Apical Dominance in the Tomato: Some Further Observations on Isogenic Lines Showing Varying Degrees of Side-shoot Development

A study has been made of the distribution of substances resemblingindol-3-ylacetic acid (IAA), abscisic acid (ABA) and cytokinin-likesubstances in the stem tissue of Craigella tomato plants ascompared with that found in two isogenic lines of this variety,Craigella Blind (blbl) and Craigella Lateral Suppressor (lsls),in both of which side shoot growth is suppressed to varyingdegrees. There was no evidence to suggest that the distributionof these hormones in the stem had any association with the differentpatterns of side shoot development of the three types, thoughsome of the lateral suppressor plants which exhibited only partialbud inhibition did show a relation between high auxin and abscisicacid levels and lack of side shoot development from the centralnodes of the shoot. Decapitation led to a stimulation of bud outgrowth from allnodes of the Craigella plants but the lateral suppressor plantsremained inhibited. The blind plants were found to initiatebud primordia at the cotyledonary nodes only when the severedapex was replaced by exogenous IAA. The results are discussed in relation to our knowledge of themechanisms controlling apical dominance in the tomato. Lycopersicon esculentumL, tomato, apical dominance, growth regulation, indol-3-ylacetic acid, abscisic acid, cytokinins     

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。     

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.     

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     

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

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

Apical Dominance, Water Deficit and Axillary Inflorescence Growth in Zea mays: The Role of Abscisic Acid

In the sweet corn cultivar, Iochief, an episode of water deficitduring early tassel development results in a subsequent promotionof the growth of the lower axillary inflorescences. This responseis also produced by the application of abscisic acid (ABA) atthis period of growth to well-watered plants, and the hypothesisthat the response to water deficit was due to an increase inendogenous ABA concentration was examined. The ABA contentsof the tassel, leaf and axillary inflorescences were found toincrease during water stress, the increase in the tassel andaxillary buds being most rapid in the first 2 days of waterdeficit. This increase in free ABA content was followed after4 days of water deficit by a progressive increase in the concentrationof ‘bound’ ABA in the tissues. There was littleincrease in free ABA concentration after 4 days water deficit;this paralleled the subsequent growth response of the axillaryinflonscences which also was unaffected by prolonging the epidoseof water deficit beyond 4 days. In order to establish whether the response of the axillary inflorescencesto ABA was dependent upon the presence of the tassel, ABA wasapplied to watered plants with or without the developing tassel.As had been previously found with water stress, removing thetassel inhibited the response of the plant to applied ABA. Zea mays, apical dominance, water stress, inflorescence growth, abscisic 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.     

受白粉菌诱导大麦抗感等基因系蛋白质变化的双向电泳分析

分别对接种与否的大麦抗—感白粉病等基因系—叶期幼苗取材进行蛋白质双向电泳分析。结果表明,病原的侵入使抗—感两系在30Kd以下的低分子量区域的蛋白质发生了明显变化。接种48小时之后,抗病系在pH5.5、6.0、6.8及8.8附近出现了对照中所没有的蛋白质,而在pH6.0和8.8附近的蛋白质则较对照有减小的趋势;感病系在pH6.0附近蛋白质明显增多,在pH8.8处不仅在量上有大幅度提高,而且种类也有增加。结果还表明,抗—感系间在未接种的情况下双向电泳图谱也有差异,接种之后由于感病系在pH8.8处蛋白质的特异性合成,使抗—感两系间的差异缩小。     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

Activation of Basal Cells of the Apical Meristem during Sepal Formation in Tomato

Although great advances have been made in research on the regulation of primordium fate in the floral meristem, our understanding of the molecular events occurring during the floral transition remains incomplete. Via a careful analysis of the expression patterns of five genes encoding housekeeping functions during the floral transition in tomato (using both in situ hybridization and enzyme histochemistry), we identified a particular phase of floral development (sepal initiation) at which cells located toward the base of the meristem show a high level of cellular metabolism, whereas cells at the tip of the meristem dome show little activity. At other stages of floral development, the probes used showed genespecific patterns of expression generally consistent with our previous investigation of the vegetative apical meristem. Our data, in conjunction with other reports in the literature, enabled us to postulate that relative activation of basal cells of the meristem may be of general occurrence during the transition to flowering. Such a hypothesis could account for recent observations using periclinal chimeras on the effect of L3 genotypes on flower development and have a bearing on the expected mechanism by which the number of primordia generated by a floral meristem is regulated.     

Differentiation of Apical Bud Cells in a Newly Developed Apical Bud Transplantation Model Using GFP Transgenic Mice as Donor

Rodent mandibular incisors have a unique anatomical structure that allows teeth to grow throughout the lifetime of the rodent. This report presents a novel transplantation technique for studying the apical bud differentiation of rodent mandibular incisors. Incisal apical end tissue with green fluorescent protein from transgenic mouse was transplanted to wild type mice, and the development of the transplanted cells were immunohistologically observed for 12 weeks after the transplantation. Results indicate that the green fluorescent apical end tissue replaced the original tissue, and cells from the apical bud differentiated and extended toward the incisal edge direction. The immunostaining with podoplanin also showed that the characteristics of the green fluorescent tissue were identical to those of the original. The green fluorescent cells were only found in the labial side of the incisor up to 4 weeks. After 12 weeks, however, they were also found in the lingual side. Here the green fluorescent cementocyte-like cells were only present in the cementum close to the dentin surface. This study suggests that some of the cells that form the cellular cementum come from the apical tissue including the apical bud in rodent incisors.     

Fish Hereditary Melanoma Cell Lines of Different Degrees of Cell Differentiation

Four cell lines including two sublines were established from hereditary melanomas in interspecific hybrids between platyfish ( Xiphophorus maculatus ) carrying the Sp gene and swordtails ( X. helleri ) and maintained in vitro for more than 34 months. Cells in each cell line grew randomly across each other with an apparent lack of contact inhibition of growth and at a population doubling time of 50 to 72 hr. They retained the characteristics of young pigment cells in regard to ultrastructure, tyrosinase activity, the DOPA and combined DOPA-premelanin reactions. In the degree of differentiation, the cells of the three cell lines seemed comparable to early melanocytes close to melanoblasts, and those of the remaining one cell line seemed comparable to young melanocytes but were in a more differentiated state than the early melanocytes. Colony forming ability on plastic plates was at a level of 10% in the three cell lines but only 1% in the one cell line. All four cell lines failed to form colonies in soft agar. Chromosome analysis revealed that these four cell lines were heteroploid with many abnormal figures of chromosomes and double minute chromosomes. None of the cell lines showed transplantability to fish.     

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。     

Apical Vesicles in Growing Bud Cells of Heterobasidiomycetous Yeasts

Clusters of cytoplasmic vesicles resembling those in growing hyphal apices of mycelial fungi are found near the tips of buds in three heterobasidiomycetous yeasts, Rhodotorula glutinis, Candida scottii, and Sporobolomyces salmonicolor.     

籼稻标记性状等基因系的构建

选用涉及水稻(Oryza sativa L．)全部12条染色体的、表现简单遗传且易于识别的形态标记材料27份,以早籼品种浙辐802为轮回亲本,经10余次回交,转育成一套籼型标记等基因系。在此基础上,对同一染色体上的标记进行聚合,育成了15份双标记等基因系。该套材料除所带标记性状外,生育期、株高、分蘖力和穗子大小等主要农艺性状与轮回亲本基本相仿。     

籼稻标记性状等基因系的构建

选用涉及水稻(Oryza sativa L.)全部12条染色体的、表现简单遗传且易于识别的形态标记材料27份,以早籼品种浙辐802为轮回亲本,经10余次回交,转育成一套籼型标记等基因系.在此基础上,对同一染色体上的标记进行聚合,育成了15份双标记等基因系.该套材料除所带标记性状外,生育期、株高、分蘖力和穗子大小等主要农艺性性状与轮回亲本基本相仿.     

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)