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Biomedical subjects

E S CASTLE

Publications and source records attributed to E S CASTLE.

6 recordsLinked to original sources
PubMed1965

DIFFERENTIAL GROWTH AND PHOTOTROPIC BENDING IN PHYCOMYCES.

Using present knowledge of the cell's optical and growth mechanisms, a theoretical bending speed of about 5 degrees min.(-1) is calculated for unilateral irradiation by a single beam of normally incident visible light; this figure is of the magnitude found experimentally. Between beams of light opposed at 180 degrees , the resultant bending speed is given by the difference-to-sum ratio of the light intensities of the two beams. Valid comparisons between cells differing in size, growth speed, or optical properties are made by expressing bending speed as a fraction of each cell's bending response to unilateral irradiation. With multiple beams differing in intensity and azimuth, the resultant bending speed follows from vector addition of phototropic components proportional to the flux fraction of each beam. The bending speed in Oehlkers' experiment where a luminous area is the light source also appears compatible with this rule. In such experiments, the bending speed quantitatively matches the scaled asymmetry of the pattern of flux incident upon the cell. Resolution experiments support the assumption that light intensity enters into steady state phototropic formulations as the first power of I.

Biophysical Phenomena↗
PubMed1962

Phototropic curvature in Phycomyces.

The distribution of curvature and of bending speed along the cell's growing region are studied during steady state phototropic bending. At the start, elemental bending speed parallels the known axial distribution of growth rate. Hence regional phototropic sensitivity is initially determined by the local growth rate, and unilateral visible light acts proportionally at all levels of the growth zone. In the later course of bending, the bending speed distribution shifts downward instead of progressing upward in step with the cell's elongation. Furthermore, during phototropic inversion reversed bending begins high in the growth zone and progresses downward while normal bending continues below. These spatial and temporal changes in the distribution of differential growth are considered to be due to a fixed rate of supply of material used in growth that is transported from lower regions of the cell and asymmetrically distributed within the growth zone.

Fungi↗
PubMed1961

Phototropism, adaptation, and the light-growth response of Phycomyces.

Phototropic bending can be initiated without the transient changes in growth speed that characterize a light-growth response. The conditions required are a change from a symmetric to an asymmetric illumination pattern while the cell receives a constant radiant flux. Phototropism is thus basically a steady state process. It cannot be founded on differential light-growth responses as in Blaauw's theory. A possible model system for the unequal partition of growth during steady bending is discussed. The fact that light-growth responses show adaptation while phototropic bending does not follows from the different natures of the two responses.

Adaptation, Physiological↗
PubMed1959

Growth distribution in the light-growth response of Phycomyces.

Elongation of sporangiophores marked with numerous starch grains was photographically recorded in the steady state and during the light-growth response when the rate is more than doubled. From these records the spatial distribution of growth within the cell's growth zone was derived. Stimulation by a single saturating flash of light speeds growth proportionally in all parts of the growing zone, maintaining the same pattern of growth distribution as in the steady state. This finding implies that light is absorbed and acts locally throughout the length of the cell's growth zone. Cohen and Delbrück's proposal of a partial spatial separation of light reception and growth is discussed.

Fungi↗
PubMed1958

The topography of tip growth in a plant cell.

Tips of young Phycomyces sporangiophores were dusted with starch grains, and growth photographically recorded. Rates of longitudinal displacement from the cell tip of individual markers were determined, also corresponding rates of change of cell diameter. From these the magnitude and spatial distribution of "relative elemental growth rates" along both longitudinal and circumferential axes of the cell were obtained. Growth rates in these two directions are functions of distance from the cell apex, and have different spatial distributions. In particular, rates of growth in cell circumference are complexly patterned. Relative elemental growth rates in length and in girth are approximately equal and maximal at the cell's apex, with a value of 2.4 mm. mm.(-1) hr.(-1). The characteristic shape of the tip is maintained constant in the face of its changing substance and position. This shape reflects a steady state of the cell's constituent growth patterns. At every point the growing membrane simultaneously expands in the two dimensions of its surface. The degree of polarization or directional preference of growth is measured by the ratio of longitudinal to circumferential relative elemental growth rate at any point. The ratio is not constant, but changes with position along the tip. This fact does not support the idea that membrane growth is based upon a quantal "growth event." Possible causal factors in oriented membrane growth are discussed.

Plant Cells↗