RNA Synthesis in the Shoot Apex of Polytrichum formosum Hedw.

RNA metabolism in the cells of the gametophyte shoot apex ofPolytrichum formosum was investigated using both microspectrophotometricand autoradiographic methods along with an accurate measurementof surfaces and volumes of nuclei, nucleoli, free cytoplasmand vacuolar systems. On a per cell basis, the amount of RNAand the rate of RNA synthesis were shown to be highest in theapical cell. On the other hand, both RNA concentration and rateof synthesis for a unit quantity of cytoplasm were found tobe higher in leaf initials and in the cells of young leavesthan in theapical cell, the segments and the segmental derivatives.For the various types of cells in the shoot apex it was establishedthat the more voluminous the nucleolus, the higher the RNA syntheticrate per cell. These results were correlated with the data previouslyobtained on the mitotic cycles in Polytrichum. It is concludedthat in the apical cell, notwithstanding its differentiatedfeatures, RNA metabolism must be considered on the whole tobe very active. These various data are compared with those obtainedon angiosperm shoot apices.     

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.     

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。     

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。     

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.     

Catalase Activity in Rice Shoot Apex during Panicle Initiation

There was a gradual increase in the catalase activity in theshoot apices of the two rice varieties—Ratna and BAM 11,till panicle initiation. Peroxide content in the Ratna shootapices decreased with time and was low during and after panicleinitiation. In Ratna plants, exogenous application of cycloheximideand 3-amino-1,2,4-triazole resulted in a delay in panicle initiationwith a corresponding decrease in catalase activity. Exogenousapplication of hydrogen peroxide caused a rise in catalase activityand delayed panicle initiation in both Ratna and BAM 11 varieties.In BAM 11 plants treated with 28 consecutive short photoinductivecycles there was an earliness in flowering accompanied by anearly peak in catalase activity. (Received May 10, 1985; Accepted August 12, 1985)     

小麦茎顶端原基分化的综合模式

研究了小麦 (TriticumaestivumL .)茎顶端不同类型原基分化的动态过程 ,以明确原基分化的综合模式 ,并建立了不同原基分化之间的定量关系。结果表明 ,小麦叶原基和苞叶原基分化与播后累积生长度日 (GDD ,growingdegreedaysaftersowing)的关系呈S形曲线 ,而小穗原基和小花原基为上升段抛物曲线。从分化模式看 ,苞叶原基具备营养器官原基特征 ;小穗和小花原基的分化进程能较好地反映基因型和生态条件对顶端发育的影响。小麦茎顶端原基分化的综合模式为由三段子模式构成的近似S曲线。叶原基数由基因型和环境条件共同决定 ,而苞叶原基、小穗原基和小花原基数以环境因子的影响为主。以平均热间距来衡量 ,适期播种处理的叶片、苞叶和小穗原基分化速率最高 ;而小花原基数与小花分化持续期之间的数量关系最为密切。研究结果有助于揭示和理解小麦茎顶端发育的生物学规律。     

小麦茎顶端原基分化的综合模式

研究了小麦(Triticum aestivum L.)茎顶端不同类型原基分化的动态过程,以明确原基分化的综合模式,并建立了不同原基分化之间的定量关系.结果表明,小麦叶原基和苞叶原基分化与播后累积生长度日(GDD, growing degree days after sowing)的关系呈S形曲线,而小穗原基和小花原基为上升段抛物曲线.从分化模式看,苞叶原基具备营养器官原基特征;小穗和小花原基的分化进程能较好地反映基因型和生态条件对顶端发育的影响.小麦茎顶端原基分化的综合模式为由三段子模式构成的近似S曲线.叶原基数由基因型和环境条件共同决定,而苞叶原基、小穗原基和小花原基数以环境因子的影响为主.以平均热间距来衡量,适期播种处理的叶片、苞叶和小穗原基分化速率最高;而小花原基数与小花分化持续期之间的数量关系最为密切.研究结果有助于揭示和理解小麦茎顶端发育的生物学规律.     

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.     

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.     

Respiration and Carbohydrate Accumulation in the Water-Stressed Wheat Apex

The effect of water stress on the respiration of the immaturefloral apex of wheat was studied in a controlled environmentand related to changes in water relations, growth, protein synthesis,and solute accumulation. Apex respiration measured in vitropolarographically showed no wounding response and was cyanide-and malonate-sensitive. It decreased with each decrease in apexwater potential _a reaching 40% of the non-stress control rateat –5·0 MPa, irrespective of whether the waterstress was induced by droughting in vivo or non-permeating osmoticain vitro. Apex respiration was not quantitatively related toturgor potential. During drought stress there was a conservation of ethanol-insolubledry matter and water in the apex while ethanol-soluble carbohydratesand amino acids accumulated. The calculated daily import ofsoluble carbohydrate into the apex during the whole droughtstress period remained nearly constant despite falling waterpotential. Respiration of the apex during a drought period wasnot limited by the suistrate supply within the apex.     

The Effects of Vernalization on the Growth of the Wheat Shoot Apex

he effect of vernalization on the growth of the wheat shootapex was examined by comparing three genetic lines of ChineseSpring (CS) wheat having strong [CS (Hope 5D)], medium (CS Euploid),or no [CS (Hope 5A)] vernalization requirement. The mean volumeof the apical dome increased gradually in all lines, and thenthe apical dome enlarged rapidly as its relative growth rate(RGR) increased prior to double ridge formation. Phytomer volumeat initiation remained constant, so that the ratio of phytomerto apical dome at primordium initiation decreased in successiveplastochrons. In CS Euploid and in unvernalized CS (Hope 5D),the RGR of the apical dome tended to decrease at least untilinitiation of the collar primordium. The rate of primordiuminitiation at double ridge formation increased in proportionto the RGR of the apex at that time; i.e. it increased greatlyin CS (Hope 5A) and vernalized CS (Hope 5D), less so in CS Euploid,but no increase was observed in unvernalized CS (Hope 5D). Thetime of formation of double ridges seemed to be independentof the growth rate or size of the apical dome. The number oftillers present at ear emergence was inversely proportionalto vernalization requirement and was reduced by vernalization.Vernalization resulted in a decrease in the RGR of the newly-initiatedleaf primordia in relation to the RGR of the apical dome andthe axial part of the phytomer. Transfer of plants from longto short days at various times during growth showed that vernalizationincreased the number of labile primordia which could developinto either leaf, collar or spikelet. Vernalization thereforeseems to alter the ability of the apex to respond to subsequentphotoperiod rather than to affect its growth directly. Triticum aeslivum, wheat, chromosome substitution lines, shoot apex growth, vernalization