Role In Apical Dominance Research Articles

Synthetic auxins concentration and application time modulates seed yield and quality of carrot by altering the umbel order

Quality seed is an essential prerequisite to achieve good yield of a crop. Carrot (Daucus carota) seed quality is affected due to uneven maturation of seeds produced in different umbel orders. Seed quality can be improved by altering the umbel order. Auxins play role in apical dominance and thus can be tested to suppress tertiary umbels in carrot seed crop. A study was conducted to explore the potential of synthetic auxins on alteration of umbel order in carrot seed crop. Significant differences were recorded among different concentrations (0, 100, 200 or 300 mg L−1) of plant growth regulators for growth, yield and seed quality. All growth related traits were improved when Indole acetic acid (IAA) was applied three times at 300 mg L−1. Naphthalene acetic acid (NAA) at 200 mg L−1 or IAA at 100 mg L−1 applied at three times, viz. planting of stecklings (PoS) + 15 days after PoS + 30 days after PoS significantly enhanced number of secondary umbels by suppressing the tertiary umbels. Seed yield and 1000-seed weight of primary, secondary and tertiary umbels was maximum for NAA or IAA at 100 mg L-1 applied three times. Seed quality attributes, viz., final germination, vigour index, enzymatic activity i.e. Superoxide dismutase (SOD), Peroxidase (POD), Catalase (CAT), total antioxidants and total phenolic contents from seeds of primary, secondary and tertiary umbels were increased when three applications of IAA or NAA were done at 200 mg L−1. Moreover, three times application of IAA or NAA at 200 mg L−1 not only minimized the conductivity of seed leachates and malondialdehyde contents from seeds of primary and secondary umbels but also in tertiary umbels seeds. It was concluded that three times foliar application of IAA or NAA at 100 or 200 mg L−1, till 30 days after planting of stecklings, can be effectively used to modify umbel order and hence to increase yield and seed quality. Therefore, seed companies and growers may apply IAA or NAA at 200 mg L−1 for obtaining higher yield of good quality carrot seed.

Expression of BpIAA10 from Betula platyphylla (birch) is differentially regulated by different hormones and light intensities

The Auxin/Indole acetic acid (Aux/IAA) genes are auxin primary response genes that play a pivotal role in apical dominance, phototropism, and embryonic development. In this study, we cloned the promoter of BpIAA10 and constructed a BpProIAA::Luc vector for transformation into Arabidopsis thaliana. The results indicated that BpIAA10 is expressed in the apical meristem, embryonic leaves, and young stem. The tissue-specific expression pattern was same in A. thaliana and Betula platyphylla. Additionally, IAA, IBA, GA, SA, and ABA could induce the expression of BpIAA10 while MeJA inhibited the expression of BpIAA10, suggesting that plant hormones influence the expression of BpIAA10. Strong light conditions also markedly induced the expression of BpIAA10, indicating that BpIAA10 is sensitive to light intensity and that light may be sufficient but not necessary for the normal expression of BpIAA10. Conversely, IBA-induced expression of BpIAA10 was suppressed with strong light, suggesting that IBA-induced BpIAA10 expression is partly light dependent. We predicted the presence of cis-acting elements in the BpIAA10 promoter and found many different types cis-acting elements. Furthermore, promoter analysis and yeast one-hybrid assay revealed that the bait2 (TGA-element) can specifically bind to transcription factors 14-3-3 and Ribosomal_L2, and the bait3 (ntBBF1ARROLB) can specifically bind to FAR1, 14-3-3 Like and kinesin-like protein. Therefore, our study characterized the expression of BpIAA10 and found five transcription factors that regulate expression of BpIAA10. This provides a basis for determining the function of BpIAA10.

New clothes for the jasmonic acid receptor COI1: delayed abscission, meristem arrest and apical dominance.

In a screen for delayed floral organ abscission in Arabidopsis, we have identified a novel mutant of CORONATINE INSENSITIVE 1 (COI1), the F-box protein that has been shown to be the jasmonic acid (JA) co-receptor. While JA has been shown to have an important role in senescence, root development, pollen dehiscence and defense responses, there has been little focus on its critical role in floral organ abscission. Abscission, or the detachment of organs from the main body of a plant, is an essential process during plant development and a unique type of cell separation regulated by endogenous and exogenous signals. Previous studies have indicated that auxin and ethylene are major plant hormones regulating abscission; and here we show that regulation of floral organ abscission is also controlled by jasmonic acid in Arabidopsis thaliana. Our characterization of coi1-1 and a novel allele (coi1-37) has also revealed an essential role in apical dominance and floral meristem arrest. In this study we provide genetic evidence indicating that delayed abscission 4 (dab4-1) is allelic to coi1-1 and that meristem arrest and apical dominance appear to be evolutionarily divergent functions for COI1 that are governed in an ecotype-dependent manner. Further characterizations of ethylene and JA responses of dab4-1/coi1-37 also provide new information suggesting separate pathways for ethylene and JA that control both floral organ abscission and hypocotyl growth in young seedlings. Our study opens the door revealing new roles for JA and its interaction with other hormones during plant development.

The effect of plant architecture on drought resistance: implications for the evolution of semelparity in Erysimum capitatum

Summary1. Constraints of resource allocation between reproduction and adult survival have been implicated in much life‐history variation, yet physiological or functional trade‐offs with juvenile survival may be just as important. Here, we examined selection on a juvenile trait that is a key determinant of semelparous (monocarpic) vs. iteroparous (polycarpic) life‐history expression.2. In Erysimum capitatum, iteroparous plants produce more rosettes at the juvenile stage than do semelparous plants; those rosettes perennate, enabling subsequent reproductive episodes. Thus, the number of rosettes produced before reproduction is a strong determinant of iteroparity. We tested whether increased rosette production compromised juvenile survival under conditions similar to those in which semelparity predominates over iteroparity.3. Using plants from six natural populations, we tested the association between rosette production and juvenile survival under drought conditions typical of the field sites of semelparous E. capitatum populations. We also manipulated rosette number by physically removing rosettes and examined the effect of rosette removal on drought resistance.4. Under drought conditions, plants with fewer rosettes had higher survival, and the physical excision of rosettes improved survival (significantly or marginally) under drought stress in five of six natural populations.5. The lower production of rosettes, typical of semelparous E. capitatum, was associated with increased juvenile survival under drought stress. The results suggest adaptive differentiation of rosette production, at least partially in response to drought stress. Given the role of apical dominance in multiple rosette development, natural selection seems to favour stronger apical dominance under drought conditions. Drought stress is predicted to be more common at high elevation as a result of climate change, and the novel drought stress could increase juvenile mortality of alpine E. capitatum. Because rosette production at the juvenile stage is necessary for iteroparity, these results demonstrate that drought‐induced selection on traits that determine early survival has significant potential to influence the evolution of adult life‐history expression.

Genome-wide identification and expression profiling of auxin response factor (ARF) gene family in maize

BackgroundAuxin signaling is vital for plant growth and development, and plays important role in apical dominance, tropic response, lateral root formation, vascular differentiation, embryo patterning and shoot elongation. Auxin Response Factors (ARFs) are the transcription factors that regulate the expression of auxin responsive genes. The ARF genes are represented by a large multigene family in plants. The first draft of full maize genome assembly has recently been released, however, to our knowledge, the ARF gene family from maize (ZmARF genes) has not been characterized in detail.ResultsIn this study, 31 maize (Zea mays L.) genes that encode ARF proteins were identified in maize genome. It was shown that maize ARF genes fall into related sister pairs and chromosomal mapping revealed that duplication of ZmARFs was associated with the chromosomal block duplications. As expected, duplication of some ZmARFs showed a conserved intron/exon structure, whereas some others were more divergent, suggesting the possibility of functional diversification for these genes. Out of these 31 ZmARF genes, 14 possess auxin-responsive element in their promoter region, among which 7 appear to show small or negligible response to exogenous auxin. The 18 ZmARF genes were predicted to be the potential targets of small RNAs. Transgenic analysis revealed that increased miR167 level could cause degradation of transcripts of six potential targets (ZmARF3, 9, 16, 18, 22 and 30). The expressions of maize ARF genes are responsive to exogenous auxin treatment. Dynamic expression patterns of ZmARF genes were observed in different stages of embryo development.ConclusionsMaize ARF gene family is expanded (31 genes) as compared to Arabidopsis (23 genes) and rice (25 genes). The expression of these genes in maize is regulated by auxin and small RNAs. Dynamic expression patterns of ZmARF genes in embryo at different stages were detected which suggest that maize ARF genes may be involved in seed development and germination.

An investigation of the effects of Ca 2+ channel inhibitors on branching and chemotropism in the oomycete Achlya bisexualis: Support for a role for Ca 2+ in apical dominance

In an attempt to better understand branching and chemotropism, we describe the effects of Ca 2+ channel inhibitors on these processes in Achlya bisexualis, using a branch induction technique and whole plate assays. Branching appears to be a two step process with the initial formation of a bump from which a branch emerges. Verapamil increased numbers of branches in whole plate assays and decreased the distance from the first branch to the tip. In induction assays verapamil increased the number of bumps formed, although in some hyphae it inhibited the transition from an initial bump to a branch. When a branch formed it did not affect the time taken to branch. It had no effect on chemotropism. Lanthanum (La 3+) and gadolinium (Gd 3+) also increased branching in whole plate assays but their effect was much less marked and they had no effect on bump/branch number in induction assays. Gd 3+ decreased the time taken to branch. Both La 3+ and Gd 3+ increased chemotropism. These data suggest firstly that the respective inhibitors may affect different parts of the branching process and secondly that Ca 2+ influx through channels may not be a requirement for branching, indeed such movements may suppress branching. This would fit with elevated Ca 2+ at the tip playing a role in apical dominance.

Differential response of trees and shrubs to browsing and pruning: the effects on Pistacia growth and gall-inducing aphids

The effects of long term browsing on growth and morphology of P. atlantica trees and P. palaestina shrubs, and on the colonization of these hosts by their respective gall-inducing aphid guilds, were studied in natural vegetation pastures in Israel. To simulate apical dominance release by browsing, trees and shrubs were pruned and observed one year later. P. atlantica responded strongly to browsing, producing a crown of dense and sharp dry branches and thorn-like shoots, and pruning, compensating or overcompensating for the lost biomass in the studied morphological variables. Morphological responses of P. palaestina were less evident: we found no compensation in most variables. Three species of aphids produced more galls on browsed than on control shoots of P. atlantica. Two species induced more galls on pruned shoots. The five aphid species on P. palaestina colonized browsed and unbrowsed shoots equally, and produced fewer galls on pruned shoots. The role of apical dominance in architectural responses of trees and shrubs to browsing and pruning, as related to resource availability and timing, is discussed.

The Role of Apical Dominance in Paradormancy of Temperate Woody Plants: A Reappraisal

Paradormancy, also known as summer dormancy, is the temporary dormancy which precedes winter or endodormancy in temperate woody plants. Apical dominance, the control exerted by the shoot apex over the outgrowth of the lateral buds, is thought to play a primary role in the paradormancy of these current lateral buds which normally do not grow out until the following spring after over-wintering. In the present study, to test apical dominance, periodic decapitation and defoliation beginning with early spring flushing and extending through the growing season were carried out on eleven tree species (white ash, green ash, red oak, black walnut, pignut hickory, shagbark hickory, sweetgum, cottonwood, sugar maple, hybrid silver/red maple and white pine) ranging in age from 6 to 50–60 years. Significant decapitation and defoliation release of current lateral buds into growing branches was found only in silver/red hybrid maple and red oak, respectively. In a greenhouse study of 1-year-old sugar maple and green ash seedlings, a significant response was found only in the latter. The lack of response in most of the older species analyzed indicates that other inhibitory influences may be overriding that of apical dominance and suggests that apical dominance does not play the primary role in paradormancy in some temperate woody species.

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.

Sprout and stem development from potato tubers of differing physiological age: the role of apical dominance

A series of experiments over three years (1984–1987) is described in which tubers of a range of early and maincrop varieties were exposed to two different storage-temperature regimes to give different physiological ages. Tubers exposed to 10–15°C from the break of dormancy and then held at 5° had a final age at planting of ca. 500 day-degrees > 4°C. Tubers held at 5°C throughout storage were physiologically younger, having accumulated only 100 day-degrees > 4°C. These temperature regimes, in the light, were considered to be representative of the treatment of tubers for commercial production of early and maincrop potatoes. For each treatment, the number and lenght of all sprouts longer than 2 mm at planting, and the number of stems produced in the field, were recorded. In a parallel study in 1985–1986, tubers of a single variety, aged in the same way, intact or with the apical sprout removed, were held in the laboratory to give full expression of sprout production. The use of physiologically younger tubers did not necessarily give more sprouts at planting, nor mainstems after planting in the field. However, the younger tubers held in the laboratory did carry significantly more sprouts, and sprout production from additional eyes was induced by desprouting. Overall, younger tubers produced at least one more mainstem than older tubers in only three out of twelve comparisons and, when the total number of stems per tuber was assessed, the younger tubers carried the same number or fewer stems in all cases. It is concluded from this investigation that, although apical dominance plays an important role in determining the number of sprouts produced per tuber, there is a high degree of variation between varieties and seasons, and within batches of tubers, in its expression. Extrapolation from a single variety, and in general from experiments confined to the laboratory, may bot be justified in the prediction of numbers of stems in the field.

Prevention of shoot-tip necrosis in shoot cultures of chestnut and oak

Shoot-tip necrosis occurs during the rooting of chestnut and oak cultures. In some cultures, the role of apical dominance is taken over by one of the lateral buds, generally that nearest the apex, and the plant survives. Attempts were made to prevent necrosis by adding a low concentration of 6-benzyladenine (BA) to the rooting medium and, whilst necrosis was to a large extent avoided, the rooting rates fell considerably. Excision of the shoot-tip and application to the cut end of a drop of 25 mg l −1 BA in agar induced axillary growth. The optimum time for carrying out decapitation and BA treatment was after 10 days in the rooting medium. It is suggested that the cause of shoot-tip necrosis is the absence of cytokinin from the rooting medium linked with the root-inducing auxin treatment.

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.

Transport of 14 C-indoleacetic Acid in the Hepatic Marchantia polymorpha

Tracer experiments using exogenous 14C-indoleacetic acid showed that its transport is localized in the midrib cells of Marchantia polymorpha vege- tative thalli. Transport occurs both acropetally and basipetally at approximately the same velocity, but basipetal transport is significantly greater in intensity. In- terference with energy-yielding metabolism due to anaerobic conditions, iodoacetic acid or sodium fluoride reduced basipetal transport by 40-50%. Disruption of cel- lular integrity via centrifugation or cytochalasin B reduced basipetal transport by 30-40%. IAA transport in M. polymorpha gametophytes is essentially the same as in vegetative axes of flowering plants with respect to all parameters compared. The presence of naturally occurring auxin in gametophytic tissue of Marchantia poly- morpha has been demonstrated by both chemical methods and bioassays. As early as 1956, an endogenous compound was isolated from thalli that gave positive results with the Avena curvature test (La Rue & Narayanaswami 1957). Schneider et al. (1967) isolated an Erlich and Salkowski-positive ethanol-soluble compound with an Rf corresponding to indoleacetic acid (IAA). La Rue and Narayanaswami (1957) also present evidence for the localized synthesis of auxin in the apical region of the thallus, and Maravolo (1976) dem- onstrated that IAA was the major transport form in Marchantia. Endogenous growth regulators exert correlative action over developmental processes in bryophytes analogous to their action in tracheophytes. Their correlative activity is dependent upon absolute concentrations, gradients, differential rates of synthesis, inacti- vation and the direction and intensity of transport. The polar distribution of auxin in Marchantia polymorpha assumes an important regulatory role in apical dominance, gem- mae-cup formation and rhizoid initiation through its influence on the balance between cell division and elongation (Maravolo & Voth 1966; Binns & Maravolo 1972; Davidonis & Munroe 1972; Rota & Maravolo 1975). Hebant (1970) and Scheirer (1977) demonstrated that some bryophytes possess spe- cialized cells within the midrib tissue with morphological characteristics of phloem sieve tube cells. Translocation of auxin in Marchantia is conducted in a similar transport system. This transport is strictly basipetal, and was adversely affected by triiodobenzoic acid, cinnamic acid and ethylene, all inhibitors of polar transport in tracheophytes (Maravolo 1976). The present investigation derives from the latter and investigates the nature of several aspects of the auxin transport mechanism in Marchantia.

Transport and Mobilization of14C-Sucrose During Regeneration in the Hepatic, Marchanti Polymorpha

The translocation of 14C-sucrose in Marchantia polymorpha during regeneration and normal growth is described. The isotope or its metabolites were found to move acropetally; higher 14C-sucrose levels were mobilized to the apical region during regeneration than during normal growth. When indoleacetic acid was supplied to the midribs of thalli without apices, sucrose transport and thallus regeneration were inhibited. Thus a correlation between auxin inhibition and nutrient availability is demonstrated, which may play a role in apical dominance.

Gibberellin-cytokinin interaction in the correlation between the cotyledon and its axillary bud in pea (Pisum sativum L.)

If one cotyledon is removed from decapitated pea seedlings and the remaining one is treated with the cytokinin BA, then a complete correlation reversal occurs in numerous cases: instead of the bud belonging to the removed cotyledon, the bud belonging to the remaining cotyledon starts to grow. However, if GA is applied to the remaining cotyledon together with BA, then the number of these correlation reversals sharply drops. This in respect to cytokinin morphogenetically (correlatively) contradictory effect could play a significant role in apical dominance in plants.

Apical Dominanace inXanthium strumarium

The influence of the spectral distribution of illumination on the gibberellin, cytokinin, auxin, and abscisic acid levels and the correlation with the degree of branching in Xanthium strum arium is presented and discussed. Gibberellins do not appear to play a major role in apical dominance but may be important for bud extension following the initial release from domin ance. The cytokinin level was much higher in inhibited buds than in released buds. It is sug gested that the cytokinins present were probably not able to participate in bud growth because of an auxin-induced accumulation of abscisic acid in the buds themselves. The con centration of abscisic acid as measured by bioassay and gas-liquid chromatography was between 50 and 250 times that occurring in all other plants parts examined. This level fell dramatically following release from apical dominance by decapitation. The results are discussed in relation to current hypotheses of apical dominance.

STUDIES ON THE LIGNOTUBERS OF EUCALYPTUS OBLIQUA L'HERIT.

SummarySeasonal variations in apical dominance, maximal in summer and minimal during winter, were noted in eucalypt lignotubers. Temperature variation was more important than photo‐period in affecting seasonal variation of apical dominance. The concentrations of growth‐promoting and growth inhibiting substances in the leaves were correlated with seasonal variation suggesting that both have a role in apical dominance. Decapitation studies indicate that amounts of mineral nutrients and carbohydrate do not prevent dormant bud development.