Purification of an Auxin-Binding Protein from Etiolated Mung Bean Seedlings by Affinity Chromatography

An auxin-binding protein with high affinity for 2,4-D and IAAwas purified from the extract of etiolated mung bean seedlingsby affinity chromatography on 2,4-D-linked Sepharose 4B andby gel nitration on Sepharose 4B. Its molecular weight was estimatedto be about 390,000 by gel nitration on Sepharose 4B and itconsisted of two different subunits with molecular weights ofabout 47,000 and 15,000. This protein had no ribulose-l,5-bisphosphatecarboxylase activity. Its dissociation constants for 2,4-D andIAA were 9.3 x 10^–6 M and 3.2 x 10^–6 M, respectively,as determined by Scatchard's method. (Received December 21, 1982; Accepted March 23, 1983)     

Auxin-Binding Protein in Etiolated Mung Bean Seedlings: Purification and Properties of Auxin-Bindmg Protein-II

An auxin-binding protein (ABP-II) was purified from the extractof etiolated mung bean seedlings by affinity chromatographyon 2,4-D-linked Sepharose 4B and by gel filtration on Sepharose4B and Sephacryl S-200. The molecular weight was estimated tobe about 190,000 by gel filtration on Sephacryl S-200. ABP-IIgave a single band corresponding to a molecular weight of about48,000 on SDS-polyacrylamide gel electrophoresis. The dissociationconstants of ABP-II for 2,4-D determined by amrnonium sulfateprecipitation and equilibrium dialysis were 9.5?10^–6 Mand 1.1?10^–5 M, respectively. ¹⁴C-2,4-D-binding to ABP-IIwas reversible and inhibited by addition of IAA, naphthalene-1-aceticacid, 2,4,5-trichlorophenoxyacetic acid or p-chlorophenoxyisobutylicacid to the assay mixture. (Received September 5, 1984; Accepted November 5, 1984)     

Relationship between Sylleptic Branching and Components of Parent Shoot Development in the Peach Tree

Sylleptic branching of main axes was investigated in three peachtree cultivars ('Armking', 'Flavorcrest' and 'Silvergem') duringthe first year of growth. An axis was considered as made upof a series of metamers (internode, node, leaf and associatedbud) and its growth was divided into two components: the increaseof the number of metamers and the lengthening of the metamersthemselves (elongation). The relationship between branchingprobability, type of cultivar, growth components and date ofmetamer production was studied by logistic regression. Branchingprobability varied according to the cultivar, increased whenthe growth components did, and decreased if metamers appearedlate in the season. The logistic model fitted the data closelyand was validated on a data set that had not been used for estimatingthe parameters. Ninety-four percent of branched and 70% of unbranchedmetamers were correctly predicted by the logistic model. Forany given growth rate and date of metamer production, the mainaxes branched most and least often in the 'Flavorcrest' and'Silvergem' cultivars, respectively.Copyright 1994, 1999 AcademicPress Peach tree, Prunus persica (L.) Batsch, branching, syllepsis, shoot growth, quantitative analysis, logistic regression     

Structure of the Gene for an Auxin-Binding Protein and a Gene for 7SL RNA from Arabidopsis thaliana

A genomic clone encoding an auxin-binding protein (ABP) fromthe endoplasmic reticulum was isolated from Arabidopsis thaliana.The ABP gene consisted of 5 exons and 4 introns and encodeda polypeptide of 198 residues. A gene encoding the 7SL RNA ofthe signal recognition particle was located downstream of theABP gene. ⁴Recipient of a scholarship from the National Education Commission,People's Republic of China.     

DNA, RNA, and Protein in the Pea Shoot Apex in Relation to Leaf Initiation

The average amounts of DNA, RNA, and protein per cell measuredhistochemically in each region of the shoot apical meristemremained unchanged during the course of a plastochron and duringthe early development of the leaf primordium. The average contentof DNA, RNA, and protein per cell was the same in all regionsof the shoot apical meristem.     

Vascular Differentiation in the Shoot Apex of Matteuccia struthiopteris

Initial vascular differentiation is generally considered tooccur in procambium. In ferns, however, a provascular tissueimmediately subjacent to the promeristem has been suggestedas an initial stage within which the procambium is subsequentlyformed. In contrast to this interpretation, a zonation conceptapplied in ferns recognizes a promeristem consisting of severallayers of cells in which no differentiation takes place. Thisstudy demonstrates that the shoot apex of Matteuccia struthiopterishas one cell layer of promeristem. Immediately subjacent tothe promeristem is the provascular tissue surrounding a centralgroup of pith mother cells. The developmental continuity betweenthe provascular tissue and the mature vascular tissue, and betweenthe pith mother cells and the pith, through transitional stages,indicates that the initial differentiation of vascular tissueand pith takes place in this prestelar tissue. The continuityof vascular differentiation in the area confronting young leavesor incipient leaf positions is interrupted by the formationof leaf gap initials. Developing leaves thus begin to exertinfluence on the vascular system at the prestelar stage. Smallprotoxylem elements with helical cell wall thickening, and distinctiveprotophloem elements are present in the leaf traces, but endabruptly near the junction regions of leaf traces to the meristele.Copyright1994, 1999 Academic Press Initial vascular differentiation, provascular tissue, pith mother cells, shoot apex, Matteuccia struthiopteris     

Cell Division and Expansion in the Growth of the Shoot Apex

The number and the total volume of cells produced in small portionsof the apical region of the shoot have been measured at differentstages of development. In non-vernalized seedlings of winter rye, grown in July, thecells in the portions examined divided about once every 1.8days during the first week of growth, and there was about a2.2-fold increase in the volume of each cell generation. Fourweeks later the apices were still vegetative, but the rate ofdivision in the portions then examined had fallen to once every5.8 days and there was slightly less than a 2.2-fold increasein the volume of each generation. The average cell volume decreasedas the apices developed. In vernalized seedlings more cells were produced in unit timeduring the first 4 days of growth than in non-vernalized seedlings,but, as in the latter, the rate of production fell during vegetativedevelopment. The rate of cell expansion in the vernalized seedlingswas probably slightly lower than in the non-vernalized seedlingsduring the first 4 days of growth and tended to increase duringvegetative development. At the time of transition to reproductivegrowth the cells were dividing about once every 2.0 days andthere was about a 2.2-fold increase in the volume of each succeedinggeneration. After transition the rates increased. From 4 to8 days after transition the cells divided once every 1.4 daysand there was then a 2.4-fold increase in the volume of eachsucceeding generation. Subsequently, the rate of division changedlittle but the rate of expansion decreased. Higher rates of division and expansion were found in the apicesof lupin seedlings grown in July than in November. In the portionsof the meristem examined during the first 5 days of growth thecells divided about once every 1.3 days in July, but only onceevery 1.8 days in November. The increase in volume of each generationin the same time was slightly higher in July than in November.Both the rates of division and expansion decreased until transitionto reproductive growth occurred, and then increased. About 5days after transition the cells divided once every 1.4 daysin July and once every 2.0 days in November. In both experimentsthere was a 2.4-fold increase in the volume of each generation.Both the rates of division and expansion decreased subsequently. The data are discussed in relation to the changes in size whichaccompany the development of the shoot apex.     

Normal and Abnormal Development in the Arabidopsis Vegetative Shoot Apex

Vegetative development in the Arabidopsis shoot apex follows both sequential and repetitive steps. Early in development, the young vegetative meristem is flat and has a rectangular shape with bilateral symmetry. The first pair of leaf primordia is radially symmetrical and is initiated on opposite sides of the meristem. As development proceeds, the meristem changes first to a bilaterally symmetrical trapezoid and then to a radially symmetrical dome. Vegetative development from the domed meristem continues as leaves are initiated in a repetitive manner. Abnormal development of the vegetative shoot apex is described for a number of mutants. The mutants we describe fall into at least three classes: (1) lesions in the shoot apex that do not show an apparent alteration in the shoot apical meristem, (2) lesions in the apical meristem that also (directly or indirectly) alter leaf primordia, and (3) lesions in the apical meristem that alter meristem size and leaf number but not leaf morphology. These mutations provide tools both to genetically analyze vegetative development of the shoot apex and to learn how vegetative development influences floral development.     

The Structure of the Shoot Apex of Glyptostrobus pensilis Koch

1. A series of studies on the structure of the shoot apices in various genera of the Taxodiaceae, except Glyptostrobus was carried out by Cross (1939, 1941, 1942, 1943a, b). In the last two pieces of his above mentioned works, he repeatedly suggested that there was a basic structure pattern which characterized the family. Results obtained from the present investigation lend support to this view. 2. From a comparative point of view concerning the structure of the apical meristem, it may be said that the family Taxodiaceae is a very natural one, any attempt on subdividing it into several separate families, as Hayata (1932) did, seems to be unnecessary. 3. It is very interesting to note that the cellular pattern of the Glyptostrobus shows more affinity with that of the sequoias than with that of Taxodium. Whereas the structures of the apices of Taxoclium and Metasequoia possess more similarities. 4. Cross (1942) proposed that an entirely discrete surface layer might be evolved in the apical meristem of the Taxodiaceae as a result of a gradual diminution and ultimate loss of the periclinal divisions in the outer cells of the shoot apex. In his subsequent papers (1943a, b), more evidence were added in this respect. The present observation is in accord with Cross' findings.     

The Shoot Apex and its Dichotomous Branching in the Nypa Palm

Seedlings of the palm Nypa fruticans van Wurmb are viviparous,the plumule becoming exserted before the fruit is ripe and possiblyassisting in fruit detachment. Established seedlings have horizontalaxes, this growth orientation being maintained throughout thelife of the palm which may be described as ‘rhizomatous’.Inflorescences are axillary in adult plants, but their distributionis irregular. The shoot apex is small and very asymmetricalsince it is more or less displaced into a lateral position byprogressive enlargement of each leaf primordium during thisleaf's first plastochrone. The plastochrone interval is apparentlya long one so that leaves have a wide developmental gap betweenthem. This results in a leaf base which is more or less cylindricalbut with a groove to accommodate the next youngest leaf. All the available evidence suggests that vegetative branchingis by equal dichotomy of the shoot apex at wide intervals. Thedichotomy is marked superficially by a leaf, enclosing the twonew shoots, which has two grooves. The twin shoots are insertedin the lateral, not the dorsiventral plane of this enclosingleaf. The daughter shoots are always at precisely the same stageof development and they always have mirror-image symmetry withrelation to each other, the phyllotaxis of the parent shootbeing maintained without obvious interruption. There is no anatomicalevidence for abortion of the original apex and its replacementby two new ones. The vascular system is divided equally betweeneach daughter shoot without interruption, suggesting stronglythat there is continuity of growth from the undivided to thedivided condition.     

Planes of Cell Division and Growth in the Shoot Apex of Pisum

The planes of cell division and growth were examined in thecourse of a single plastochron in the shoot apical meristemby observing the orientations of mitotic spindles. In the I₁region of the apical dome, cell divisions were at first anticlinalbut 30 h before a leaf primordium emerged at this site 20 percent of the cell divisions became periclinal. These periclinaldivisions were found only in the corpus. Periclinal divisionsin the tunica were coincident with the appearance of the primordiumas a bulge. The change in the direction of growth in I₁ at thesite of the incipient leaf primordium occurred without any changein the rate of growth in this region of the meristem.     

KDEL-Containing Auxin-Binding Protein Is Secreted to the Plasma Membrane and Cell Wall

The auxin-binding protein ABP1 has been postulated to mediate auxin-induced cellular changes associated with cell expansion. This protein contains the endoplasmic reticulum (ER) retention signal, the tetrapeptide lysine-aspartic acid-glutamic acid-leucine (KDEL), at its carboxy terminus, consistent with previous subcellular fractionation data that indicated an ER location for ABP1. We used electron microscopic immunocytochemistry to identify the subcellular localization of ABP1. Using maize (Zea mays) coleoptile tissue and a black Mexican sweet (BMS) maize cell line, we found that ABP1 is located in the ER as expected, but is also on or closely associated with the plasma membrane and within the cell wall. Labeling of the Golgi apparatus suggests that the transport of ABP1 to the cell wall occurs via the secretory system. Inhibition of secretion of an ABP homolog into the medium of BMS cell cultures by brefeldin A, a drug that specifically blocks secretion, is consistent with this secretion pathway. The secreted protein was recognized by an anti-KDEL peptide antibody, strongly supporting the interpretation that movement of this protein out of the ER does not involve loss of the carboxy-terminal signal. Cells starved for 2,4-dichlorophenoxyacetic acid for 72 h retained less ABP in the cell and secreted more of it into the medium. The significance of our observations is 2-fold. We have identified a KDEL-containing protein that specifically escapes the ER retention system, and we provide an explanation for the apparent discrepancy that most of the ABP is located in the ER, whereas ABP and auxin act at the plasma membrane.     

Adaptation of Cotton Shoot Apex Culture to Agrobacterium-Mediated Transformation

A protocol is presented for rapid genotype-independent transformation and regeneration of cotton (Gossypium spp.) from shoots isolated from germinating seedlings. Isolated shoots are inoculated with a super-virulent strain of Agrobacterium tumefaciens, subjected to a mild antibiotic selection, and directly regenerated as shoots in vitro. Shoots do not dedifferentiate and mutation rates are low. Rooted shoots can be obtained within 6–10 weeks of isolation and inoculation depending on the cotton cultivar.     

A Catastrophe Model for the Switch from Vegetative to Reproductive Growth in the Shoot Apex

A mathematical model is constructed to describe the morphopneticswitch that occurs when a vegetative plant apex becomes reproductive.The cusp equation from catastrophe theory is modified, and isused to relate primordial size at initiation to apex size. Theresulting equation may be viewed as an equation of state definingthe allowed organizational modes of the shoot apex. The modelsimulates the growth of the apex from the vetative stage toearly reproductive growth, and makes reasonable predictionsabout apex size and growth rate, primordial sizes, and the lengthsof the plastochron. flowering, mathematical model, catastrophe theory, shoot apex     

Solubilization and Characterization of a Membrane-Bound Auxin-Binding Protein from Cell Suspension Cultures of Nicotiana tabacum

A membrane-bound auxin-binding protein (MABP) was solubilized by Triton X-100 from cell suspension cultures of Nicotiana tabacum L. Solubilization of MABP was dependent on the detergent concentration and more than 80% of naphthalene-1-acetic acid (NAA)-binding activity was recovered by an optimum concentration of 0.2%. The solubilized MABP was highly heat-unstable and sensitive to protease. The properties of MABP (affinity, temperature dependence, pH optimum, and analog specificity for auxin binding) did not significantly change after solubilization, e.g. the solubilized MABP showed no or very low levels of NAA-binding at 0 to 4°C but showed a high-affinity binding (dissociation constant K_d = 2.7 ± 0.3 × 10⁻⁷m) at 25°C at an optimum pH of 5.0. NAA-binding of the solubilized MABP proceeded very slowly, i.e. a time of half-maximum binding was at least 15 minutes, although the solubilized MABP showed higher rates of association (k₁ = 1.3 versus 0.9 × 10⁵m⁻¹ min⁻¹) and dissociation (k₋₁ = 2.2 versus 1.6 × 10⁻² min⁻¹) with NAA than the bound MABP. These results show that specific, saturable, and reversible auxin binding to MABP from dicotyledonous N. tabacum differs from that from monocotyledonous Zea mays, and confirm that MABP is distinct from a soluble auxin-binding protein which also is present in N. tabacum.     

甘蔗茎尖细胞有丝分裂过程中微管骨架的变化

利用改进的冰冻切片法结合间接免疫荧光标记技术对甘蔗茎尖细胞有丝分裂过程中微管骨架的变化进行了研究。结果表明,在甘蔗茎尖细胞有丝分裂过程中存在4种循序变化的典型微管列阵,即周质微管、早前期微管带、纺锤体微管及成膜体微管。同时,还观察到在各种典型微管列阵相互转变过程中存在各种微管列阵的过渡状态。甘蔗茎尖正在伸长的幼叶部位细胞的周质微管主要为与细胞伸长轴相垂直的横向周质微管：茎尖幼叶部位伸长缓慢细胞的微管主要为纵向及斜向排列的周质微管,在甘蔗茎尖幼叶基部初生增粗分生组织处,横向、斜向、纵向及随机排列的周质微管列阵均有分布。在少数分裂前期的细胞中,发现细胞具有2条早前期微管带,其具体功能还不清楚。表明甘蔗茎尖细胞微管列阵的变化与许多双子叶植物及部分单子叶植物具有共同的变化规律,进一步证明微管骨架的周期性变化在植物中具有普遍性。