Nodule Development in Legumes—The Early Stages: Involvement of Early Nodulins, Lectins, and Other Proteins
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Nodule (geology)
Primordium
Nod factor
The mechanism controlling the production of primordia by the apical meristem of apple buds has been studied by means of defoliation experiments and the dissection of buds. It is shown that the apical meristem of the bud passes through a series of comparatively stable phases of activity, changing relatively abruptly from one phase to another. The relation of the activity of the apical meristem to the development of the bud and foliage is discussed, and it is concluded that the rate of production of primordia is controlled by the younger leaf primordia in the bud, which may themselves be controlled by the foliage.
Primordium
Bud
Apical dominance
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ABSTRACT We report two new recessive mutations in Arabidopsis, mgoun1 and mgoun2 which cause a reduction in the number of leaves and floral organs, larger meristems and fasciation of the inflorescence stem. Although meristem structure is affected in the mutants, we provide evidence that its overall organisation is normal, as shown by the expression patterns of two meristem markers. Microscopical analyses suggest that both mutations affect organ primordia production. mgo1 strongly inhibits leaf production in a weak allele of shoot meristemless, stm-2. In addition, mgo1 and 2 severely reduce the ability of the fasciata1 and 2 mutants to initiate organs, although meristem formation per se was not inhibited. The strong allele, stm-5, is epistatic to mgo1, showing that the presence of meristematic cells is essential for MGO1 function. These results suggest a role for the MGO genes in primordia initiation although a more general role in meristem function can not be excluded. We describe a form of fasciation which is radically different from that described for clavata, which is thought to have an increased size of the meristem centre. Instead of one enlarged central meristem mgo1 and 2 show a continuous fragmentation of the shoot apex into multiple meristems, which leads to the formation of many extra branches. The phenotype of mgo1 clv3 and mgo2 clv3 double mutants suggest that the MGO and CLV genes are involved in different events In conclusion, our results reveal two new components of the regulatory network controlling meristem function and primordia formation. A model for MGO genes is discussed.
Primordium
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Axillary and floral meristems are shoot meristems that initiate postembryonically. In Arabidopsis, axillary meristems give rise to branches during vegetative development while floral meristems give rise to flowers during reproductive development. This review compares the development of these meristems from their initiation at the shoot apical meristem up to the establishment of their specific developmental fates. Axillary and floral meristems originate from lateral primordia that form at flanks of the shoot apical meristem. Initial development of vegetative and reproductive primordia are similar, resulting in the formation of a morphologically defined primordium partitioned into adaxial and abaxial domains. The adaxial primordial domain is competent to form a meristem, while the abaxial domain correlates with the formation of a leaf. This review proposes that all primordia partition into domains competent to form the meristem and the leaf. According to this model, a vegetative primordium develops as leaf-bias while a reproductive primordium develops as meristem-bias.Key words: SHOOTMERISTEMLESS, LATERAL SUPPRESSOR, AINTEGUMENTA, adaxial primordial domain, abaxial primordial domain, shoot morphogenesis.
Primordium
Lateral shoot
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Primordium
Lateral shoot
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In order to obtain more microstructure information on development of soybean,the methods for apical meristem sections were studied in the paper.Based on the process of fixation,dehydration,transparency,saturated paraffin,embedding,section and dye,straight-sections of the shoot apical meristem of soybean were obtained.The results from this study indicated that the regions splitting actively,such as the top of apical meristem,leaf primordia and flower primordia,were dyed deeply.At the same time,pith meristem zone was dyed lightly.At vegetative growth stage,leaf primordia were found at the basal part of apical meristem,and they became bigger gradually.At reproductive growth stage,the dome-liked apical meristem became longer slightly,then each of floral primordia began to appear in turn.The results could provide the base for further investigation on anatomical structure and developmental biology of shoot apical meristem in soybean.
Primordium
Lateral shoot
Apical cell
Apical dominance
Phyllotaxis
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Organogenesis in plants is controlled by meristems. Shoot apical meristems form at the apex of the plant and produce leaf primordia on their flanks. Axillary meristems, which form in the axils of leaf primordia, give rise to branches and flowers and therefore play a critical role in plant architecture and reproduction. To understand how axillary meristems are initiated and maintained, we characterized the barren inflorescence2 mutant, which affects axillary meristems in the maize inflorescence. Scanning electron microscopy, histology and RNA in situ hybridization using knotted1 as a marker for meristematic tissue show that barren inflorescence2 mutants make fewer branches owing to a defect in branch meristem initiation. The construction of the double mutant between barren inflorescence2 and tasselsheath reveals that the function of barren inflorescence2 is specific to the formation of branch meristems rather than bract leaf primordia. Normal maize inflorescences sequentially produce three types of axillary meristem: branch meristem, spikelet meristem and floral meristem. Introgression of the barren inflorescence2 mutant into genetic backgrounds in which the phenotype was weaker illustrates additional roles of barren inflorescence2 in these axillary meristems. Branch, spikelet and floral meristems that form in these lines are defective, resulting in the production of fewer floral structures. Because the defects involve the number of organs produced at each stage of development, we conclude that barren inflorescence2 is required for maintenance of all types of axillary meristem in the inflorescence. This defect allows us to infer the sequence of events that takes place during maize inflorescence development. Furthermore, the defect in branch meristem formation provides insight into the role of knotted1 and barren inflorescence2 in axillary meristem initiation.
Primordium
Organogenesis
Lateral shoot
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The morphology of Rhizobium loti induced root nodules and the flavolan content of nodulated roots of several Lotus species, Leuceana leucocephala, Carmichaelia flagelliformis, Ornithopus sativus, and Clianthus puniceus were examined. Rhizobium loti strain NZP2037 formed effective (Nod + Fix + ) nodules on all legumes, but strain NZP2213 formed Nod + Fix + nodules only on Lotus corniculatus var. cree and ineffective (Nod + Fix − ) nodules on all other legumes. The Nod + Fix − nodules developed by NZP2213 showed morphologies ranging from the complete absence of bacteria within “tumour-like” structures to the development of nodules containing bacteria that were either not released or only incompletely released from infection threads. Within nodules formed by NZP2213 on Lotus corniculatus var. hirsutus and Carmichaelia flagelliformis the rhizobia had multiplied extensively within unwalled, plasma membrane bound, infection droplets. Flavolans rich in prodelphinidin, which is toxic towards NZP2213, were present in the roots of Lotus angustissimus, Lotus pedunculatus, Lotus subbiflorus, and Leuceana leucocephala, but only trace amounts of flavolan were found in the roots of Carmichaelia flagelliformis, Ornithopus sativus, and Clianthus puniceus.
Lotus corniculatus
Nod factor
Lotus japonicus
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Preface: the shoot apex: what it is and what it does 1. A source of cells: the apical cell 2. A source of cells: the meristem 3. Growth rates within the shoot apex 4. Cell cycles 5. The subcellular and biochemical structure of the meristem 6. The mechanism of primordium initiation 7. Positioning the primordia 8. Partitioning the apex: the size of the apical meristem and the primordia 9. The transition to flowering 10. The new floral meristem Index.
Primordium
Apex (geometry)
Lateral shoot
Apical cell
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Primordium
Leaf blade
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Summary In plant development, leaf primordia are formed on the flanks of the shoot apical meristem in a highly predictable pattern. The cells that give rise to a primordium are sequestered from the apical meristem. Maintenance of the meristem requires that these cells be replaced by the addition of new cells. Despite the central role of these activities in development, the mechanism controlling and coordinating them is poorly understood. These processes have been characterized in the Arabidopsis mutant forever young (fey) . The fey mutation results in a disruption of leaf positioning and meristem maintenance. The predicted FEY protein shares significant homology to a nodulin and limited homology to various reductases. It is proposed that FEY plays a role in communication in the shoot apex through the modification of a factor regulating meristem development.
Primordium
Apex (geometry)
Homology
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