Reproductive Meristem22 is a unique marker for the early stages of stamen development

Floral buds of different sizes of the single-gene recessive mutant stamenless-2 (sl2/sl2) of tomato were treated with gibberellic acid (GA3) and the development of staminal features in each bud was followed. The results show that the application of GA3 to buds with stamen primordia at the early stages of initiation (up to 0.1 mm in length) induced the formation of normal-looking stamens. However, with a progressive increase in stamen size, less and less of the normal stamen features were produced following the GA3 treatment. Ultimately, buds with stamen primordia 0.8 mm long or longer failed to respond to GA3 and produced all the mutant characteristics. These results are discussed in terms of Waddington's concept of “determination” and “canalisation” of development.

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Spherulitic crystal growth in the prodissoconch larval of Crassostrea virginica

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100076263 ◽

1983 ◽

Vol 41 ◽

pp. 518-519

Author(s):

George G. Cocks ◽

Louis Leibovitz ◽

DoSuk D. Lee

Keyword(s):

Crystal Structure ◽

Crassostrea Virginica ◽

Crystal Orientation ◽

Developmental Changes ◽

Gastrula Stage ◽

Orthorhombic Crystal ◽

Orthorhombic Crystal Structure ◽

Stages Of Growth ◽

Early Stages ◽

Initial Deposition

Our understanding of the structure and the formation of inorganic minerals in the bivalve shells has been considerably advanced by the use of electron microscope. However, very little is known about the ultrastructure of valves in the larval stage of the oysters. The present study examines the developmental changes which occur between the time of conception to the early stages of Dissoconch in the Crassostrea virginica(Gmelin), focusing on the initial deposition of inorganic crystals by the oysters.The spawning was induced by elevating the temperature of the seawater where the adult oysters were conditioned. The eggs and sperm were collected separately, then immediately mixed for the fertilizations to occur. Fertilized animals were kept in the incubator where various stages of development were stopped and observed. The detailed analysis of the early stages of growth showed that CaCO3 crystals(aragonite), with orthorhombic crystal structure, are deposited as early as gastrula stage(Figuresla-b). The next stage in development, the prodissoconch, revealed that the crystal orientation is in the form of spherulites.

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Formation of Dislocation Channels in Neutron Irradiated Molybdenum

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096618 ◽

1972 ◽

Vol 30 ◽

pp. 672-673

Author(s):

S. Mahajan

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Ambient Temperature ◽

Room Temperature ◽

Channel Formation ◽

Early Stages ◽

Transmission Electron ◽

Three Stages ◽

Two Stages ◽

Polycrystalline Molybdenum

The evolution of dislocation channels in irradiated metals during deformation can be envisaged to occur in three stages: (i) formation of embryonic cluster free regions, (ii) growth of these regions into microscopically observable channels and (iii) termination of their growth due to the accumulation of dislocation damage. The first two stages are particularly intriguing, and we have attempted to follow the early stages of channel formation in polycrystalline molybdenum, irradiated to 5×1019 n. cm−2 (E > 1 Mev) at the reactor ambient temperature (∼ 60°C), using transmission electron microscopy. The irradiated samples were strained, at room temperature, up to the macroscopic yield point.Figure 1 illustrates the early stages of channel formation. The observations suggest that the cluster free regions, such as A, B and C, form in isolated packets, which could subsequently link-up to evolve a channel.

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