is known about the influence of plant growth regulators (PGRs) on turfgrass sward dynamics (including shoot development and mortality) and reproductive development. PGR‐induced growth suppression might increase assimilate supply to axillary buds, resulting in their release. A 2‐yr study was conducted to determine the impact of four PGRs applied in late March on the sward dynamics of ‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.). Maleic hydrazide [1,2‐dihydro‐3,6‐pyridazinedione] and mefluidide N‐(2,4‐dimethyl‐5‐[([trifluoromethyl]‐sulfonyl)amino]phenyl)acetamide], two PGRs that suppress vegetative and reproductive growth, were applied at 4.48 and 0.56 kg ha−1, respectively. Flurprimidol [α‐(1‐methylethyl)‐α‐[4‐(trifluoromethoxy)phenyl]‐5‐pyrimidinemethanol] and paclobutrazol [(R*,R*)‐(±)‐β‐[(4‐chlorophenyl)methyl]‐α‐,(1,1dimethylethyl)‐1H‐1,2,4‐triazole‐1‐ethanol], two PGRs that suppress vegetative growth only, were each applied at 1.12 kg ha−1. Twenty shoots were labeled at random in each plot and observed 3, 6, 10, 14, 19, and 31 weeks after treatment (WAT). Maleic hydrazide and mefluidide treatments caused 75% shoot mortality (55% greater than the control) by 10 WAT; however, stand density was unaffected by maleic hydrazide and mefluidide, due to the release of axillary buds beginning 2 WAT. Maleic hydrazide and mefluidide induced a postinhibition growth response, with proliferation of new shoots and rapid growth of shoots surviving chemical treatment. Leaf and crown total nonstructural carbohydrates (TNC) declined during the postinhibition response from 4 to 6 WAT. Flurprimidol and paclobutrazol, despite effective foliar growth suppression, failed to influence shoot mortality, axillary bud release, or TNC levels. Patterns of TNC partitioning in response to PGRs, though different, did not appear to be the result of the effectiveness of seedhead suppression.

Effect of Cytokinin and Anticytokinin on the Tillering of Barley.

Cytokinin, N-[2-isopentenyl] adenine (2iP), increased and anticytokinin, 4-chloro-2-cyclobutylamino-6-ethylamino-s-triazine (CCET), retards tillering of barley. Tillering was also shown to be retarded by auxin, α-naphthalene acetic acid (NAA) and promoted by antiauxin, 2, 3, 5-triiodobenzoic acid (TIBA). TIBA and 2iP treatment promoted tillering by altering the parallelism of leaf emergence between main stem and tiller ; and the tillering itself, including secondary or tertiary tillers, was hastened which resulted in more tillers being produced at high leaf positions where the untreated control plants had not produced any tillers. Conversely anticytokinin CEET and auxin NAA inhibited or delayed the release of tiller buds even when corresponding leaves on the main stem had already developed to the point where tiller buds normally occur.

The Role of Chilling in Releasing Olive Floral Buds from Dormancy

Experiments with olive (Olea europaea L.) shoot explants were carried out to determine the influence of winter chilling on the release of axillary buds from dormancy. This investigation was designed to explore an alternative explanation for the confusing concept surrounding the role of chilling in olive floral induction. Leafy explants collected from 10 Nov. to 6 Mar. were grown in a greenhouse under mist at 13/24C (night/day) and in a growth chamber at 10/21C (night/day) to determine the end of dormancy. Growth of floral buds from leafy explants was first recorded from 5 Jan. samples. After that date the percentage of developing floral buds and rate of their development increased. Floral bud abscission, increase in bud fresh weight, and simultaneous decrease of relative bud dry weight were associated with growth initiation of floral buds. Manual defoliation of adult trees during the period of shoot explant collection indicated that leaves play a critical role in development once the floral buds had completed dormancy. Supplementary chilling of isolated shoots collected 20 Jan. demonstrated that 7.2C was sufficient to complete chilling requirements, while 12.5C allowed both the completion of chilling requirements and the proper temperature for subsequent floral bud growth. Winter chilling is required to release previously initiated floral buds from dormancy, and we question the previous concept that the role of chilling is to induce olive floral initiation.

Apical dominance in Phaseolus vulgaris: effect of the nitrogen supply

Nitrogen is one of the most effective of the many factors that can influence the degree of apical dominance, but the mechanism involved has not been determined. In experiments with Phaseolus vulgaris, grown in sand culture under controlled conditions, increasing the nitrogen concentration in the nutrient solution from 52.5 to 315 mg/L released the bud at the primary leaf node from inhibition. Precise measurements (± 1 μm) with a strain gauge transducer showed that the bud growth response was initiated ca. 3 h after increasing the N supply. The increase in the total N content of the buds of the high-N plants was significantly correlated with their uptake of water. Increases in the amino-N content of the buds of the high-N plants over the first 24 h of the treatment period were correlated with significant increases in their total water potential and pressure potential, but their solute potential was unaffected. The absence of any reduction in their solute potential was attributed to the dilution effect of the increased uptake of water. These results are consistent with the hypothesis that N initiates the release of buds from apical dominance by an osmotic effect that increases their capacity to compete for water with the parent shoot. Key words: apical dominance, nitrogen, Phaseolus, water potential.

Stolon development and some aspects of musculature in the characterization of Ihlea racovitzai (van Beneden, 1913) and Ihlea magalhanica (Apstein, 1894) (Tunicata, Thaliacea)

A new contribution to the characterization of the salps Ihlea racovitzai and I. magalhanica, particularly their reproductive features, is presented. In both species two oocytes develop in the aggregate form, in the solitary form stolon growth is continuous. Buds grow continuously from the zone of deployment to the distal region without forming blocks or intermediate pieces. In Ihlea racovitzai the exit of the stolon and the resulting release of buds occurs later than in I. magalhanica. In the latter it takes place at the beginning of the strobilation of the stolon, which means an earlier and perhaps more continuous release of buds. The opening for the release of the buds is ventral and anterior to the nucleus in I. magalhanica and ventrolateral and posterior to the nucleus in I. racovitzai. Differences in the pattern of body muscle VII and the atrial retractors in the solitary forms are underlined.

Field evaluation of tissue-cultured bananas in south-eastern Queensland

Field performance is described for tissue cultured plants and conventional propagules of planting material of banana cultivar 'New Guinea Cavendish' (Musa sp., AAA group, Cavendish subgroup). Tissuecultured plants were produced by either regeneration of plants from callus culture or by micropropagation of plants following the release of dormant buds at the leaf axils of explants. The conventional material consisted of suckers and 'bits' (lateral buds and associated corm material). Tissue-cultured plants established more quickly, were taller, and had a shorter time to bunch emergence and harvest of plant crop than conventional planting material. They had significantly (P<0.05) higher yields in terms of bunch weight, which was a function of greater numbers of fingers and hands. These advantages did not extend to the ratoon crop. Sucker production on tissue-cultured plants was significantly (P<0.01) higher up to 8 months after planting, equal to conventional material from 8 months to harvest, and then significantly lower. Twenty-two per cent of the plants derived from callus were off-types compared with 3% in the line produced by axillary bud proliferation. No off-types were observed in conventional planting material.

In vitro development of adventitious shoots in Euonymus alatus (Celastraceae)

Mature embryos of Euonymus alatus (Thunb.) Sieb. were excised aseptically from seeds before or after cold treatment and germinated in light on half-strength Murashige and Skoog (MS) medium with 2% sucrose, 0.7% agar, naphthalene acetic acid (NAA) at 0.01 mg l −1 and benzylaminopurine (BAP) at 0.1–0.5 mg l −1. Hypocotyls of these seedlings were cut into 1–2-mm segments and induced to form adventitious shoots on the same medium. Large numbers of shoots, most bearing several pairs of leaf primordia, were produced per isolated hypocotyl segment. These shoots could be further multiplied by axillary bud release on medium containing 0–0.1 mg l −1 NAA and 0.0–0.3 mg l −1 BAP. Adventitious shoot formation began with profuse callus formation, originating in the epidermis of the hypocotyl. Vascular strands differentiated from callus parenchyma were observed extending into surface protuberances and, in older cultures, into adventitious shoot buds. Rooting was induced in vitro by culturing shoots on medium containing 0.4% agar and 3 mg l −1 indolebutyric acid (IBA). Rooted shoots were successfully transferred to vermiculite, hardened off and had the appearance of normal field-grown plants, including the characteristic winged periderm of this species.

Alterations of Endogenous Cytokinins in Transgenic Plants Using a Chimeric Isopentenyl Transferase Gene.

Cytokinins, a class of phytohormones, appear to play an important role in the processes of plant development. We genetically engineered the Agrobacterium tumefaciens isopentenyl transferase gene, placing it under control of a heat-inducible promoter (maize hsp70). The chimeric hsp70 isopentenyl transferase gene was transferred to tobacco and Arabidopsis plants. Heat induction of transgenic plants caused the isopentenyl transferase mRNA to accumulate and increased the level of zeatin 52-fold, zeatin riboside 23-fold, and zeatin riboside 5[prime]-monophosphate twofold. At the control temperature zeatin riboside and zeatin riboside 5[prime]-monophosphate in transgenic plants accumulated to levels 3 and 7 times, respectively, over levels in wild-type plants. This uninduced cytokinin increase affected various aspects of development. In tobacco, these effects included release of axillary buds, reduced stem and leaf area, and an underdeveloped root system. In Arabidopsis, reduction of root growth was also found. However, neither tobacco nor Arabidopsis transgenic plants showed any differences relative to wild-type plants in time of flowering. Unexpectedly, heat induction of cytokinins in transgenic plants produced no changes beyond those seen in the uninduced state. The lack of effect from heat-induced increases could be a result of the transient increases in cytokinin levels, direct or indirect induction of negating factor(s), or lack of a corresponding level of competent cellular factors. Overall, the effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation. Since no alterations in the programmed differentiation pattern were found with increased cytokinin levels, this process may be controlled by components other than absolute cytokinin levels.

Apical dominance in Phaseolus vulgaris. The triggering effect of shoot decapitation and leaf excision on growth of the lateral buds

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node of Phaseolus vulgaris (L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth.Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral buds.

Cytokinin activities ofN 6-benzyladenosine derivatives hydroxylated on the side-chain phenyl ring

Cytokinin activities ofN 6-benzyladenosine (bzl6Ado) and its derivatives hydroxylated on the side chain phenyl ring inortho, meta, andpara positions were compared in four bioassays based on stimulation of growth of tobacco callus, retention of chlorophyll in excised wheat leaves, dark induction of betacyanin synthesis inAmaranthus cotyledons, and release of lateral buds of pea from apical dominance. In all these bioassays hydroxylation of the phenyl ring of bzl6Ado inortho andpara positions significantly decreased cytokinin activity. Compared with bzl6Ado, the activity was decreased about 10× in the tobacco callus bioassay and wheat leaf chlorophyll retention test, 100× in theAmaranthus betacyanin bioassay, and 20× and 200×, respectively, in the pea bud test. Hydroxylation of the phenyl ring inmeta position increased activity in the tobacco callus, and wheat leaf chlorophyll retention bioassays, 9× and 1.7×, respectively, decreased activity about 2.4× in the pea bud test and was without effect in theAmaranthus bioassay. Cytokinin activity of themeta hydroxy derivative,N 6-(m-hydroxybenzyl) adenosine, was as high as that oftrans-zeatin in all four bioassays. Possible regulation of biological activities of cytokinins by positionally specific hydroxylation of the side chain phenyl ring is discussed with respect to the reported occurrence of natural purinyl cytokinins with aromatic side chains.

In vitro propagation of Hydrangea quercifolia Bartr.

In vitro propagation of Hydrangea quercifolia is possible through differentiation of leaf callus into plantlets and stimulation of axillary bud release from the dormant shoots. The plantlets derived from leaf callus appeared to be suitable for commercial propagation due to their uniform growth pattern and ease of rooting.

Role of water relations and photosynthesis in the release of buds from apical dominance and the early reinvigoration of decapitated poplars

A decrease in xylem pressure potential starting 1 h after decapitation of young hybrid poplars (Populus deltoides Bartr. ×Populus nigra L. cv. DN22) reduced stomatal conductance and transpiration rates for the first 3 days after decapitation. This early moisture stress was alleviated 4 to 5 days after decapitation, resulting in substantial increases in stomatal aperture, transpiration and net photosynthetic rates which continued for the remainder of the one week measurement period. The results suggest the following sequence of events in the decapitated plant: After a brief moisture stress, decapitation increases moisture availability by increasing the root/shoot ratio and by reducing shoot competition for moisture. Improvement in hydration releases buds from apical dominance and increases stomatal conductance and rates of net photosynthesis. This, in turn, leads to the acceleration of growth observed when plants are reinvigorated by decapitation.

Mechanical perturbation-induced ethylene releases apical dominance in Pharbitis nil by restricting shoot growth

Mechanical perturbation (MP, rubbing) of internodes of Pharbitis nil shoots initiates release of lateral buds (LB) from apical dominance within 48 h. Evidence is presented which suggests that MP promotion of LB outgrowth is mediated by ethylene-induced restriction of main shoot growth. Ethylene production in the internodes is stimulated by MP within 2 h. Effects of MP are mimicked by treatments with 1-aminocyclopropane-1-carboxylic acid (ACC) and are negated by the inhibitors of ethylene production or action, aminoethoxy vinylglycine (AVG) and AgNO 3. The fact that effects of MP, ACC and ethylene inhibitors are observed to occur on main shoot growth at least 24 h before they are observed to occur on LB growth suggests a possible cause and effect relationship. MP also causes an increase in internode diameter. MP stimulation of ethylene production appears to be mediated by ACC synthase. The results of this study and our previous studies suggest that apical dominance may be released by any mechanism which induces ethylene restriction of main shoot growth.