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
Radiosensitivity of seeds. I. Reduction or stimulation of seeding growth as a function of gamma-ray dose.
Dormant seeds of one or more varieties of l2 species, totaling 15 tests, were irradiated with Co/sup 60/ gamma rays over a wide range of doses. Treatments were randomized and replicated, with growth of first true leaf under greenhouse conditions as the criterion of radiation effect. About 40,000 seedlings were measured individually to the nearest millimeter. Statistical analysis delineated the doses between which seedling growth fell significantly below that of untreated controls. In the case of one wheat variety, there was apparent stimulation by the lowest three doees of radiation. Further tests are in progress. (auth)
Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress
Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radicle emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.