心脏原基的起源和发育

有关心脏前体位置的报道并不一致.主要对心脏前体的研究,包括命运图、细胞移植和培养及在心脏发育过程中起作用的组织相互作用、信号分子及基因调控机制几个方面进行了综述.另外,对最近报道的次生心脏形成区也进行了介绍.早期心脏发育的调控事件的确定可为新的治疗心肌症的途径提供必要的基础.     

Endogenous Development of Adventitious Root Primordia in Lettuce Hypocotyls

Rudimentary adventitious root primordia were observed in optically-sectionedFeulgen-stained hypocotyls of 8-d-old lettuce seedlings germinatedin the dark and in a low light intensity environment. It issuggested that formation of these primordia may represent anaspect of normal development in the seedling. Adventitious, root primordia, hypocotyls, lettuce, Lactuca sativa     

The Carpel of Moringa

The gynoecium of Moringa is tricarpellary, syncarpous and unilocularwith parietal placentation. The three carpel primordia ariseindependently but soon become connected resulting in an annularstructure which develops into the tubular gynoecium. The gynoeciumis supplied with three dorsal and three marginal bundles. Thelatter represent the fusion product of the marginal bundlesof adjacent carpels and each splits into three in the ovarywall. The ovules receive their vascular supply from a commonbundle, which branches from the dorsal trace of the carpel atthe base of the ovary. The derivation of the gynoecium fromconduplicate carpels is postulated. Moringa oleifera, carpel morphology, conduplicate carpel, carpel ontogeny     

Development of Lateral Primordia in Decapitated Adventitious Roots of Allium cepa

In decapitated adventitious roots of Allium cepa L. var. French,the time taken for lateral primordia to appear in five sectorshas been studied. This time is approx. 4–5 d after theapex of the adventitious root gave rise to the primordial initialcells. Allium cepa, adventitious root, lateral primordia     

Phyllotaxis and the Initiation of Primordia During Flower Development in Silene

The measured divergence angles between successive primordiain the developing flower were compared with angles expectedon several hypotheses concerning primordial initiation. Theresults lead to the conclusion that the position and sequenceof initiation of the younger sepals is determined by the olderones but that the influence of an older primordium lasts foronly two plastochrons. The petals and carpels are apparentlypositioned by the sepals. The positions of the stamens are consistentwith their king determined by the sepals (antesepalous stamens)or petals (antepctalous stamens), but their sequence of initiationis consistent with its being determined, like the sepals, bythe two youngest primordia. The data indicate that there aretwo sets of factors governing the initiation of the primordiasubsequent to the sepals: one governing the positioning of theprimordia and resembling the factors governing the positionsof axillary buds, and the other governing the sequence of primordiaand resembling the factors which determine the initiation ofleaves. Measurements of the plastochron ratios were used tocalculate the sizes of the sepal, petal and stamen primordiaat initiation. At the moment of initiation the sepal primordiawere about one third, and the petal and stamen primordia aboutone sixth, of the size of the leaf primordia. In its early developmentthe Silene flower therefore resembles a condensed leafy shootwith precocious axillary buds but with primordia which are smallcompared to leaf primordia. Silene coeli-rosa, flower development, primordia, phyllotaxis     

Flower Development in Silene: Morphology and Sequence of Initiation of Primordia

The initiation and development of the flower of Silene coeli-rosawas followed by examining apices by scanning electron microscopy.The sepals, stamens and carpets are initiated in a spiral sequence,the direction of the spiral king the opposite of the acropetalhelix of unequal axillary buds at the nodes below the flower.The petals are initiated almost simultaneously and at the sametime as the first few stamens. The change in phyllotaxis fromopposite and decussate in the vegetative shoot to spiral inthe flower occurs with the displacement of the first two sepalsaway from the mid-line of the apex and towards the axillarybud at the node below the flower. The sizes of the sepals andstamens are a function of their age since initiation but thepetals grow more slowly. The Silene flower can be interpretedas a shoot bearing primordia with associated axillary primordia,some of the latter being precocious in their development. Silent weli-rosa, flower initiation, flower development, phyllotaxis, primordia     

Origin of Epidermis and Development of Root Primordia in Pistia, Hydrocharis and Eichhornia

All three floating plants have roots bearing laterals derivedfrom both pericycle and endodermis. In Pistia and Eichhornialaterals arise within the meristem of the mother root; in Hydrocharisthey arise from mature tissue. In Pistia and Hydrocharis theepidermis becomes anatomically discrete between cortex and cap:in Pistia it is derived from the endodermis of the mother root,in Hydrocharis from the pericycle. The epidermis is not discretein Eichhornia and is derived from the pericycle of the motherroot with the cortex. Stathmokinetic data were used to construct timetables of developmentwhich show how the differences arise. In Pistia the first periclinaldivision of the endodermis-derived tissue individualizes theepidermis and occurs early, before a quiescent centre forms.In Hydrocharis the epidermis also becomes discrete before thepole of the meristem becomes quiescent, but it does so by apericlinal division of the pericycle-derived tissue. In Eichhorniapericlinal divisions occur in the outermost layer of the pericycle-derivedtissue long after quiescence has set in at the pole and afterthe fourth periclinal division in the endodermis derived cap.Its epidermis therefore never becomes anatomically discretethough it becomes functionally discrete because its polar cellsstop dividing as in the other plants. The involvement of the endodermis of mother roots in the formationof laterals is discussed in relation to the state of differentiationat sites of primordium formation, discreteness of the epidermisand subsequent fate of primordia. Pistia stratiotes L., Hydrocharis morsus-ranae L., Eichhornia crassipes Solms., primordia, lateral root, discrete epidermis, development, chimera, stathmokinetics     

Cell Population Studies in Developing Root Primordia

The proliferation of polyploid and diploid cells was followedduring the development of lateral root primordia of Vicia faba.Presumptive primordial cells were treated with weak solutionsof colchicine, 0.003, 0.006, and 0.0125 per cent, for 3 h. Somecells are induced to become polyploid and they form a markedsub-population. The relative frequencies of diploid and polyploidcells were determined from the time small primordia were presenttill lateral roots were fully emerged. These frequencies havebeen found to change in a regular fashion and the changes reflectdifferent levels of mitotic activity in different parts of aprimordia as it develops. Polyploid cells occupy the centralcore of the primordia and they divide actively except for theperiod just before lateral root emergence. Coincident with thistemporary quiescence of the core cells, the peripheral cells,which remain diploid after treatment with the weaker solutionsof colchicine, continue to divide. These changes in mitoticactivity of the central and peripheral cells are shown bothin the changes in the relative frequencies of polyploid anddiploid mitoses as a primordium grows and in changes in mitoticindex. A microspectrophotometric study indicates that the centralcells are held, temporarily in the G₁ phase of the cell cycle.     

The Development of Flower Primordia of Phaseolus vulgaris (L.) Savi.

The first-formed flower primordium on determinate varieties(plants with terminal inflorescences) of Phaseolus vulgarishas been identified and located. Irrespective of the numberof leaves on the main stem, it is formed directly in the axilof the uppermost leaf. The physiological significance of thisis discussed.     

Reserve Lipids in Stem Root Primordia of Poplar

Lipids are reserve substances in stem root primordia of poplarand occur as droplets approximately uniformly in all cells ofroot primordia. In ultrathin sections they appear as sphericalelectron-dense particles (0.5–1.4 µm diameter),filling up virtually all the available space in the cytoplasm.The presence of lipids in stem root primordia was demonstratedin several species of the genus Populus from the section Aigeirosand Tacamahaca, as well as in another representative of thefamily Salicaceae, viz. in the genus Salix.     

Heterogeneity in Cell Behaviour in Primordia ofVicia faba

The response of cells of small primordia ofVicia faba to³H-TdR and colchicine is discussed. The delayed uptake of³H-TdR shown by cells of small primordia appears to be a property of only 50% of the cells; the remaining never become capable of incorporating³H-TdR. Prom the labeled cells and polyploid cells induced by colchicine the shortest cycle time in small primordia is estimated to be 12 hours. Within a period equal to 1 mitotic cycle, 31–35% of all mitoses are tetraploid, following treatment with colchicine. The remainder are diploid and diploid mitoses were seen for up to 30 hours. These observations are indicative of a heterogeneity for mitotic cycle time in populations consisting of up to 1,500 cells. The percentage labeled mitosis curve of diploid cells was changed in primordia treated with colchicine; higher peaks were found. These results show that even small populations of cells, at the beginning of a morphogenetic system, are very heterogeneous for key cell properties. This research has been supported by the U.S.A.B.C. [AT (11-1) 1625-21].     

The Development of Lateral Root Primordia in Vicia faba L. and Their Response to Colchicine

Lateral root primordia in i are first initiated 2–3 daysfollowing the onset of germination, after which they take 5.17–6.35days to complete their development and emerge as lateral roots.Variation in the amount of time elapsing between primordiuminitiation and emergence as a lateral is probably a reflectionof the cell number attained by any one primordium at the timeof emergence. The number of primordia produced per cm of primaryroot growth (5.35–6.65) was not affected by variationin the rate of root elongation, although the number of primordiaproduced each day increased with increase in the rate of rootgrowth. In colchicine-treated roots, the amount of time between primordiuminitiation in the C-tumour and the subsequent emergence of alateral (5.43–6.43 days) was similar to the value obtainedin control roots. Primordia which were present at the time ofcolchicine treatment responded to treatment in a number of differentways, depending on the stage of development reached. Primordiain the first 2.66 days of their development die following treatment;those between 2.66 and 3.69 days old have their developmentinhibited but stay alive; primordia which have been developingfor 3.69–4.91 days following initiation grow out as straightlaterals, while those between 4.91 and 5.77 days old form C-tumoursand emerge as inhibited laterals.     

Patterns of Distribution of Lateral Root Primordia

The distribution of lateral root primordia has been examinedin Pistia stratiotes and Potentilla palustris, and re-examinedin Pontederia cordata. The major feature of the distributionpattern is a rather regular spacing along protoxylem-based ranks.There appears to be some correlation of activity between ranks,but simulations of patterns based on the data from Pontederiasuggest that the observed correlation is spurious. Pistia stratiotes, Pontederia cordata, Potentilla palustris, roots, lateral roots, pattern     

Relationship Between Lateral Root Primordia in Different Ranks

Comparisons with theoretical random distributions indicate thatthe longitudinal positional relationships between lateral rootsin different ranks are random in roots of Musa acuminata, Pistiastratiotes and i, species in which lateral root primordia arisein the root tip. In Potentilla palustris, where lateral rootprimordia arise further back in the root, there is a deficiencyof close spacings, which indicates that there is some interactionbetween ranks. Musa acuminata, Pistia stratiotes, Pontederia cordat, Potentilla palustris, roots, lateral roots, pattern     

Change in Size and Cell Number during the Development of Lateral Root Primordia in Zea mays L.

Increase in cell number, anlage volume and length have beeninvestigated during the overall period of lateral root primordiumdevelopment in excised primaries and in attached roots of Zeamays L. Each of these aspects of anlage growth was found toincrease more or less exponentially during the interval betweenprimordium initiation and subsequent emergence as a lateralin both batches of roots. Values were then determined for celldoubling time (Td), the size of the proliferative fraction (Pf),and for anlage volume (Tv) and length (Tt) doubling times duringthe overall period of primordium development and at intervalsduring this period in both the excised and attached roots. Thepattern of change which took place in Td, Tv, Tl and Pf duringlateral primordium development was found to be similar in bothbatches of roots. However, the overall period of anlage developmentwas shorter in the excised roots than in the attached ones.Moreover, when laterals grew out of the excised roots they didso with fewer cells than comparable laterals emerging from theattached roots. Zea mays L., maize, root primordia, lateral emergence, cell doubling time     

Effects of Actinomycin D and 2,4-Dinitrophenol on the Development of Root Primordia in Azuki Bean Stem Cuttings

In the rooting of disbudded azuki bean stem cuttings, actinomycinD and 2,4- dinitrophenol (DNP) acted as auxin synergists. Althoughcuttings treated with actinomycin D or DNP alone formed almostthe same number of roots as water-treated cuttings, cuttingstreated with actinomycin D or DNP for 24 hr then with auxinfor another 24 hr formed more roots than cuttings treated onlywith auxin during the second 24 hr. Both actinomycin D and DNPincreased the number of root primordia with longitudinally dividedcells, but they acted differently on the first transverse celldivision which led to root primordium formation. ActinomycinD delayed the start of the first transverse cell division, butDNP hastened it. (Received July 7, 1981; Accepted September 21, 1981)     

Distribution of Lateral Root Primordia in Root Tips of Musa

The distribution of lateral root primordia in the root tipsof four Musa landraces (Grande Naine, Pisang Berlin, Ngok Egomeand Yangambi Km5) grown in the field has been investigated toevaluate the range of genetic variation of lateral root initiation.In banana (Musa sp.), lateral roots are initiated in the roottip, 0.6–4 mm behind the root/cap junction and arise inseveral protoxylem-based longitudinal rows or ‘ranks’.Significant differences were observed among landraces for theposition of the most distal primordium, however the longitudinalspacing between successive primordia along the ranks was similarfor all landraces. All ranks were involved in lateral root initiation.The number of ranks also showed significant variations amonglandraces and was proportional to the stelar diameter. Hencethe density of lateral roots (roots cm^-1) was affected by stelardiameter variations. Finally, root elongation in the root tipwas landrace-specific and not necessarily exponential, unlikesuggested in previous studies. It is concluded that lateralroot initiation in Musa is not involved in the genetic variationsof root architecture in the field. A dissection of root architectureinto components which may account for these variations is proposedin relation to the improvement of root system architecture.Copyright 1999 Annals of Botany Company Lateral root initiation, root architecture, Musa, banana.     

黄瓜雄花形成过程中心皮的发育

黄瓜(Cucumis sativus L)为重要的经济作物,雌雄同株异花,是研究植物性别分化的经典材料。人们对黄瓜性别分化进行了广泛的研究。Astmon和Galun,任吉君和王艳对黄瓜性别分化的形态特征和器官发生进行了初步研究,表明黄瓜单性花分化和发育过程中经历了无性期、两性期和单性期,最