Radiation Botany最新文献

Gamma irradiated medium induces the formation of buds in non-irradiated dark grown tobacco callus (Nicotiana tabacum Var. Wisconsin no. 38). Experiments were conducted to determine the component(s) of the medium that is effective in this radiation-induced organogenesis. Fractions of medium were irradiated singly and in combination, then combined with non-irradiated fractions to form the complete growth medium.

The results show that irradiated indoleacetic acid (IAA) was not the effective component in the induction of organogenesis. Omission of IAA from the medium resulted in the formation of buds, as expected. Irradiated myo-inositol induced organogenesis more consistently than the other irradiated components.

The age of the inoculum tissue and its passage number from the tobacco stem affected the potency of the tobacco callus to organise.

Dry seeds of uniform size of the rice variety T(N)1 were treated with DES alone and in combination with X-rays. The combined treatments affected more adversely the different growth metrics in the M₁ generation and increased the frequency of appearance of chlorophyll and other mutations affecting various morphological characteristics in the M₂ generation as compared to the treatment with DES or X-ray radiation alone. With respect to the spectrum of mutations induced by DES treatment, the frequency of chlorophyll mutations was noted to be relatively higher than that of other morphological mutations. The appearance of xantha mutations was noted to be the most frequent in the DES treatment in contrast to their rare appearance in irradiated material. The combined treatment had a considerable effect in altering the frequency and spectrum of morphological mutations as well as increasing the frequency of micromutations for grain yield and plant height.

Rice seeds treated with 0·2–1·2 v/v % of ethyleneimine (EI) demonstrated increasingly delayed germination concomitant with increasing dose. At the time of germination, the release of storage products was slightly inhibited at lower doses and completely reduced at higher doses. With increasing time after germination the development of shoot length, content of reducing sugar and free amino acid, and synthesis of nucleic acid and protein in treated seeds, showed the same response pattern as the control, although at reduced levels in the treated seeds. Consequently, it is interpreted that the delay of germination is due to physiological dormancy, i.e. impaired release of dormancy which would normally yield active forms of enzymes.

When treated seeds were cultured in [¹⁴C]-glucose medium, the specific activity of [¹⁴C]-glucose was higher in late-germinating seeds than in early-germinating seeds. Furthermore, the provision of glucose prevented the delay of germination, resulting in about a 10% increase in germination rate (survival rate), and yet had no effect on subsequent growth.

Finally, it is concluded that the damage resulting in delayed germination and reduction of survival differs from the damage leading to inhibition of subsequent growth in that the former can be compensated for by provision of glucose while the latter cannot.

Metabolic disturbances resulting in growth retardation and death of rice irradiated with ⁶⁰Co γ-rays at 10 to 40 kR dose levels were investigated. Seedling growth, release of storage products (reducing sugar and free amino acids) and incorporation of radioisotopic substances ([³H]-uridine, [³h]-thymidine and [³h]-leucine) remained almost uninhibited at doses up to 20 kR but were much reduced at 40 kR. Following the 40 kR treatment, shoot elongation was terminated at the 5th day of germination, corresponding to an interruption in the release of reducing sugar. Furthermore, the onset of active increase in [³h]-thymidine incorporation after germination was also delayed in the 40 kR irradiated samples.

When the seeds had been cultured in glucose-medium immediately after irradiation there were significant regular increases of survival and a disappearance in the delay in [³h]-thymidine incorporation. However, glucose had no marked effect on subsequent growth and overall metabolic damage even though incorporation of [¹⁴C]-glucose was slightly higher in the irradiated than in the control in the early stage of germination.

It is suggested that the recovery from radiation damage in the early stages of germination can be enhanced by the provision of glucose while recovery from damage leading to reduction of subsequent growth is less sensitive to glucose.

The effect of gamma radiation on dormant seeds of Avena fatua L. (wild oats) has been investigated. A. fatua seeds require a long after-ripening period for germination. Gibberellic acid and cold treatments are known to break seed dormancy. 10 kR of gamma radiation also produced an effect similar to these treatments. Shoot length and dry matter content of seedlings raised from 10 kR gamma-irradiated seeds were similar to those raised from control seeds. Higher radiation doses promoted seed germination but they also caused a reduction of seedling growth. Probable mechanisms by which gamma radiation may bring about these effects have been discussed.

Soil nutrients (extractable P. and NO₃-N, exchangeable Ca, Mg and K), exchangeable Al, pH and organic matter content were measured over the top six inches of the soils of the seven-year old-field portion and the cultivated portion of the Brookhaven gamma field. Although concentrations of all nutrient elements were higher in the agricultural soil, the distributions of Ca, P, Al, pH and organic matter were similar along the radiation gradient in both fields. There was also a regular reduction in phosphorus with decreasing exposure, but distribution of other elements was not clearly related to radiation effects. The distribution of all elements except K was significantly correlated with pH in the agricultural soil. In the old-field only Ca, Mg and Al showed this relationship. The most conspicuous effects of nearly 25 yr of chronic irradiation of the site were a reduction in soil organic matter content and an increase in soil P in both fields.

This paper summarizes experiments carried out in the south of France to define some radiobiological characteristics of a certain variety of rice seeds in the Camargue: Oryza sativa L. c. v. Cigalon Marie, and to test treatments which provide radioprotection or promote recovery. Radio-induced damage is measured by means of the sum of seedling heights, this criterion being sometimes specified by the examination of its two components: the average height of the seedlings and the number of survivors.

The results show that if high exposures to ⁶⁰Co γ-rays are used then seeds must be used with a water content of not less than 13% and sowing must take place as soon as possible after exposure to minimize storage effect.

A natural result of protection appears after soaking seeds at a low temperature (5°C) then dehydrating them at 32°C to bring back their initial moisture content, before irradiation. This effect is maximum when the time sequence of the treatment allows a complete hydration of the seeds. It is not due to the elimination of a radiosensitizer through soaking but might be ascribed to modifications in enzymatic protein structure during soaking at a low temperature. On the contrary, soaking at a high temperature (32°C) results in an increased radio-sensitivity.

It is possible to induce recovery after irradiation if irradiated seeds are grown on a medium containing commercial yeast extract. The earlier and longer the application, the better the recovery. Extracts prepared from yeast cell culture, as well as RNA extracted from them, promote a recovery effect. All these extracts which stimulate growth of rice seedlings during their exponential stage in the laboratory and increase the number of surviving plants in the field, might contain a recovery-promoting constituent whose chemical composition is still to be found.