Removal Of Apex Research Articles

Changes in Phytohormone Status in Stems and Roots after Decapitation of Pea Seedlings

Experiments were performed on the first and second internodes and 4-cm-long apical segments of main roots of pea (Pisum sativum L.) seedlings, grown in the light and decapitated above the second node on the seventh day after seed germination. Endogenous phytohormones were measured by the enzyme-linked immunosorbent assay during three days after decapitation of seedlings. The IAA level in the internodes decreased 2–3 times on the second day after decapitation of seedlings while the cytokinin level increased 5–6 times for zeatin and zeatin riboside (Z and ZR) and 1.5–2 times for isopentenyl adenine and isopentenyl adenosine (IP and IPA). In contrast to internodes, the IP and IPA contents in the roots of decapitated seedlings did not change, but the levels of Z and ZR increased 1.5–2 times compared to intact plant roots. The IAA level in the apical region of root remained almost unchanged after the removal of shoot apex. It was concluded that the apical meristem of the main root is not the site of the cytokinin response to the auxin signal coming from the stem apex and that a slight accumulation of Z and ZR after decapitation is due to upper zones of the root. There was no difference in the content of gibberellin-like substances between the internodes of intact and decapitated seedlings. However, the content of gibberellins (GA) in the root tip decreased after decapitation of seedling, which suggests an essential role of apical bud in supplying the root with GA and/or intermediates for their biosynthesis.

Gradients in stomatal conductance, xylem sap ABA and bulk leaf ABA along canes of Vitis vinifera cv. Shiraz: molecular and physiological studies investigating their source.

Gradients were observed in xylem sap ABA and in stomatal conductance along canes of Vitis vinifera L. cv. Shiraz. To investigate the source of the ABA responsible for these gradients a series of girdling and decapitation experiments were carried out. Leaf stomatal conductance and bulk ABA of leaves and apices were measured in control plants and in response to apex removal or girdling. Gradients in leaf ABA were observed over the first eight expanded leaves of field-grown Shiraz, with higher concentrations of ABA observed towards the apex. Gradients in stomatal conductance that correlated negatively with the concentration of ABA in the leaf ([ABA]leaf) were also observed over the first eight leaves. No significant effect of decapitation was observed on either leaf ABA or stomatal conductance except for the leaf immediately below the apex where a transient increase in [ABA]leaf was observed after 24 h with no corresponding decrease in conductance. Girdling resulted in an increase in [ABA]leaf in leaves distal to the girdle without the corresponding effect on conductance. These effects were further studied at the level of gene activity. To facilitate this, gene sequences encoding two key enzymes involved in the biosynthetic pathway of ABA in grape, zeaxanthin epoxidase (Zep) and 9-cis-epoxycarotenoid dioxygenase (NCED), were isolated and characterised. The cDNA sequences were used as probes to measure the abundances of their respective mRNAs in the leaf and apical material. Levels of expression of one of the two genes encoding NCED, VvNCED1, reflected the gradients in [ABA]leaf in control vines, however treatment-induced changes in ABA were not always associated with corresponding changes in VvNCED1 expression. The abundances of both the VvNCED2 mRNA and Zep mRNA increased with increasing leaf age and did not appear to be associated with either the [ABA]leaf or the expression of VvNCED1.

Spatial and temporal changes in multiple hormone groups during lateral bud release shortly following apex decapitation of chickpea (Cicer arietinum ) seedlings

Although the co-ordination of promotive root-sourced cytokinin (CK) and inhibitory shoot apex-sourced auxin (IAA) is central to all current models on lateral bud dormancy release, control by those hormones alone has appeared inadequate in many studies. Thus it was hypothesized that the IAA : CK model is the central control but that it must be considered within the relevant timeframe leading to lateral bud release and against a backdrop of interactions with other hormone groups. Therefore, IAA and a wide survey of cytokinins (CKs), were examined along with abscisic acid (ABA) and polyamines (PAs) in released buds, tissue surrounding buds and xylem sap at 1 and 4 h after apex removal, when lateral buds of chickpea are known to break dormancy. Three potential lateral bud growth inhibitors, IAA, ABA and cis-zeatin 9-riboside (ZR), declined sharply in the released buds and xylem following decapitation. This is in contrast to potential dormancy breaking CKs like trans-ZR and trans-zeantin 9-riboside 5′phosphate (ZRMP), which represented the strongest correlative changes by increasing 3.5-fold in xylem sap and 22-fold in buds. PAs had not changed significantly in buds or other tissues after 4 h, so they were not directly involved in the breaking of bud dormancy. Results from the xylem and surrounding tissues indicated that bud CK increases resulted from a combination synthesis in the bud and selective loading of CK nucleotides into the xylem from the root.

Effect of top excision and replacement by 1-naphthylacetic acid on partition and flow of potassium in tobacco plants.

The effect of removal of the shoot apex of 92-d-old tobacco plants and its replacement by 1-naphthylacetic acid (NAA) on sink-source relationships and on the flows and partitioning of potassium and water has been studied over a short-term period of 7 d (intact control plants) or 8 d (decapitated and NAA-treated plants). For determining flows an upper, middle and lower stratum of three leaves each were analysed. Within the study period three new leaves were formed in control plants and 57.7% of the total dry matter increment during the experimental period was allocated to the apex and these newly formed leaves. An even higher proportion of the K+ taken up (93.8%) was deposited in these organs and this was imported via xylem (72%) and phloem (28%). Only 18.7% and 9.8% of the total dry matter increment were found in the previously present upper leaves and the roots, respectively, and substantial net K+ export occurred from middle and lower leaves and roots. Decapitation removed the dominant phloem sink and caused marked changes in sink-source relationships. After decapitation the net increase in root dry matter was twice that of control plants. 56.2% of the total net increments in dry matter and 70% of the absorbed K+ were deposited in upper leaves (below the excised apex). There was only slight net K+ export from the middle leaves. Application of NAA on the cut surface of the stem stump did not change the growth of plants that much, apart from a substantial increase in stem growth, correspondingly it stimulated the partitioning of K+ into the upper leaves and most dramatically into the stem, which deposited 64.5% or 27% of the K+ uptake, respectively. In these plants K+ uptake was increased and the K+ concentrations in upper, middle and lower leaves were increased from 4.7, 5.4 and 5.6 to 5.1, 6.1 and 6.1% of dry matter, respectively. Possible mechanisms of this effect of NAA on the improvement of K+ concentration in tobacco leaves are discussed in detail.

Loop electrosurgical excision procedure for partial upper vaginectomy

Objectives: Partial upper vaginectomy consists of removal of the vaginal apex and is indicated for the diagnosis and treatment of vaginal intraepithelial neoplasia and recurrent cancer. We present a novel surgical approach to partial upper vaginectomy by use of the loop electrosurgical excision procedure. Study Design: A total of 15 consecutive patients with abnormal vaginal cytologic results were treated by the loop electrosurgical excision procedure for partial upper vaginectomy. After submucosal injection of local anesthetic, the loop electrode was used to resect the upper third of the vagina. An iodoform vaginal pack was placed for 24 hours. All patients with high-grade vaginal intraepithelial neoplasia received intravaginal 5-fluorouracil cream postoperatively. Results: The mean blood loss was 0 mL, and the mean surgical time was 30 minutes. A complication developed in 1 patient (7%). One case of invasive carcinoma was diagnosed. No recurrences have developed in any patients with vaginal intraepithelial neoplasia after hysterectomy. Conclusions: The loop electrosurgical excision procedure for partial upper vaginectomy can be performed quickly, with minimal blood loss, minimal complications, and minimal recurrence of neoplasia, and it provides a histologic specimen for evaluation. (Am J Obstet Gynecol 1999;181:1382-5.)

LIGHT-STIMULATED LEAF GROWTH ON INTACT AND EXCISED BEAN PLANTS (PHASEOLUS VULGARIS L.). I. CHARACTERIZATION OF BASIC RESPONSES

The effect of root excision on the growth of primary leaves, petioles, and epicotyls of bean plants (Phaseolus vulgaris L.) has been investigated for plants growing in various light conditions. Plants were initially grown in either continuous dim red light (RL; 4 μmol m−2S−1) or bright white light (WL; 100 μmol; m−2S−1, 16 h light: 8 h dark photoperiod) for 10 days. On day 10, some plants were excised. Then, both intact and excised plants were returned to RL or WL, or switched to the other light treatment (RL to WL, WL to RL). Exposure to WL on day 10 promoted leaf expansion and inhibited petiole and epicotyl growth, regardless of light pretreatments before day 10. Root excision reduced leaf expansion by 40–50% both in WL and RL. Petiole and epicotyl growth were less affected. Removal of the cotyledons or the stem apex caused a slight but significant reduction of leaf elongation in both intact and excised plants. Apex removal reduced epicotyl elongation but did not stop it. Although excision of roots partially inhibited leaf and epicotyl development, the relative response of excised plants to the light treatments was similar to that of intact plants. These results justify the use of derooted plants to study leaf growth in a “whole plant” excised system.

Glechoma hederaceaL. (Nepeta glechomaBenth.,N. hederacea(L.) Trev.)

A polycarpic, aromatic, often purplish, softly hairy or nearly glabrous perennial herb. Flowering shoots 10–30 (–60) cm long, square in section and ascending or erect. Non-flowering stems also square in section, creeping and rooting at many, but not all, nodes. Leaf laminae 4–35 (–80) × 6–40 (–80) mm, reniform to ovate–cordate, obtuse or subacute and coarsely crenate. Petioles highly variable in length from 10 mm in grassland to over 200 mm in woodland with dense canopy cover and dense ground vegetation. Bracteoles 1–1.5 mm, shortly hispid or pubescent. Flowers zygomorphic and hypogynous, borne in few (2–5)-flowered secund axillary whorls, the bracts not differing from the foliage leaves. Calyx tubular or tubular-campanulate, 15-veined, not gibbous at base, and somewhat two-lipped. Upper lip of the corolla flat with three triangular acuminate teeth that are 0.2–0.3 times as long as the tube. Lower lip with two teeth. Corolla tube narrowly obconical, straight and hairy within at the base of lower lip. Corolla (6–) 15–22 (–25) mm, usually blue–violet with purple spots on the lower lip; rarely pink or white. Stamens four, two long and two short, borne on corolla tube and lying below upper lip; anther cells at right angles to each other, each opening by a separate slit. Ovary four-celled and deeply four-lobed, each cell with one ovule. Style gynobasic, its branches equal. Hermaphrodite and male-sterile forms of flowers occur, the latter usually with smaller corollas than hermaphrodite flowers, and much-reduced, pollen-less stamens that are often included in the corolla tube. Clones usually bear either only hermaphrodite or only male-sterile flowers, but in rare cases both types are found on the same individual (Price 1991). Each flower produces a maximum of four obovoid, slightly angled, smooth nutlets with a mean air-dry mass of 0.69 mg (n = 100). Each is slightly angled owing to pressure exerted by the adjacent developing nutlets before dispersal, and each bears a grey protuberance which may be an elaiosome. The dimensions of the seed are 1.9 × 1.1 mm. Glechoma serbica Halacsy & Wettst., which has been recorded in former Jugoslavia, is probably an ecological modification of G. hederacea (Fl. Eur. 3). The southern counterpart of G. hederacea in Europe is ssp. hirsuta (Waldst. & Kit.) F. Hermann, sometimes referred to as G. hirsuta (Elias 1979, 1983). This has denser and longer hairs and longer calyx teeth than G. hederacea, and the corolla is pale blue. It has been recorded in Albania, Austria, Bulgaria, the Czech Republic, Greece, Hungary, Italy, former Jugoslavia, Poland, Rumania, central and south-west Russia, Sardinia and Sicily (Fl. Eur. 3). Intermediates, which are presumably hybrids between G. hederacea and G. hirsuta, sometimes occur (Fl. Eur. 3). In eastern Asia a more or less distinct, short-pubescent race occurs that is called ssp. grandis (A. Gray) Hara [also var. grandis A. Gray and var. longituba (Nakai) Kuprian] (Hulten 1971). In North America the variety micrantha Moricand [or var. parviflora (Benth.) House] is distinguished (Hulten 1971).

Partial labyrinthectomy in skull base and cerebellopontine angle surgery

It is now recognized that portions of the vestibular labyrinth can be surgically manipulated without producing significant loss of hearing. Consequently, controlled occlusion or removal of portions of the inner ear have been utilized both to treat specific diseases of the ear as well as improve access to areas of the medial skull base. The common theme in all of these procedures is the preservation of a distinct membranous labyrinth that separates endolymphatic and perilymphatic compartments. This article discusses a novel approach incorporating the partial removal of the inner ear combined with removal of the petrous apex, the partial labyrinthine petrous apicectomy (PLPA) in the treatment of medial skull base lesions. The surgical technique is outlined as is treatment outcome. The benefits of this new approach are assessed by morphometric analysis of three-dimensional CT images. The indications for the PLPA approach are discussed.

Effects of Shoot Apex Removal and Fruit Herbivory on Branching, Biomass and Reproduction in Verbascum thapsus (Scrophulariaceae)

The purpose of this study was to interpret patterns of branching in natural populations of Verbascum thapsus L. (Scrophulariaceae) and to investigate whether the suppression of lateral meristems by apical dominance imposes a potential fitness cost in this species. Disruption of apical dominance by removal (clipping) of shoot apices resulted in shorter plants and greater branching but did not affect total biomass, number of fruits, number of seeds per plant or percent germination of seeds. Seeds from clipped plants, however, were approximately 30% heavier than those from unclipped plants, indicating that apical dominance imposes a potential fitness cost to V. thapsus. Plants with shoot apices intact were mostly unbranched but were more likely to be branched if they were taller. The fruits on the main stalks of these taller and more branched plants were significantly more heavily infested by a curculionid weevil (Gymnaetron tetrum Fab.). Lateral branches of these naturally branched plants, however, were less infested than the main stalks. These results indicate that the weevils are attracted to larger plants and that weevil damage may induce branching. An alternative hypothesis could not be discounted, i.e., that larger plants are more branched because they have greater resource availability, thus allowing release of lateral meristems from inhibition by apical dominance.

Interaction of endodormancy and paradormancy in raspberry (Rubus idaeus L.)

SummaryBud break in protected Northern European raspberry crops is often poor and uneven with many of the sub‐apical buds remaining in a dormant state. In order to improve bud break and therefore yields, the mechanism controlling bud dormancy must be determined. Canes of the biennial cultivar ‘Glen Moy’ were forced as isolated single nodes, trisections, or as intact canes after different lengths of cold storage chill unit (CU) accumulation in order to determine whether the buds were in an endodormant or paradormant state. The results showed that buds on the lower parts of the intact canes remained in a dormant state long after buds from higher up the intact cane and also the single nodes from all parts of the cane had emerged from the deepest phase of endodormancy. This would imply that these buds were being held in a paradormant state until large amounts of chilling units (>1000 CU) had been accumulated. The trisected cane portions revealed almost no significant differences in bud break levels throughout the experiment when compared with the single nodes. This suggests that removal of the apical part of the cane would be effective in improving bud break by reducing the paradormant condition. A period of secondary dormancy was also observed in the intact canes which may also exacerbate the poor bud break observed in protected crops. This was not seen in the single nodes or the trisected canes which indicates that treatments which reduce paradormancy may also minimise the risk of secondary dormancy. By identifying the phase of bud dormancy which causes poor bud break, attention can now be focused on methods which overcome paradormancy in protected crops. Such methods might include tipping (removal of the cane apex), horizontal training methods, more efficient chilling methods, and chemical treatments.

Anterior petrosectomy approach to infraclinoidal basilar artery aneurysms: the emerging role of the neuro-otologist in multidisciplinary management of basilar artery aneurysms.

Aneurysms of the basilar artery are uncommon. Historically, because of the central location of these basilar lesions, surgical access has been difficult. Moreover, while this disease and its surgical management inherently carry a high risk of patient morbidity, the presence of neighboring vital neural and vascular structures introduces additional intraoperative challenges. Since 1986 we have employed a transpetrous approach for access to selective aneurysms involving the basilar artery. Removal of the petrous apex has provided an expanded deep window through which infraclinoidal basilar artery aneurysms can be controlled. Reported herein are our results utilizing an anterior petrosectomy approach to the management of infraclinoidal artery aneurysms.

Apical Dominance as an Adaptation in Verbascum thapsus: Effects of Water and Nutrients on Branching

Larger plants tend to be more branched than smaller plants in some species. The nutrient diversion hypothesis for apical dominance proposes that the apical meristem of a plant acts as a strong metabolic sink, depriving nutrients from latent axillary meristems and thereby promoting strong directional (e.g., vertical) growth with little branching. Hence, larger plants may be more branched because they may have more resources that cannot all be sequestered by the apical meristem, leaving an excess available for branch production from axillary meristems. However, larger plants may also be more branched because they incur greater damage from herbivores that disrupt apical dominance. Hence, the availability of nutrients may be a confounding factor for studies of response to herbivory through effects on apical dominance. In order to distinguish these effects, we applied nutrient and water supplementation to two natural populations of Verbascum thapsus in which herbivores were excluded to test the hypothesis that nutrition level, including water, plays a role in determining the extent of branching. We used a full factorial experimental design involving three levels of resources (control, water, and water with fertilizer) and shoot apex removal. Both a single-season experiment and a two-season experiment were performed, the latter involving only the three levels of resources as treatments. Branching was increased by shoot apex removal and was enhanced by the addition of nutrients but only in clipped plants. Thus, the nutrient diversion theory does not solely explain the strong apical dominance exhibited by V. thapsus; an alternative hypothesis involving weevil herbivory is indicated that may further explain the growth form and branching patterns in this species.

Pinch Treatment and Photoperiod Influence Flowering of Delphinium Cultivars

Two studies were conducted to determine the influence of decapitation (pinch treatment) and photoperiod treatments on stem length, days from planting to harvest, and flowering stem yield in two delphinium cultivars. Plants of Delphinium ×belladonna Hort. ex Bergmans `Völkerfrieden' received a hard pinch (removal of apex and all stem and leaf tissue associated with leaves ≤10 cm), soft pinch (removal of apex and all stem and leaf tissue associated with leaves ≤4 cm), or no pinch. Plants of the D. elatum L. `Barbara' series were grown under either long- or short-day photoperiod, each treatment with or without receiving a soft-pinch. Time from planting to harvest was longer in pinched plants than in nonpinched plants of both cultivars regardless of photoperiod. Flowering stems were longer in hard- and soft-pinched plants of `Völkerfrieden' compared to nonpinched plants, and with `Barbara', stem length of pinched plants was either longer or similar to that of nonpinched plants regardless of photoperiod. At 30 days after the commencement of harvest, yield of flowering stems for hard-pinched plants of `Völkerfrieden' was higher than that for nonpinched plants, but yield from soft-pinched plants was similar to that for those not pinched. Stem yield for `Barbara' was higher for pinched plants under the long-day photoperiod, but under short days, yield from pinched plants was similar to that for those not pinched. Long days appear to increase yield and reduce production time in delphinium cultivars. Commercial benefits may be realized by growing nonpinched plants for earliness and pinched plants for longer stems and higher yield.

The role of apical dominance in the interpretation of adaptive architecture in prostrate plant species

:The role of apical dominance in the interpretation of adaptive architecture was investigated for six prostrate plant species representing a range along the ‘phalanx-guerilla’ continuum: Euphorbia polygonifolia, Polygonum aviculare, Trifolium repens, Glechoma hederacea, Fragaria virginiana, and Potentilla anserina. According to the phalanx efficiency and guerilla efficiency hypotheses, the removal of shoot apices disrupts apical dominance and increases branching, which in turn, increases shoot interference within the plant and/or reduces foraging efficiency. Hence, we predicted that shoot apex removal would result in an undercompensation growth response rather than the compensation or overcompensation commonly reported for upright species. Plant architecture was represented by patterns of allocation of meristems to three possible developmental fates: growth, reproduction, and inactivity. Clipping had no effect on architecture or fitness estimates (biomass, total number of meristems, and ramet production) in T. repens or G. hederacea. Fitness estimates were reduced by clipping in P. anserina, but branching intensity was unaffected. Foraging was compromised since clipped plants were unable to resume horizontal extension. In E. polygonifolia, clipping also reduced fitness estimates but without any effect on branching intensity. Since this species is naturally highly branched (i.e., with weak apical dominance), there may be little opportunity to increase branching intensity by removing apical meristems. In P. aviculare and F. virginiana, the removal of shoot apices resulted in reduced apical dominance and increased branching intensity and this was accompanied by reduced fitness estimates. These results suggest that apical dominance plays an important role in determining the adaptive architectural strategy of these latter two species.

The role of the shoot apex in controlling rhizogenesis in vitro

This paper reports that rhizogenesis in woody plant species in vitro was mediated through the basipetal transport of auxin from the shoot apex. This can directly induce roots in easy-to-root species such as Betula pendula, but was dependent upon an interaction with exogenous auxin in more difficult-to-root species such as Daphne cneorum, and to a lesser extent in Quercus robur. Shoot apex removal reduced rhizogenesis in Quercus, and inhibited it in Daphne, even in the presence of exogenous auxin, whereas rooting in Betula was unaffected. That basipetally transported auxin modulates rhizogenesis was demonstrated by the inhibition of root induction in Betula shoots by the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA), and by the substitution of indole-3-acetic acid (IAA) for a bud in Betula internodal sections.

Axillary Bud Development of Poinsettia `Eckespoint Lilo' and `Eckespoint Red Sails' (Euphorbia pulcherrima Willd.) Is Inhibited by High Temperatures

The effect of temperature on axillary bud and lateral shoot development of poinsettia (Euphorbia pulcherrima Willd.) `Eckespoint Lilo' and `Eckespoint Red Sails' was examined. Rooted `Eckespoint Lilo' cuttings were transplanted and placed into growth chambers maintained at 21, 24, 27, or 30 °C for 2 weeks before apex removal. The percentage of nodes developing lateral shoots after apex removal was 68%, 69%, 73%, or 76% at 21, 24, 27, or 30 °C, respectively. Cuttings were removed from the lateral shoots, rooted, and placed into a 21 °C greenhouse, and the apices were removed. The percentage of nodes developing into lateral shoots on cuttings taken from plants held at 21, 24, 27, and 30 °C were 74%, 65%, 66%, and 21%, respectively. Of the cuttings in the 30 °C treatment, 83% of the nodes not producing a lateral shoot had poorly developed axillary buds or no visible axillary bud development. Visual rating of axillary bud viability decreased from 100% to 0% when `Eckespoint Red Sails' plants were transferred from a 21 °C greenhouse to a greenhouse maintained at 27 °C night temperature and 30 °C for 3 hours followed by 33 °C for 10 hours and 30 °C for 3 hours during the 16-hour day. Transfer from the high-temperature greenhouse to a 21 °C greenhouse increased axillary bud viability from 0% to 95%. Axillary buds of leaves not yet unfolded were sensitive to high temperatures, whereas those of unfolded leaves (i.e., fully developed correlatively inhibited buds) were not. Sixteen consecutive days in the high-temperature treatment were required for axillary bud development of `Eckespoint Red Sails' to be inhibited.

Effects of Nutrient Level on Cost and Benefit of Apical Dominance in Epilobium ciliatum

-The disruption of apical dominance has been considered fundamental to the overcompensatory response to herbivory in many plant species. For isolated plants, such overcompensation can be interpreted as a cost of apical dominance since the growth of apically intact plants is limited by the number of active meristems. When apical dominance is disrupted, growth becomes limited more by nutrient levels and so the greatest overcompensation is generally predicted for plants grown under high nutrient levels. This relationship, although possible for plants growing free from competition, may not hold true when plants are competing for light. In competing plants, the retention of apical dominance, expressed through a strong vertical component of growth, represents a benefit, as plants may outcompete those from which apical dominance is removed. In this case, undercompensation rather than overcompensation may be expected following shoot apex removal under high nutrient levels, since high nutrient levels generally promote competition for light. We tested these predictions concerning cost and benefit of apical dominance in Epilobium ciliatum. Fitness estimates (i.e., dried biomass, capsule weight and number) were compared between apically decapitated and intact plants grown in the presence and absence of neighbors and under three different nutrient levels. Cost of apical dominance (overcompensated capsule production following shoot apex removal in the absence of neighbors) was detected only under the intermediate nutrient level, not the highest nutrient level as generally predicted. This was interpreted by recognizing that increases in nutrient level may decrease the strength of apical dominance. Thus, under high nutrient levels, architectural modifications, and thus the potential fitness benefits following the disruption of apical dominance, may be minimal. This leads to the general prediction that overcompensation (cost of apical dominance) should be most common in habitats of intermediate fertility. Benefit of apical dominance in E. ciliatum (in terms of capsule production) was most evident for competing plants grown under high nutrient levels where competition for light is expected to be most intense.

Effects of Cytokinin-Containing Seaweed Extract on Phaseolus lunatus L.: Influence of Nutrient Availability and Apex Removal

Article Effects of Cytokinin-Containing Seaweed Extract on Phaseolus lunatus L.: Influence of Nutrient Availability and Apex Removal was published on January 1, 1996 in the journal Botanica Marina (volume 39, issue 1-6).

Hypotheses for the Evolution of Apical Dominance in Plants: Implications for the Interpretation of Overcompensation

Apical is the preferential growth of a plant shoot (or root) from the or terminal meristem, and the corresponding suppression of lateral subtending meristems and branches. The most obvious consequence of is a linear directional growth pattern resulting in an extended shoot axis, e.g. tall rather than bushy growth forms. Although the physiology of has been the subject of a vast of body of literature (Cline 1991), the ecological and evolutionary implications of have been scarcely addressed (Salisbury and Marinos 1985). Under what circumstances is favoured by natural selection? Are there predictable patterns in the strength of across different habitat types or different life history strategies? Are there tradeoffs associated with strong that may define potential fitness costs? In this paper I present a framework for addressing these questions by considering several hypotheses for the adaptive significance of in plant shoots, and the interpretation of plant responses to the disruption of by ecological factors. I use the term apical dominance in a broad sense to also include apical which is sometimes used to distinguish the control exerted by an meristem on daughter branches (Cline 1991). Apical may be disrupted by damage resulting from a variety of factors, but the one that has received the most attention recently in the literature is herbivory. In several species, flower, seed and/or biomass production have been shown to increase following herbivory or simulated herbivory involving removal or destruction of the shoot apex (e.g. Inouye 1982, Argall and Stewart 1984, Sheldon 1986, Aarssen and Turkington 1987, Paige and Whitham 1987, Benner 1988, Maschinski and Whitham 1989, Michaud 1991, Mopper et al. 1991, Strauss 1991). Such examples of overcompensation following herbivore damage have been interpreted by some as an adaptive response that has evolved as a consequence of natural selection due to herbivory, although reports of effects on lifetime fitness are lacking (see Belsky (1986) and Belsky et al. (1993) for recent critiques). Aarssen and Irwin (1991) however, interpreted such overcompensation as a product of release from and hence an indirect consequence of whatever selection factors favour dominance. Under this interpretation, incurs an apparent cost in terms of reduced growth potential resulting from lateral meristem inhibition. The critical question however is, does this reduced growth potential translate into realized fitness costs, i.e. does overcompensation result in increased fitness when is disrupted? Below I address this question through several predictions associated with alternative hypotheses for the adaptive significance of (Table 1).

Translocatable leaf signal autoregulates soybean nodulation

In soybean ( Glycine max (L.) Merr.), expression of the hypernodulation phenotype appears to be controlled by the shoot. The current study attempted to localize the source of the nodulation signal in soybean cv. Wiliams 82 and its hypernodulating mutant NOD1-3. Wedge grafts (replacement of entire shoot) and approach grafts (addition of a shoot) were utilized and the shoot (scion) treatments ranged from complete shoots to various combinations of leaf, cotyledon, and apex removal from the grafted scion. Leaf-bearing wedge-grafted or approach-grafted scion types dictated the nodulation phenotype of the host plant. Scions with more leaves were clearly more effective in altering nodulation. Scions with leaves and without apices were as effective in altering nodulation as were scions with both leaves and apices. This confirmed the report by Delves et al. (Plant Cell Environ., 15 (1992) 249–254), but in neither case are results definitive as new buds continued to form which may provide stimulus for nodulation control. Leaf and shoot cuttings which were stimulated to form roots were also examined for expression of nodulation. Leaf cuttings, which were devoid of any meristematic apices, exhibited nodulation phenotypes similar to that of the shoot cuttints, i.e. leaf and shoot cutting of Williams 82 were normally nodulated while those of NOD1-3 were hypernodulated. The leaf cutting approach definitively showed that the leaf, and not the apex, was the synthesis site of a translocatable signal controlling autoregulation of nodule number.