Radiation Botany最新文献

A recent study of the kinetics of developing microspores in half anther populations of Campelia zanonia has led to a better understanding of the fluctuations in compartmental indexes (e.g. the mitotic index) normally observed in plants grown under rigidly controlled environmental conditions.

Following an acute dose of X irradiation, additional fluctuations are observed in these indexes, and these are described and interpreted in the light of the above study. The induced perturbation is similar to the response found in other partially synchronised cell populations, and is consistent with the existence of two events of particular sensitivity in the mitotic cycle.

The first symptoms of radiation damage to citrus fruit were noted 24 to 48 hr after irradiation with 240 krad of gamma rays. At about the same time, radiation-damaged cells were observed in peel cross sections in the flavedo, the outer colored peel layers. The damaged cells were deformed and their protoplasts stained much darker with haematoxylin-safranin than protoplasts of intact cells. The cytoplasm in damaged cells either thickened at one side of the cell, sometimes filling up most of the cell space, or contracted into a small mass. Using several histochemical reagents, a considerable accumulation of phenolic compounds was found to occur in the damaged cells shortly after irradiation. No accumulation of phenolic compounds was observed in intact cells of irradiated fruit. It is suggested that the phenolic compounds which accumulate in flavedo cells following irradiation cause cell death and consequent peel necrosis (pitting).

The post-irradiation modification of radiosensitivity of barley seeds with about 7% water content by hydrogen sulphide and N-ethylmaleimide (NEM) applied during oxygenated or oxygen-free hydration was studied. H₂S, which causes about 18% seedling injury to unirradiated seeds, effectively decreases the post-irradiation oxygen-dependent damage (Powers' class III). NEM dramatically enhances the magnitude of an O₂-independent component of damage. It also affords a small degree of protection against the post-irradiation oxic damage. The mechanisms possibly involved are briefly discussed.

Sprout inhibition of onions by gamma irradiation was found to be influenced by the physiological state of the bulbs at the time of irradiation, radiation dose and the storage temperature after irradiation. Sprouting was minimal during storage at ambient temperature (26 to 32°C) while exposure to low temperature (4 to 20°C) or widely fluctuating diurnal temperature (20°C min to 30°C max) accelerated it. Six to nine Krad inhibited sprouting during storage under the above conditions only if the bulbs were irradiated within a fortnight of harvest when they were in the dormant state. Twenty-five Krad caused a transient stimulation of sprouting regardless of the time of irradiation while 6 to 12 Krad only stimulated sprouting when the time interval between harvest and irradiation exceeded three weeks. Irradiation at all dose levels caused discoloration of the growth centre, the extent of which was minimal in bulbs exposed to low doses soon after harvest and in those stored at ambient temperature.

The influence of treatment pH on the relative mutagenic efficiency and specificity of the base-specific chemicals hydrazine (HZ) and hydroxylamine (HA) in comparison to that of the potent alkylating agent ethyl methanesulfonate (EMS) was studied, under five different pH levels employing two different test systems viz., the popular rice variety IR-8 and its viable, chlorophyll-deformed mutant, virescent. No mutations were observed in the M₁ generation itself. EMS was found to be the most potent of the three mutagens inducing the highest frequency of mutations under all the pH levels. HZ and HA were more cytotoxic and less mutagenic. However, the mutagenic effects of HZ and HA were much more pronounced in virescent as compared to their effect on IR-8. Thus, the efficiency of the mutagens were found to be dependent on the treatment pH as well as the test systems employed.

In these experiments ³H-labelled ethyl methanesulfonate (EMS) was used to study the effect of gamma rays on the uptake of EMS by barley seeds and the resultant alkylation of macro-molecules. In a parallel experiment the combined effect of gamma rays and EMS on mutation frequency and efficiency was investigated. Gamma irradiation (10, 20 and 30 kR) inhibited the uptake of [³H]-EMS, resulting in fewer alkylations in the macromolecular fraction. In the combined treatments with unlabelled EMS, seedling injury as well as frequency of mitotic and meiotic chromosomal aberrations were less than additive. However, a synergistic effect of combined treatment was observed for the induction of chlorophyll mutations in the M₂ generation. The results rule out the increased uptake of the chemical mutagen as the cause of the observed synergism, and suggest the interaction of radiation- and chemically-induced lesions.

Dried and soaked seeds of Ricinus communis L. cv Tindivanam, two were treated with X rays ranging from 10 kR to 100 kR with 10 kR increments. The mutants were studied for their variability. Three mutants possessing all the staminate flowers with fused perianth were spotted in the M₂ population obtained by treating the dried seeds at 30 kR, the breeding behaviour of these mutants in M₃ and their importance in hybrid seed production are discussed.