Radiation Botany最新文献

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.

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.

The seeds of Co. 1 red gram (Cajanus cajan (L) Millsp.) were treated with gamma rays (0, 14, 16, 18, 20, 22, 24 and 26 kR) and EMS (0, 60, 70 and 80 mM for 4 hr at room temperature) and observations were recorded in the M₁ and M₂ generations. The chlorophyll mutations in M₂ were maximum at 24 kR of gamma rays and 70 mM of EMS, but the maximum frequency of viable mutations was noted around 16 kR and 60 mM. The percentage of viable mutations was found to be greater for gamma ray treatments compared to those for EMS. Some morphological mutants have been reported for the first time.