Radiation Botany最新文献

Oxygen enhancement ratios (OERs) were determined for pink mutations in stamen hairs of Tradescantia clone 02. These were determined for X-rays (OER of 3·2) and neutrons at six energies ranging from 0·395 to 13·4-MeV (OERs ranging from 1·32 to 1·68). Unlike RBE, OER values showed only a slight dependence on neutron energy and were not found to vary as a function of dose. Our results appear consistent with OERs generally reported from other systems, but at certain energies do not agree with results previously reported for Tradescantia.

Germination of Grand Rapids lettuce seeds was effectively delayed by exposure to 100 kiloroentgens (kr) gamma-irradiation. Both gibberellic acid and kinetin were able to slightly overcome this delay in germination imposed by ionizing radiation. Incubation in 5-fluorouracil significantly depressed germination in irradiated seeds while it did not affect unirradiated seeds.

A dose of 100 kr ionizing radiation was effective in decreasing incorporation of [³H]-uridine into high molecular weight RNA but did not decrease incorporation into transfer RNA. 5-Fluorouracil reduced incorporation of labeled precursor into both RNA components while gibberellic acid stimulated the synthesis of ribosomal and transfer RNA.

The results indicated that ribosomal RNA synthesis was not necessary for germination to occur as 5-fluorouracil did not prevent germination in unirradiated seeds. However, 5-florouracil did delay germination after exposure to ionizing radiation indicating that ribosomal RNA synthesis may be involved in radiation damage and subsequent repair processes. From these data it appeared that ionizing radiation delayed germination of Grand Rapids lettuce seeds through an inhibition of ribosomal RNA synthesis.

Interaction of heat and radiation treatments on the survival of conidia of Aspergillus flavus was studied, using five different temperatures, ranging from 35 °C to 55 °C, and five different doses, ranging from 25 to 125 Krad. In most combinations these treatments showed a synergistic rather than simply an additive lethal effect. The extent of synergism depended considerably on the sequence in which these treatments were applied. Heating at 45 °C, 50 °C or 55 °C followed immediately by irradiation was the most effective synergistic combination for the inactivation of conidia.

The exposure of potatoes to gamma rays (10 krad) caused on induction of phenylalanine ammonia lyase (PAL) in the tubers. The induced activity was localized essentially in cortex tissue, mainly concentrated around the bud region. Whereas in parenchymatous tissue no induction was observed. The enhancement in PAL activity in buds was observed to be dependent on dose of irradiation and the duration of storage thereafter. The tubers exposed to a 10 krad dose showed maximal activation on storage at ambient conditions with 20 fold activity observed within three hours after irradiation. On further storage the activity declined and reached a constant level within a period of one week.

The increase in PAL activity was partly due to activation of the inactive form of the enzyme (30–40%) and partly due to de nova synthesis of the protein (60–70%).

Criteria for predicting optimum selection procedure in mutation breeding of self-pollinating crops were discussed and formulated. Based on the mathematical formulae and some numerical computations, the efficiency of delayed selections was examined and the following derived as a general conclusion.

Delayed selection in M₃~M₅ generations is of great practical merit when plants mutated at multiple loci are to be obtained. This method is considered promising even for the detection of single-locus mutants when difficulty in discrimination of the objective mutants is large, and/or when permissible population size per generation is small, probably below 10,000, as a rough estimate. It is, in general, thought that fifteen or more M₂ plants should be derived per M₁ spike or panicle. Small progeny size per M₁ spike such as one, two or three as proposed by Yoshida et al. seems of limited utility.

Experiments showed that ionizing radiation increased decay of leaves and caused greater release of organic compounds (9–20 per cent, depending on the species, relative to carbon content) and mineral elements (20–50 per cent depending on the species and the element considered). The irradiated samples also showed substantial lowering of water storage capacity, variation in the free radicals (in particular phenolics and carbonylics) and in the release of organic compounds.

The effect on the soil surface horizons was an enhancement of leaching of organic and mineral compounds (fulvic acid and accelerated manganese and zinc). Humus loss was 8–10 per cent per annum in the surface horizon and 3–5 per cent in the subjacent horizon.