Radiation Botany最新文献

An experimentally-produced hybrid between red and green plants of Beta palonga and the segregating population in F₂ showed more resistance to acute X-irradiation of seed than did their parents, as measured by seed germination, plant height, abnormal plant growth, chromosomal abnormality during meiosis and pollen grain sterility. In every measurement the F₂ plants were more sensitive than the F₁ hybrid. The radiosensitivity could not be interpreted in terms of average interphase chromosome volume. The resistance of the hybrid is suggested to be due to factors associated with heterozygosity and heterosis, although this has not been definitely established.

A northern Mojave Desert shrub community was irradiated by a ¹³⁷Cs source for a ten-year period. Leaf and fruit production, cover, and percent live stem of Krameria parvifolia shrubs were found to respond significantly to a radiation gradient with exposure rates ranging from 0·1 to 10 R/day. Fruit and leaf production were greatly reduced at exposures over 6 R/day. Above 7 R/day 16% of the shrubs were dead compared to 1·2% in a non-irradiated area. Reduced cover, density and live stem values indicate a trend toward a lower status of Krameria in the community at cumulative exposures above 25 kR. Observations indicate that an equilibrium in response to irradiation has not yet occurred. Radiosensitivity of K. parvifolia is attributed in part to its phenology.

Sodium azide has been utilized recently both as an agent for the study of repair of radiation-induced chromosome damage, and as a mutagen in barley caryopses (seeds). However, the effect of this agent on the cell cycle and optimum time of treatment during the cell cycle in these studies is not known. To better understand the effects of sodium azide on the embryonic barley shoot cells, a detailed study of the effect of azide on the cell cycle was conducted.

Himalaya barley seeds were treated for 2 hr with 10⁻⁴, 5 × 10⁻⁴, and 10⁻³M oxygenated sodium azide solutions at pH 3. The principal effect on the cell cycle due to sodium azide treatment was a delay in the initiation of metabolism following germination. This resulted in a uniform delay in the following parameters: mitotic activity, seedling growth, and ATP and DNA syntheses. This delay was interpreted as being due to an ATP deficiency which when alleviated allows the cells to progress normally through mitosis.

Chromosome damage caused by sodium azide was not reflected in the seedling heights as the reduction in height was due entirely to mitotic delay. No variation occurred in the progression of cells through mitosis between various regions of the shoot within the first 29 hr of germination.

Testing the “old” micro-mutant lines from M₁₂ to M₁₆ generations, which were selected for characters other than disease resistance, revealed that variability in leaf-rust resistance was maintained between lines and within them. The variability of severity of infection by specific races was found in the mutant lines at the level of sublines. In the field, significant variability of the severity of infection and tolerance of infection appeared at the level of lines. Mutants in the type of infection were rare. They appeared in two lines at the level of sublines.

The effect of four straw and two ¹³⁷cesium levels, with and without fertilization, on ¹³⁷cesium uptake by wheat plants was studied using soils from the Blaine Lake and Waiteville soil associations of Saskatchewan (Canada).

Uptake of ¹³⁷cesium using either soil type, when fertilized and treated with any of the four straw and two ¹³⁷cesium levels, significantly decreased with plant age. Such a trend was generally not observed in an unfertilized Blaine Lake soil. Increasing straw application, with and without fertilization, increased the dry matter yields in both the soils although the heavier (particularly the 3 tons/acre) straw addition produced slightly depressed yields for the fertilized soils.

Increasing straw application to both fertilized soil types did not significantly enhance the ¹³⁷cesium uptake in plants grown at either ¹³⁷cesium level. However, increasing the straw levels, without fertilization, in the Blaine Lake soil contaminated with either ¹³⁷cesium level, did not appreciably and consistently affect the ¹³⁷cesium uptake by the plants.

Plants absorbed highly significantly greater ¹³⁷cesium from the 100 compared to the 50 μCi ¹³⁷cesium level in both the soils applied with any straw-fertilizer combination. This trend did not occur with unfertilized Blaine Lake soil.

After X-irradiation of dormant caryopses of the different radiosensitive winter wheat varieties “Bayro” and “Walthari” from five successive harvest-years, a negative correlation between phosphorus content of caryopses and their radiosensitivity was observed. To interpret the results two possibilities were discussed: 1. The amount of phosphorus content in developing embryos influences the size of chromosomes in the nuclei of the embryos and therefore also their radiosensitivity. 2. The intensity of physiological activities during the premitotic phase of germination, which depends on the phosphorus content, influences the duration of radiation-induced “mitotic delay” and therefore also the process of repair in this phase.

The increase in pseudo-self-compatibility, obtained during chronic gamma irradiation of Nicotiana alata plants, was found to result from an effect of irradiation on the pistil of the flower.

Ethylene gas and X rays, alone and in combination, were applied to petioles of Saintpaulia ionantha Wendl. to test their effect on peroxidase activity. Both agents increased peroxidase activity, although ethylene was the most effective. X ray treatment of petioles at five different peroxidase levels showed that as the initial activity of peroxidase increased the effect of a given dose of radiation decreased. Also, high doses, near the lethal limit for the species, were proportionately less effective in inducing peroxidase activity than were lower doses. Polyacrylamide disc electrophoresis showed no change in isozyme patterns with increases in peroxidase activity.

Effects of gamma irradiation (10,000 Ci ¹³⁷Cs source) for one growing season on biomass production of ground vegetation under northern Wisconsin aspen and maple-aspen-birch forests and on an abandoned logging road were evaluated during and one year after irradiation. No significant changes in production were determined during the irradiation year. One year later three distinct zones—semi-devastated, herbaceous, and original forest—developed along the radiation gradient. Biomass production under forest canopies decreased significantly in the semi-devastated zone, increased significantly in the herbaceous zone (primarily responding to additional light), and remained unchanged under the original forest. Logging road vegetation responded similarly but the changes were restricted within higher radiation doses. At comparable levels of radiation, production of species of the logging road vegetation was affected less than that of species under forest canopies. Such a trend was predictable from the generally smaller interphase chromosome volumes, ICV's, of the species on the logging road and from their ability to survive in severe habitats.

The possibility that root growth rate reduction following ultrasonication might be the result of loss of reproductive integrity in cells bearing ultrasound-induced chromosomal anomalies was considered. Root meristems of Vicia faba were ultrasonicated at a frequency of 2MHz and an intensity of 8 W/cm² for one minute. The surviving fraction of cells, calculated from root growth rate according to the model of Hall, Lajtha and Oliver⁽¹⁴⁾ was 0·58. The weighted average yield of chromosomal-anomaly-bearing cells at the first post-sonication mitosis was 0·105. Thus, the number of cells with chromosomal anomalies is only $\text{1}\text{4}$ the number needed to account for the calculated cell surviving fraction. This result suggests that root growth rate reduction following ultrasonication may be due largely to effects of the sound field on elongating cells rather than to effects on meristematic cells.