Increase induced by colchicine in the incidence of somatic crossing over in Glycine max

Soybean (Glycine max [L.] merrill) as a short-term assay for study of environmental mutagens. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The soybean (Glycine max [L.] Merrill) spot test is suggested as a preliminary screening test for environmental mutagens. This system makes use of various types of spots that originate from the treatment of seeds or seedlings with mutagens. The homozygous dominant y11y11 dark green leaves may show light green and very dark green spots; the heterozygous y11y11 light green leaves may show dark green, yellow or twin spots; and the homozygous recessive y11y11 yellow leaves show light green receptors. The interpretation is that twin spots on the y11y11 leaves originate from somatic crossing-over, and the singles originate primarily from losses or gains of the segments or chromosome carrying the gene y11 or y11. The yellow plants (y11y11) can produce light green sectors if y11 mutates to y11. Studies carried out with a host of chemical and physical agents lend support to the idea that the soybean system can distinguish between several genetic mechanisms underlying the formation of spots. Spots are detected against their native genetic and phenotype background, thus minimizing the effects due to physiological changes. The system is rapid (4-5 weeks per chemical), inexpensive, and involves an eukaryotic organism. It has the advantage of being adaptable for liquid solutions of chemicals, solid wastes, emulsions of chemicals (e.g., in lanolin), and gaseous products.

Arrangement of chromosomes in the interphase nucleus of plants

Chromosomal arrangement in the interphase nucleus has two main aspects: (1) arrangement of chromosomes with respect to nuclear polarity and to other nuclear components, and (2) arrangement of chromosomes with respect to one another. The latter aspect consists of two main types of spatial relationships; (1) relationships between different members of one chromosomal set, (b) relationships between different chromosomal sets. Data concerning various aspects of chromosomal arrangement in the interphase nucleus are presented and discussed and the genetic control as well as subcellular mechanisms which are involved in nuclear organization, are elucidated. Evidence is presented indicating that, in common wheat, the gene system that determines the specific pattern of chromosomal arrangement in the nucleus is operating via the microtubular elements of the spindle system. The significance of ordered arrangement of chromosomes in the nucleus for the regularity of genetic activity and chromosomal behavior, is pointed out.

Somatic crossing over in Glycine max L. (Merrill): sensitivity to and saturation of the system at low levels of tritium emitted beta-radiation

Seeds of varieties L65-1237 and T219 of soybean were soaked in 20-50 ml of tritiated water (HTO) containing between 0.01 and 50 μCi/ml of tritium (T) for various periods from 24 to 142hr. Genetic damage was determined by counting the number of Y11Y11-y11y11 spots on the Y11y11 leaves. No effect was noticeable in treatments lasting up to 24hr independent of the concentration. However, somatic crossing over occurred when the seeds were treated with tritium for 92 hr or longer even with concentrations as low as 0.01 μCi/ml. The data indicate that the soybean system being used is sensitive to very low doses of beta radiation. The damage to the seeds treated with the lowest concentration was not significantly different in quality or quantity from that induced by higher concentrations. This indicates some type of saturation effect to tritium-emitted beta radiation. Analytical results showed that synthesis of organic matter and incorporation of tritium into the organic fraction was delayed until about 96 hr after the imbibition was started. This indicates a relationship between spot induction by tritium and organic synthesis.