X-RAY EFFECTS ON THE GROWTH AND REPRODUCTION OF WHEAT.
Evidences of miiodification and injury to plant parts are numerous in the extensive literature on the effects of x-ray treatment of plants. JOHNSON (2) lists the effects produced on seventy species of flowering plants. Her work with wheat (3) shows that growing material is more strongly affected than non-growing by equal doses of radiation given in the same way. Seedlings from soaked grains given treatments of 1000 r-units and 5000 r-units made less growth in all respects than did controls, but showed inereased tillering. No flowering data were included. SHULL and MITCHELL (4) obtained deleterious effects when unfiltered radiations were used but the use of metallic screens, high voltage, low amperage, and brief exposures giving approximately 100 r-units, resulted in stimulative action on wheat, corn, oats, and sunflower seedlings. Twentyfour-hour-old wheat seedlings were irradiated with doses of x-rays varying from 565 to 13,560 r-units by FRANCIS (1). Retardation of fresh weight and dry weight production by the growing parts of the seedlings and retardation of linear growth of the coleoptile, the leaf, the primary root, and the lateral roots was obtained with all doses and time intervals employed. Respiration was likewise depressed with the exception of those seedlings which had received the smallest dose of radiation (565 r-units) and which were tested 5 or 6 hours after irradiation. The procedure of SHULL and MITCHELL was closely followed in an attempt to obtain further data on the stimulative effects of filtered x-radiation on growth, height, tillering, heading and flowering, green and dry weights, and moisture content of Marquis spring wheat. An attempt to determine the influence of age of seed on response to irradiation was made by the use of two samples of seed; one 57 months old (4 years, 9 months), the other 9 months old. A preliminary trial was made with Fulhio winter wheat. Methods
Radiation hormesis: its historical foundations as a biological hypothesis
This paper represents the first systematic effort to describe the historical foundations of radiation hormesis. Spanning the years from 1898 to the early 1940‘s the paper constructs and assesses the early history of such research and evaluates how advances in related scientific fields affected the course of hormetic related research. The present effort was designed to not only address this gap in current knowledge, but to offer a toxicological basis for how the concept of hormetic dose-response relationships may affect the nature ofthe bioassay and its role in the risk assessment process.
Effects of X-Rays upon Growth, Development, and Oxidizing Enzymes of Helianthus annuus
1. Irradiation of soaked seeds of Helianthus annuus causes a slight decrease in percentage of germination. The average total growth of the plants is less, and the average time of blossoming is shortened, even with doses so light that there are no immediate visible effects. A checking effect, proportional to the doses, is evident during the first three weeks of growth after seeds have been irradiated with medium doses. On unfolding, the leaves present a peculiar pitted or mosaic appearance, which seems to be due to an unequal distribution of chlorophyll, when medium or heavy doses are given the seeds. Heavy dosage does not stop development of soaked seeds until the cotyledons have been partially or wholly pushed through the soil. The root tip becomes brown in color and no growing stem tip appears. 2. Fasciations of stems, leaves, and flowers are induced by irradiation of seeds and seedlings with medium doses. Stem fasciations commonly took the form of flattening and dichotomous splitting of the main stem, which showed the presence of many blossoming branches instead of a single flower head. Fasciation of the flower head was represented by fusion in the involucral region and by forking of the stalk below the involucre, with two or three distinct heads resulting. Many leaf abnormalities,-ligulate leaves, altered phyllotaxy, and incipient fasciation, which marked earlier periods of growth, often disappeared before maturity. 3. Catalase activity is depressed in young seedlings whose seeds have been exposed to medium doses of X-rays. With older seedlings which are beginning to show recovery, however, there is but slight reduction in activity noticed. 4. Depressed respiration is associated with stunted growth when this accompanies heavy irradiation. The amount of carbon dioxide liberated from irradiated seedlings is less than that from controls similarly treated. 5. Normal oxidase activity is found in seedlings whose growth has been inhibited by heavy doses of X-rays. 6. Cells of the radicle tip from seedlings whose growth has been inhibited by heavy irradiation show elongation, great vacuolation or entire absence of protoplasm, and the absence of nuclei from many cells. The average size of the cells in the meristematic region of the radicle tip of irradiated material is greatly increased over that of the control. Xylem is increased at expense of the pith, and there is a greater suberin development in the hypocotyl regions of mature plants from irradiated seeds than in those of the control. The increase in vascular tissue in irradiated material is apparent even in seedlings but nine days old.