Radiation Botany最新文献

A beta-emitting fallout simulant (very fine sand labeled with varying levels of ⁹⁰Y) was applied to a field bean crop Phaseolus vulgaris L.). The foliage was wet or dry in alternate rows at time of application, thus simulating presence or absence of dew conditions. The presence of moisture caused a much larger initial retention of the simulant by the foliage. Dosimetry indicated that the contact dose under moist conditions was substantial, with the wet plants receiving a total dose 60 per cent greater than the dry plants. The yield of string beans was very sensitive to beta radiation and a dose of about 1000 rads to the surface of the apical buds severely reduced the string bean yield. It was estimated that this corresponded to a dose of about 400 rads to the meristematic tissue of these buds. Vegetative growth was much more resistant to the radiation with serious vegetative yield reductions occurring at about 10,000 rads to the surface of the apical buds.

The effects of germicidal u.v. and near-u.v. irradiation on bean leaf peroxidase activity were studied by means of isoelectric focusing techniques. The results indicated that peroxidase levels can be stimulated in detached leaves by an appropriate dose of germicidal u.v. The peroxidase stimulation due to germicidal u.v. irradiation could be partially reversed by a subsequent exposure to near-u.v. Near-u.v. alone at lower exposures failed to stimulate peroxidase activity. By isoelectric focusing of samples of leaf extracts it was determined that two peroxidase isoenzymes were induced by germicidal u.v. These two isoenzymes were absent in control leaves receiving no irradiation. The isoenzymes could be induced by germicidal u.v. and then reduced in activity by exposing the leaves to near-u.v. Among several peroxidase isoenzymes induced by the tumor producing bacterial pathogen, Agrobacterium tumefaciens, two were similar in isoelectric points to the two isoenzymes induced by germicidal u.v.

The effects of 3 cycles of recurrent seed treatment with thermal neutrons (TN), ethyl methane sulfonate (EMS), and diethyl sulfate (DS) on mutant frequency and combining ability in pearl millet (Pennisetum americanum (L.) K. Schum., formerly P. typhoides) were studied for eleven years. TN seed treatments gave the highest percentages of M₁ striped plants, the lowest percentage of M₁ selfed seed set, and the highest M₂ frequency of chlorophyll-deficient seedlings of the mutagens tested. Combining a low dose of EMS or DS with high and low TN treatments generally increased these effects. Normal lines, which looked like the controls, selected from lines subjected to 3 cycles of mutagen treatment, were compared with controls in 3 × 3 or larger Design II hybrid matings in 9 × 9 forage-yield trials. The 1,637 singlecrosses between normal lines from mutagen treatment failed to exceed the 825 control singlecrosses in average forage yield or highest forage yield. These results suggest that pearl millet has many specific-yield genes, none of which exerts a very great effect on yield. Genetic variances estimated from the Design II diallels were not significantly altered by mutagen seed treatment. EMS treatments increased the percentage of non-additive genetic variance over that in the control and TN treatments, but the failure of any of the 486 hybrids from EMS lines to outyield the best control hybrid suggested that these variance estimates might not be significant. The study suggests that attempts to improve the combining ability of inbred lines of pearl millet by mutagen treatment without several cycles of recurrent selection are not likely to succeed.

Early effects of ethyl methanesulfonate (EMS) on five barley cultivars (Clipper, G. I. 3576, Proctor, Ketch and Prior) with contrasting yield and adaptation characteristics were investigated.

Considerable increases in the M₁ sterility and the frequency and the spectrum of M₂-chlorophyll mutations were noted. The highest sterility and mutation frequencies were obtained with treated Proctor and Prior cultivars whereas with Clipper, both these responses were minimal.

Peanut embryos at successive stages of development were treated while still attached to the parent plant with the mutagens DES, EMS, MNNG, ICR-170, acriflavine, ethidium bromide, hydroxylamine, nitrous acid and sodium azide, and with the protein synthesis inhibitors chloramphenicol and erythromycine, for periods varying from 2 hr to 15 days. The results show that chronic treatments of fertilized ovaries with chemical mutagens are possible. However, differences in sensitivity were found between the stages of development of the embryos, with the earlier stages being the most sensitive. The alkylating agents were the most injurious while the acridines (ethidium bromide, ICR-170 and especially acriflavine) caused little damage as measured by the survival of the treated embryos and their subsequent germination. Within the mutagens, especially in treatments lasting more than 24 hr, the concentration of the mutagen during the treatment was the most important factor affecting the survival of the treated embryos. In the short treatments, the duration was as important as the concentration. Treatments of young embryos with chemical mutagens could be valuable in crops whose ovaries contain many ovules, because of the large M₁ seed populations obtainable from each fruit. The advantages of embryo treatments are discussed.

Gamma irradiation interfered with the synthesis of the IAA synthesizing system and exogenous application of 20 ppm IAA within 6 hr after irradiation, triggered the synthesis of this enzyme. This fact is ascertained by the inhibition with protein synthesis inhibitors such as actinomycin D, puromycin and cyclohexamide, on the recovery of enzyme activity on treatment with IAA. Irradiation accelerated the degradation of the existing enzyme by activating proteolytic activity. IAA in irradiated potatoes is completely depleted and this is associated with the activation of H₂O₂ dependent IAA oxidase. A 50 per cent decrease in the level of tryptophan, the substrate for IAA synthesis is observed at 24 hr after irradiation.