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Biomedical subjects

F C Steward

Publications and source records attributed to F C Steward.

At least 19 recordsLinked to original sources
PubMed1981

Growth and development of cultured carrot cells and embryos under spaceflight conditions.

Morphogenetically competent proembryonic cells and well-developed somatic embryos of carrot at two levels of organization were exposed for 18.5 days to a hypogravity environment aboard the Soviet Biosatellite Cosmos 1129. It was confirmed that cultured totipotent cells of carrot can give rise to embryos with well-developed roots and minimally developed shoots. It was also shown that the space hypogravity environment could support the further growth of already-organized, later somatic embryonic stages and give rise to fully developed embryo-plantlets with roots and shoots.

Cells, Cultured↗
PubMed1979

Is gravity a morphological determinant in plants at the cellular level?

It is not yet known whether higher plants, which have evolved in a gravity oriented environment, can reproduce normally or develop via single cells (somatic or zygotic) and pass normally through all phases of development, tissue differentiation and reproduction through consecutive generations at near-zero g. Most published work deals with directional gravitational stimuli (geotropisms) as they operate on the subsequent growth of preformed plant organs that have acquired the ability to perceive and respond to gravity during development at 1 g. But it should be established whether plant development can proceed normally in the weightless state, especially that critical stage in which single cells produce multicellular units leading to embryos with the growing regions of shoot and root which, in turn, give rise to all the tissues of the plant body. We consider here an experiment that tested whether carrot embryos, capable of developing from cultured somatic cells, could do so under conditions of near-weightlessness. Space flight seemed to have no adverse affects on the induction of such embryos or on the initiation of their organs. But there are still reservations which are discussed. Other systems adaptable to the study of embryogenesis and development in space and to resolve the current reservations are described and their place in future space research is indicated.

Arabidopsis↗
PubMed1974

The labeling of cultured cells of Acer with (14C)proline and its significance.

The distribution of the radioactivity from [(14)C]proline that is bound in cultured cells of Acer has been determined by electron microscope autoradiography. In this way proline may be related to the cell wall as a morphological entity rather than as a fraction in a biochemical separation of a heterogeneous crop of cells. The cells in culture may vary greatly. Some are active growing, turgid cells, with thin protoplasts tightly pressed against their walls; in others the protoplasts may spontaneously withdraw from the wall; in still others the protoplasts disorganize, and walls thicken and become sculptured as the cells differentiate and even senesce. Different culturing practices may affect the status of the cells, and this, in turn, affects the distribution of radioactivity from proline in the cells. Cells which are actively growing, turgid, and nucleated have the highest grain density in their protoplasts and nuclei; as the protoplasts of such cells withdraw from their walls, they retain the bulk of the radioactivity. On the other hand, in cells which have thickened walls and sparse protoplast contents, the radioactivity is accumulated in their walls. A high content of proline and hydroxyproline-rich protein is, therefore, not a necessary or invariable feature of the cell walls of cultured Acer cells but depends on the state of development of these cells.

Carbon Radioisotopes↗
PubMed1968

The incorporation of radioactive proline into cultured cells. Interpretations based on radioautography and electron microscopy.

Cultured carrot explants, stimulated to grow rapidly in a medium containing coconut milk, were labeled with radioactive proline. After an initial period of absorption (8 hr for proline-(3)H; 24 hr for proline-(14)C) the tissue was allowed to grow for a further period of 6 days in a similar medium free from the radioactivity. Samples were prepared for electron microscopy and radioautography at the end of the absorption period and also after the further growth. The distribution of the products from the radioactive proline in the cells is shown by high-resolution radioautography and is rendered quantitative for the different regions of the cells. The results show that the combined label, which was present in the form of proline and the hydroxyproline derived from it, was all in the protoplasm, not in the cell walls. Any combined label that appeared to be over the cell walls is shown to be due to scatter from adjacent cytoplasmic sites. Initially the radioactivity was concentrated in nuclei, even more so in nucleoli, but it subsequently appeared throughout the ground cytoplasm and was also concentrated in the plastids. The significance of these observations for the general concept of a plant cell wall protein and for the special problem of growth induction in otherwise quiescent cells is discussed.

Autoradiography↗