Effect of post-irradiation ageing on onion seeds

Seeds of onion (Allium cepa) cv. Ailsa Craig were exposed to various doses of gamma radiation (0, 10, 20, 40, 80 and 100 krad) and subjected to accelerated ageing (RH 100%, 42°C) for 12 h. Radiation doses significantly affected the percentage of normal seedlings, abnormality types (%) and seedling growth. Seed viability, conductivities of seed leachates, final germination (%), germination speed and time to reach 50% germination (T ₅₀) were not affected by the seed irradiation. Accelerated ageing after irradiation had significant influence on seed viability, conductivities of seed leachates, final germination (%) and percentage of normal seedlings. Germination speed, T ₅₀ and seedling growth were not affected by the accelerated ageing. However, all the parameters studied were significantly influenced by the interaction of radiation doses and accelerated ageing. Accelerated ageing generally enhanced the damaging effects of irradiation on seeds. Therefore, it was concluded that onion seeds should not be exposed to adverse environmental conditions after irradiation.     

Radiation-induced mutations from accessory buds of sweet cherry, Prunus avium L. cv ‘Bing’

 Dormant scions of ‘Bing’ were exposed to 1–2.5 krad of gamma radiation in order to induce useful mutations. The main buds were excised and the scions grafted to allow the growth of accessory buds into primary (V1) shoots. The frequency and types of mutations on secondary (V2) populations are described. In a population of 3324 V2 shoots, the overall mutation frequency was 6.4%: 4.2% partial, 1.6% total and 0.3% growth-reduced mutants were identified. The experiment was repeated using 3 krad- and 4 krad-fractionated doses in water. Differences in mutation frequency at 3 krad and 4 krad were not significant. Of 2562 surviving V2 shoots derived from the irradiation of accessory buds of both standard and V1 shoots, the overall mutation frequency was 3.3%: 1.7% were partial-leaf mutants, 1.0% were total-leaf mutants, and 0.54% were growth-reduced mutants. For maximum mutation rate with adequate survival we suggest acute irradiation of accessory buds in air at dosages approximating LD₅₀ (2.75–3 krad). A larger mutant sector was present in V₁ shoots derived from accessory buds than those from main buds as revealed by the higher number of total mutant repeats in the families. Received: 21 August 1997 / Accepted: 17 November 1997     

Endosperm responses to irradiated pollen in apples

Summary The cytological effects of pollen -irradiation at 50 and 100 krad on both embryo and endosperm development were studied in Malus × domestica. Fruit and seed set were reduced by increasing doses of pollen irradiation, while embryo sacs resulting from the treatments differed in number and morphology of endosperm nuclei and in the presence or absence of an embryo. Nuclear abnormalities, distinguished from normal nuclear behaviour in embryo sacs derived from unirradiated pollen, included enhanced numbers of polyploid restitution nuclei, bridges between nuclei, excluded metaphase chromosome fragments and disrupted mitotic synchrony. Generally, a high dose of pollen irradiation (100 krad) generated an all-or-nothing response in the embryo sac, either creating highly abnormal embryos and/or endosperms which aborted, or showing relatively normal development. Callus produced from excised cellular endosperm differed in average genome size, that derived from 100 krad pollen being smaller than that from unirradiated pollen.     

Sunflower germination and growth behavior under various gamma radiation absorbed doses

Gamma radiation, various absorbed doses (0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 krad) effects were evaluated on sunflower (Helianthus annus. L.) germination and growth characteristics. Sunflower healthy seeds were exposed to gamma radiation source Co⁶⁰ at nuclear institute for food and agriculture and exposed seeds were grown under controlled laboratory conditions. In comparison to control, gamma radiation absorbed doses affected the measured response positively i.e., radical length, plumule length, number of roots, seedling fresh weight, seedling dry weight, germination percentage, time of germination and diameter of hypocotyl of sunflower enhanced up to 83.15%, 70.32%, 73.03%, 4.80%, 3.26%, 72.0%, ? 18.88% and 12.58%, respectively. The time of germination, fresh weight and percent moisture contents enhanced insignificantly, however, the response was higher than control. All gamma radiation absorbed doses showed a stimulatory effect on sunflower germination and seedling growth characteristics. The low gamma radiation absorbed doses were found to be more effective versus higher doses for enhancing the germination and growth characteristics of sunflower. In view of positive effect of gamma radiation of sunflower germination and growth characteristics, it is concluded that this techniques could possibly be used for the enhancement of germination, growth and ultimately yield in sunflower in areas where germination is low due to unfavorable conditions.     

Combinational dormancy in seeds of Sicyos angulatus (Cucurbitaceae,tribe Sicyeae)

Seeds with a water‐impermeable seed coat and a physiologically dormant embryo are classified as having combinational dormancy. Seeds of Sicyos angulatus (burcucumber) have been clearly shown to have a water‐impermeable seed coat (physical dormancy [PY]). The primary aim of the present study was to confirm (or not) that physiological dormancy (PD) is also present in seeds of S. angulatus. The highest germination of scarified fresh (38%) and 3‐month dry‐stored (36%) seeds occurred at 35/20°C. The rate (speed) of germination was faster in scarified dry‐stored seeds than in scarified fresh seeds. Removal of the seed coat, but leaving the membrane surrounding the embryo intact, increased germination of both fresh and dry‐stored seeds to > 85% at 35/20°C. Germination (80–100%) of excised embryos (both seed coat and membrane removed) occurred at 15/6, 25/15 and 35/20°C and reached 95–100% after 4 days of incubation at 25/15 and 35/20°C. Dry storage (after‐ripening) caused an increase in the germination percentage of scarified and of decoated seeds at 25/15°C and in both germination percentage and rate of excised embryos at 15/6°C. Eight weeks of cold stratification resulted in a significant increase in the germination of scarified seeds at 25/15 and 35/20°C and of decoated seeds at 15/6 and 25/15°C. Based on the results of our study and on information reported in the literature, we conclude that seeds of S. angulatus not only have PY, but also non‐deep PD, that is, combinational dormancy (PY + PD).     

Imbibition phases and germination response of Mimosa bimucronata (Fabaceae: Mimosoideae) to water submersion

Mimosa bimucronata is a pioneering tree that occurs predominantly in moist lowlands, floodplains and on margins of rivers and lakes in Latin America. The effect of submergence on seed germination in M. bimucronata was firstly studied. Patterns of water absorption by M. bimucronata seeds were investigated thereafter to assess the imbibition phases of scarified and unscarified seeds. The germination percentage was significantly higher in scarified than in unscarified seeds, and the velocity of seed germination also increased considerably in scarified seeds. Submergence duration did not significantly affect germination percentages of scarified and unscarified seeds. Therefore, seed viability after submersion suggests that M. bimucronata may display hydrochorous dispersal and also that seeds are able to germinate successfully in areas with frequent seasonal flooding. With respect to imbibition phases, phase II was very short or even absent for scarified and unscarified seeds; therefore, a plateau, where water absorption by seeds is established, was not observed. Finally, we verified that the passage from phase I to III was very tenuous and took a long time in seeds without scarification.     

Radiation-induced improvement of the freeze-resistance of a cold-sensitive wheat variety: Freeze-tolerance and fatty acid patterns

Effects of 3–15 krad ⁶⁰Co gamma radiation on cereal seeds were investigated with regard to the frost hardiness of leaves of 5–7-day-old seedlings. Comparative studies were carried out on the gas-chromatographically determined distribution patterns of fatty acids in different pools (total fatty acid, total lipid, polar lipids) of a cold-resistant (cv. Mironowskaya 808) and a cold-sensitive (cv. Penjamo 62) cultivar of wheat (Triticum aestivum L.). Parallelism between fatty acid distribution pattern, empirical parameters suggested for quantitative measures of cold tolerance (the ratio unsat/sat and double-bond index), and the low-temperature behaviour of shoots grown from radiation treated seeds of ‘Penjamo 62’, was also examined. To monitor differences in the fatty acid syntheses of ‘Mironowskaya 808’and ‘Penjamo 62’, and to demonstrate radiation-induced changes in fatty acid turnover a [1–¹⁴C]-acetate incorporation technique was employed. The results of practical importance are: 1. A significant improvement in the frost-resistance of the cold-sensitive ‘Penjamo 62’variety could be achieved with 6–9 krad irradiation, the half-freeze-killing temperature dropping from ?6 to about ?18°C. 2. Freeze-hardiness, no matter whether inherited or gained, could be abolished by gamma irradiation with higher dose. The following conclusions of theoretical interest can be drawn: 1. Low-temperature behaviour of plant tissues is a dynamic property rather than a static one, not only the formation but also the breakdown of certain hydrocarbon chains may be of paramount relevance in cold-tolerance. 2. Not the linolenic (18:3) component, but rather the overall distribution pattern of the C₁₈ family seems to correlate with low-temperature-responses of shoots. 3. Empirical parameters investigated do not provide reliable quantitative measures of the susceptibility to freeze (and cold-) injuries. 4. Changes in the syntheses of some key proteins (e.g. peroxidase, water-soluble proteins, etc.) may also be important in adaptation to low-temperature conditions.     

Seed dormancy of Cardiospermum halicacabum (Sapindaceae) from three precipitation zones in Sri Lanka

• This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species.
• We compared mass, moisture content (MC), dormancy and dormancy‐breaking treatments and imbibition and germination of scarified and non‐scarified seeds of C. halicacabum from a low‐elevation dry zone (DZ), low‐elevation wet zone (WZ1) and mid‐elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water‐impermeable seed coats (physical dormancy, PY) decreases with increased precipitation.
• Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non‐scarified DZ and WZ1 seeds imbibed water, but only a few non‐scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA₃ promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds.
• At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low‐cost method to produce C. halicacabum plants for medicinal and ornamental purposes.

     

Uptake of Gibberellic Acid in Intact and Scarified Seeds of Barbarea vulgaris

Uptake of gibberellic acid as a function of duration of exposure, external concentration, and seed lot was measured in seeds of yellow rocket (Barbarea vulgaris R. Br.) by means of lettuce hypocotyl bioassays of the acidic, basic, or neutral fractions of seed extracts and by uptake of ¹⁴C-GA₃. In intact seeds, where mM levels of GA₃ promoted only 25% germination, uptake was completed within 24 h of exposure. The maximum uptake was about 0.2% of external amount. Although germination promotion by GA₃ differed among seedlots of yellow rocket, relative uptake (percentage of the external GA₃) was nearly the same. The relative rate of uptake of GA₃ was similar for scarified and intact seeds, but germination was promoted in scarified seeds by much lower levels of GA₃ than in intact seeds. Total uptake in scarified seeds was much higher, however (about 10% of the external amount). In seeds imbibed in H₂O, practically no endogenous GA-like activity was detected in either the acidic, basic, or neutral fractions. It was also apparent that intact seeds could take up quantities of GA₃ that failed to promote germination, but were comparable to quantities that promoted germination in scarified seeds.     

Gamma radiation effects on growth and yield attributes of <Emphasis Type="Italic">Psoralea corylifolia</Emphasis> L. with reference to enhanced production of psoralen

The present work describes radiation-induced effects on vegetative, reproductive traits and psoralen content in Psoralea corylifolia L. The effects of gamma radiation on Psoralea seeds were investigated by exposing seeds with doses of 2.5, 5, 10, 15 and 20 kGy at dose rate of 1.65 kGyh⁻¹ and studying the plant growth at three developmental stages: preflowering, flowering and post flowering (seed to seed) after irradiation. Irradiation with lower doses of gamma rays significantly improved vegetative traits while higher doses proved depressing for same parameters. Similar trend was followed in reproductive traits. Psoralen, showed highest concentration in seeds (7.56%) at 20 kGy and lowest in control roots (0.23%). Increment in psoralen was striking for higher gamma doses applied. These long-term changes in plant development may be attributed to alteration in plant genome induced by irradiation. The results show in depth development stimulation and enhancement of secondary metabolite in Psoralea corylifolia L. following low and high dose treatment respectively depicting the potential of gamma rays in plant biotechnology and metabolomics.     

Chemical and physical factors affecting the excystation of Cryptosporidium parvum oocysts.

Cryptosporidium parvum oocysts were examined to ascertain excystation requirements and the effects of gamma irradiation. Oocysts and excysted sporozoites were examined for dye permeability and infectivity. Maximum excystation occurred when oocysts were pretreated with acid and incubated with bile salts, and potassium or sodium bicarbonate. Pretreatment with Hanks' balanced salt solution or NaCl lowered excystation; however, this effect was overcome with acid. Sodium ions were replaceable with potassium ions, and sodium bicarbonate was replaceable with sodium phosphate. Oocysts that received 200 krad irradiation excysted at the same rates as nonirradiated oocysts (95%), the excystation rates were lowered (50%) by 2,000 krad, and no excystation was observed by 5,000 krad. No differences were observed between the propidium iodide (PI) permeability of untreated oocysts and oocysts treated with 200 krad, while 92% of oocysts were PI positive after 2,000 krad. Most of the sporozoites exposed to 2,000 krad were not viable as indicated by the dye permeability assay. The oocysts irradiated with 200 and 2,000 krad infected cells, but no replication was observed. The results suggest that gamma-irradiated oocysts may still be capable of excystation and apparent infection; however, because the sporozoites could not reproduce they must not have been viable.     

Gamma radiation effects on seed germination, growth and pigment content, and ESR study of induced free radicals in maize (Zea mays)

The effects of gamma radiation are investigated by studying plant germination, growth and development, and biochemical characteristics of maize. Maize dry seeds are exposed to a gamma source at doses ranging from 0.1 to 1 kGy. Our results show that the germination potential, expressed through the final germination percentage and the germination index, as well as the physiological parameters of maize seedlings (root and shoot lengths) decreased by increasing the irradiation dose. Moreover, plants derived from seeds exposed at higher doses (≤0.5 kGy) did not survive more than 10 days. Biochemical differences based on photosynthetic pigment (chlorophyll a, chlorophyll b, carotenoids) content revealed an inversely proportional relationship to doses of exposure. Furthermore, the concentration of chlorophyll a was higher than chlorophyll b in both irradiated and non-irradiated seedlings. Electron spin resonance spectroscopy used to evaluate the amount of free radicals induced by gamma ray treatment demonstrates that the relative concentration of radiation-induced free radicals depends linearly on the absorbed doses.     

PHOTOCONTROL OF DEVELOPMENT OF EXCISED ERAGROSTIS EMBRYOS

• 1 Both the germination of intact seeds and the development of excised embryos depend on their after-ripening. Shortly after the harvest, the intact seeds of Eragrostis ferruginea are in dormancy and germinate neither in the light nor in the dark. The ability of seeds to germinate under both conditions, however, gradually increases with the progress of after-ripening. The development of excised embryos, on the other hand, is readily induced in the light and dark even shortly after the harvest. As the after-ripening proceeds, however, the ability of excised embryos to develop gradually decreases and is finally lost 18 months after the harvest. The after-ripened embryos whose ability to develop is completely reduced become light sensitive again when they are supplied with the yeast extract of a low concentration, and develop readily even in darkness at a high concentration of the extract.
• 2 The photorequirement for development of excised embryos is scarcely affected by oxygen concentrations, and the embryo growth can take place equally in both light and darkness in the atmosphere containing 100 to 10 percent of air, while it can not be induced in pure nitrogen.
• 3 The promotion of embryo development by light is observed at the time when the ability of embryos to develop declines. The effectiveness of the irradiation is very similar to that in intact seed germination.

     

Induction of free radicals in seeds by high intensive flashes and the relevant phosphorus metabolism in the seedling

Influence of high intensive flashes on the yield of free radicals in intact seeds and excised embryonic axis, endosperm, and seed coat, and its resulting effect on seedling growth, total biomass production and phosphorus metabolism in wheat (Triticum aeativum), vetch (Vicia sativa L.) and onion (Allium cepa L.) was studied. Free radicals (f.r.) were formed mainly in seed coat and not in the endosperm. Vetch seeds after irradiation had 20.76 X 10¹³ f.r. g^-1 dry intact seed and 17.30 X 10¹³ f.r. g^-1 dry seed coat. Excised seed coats exposed to irradiation also yielded 17.28 × 10¹³ f.r. g^-1 dry matter. High irradiance “white light” flashes induced more f.r. than a monochromatic one of the same photon content. Red (650 nm), farred (750 nm) and even infra-red (1100 nm) radiation did not initiated f.r. formation but resulted in their decay in samples irradiated earlier by “white”, blue and green parts of the spectrum. Blue irradiation of seeds led to the decrease in the length of shoots and roots in comparison to “white”, green and red irradiation but their biomass increased faster than in the seedlings obtained from non-irradiated or irradiated with “white” and green radiation. The quantity of total acid soluble phosphorus followed a sequence with respect to wavelength of radiation: 436 nm > 650 nm> > 540 nm > non-irradiated > 300–800 nm. Quantity of inorganic phosphorus remained unaffected by different spectral character of radiation. The quantity of organic acid soluble nucleic phosphorus and acid insoluble polyphosphates was higher in samples irradiated with red beams (650 ± 6 nm).     

Mutation induction by γ and X-ray irradiation in tissue cultured lotus

Mutations of tissue cultured lotus were induced by treating plantlets with either acute -rays at doses of 0, 2, 3, 4, 5 or 6 krad or X-rays at doses of 0, 1, 2, 3, 4 or 5 krad. The 2-krad dose of either - or X-ray treatments resulted in a 50% survival rate. The use of - and X-rays to induce mutation in lotus resulted in 21 altered characteristics. Mutants from 1- and 2-krad of either or X-rays had long secondary roots and numerous adventitious roots. These mutants also exhibited good shoot growth and healthy rhizome development. Most plants treated with 3–5 krad of either - or X-rays exhibited abnormal characteristics including vitrification, chlorosis, deformed petioles and in addition had inhibited growth of lateral buds, secondary roots and rhizomes. All plants treated with 6 krad of -rays died within 4 weeks. Control plants had stoma lengths of 2.56 m and cytological analysis of the root tips confirmed the diploid chromosome number of 16. Two groups of aneuploid cells were achieved using irradiation at doses of 3 and 4 krad of either - or X-ray. Chromosome numbers were 2n=18 and 20 with associated stoma lengths of 3.43 and 4.34 m, respectively. Abnormal stomata (cyclocytic and deformity) were observed in plants treated with 4 krad of -ray.     

Effects of gamma radiation on development, sterility, fecundity, and sex ratio of Dermanyssus gallinae (DeGeer) (Acari: Dermanyssidae)

Protonymphal Dermanyssus gallinae were irradiated with 0.50, 0.75, 1.0, 3.0, and 6.0 krad of gamma radiation and subsequently monitored regarding their developmental, feeding, and mating success. Also, sex ratios of adults treated as protonymphs were recorded as were sex ratios of embryos and F1 adults produced by these adults. Doses up to 1.0 krad did not prevent development of treated protonymphs to the adult stage or stop mating. Three krad reduced the number of treated protonymphs attaining adulthood and 6.0-krad treatment prevented all mites from developing to the adult stage. Egg (embryo) production was normal for mites treated with 0.50 krad, but significantly curtailed by doses of 0.75 krad and greater. Radiation doses used in this study did not appear to affect the normal variable sex ratios observed in untreated mites.     

Induction by gamma-radiation of DNA synthesis in radicle cells of germinating seeds of Pisum sativum l.

In radicle meristem cells of germinating seeds of the pea (Pisum sativum L) before the onset of replicative synthesis of DNA, irradiation with 2-3 krad of gamma-rays induced the incorporation of 3H-thymidine (3H-TdR). Maximum isotope incorporation was noted during the first 2 hours after irradiation. Higher doses of radiation suppressed 3H-TdR incorporation. It was not seen after gamma-irradiation of air-dried seeds, nor after fast-neutron irradiation. The replication inhibitors hydroxyurea and 5-aminouracil had no effect on the gamma-induced incorporation of 3H-TdR, Whereas caffeine and acriflavine inhibited it to some extent. It is suggested that the gamma-radiation-induced incorporation of 3H-TdR in meristem cells during the pre-replicative period may be connected with repair phenomena.     

The action of the testa upon the germination of seeds ofCucumis anguria L.

In negatively photoblastic seeds of Cucumis anguria L. the scarification of micropyle overcame the inhibitory effect of “white light ”, although far-red radiation inhibited the germination in both intact and scarified seeds. The moistened testa powder transmitted more far-red than red radiation. Thus the testa could act as a filter of radiation and maintain a high far-red/red ratio at the photosensitive site of the embryo, which must be localized near the micropyle.     

Influence of Gamma Radiation on the Transport of Indolyl-3-Acetic Acid in Bark Tissue from Apple Trees

The influence of gamma radiation on the polarity of IAA translocation was investigated. Pieces of apple tree shoots, taken from 3-year-old trees, were irradiated in a dark irradiation chamber BK-⁶⁰Co source, 10 kCi. Doses from 20 to 150 krad were given. Strips of bark were peeled off both irradiated and control shoots. The middle parts of the bark strips were placed on agar blocks loaded with IAA-1-¹⁴C. The radioactivity of basal and acropetal segments was determined after about 20 h and results expressed as polarity quotient. It has been shown that irradiation with 20 krad (200 Gy) decreases the polarity quotient remarkably (polarity quotient of control equals 7; for 20 krad—2.9; 100 krad—1.6). The decrease in polarity results from inhibition of the basipetal translocation of IAA. Irradiated tissue shows a decrease in IAA uptake. Possible mechanisms of gamma irradiation effects on polar translocation of IAA are discussed.     

Tissue Browning of Potato Tubers Induced by Gamma Irradiation

A considerable browning was observed especially in cortex tissue and along xylem of potato tubers harvested at Sakai in Osaka Prefecture, after irradiation with 10, 20 and 50 krad doses of cobalt-60 gamma rays. This phenomenon was accompanied by the marked increase in polyphenol content and peroxidase activity, and the transient increase in o-diphenol oxidase activity. Total reducing compounds in the tissue were also increased by gamma irradiation.

The browning phenomenon depended on the storage period from the harvest to gamma irradiation treatment. The browning and the transient increase in o-diphenol oxidase activity were completely suppressed in the case of tubers irradiated 3 months after harvest.

There was no significant change in α-amylase activity in all tubers tested.