Radiation Botany最新文献

Effects on the developmental morphology of Cajanus seeds irradiated with ⁶⁰Cogamma rays have been investigated in vitro. Seeds exposed to 5 kR produced a cluster of adventitious roots on a “callusing medium” (modified Murashige and Skoog nutrient solution) while the hypocotyl explants of germinated seedlings were stimulated to cell proliferation and abundant callusing which, on a “differentiating medium” (modified medium) regenerated shoot buds and plantlets. In controls and with higher doses growth was limited to the development of a spongy tissue to form a small callus mass from seeds and a restricted callus proliferation from excised hypocotyls of irradiated seeds. Only calluses exposed to 5 kR differentiated plantlets. However, callus tissues derived from the 5 kR treatment were highly friable and amenable for release of protoplasts in large numbers on enzymatic digestion of cell walls of cells grown as suspensions. Mesophyll cell protoplasts obtained from the tissue culture-induced plant showed spontaneous adhesion and fusion.

Three separate experiments were conducted with cultivated peanuts to (a) study the effect of four controlled temperatures on the expression of seven radiation-induced macromutants and the mother line; (b) determine the responses of normal appearing F₁ hybrids involving four macromutants to three controlled temperature regimes and (c) evaluate the same macromutant, parental and F₁ hybrid populations (described in b) when grown for a full season under field conditions.

Macromutant plant weights and flower production were generally lower than that of the mother line in all three experiments. The macromutants also tended to flower later than the mother line. The leaflet expression of two of the macromutants was drastically influenced by changes in temperature. Lupinus reached maximum leaflet curvature when grown at 34/30°C but appeared near normal when grown at 22/18°C. The reverse was true for the macromutant Recurved. The macromutant Flop contained maximum percentages of nitrogen and phosphorus in its vegetative parts when grown at the highest temperature (34/30°C). All other mutants and the mother line had highest proportions of these nutrients when grown at the lowest temperature regime (22/18°C).

Expressions of heterosis were maximized when hybrids of macromutant parentage were grown at suboptimal temperatures. General combining ability estimates were higher than specific combining ability estimates with the macromutant Hedera (a dwarf type) making the greatest contribution to the general combining ability effects for peg (fruit-bearing structure) production and pegging efficiency. The same macromutant was found to make substantial contributions to general combining ability effects for fruit and seed weight when hybrids were grown under field conditions.

Strains of di-, tetra-, and hexaploid oats derived from untreated and EMS-treated seeds were used to estimate mutation rates for spontaneous and induced mutations at loci that affect quantitatively inherited traits. The oat strains were produced by using a dichotomous progeny scheme.

The study was initiated with one plant from each of two cultivars for each ploidy level. From a first-generation plant, four seeds were chosen to produce second-generation plants. Two were sown without treatment, and the other two were treated with 0·04 M solution of ethyl methanesulfonate (EMS) for four hours. For the third and subsequent generations, two progenies were grown from each plant in the previous generation. Seeds in the treated line of descent were given EMS through generation 5. Both lines of descent were carried through six generations. The 125 strains (62 in the untreated line of descent, 62 in the treated line of descent, and one from the original plant) from one cultivar were sown in a field experiment and traits measured were grain yield, heading date, plant height, flag leaf length, number of spikelets per panicle, 100-seed weight, seed width, seed length, and protein percentage.

A mutation was judged to have occurred when two criteria were met: (a) the observed value for a trait of a parent strain differed from comparable values in one or both of its progeny by an LSD unit and (b) the deviant value was inherited into later generations. Mutation rates were expressed as mutations per trait per 100 gametes.

Genotypes differed with respect to the rates of occurrence of spontaneous and induced mutations. There was no obvious relationship between spontaneous and induced mutation rates that genotypes showed, but mutability was trait related. Traits most susceptible to mutation induction were grain yield, heading date, plant height, number of spikelets per panicle, and seed length.

Spontaneous mutation rates for di-, tetra-, and hexaploid oats were 1·2, 0·5, and 0·3 mutations per trait per 100 gametes, respectively, whereas induced mutation rates were 1·2, 1·3, and 2·0 mutations per trait per 100 gemetes, respectively.

Dormant seeds of Ph. vulgaris were treated with 24, 48 and 72 mM solutions of EMS. The highest frequencies of mutations (chlorophyll, morphological and seed-coat color) were induced by the 48 mM dose. The M₁ plants were chimeric often having only a small mutated sector. Based on the segregation ratios obtained, the number of initial cells present in the apical meristem ranges from three to eight for the whole plant and from one to three for the primary branches. The experimental results indicate a post-treatment origin of the primary branch initials. No evidence was found for the occurrence of diplontic selection during the ontogeny of a mutated plant in the variety studied.

Rice plants were exposed to 1, 2·5, 5, 7·5 and 10 kR of acute gamma rays at 4 critical developmental stages, i.e. pre-tillering, earprimordia formation, meiosis and heading.

Doses of 1 and 2·5 kR, in general, had a stimulatory effect on culm length, tillering, ear number per plant, spikelet number per ear and seed yield per plant, at the first two developmental stages, particularly at the pre-tillering stage. There was a significant reduction in all the above characters at 5 and 7·5 kR for all irradiated stages. Of the different developmental stages, pre-tillering was most radiosensitive (LD₁₀₀-7·5kR), followed by meiotic and heading stage.

Stage of development, exposure rate and differences in interphase chromosome volume (ICV) are discussed as possible factors affecting radiosensitivity.

The merits and demerits of the various methods for scoring mutation frequency offered hitherto, namely, M₁-plant method, M₁-spike method, Gaul's M₂-plant (or seedling) method, modified M₂-plant method (M₂-plant method by randomly sampled M₂-plants), Yamaguchi's revised M₁-spike method (revised form of Gaul's indirect method) and Panicle-Branch method, Li and Rédei's standardized M₁-spike method, Ukai and Yamashita's expression of cell mutation rate and Walther's expression of ‘Factor of Effectiveness’, were comparatively discussed based on some theoretically derived formulae.

Based on our criteria for measuring the suitability of scoring methods, the M₁-plant, modified M₂-plant, Yamaguchi's Panicle-Branch and Walther's Factor-of-Effectiveness methods were considered inapplicable for our general use. Among the other methods, no one method seemed to be invariably the best, the utility of each scoring method being dependent on the aim and conditions of the particular experiment. Scoring methods regarded as least subject to error for some typical experimental conditions were presented. The necessity of recording the numbers and sizes of M₂-lines and the segregation ratios of the mutants regardless of the scoring method adopted in individual cases was made. These records should be useful not only for the transformation or standardization of mutation scores for our future needs, but also for refining our knowledge of the various factors causing distortions in the scores. It was also noted that the greatest care should be taken in all cases, so that each M₂-line might be derived from equally- or closely-ranked tillers. By this method, the errors stemming from irregularity in the numbers of germ-line cells contained in a spike primordium could be greatly reduced.