Antioxidant role of glutathione associated with accelerated aging and hydration of triploid watermelon seeds

Hydration offers an effective means for raising seed performance in many crop species. The objective of the present study was to evaluate the effect of hydration in vermiculite on germinability and antioxidant capacity of glutathione in artificially aged triploid seeds of two watermelon cultivars. Aging was achieved by incubating the seeds at 45°C and 79% relative humidity for 6 days and then air-drying them to their original moisture level (4%). Hydration was achieved by mixing untreated and aged seeds with moist vermiculite No. 3 at 25°C for 24 h. The partially hydrated seeds were air-dried at 25°C for 36 h to 4.7% moisture level. Aged seeds germinated more slowly and poorly than unaged seeds. Aging also decreased the level of glutathione and reduced the activity of several enzymes involved in glutathione antiperoxidation. The germinability of aged triploid seeds was restored partially by hydration in vermiculite. The glutathione content and the activity of antiperoxidative enzymes using glutathione as substrate were also increased by hydration. The changes in germination and glutathione level in relation to aging and hydration were similar for the two cultivars, despite differences in their germination performance and related physiological traits.     

Priming bitter gourd seeds with selenium solution enhances germinability and antioxidative responses under sub-optimal temperature

Priming offers an effective means for counteracting sub-optimal temperature induced oxidative injury and raising seed performance in many crop species. In Taiwan, bitter gourd is frequently seeded when ambient temperatures are below the optimum. The objectives of the present study were to evaluate the effect of priming on germinability and antioxidative capacity in two bitter gourd cultivars germinated under 20 and 25°C conditions. Sodium selenite was also added to the priming solution. Priming was achieved by moistening the seeds with 1, 2, 5, or 10 mg l−1 sodium selenite solutions on germination paper at 25°C for 48 h and then air-drying them to their original moisture levels. A sub-optimal temperature of 20°C decreased seed performance by enhancing peroxidative injury. The sub-optimal temperature germinability was partially restored by priming the seeds with selenium solutions up to the 2 mg l−1 level. The improved seed performances were linked to the priming-enhanced free radical and peroxide-scavenging activities linked to the ascorbate-glutathione cycle. However, glutathione peroxidase was the only enzyme showing positive response with increasing selenium level up to 10 mg l−1, suggesting that this enzyme is selenium-inducible. The changes in germination and antioxidative activities in relation to selenium priming and sub-optimal temperature were similar for the two cultivars, despite differences in their germination performance and related antioxidative traits.     

Changes in malondialdehyde content and in superoxide dismutase, catalase and glutathione reductase activities in sunflower seeds as related to deterioration during accelerated aging

Sunflower ( Helianthus annuus L.) seeds progressively lost their ability to germinate at 25°C, the optimal temperature for germination, after accelerated aging was carried out at 45°C (a temperature too high to permit germination) in water or at 76 or 100% relative humidity (RH). The deleterious effects of the high-temperature treatment increased with increasing seed moisture content. Incubation of seeds at 45°C in water resulted in electrolyte leakage, which indicated a loss of membrane integrity. A relationship between leakage and loss of seed viability could not be assumed, since no increase in electrolyte efflux occurred after aging al 100% RH. Accelerated aging induced accumulation of malondialdehyde, suggesting that seed deterioration was associated with lipid peroxidation. However, there was no direct relationship between lipid peroxidation and deterioration in membrane integrity. Loss of seed viability was also associated with a decrease in superoxide dismutase, catalase and glutathione reductase activities. Finally, the results obtained suggest that sunflower seed deterioration during accelerated aging is closely related to a decrease in the activities of detoxifying enzymes and to lipid peroxidation.     

Lipid peroxidation and peroxide-scavenging in soybean seeds during aging

The possible role of lipid peroxidation in seed deterioration was investigated during natural aging and accelerated aging of seeds of edible soybean ( Glycine max [L], Merr. cv. Kaohsiung Selection No. 1). Natural aging was achieved by sealing the seeds in aluminum foil bags coated with polyethylene and storing the seeds at room temperature for 3 to 12 months. Accelerated aging was obtained by incubating the seeds at 45°C and close to 100% relative humidity for 3 to 12 days, after which the seeds were air dried to their original moisture level (8%). The results indicate that both natural and accelerated aging enhanced lipid peroxidation, as germination was depressed. Aging also inhibited the activity of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase. The changes in germination and physiological activities, expressed as a function of aging duration, were somewhat similar in the two aging treatments.     

Changes in oxidative stress enzymes during artificial ageing in cotton (Gossypium hirsutum L.) seeds

The present study was carried out to elucidate the mechanism of seed deterioration in two cotton (Gossypium hirsutum L.) cultivars (HS6 and H1098). The seeds were artificially aged at 40 +/- 1 degree C and 100% relative humidity for 4 days. In both cultivars, germinability decreased, whereas membrane deterioration, as assayed by electrical conductivity of the seed leachates, increased progressively with artificial ageing. The decrease in germinability was well correlated with increased accumulation of total peroxide and malondialdehyde content and decreased activities of antioxidant enzymes peroxidase, catalase, ascorbate peroxidase, glutathione reductase and superoxide dismutase. Hydropriming for 2 h and ascorbic acid priming for 12 h partially maintained germination and the activities of various antioxidant enzymes under artificial ageing and the accumulation of peroxide and MDA content was decreased. The results suggest that cotton seed deterioration during accelerated ageing is closely related to a decrease in activities of various peroxide scavenging enzymes and to lipid peroxidation.     

Prolonged aerated hydration for improvement of seed quality in Brassica oleracea L.

Seeds of cauliflower cv. Hipop and Brussels sprouts cv. Asmer Aries were aged at 20% moisture content for 24 h; all seeds retained a germination of over 70% after ageing although the mean germination time increased. Prolonged aerated hydration for up to 32 h at 20°C followed drying resulted in improved performance of both unaged and aged cauliflower seeds and aged Brussels sprouts. Thus, all seed showed reductions in the mean germination time to the extent that after 32 h hydration the aged cauliflower seeds performed as well as high quality unaged seed. The improvement of aged seeds was also revealed an increase in germination after the controlled deterioration test following up to 24 h (cauliflower) or 32 h (Brussels sprouts) aerated hydration. This increase was indicative of a decrease in the extent of deterioration present after aerated hydration. Deleterious effects of prolonged hydration were observed in Brussels sprouts after 32 h although these may be explained desiccation injury after treatment since radicle emergence had occurred during hydration. The improvements in seed performance may be explained the activation of metabolic repair occurring during the early part of the hydration period therereducing the extent of deterioration that has been sustained during ageing, with further improvements due to the advancement of the germination process.     

Changes in germinability,lipid peroxidation,and antioxidant enzyme activities in pear stock (<Emphasis Type="Italic">Pyrus betulaefolia</Emphasis> Bge.) seeds during room- and low-temperature storage

The aim of this study was to determine if loss of germinability in Pyrus betulaefolia seeds stored at 4°C and at room temperature is associated with a loss of membrane lipid peroxidation or changes in antioxidant enzyme activities. The results indicated that germination percentage clearly decreased when seeds were stored at room temperature rather than at 4°C from 6 to 12 months. Room-temperature storage of the pear stock seed for 12 months decreased germination to 15.52%, but germination percentage was not changed when seed was stored at 4°C for 12 months. MDA, a marker for membrane lipid peroxidation, increased significantly under room-temperature storage conditions. Antioxidant enzyme (SOD, POD, and CAT) activities were a good indicator of germination percentage in pear stock seeds. Antioxidant enzyme activities of pear stock seeds at 4°C were higher than antioxidant enzyme activities in seeds stored at room temperature from 6 to 12 months. Antioxidant enzyme activities of the pear stock seed decreased markedly under conditions of room-temperature storage from 6 to 12 months. The results of this study showed that long-term room-temperature storage was detrimental for maintaining the vigor of P. betulaefolia seeds. The mechanisms responsible for this outcome are a higher level of membrane lipid peroxidation and a lower level of activity of antioxidant enzymes.     

Reversal of the effects of aging in soybean seeds

Accelerated aging predisposed seeds to imbibition injury. Slowing the rate of hydration prevented the loss of germinability due to imbibition injury. Germinability of accelerated aged seeds (50 hours) was increased from 10 to 90% by controlling the rate of imbibition. Slow hydration also prevented seed electrolyte leakage. This may indicate that cell membrane permeability or rupture was a major factor contributing to the loss of germinability after aging.

Reversal of the effects of aging (repair) was accomplished by slowly inbibing and then redrying seeds (priming). This treatment lowered steep water conductivity by a factor of 2 to 5. Priming also increased the per cent germination of low vigor seeds. The mechanism of this reversal was probably metabolic because it depended on temperature, seed moisture, and treatment duration.

Priming doubled the survival of seeds in the accelerated aging vigor test. The `rejuvenation' was accepted as evidence for metabolic repair. Since the `vigor' of seeds was increased by priming, metabolic repair probably included other subcellular components as well as the plasma membrane.

     

Lipid peroxidation and peroxide-scavenging enzymes associated with accelerated aging of peanut seed

Accelerated aging is known to reduce seed viability and vigor in many crop species. The phenomenon is due in part to aging-induced lipid peroxidation, which has the potential to damage membranes of the seed tissues. This study was undertaken to evaluate the effect of accelerated aging on germinability and several physiological characteristics related to peroxidation in the seed of two peanut cultivars. Accelerated aging was achieved by incubating seed at 45°C and 79% relative humidity in a closed chamber for 3, 6, or 9 days. The results indicate that accelerated aging inhibited seed germination and seedling growth. Enhanced lipid peroxidation and increased peroxide accumulation were observed in the axis and cotyledons of aged seed. Accelerated aging also inhibited the activity of superoxide dismutase, peroxidase, ascorbate peroxidase, and lipoxygenase. Seed axes appeared to be more susceptible to aging than cotyledons. The changes in germination and physiological activities, expressed as a function of aging duration, were similar in the two cultivars, despite differences in their seed weight.     

Effects of matriconditioning on onion seed germination, seedling emergence and associated physical and metabolic events

The effect of matriconditioning, the physiological presowing seed technique, using Micro-Cel E on Allium cepa L. cv. Czerniakowska seed quality was studied. Several ratios of seeds, carrier, water and time of priming were tested. The most effective treatment for improving onion seed germination at most tested temperatures was priming to a ratio of 2 g seed:1 g Micro-Cel:3 g water for 5 days in light at 15 °C. Matriconditioning greatly improved the germination and emergence percentage, seedling fresh and dry weight and reduced electrolyte leakage compared to that of untreated seeds; this beneficial effect was especially evident at suboptimal temperatures. Matriconditioning improved the germinability of aged seeds, the effect being more pronounced in the more aged seeds. No significant differences in ethylene production by primed and non-primed seeds were observed in the absence of its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), but its presence during imbibition caused an increase in ethylene production; an enhanced activity of in vivo ACC oxidase in Allium cepa matriconditioned seeds in comparison to untreated seeds, indicates that the endogenous level of ACC is a limiting factor of ethylene production. Likewise, the activity of ACC oxidase isolated from matriconditioned seeds was higher than that from untreated seeds. Higher endo--mannanase and total dehydrogenase activities were observed in primed air-dried seeds in comparing to non-primed seeds.     

Characterization of water distribution and activities of enzymes during germination in magnetically-exposed maize (Zea mays L) seeds

Magnetic seed treatment is one of the physical pre-sowing seed treatments to enhance the performance of crop plants. In our earlier experiment, we found significant increase in germination and vigour characteristics of maize (Zea mays L.) seeds subjected to magnetic fields. Among various combinations of magnetic field (MF) strength and duration, best results were obtained with MF of 100 mT for 2 h and 200 mT for 1 h exposure. The quicker germination in magnetically-exposed seeds might be due to greater activities of germination related enzymes, early hydration of membranes as well as greater molecular mobility of bulk and hydration water fractions. Thus, in the present study, changes in water uptake during imbibition and its distribution and activities of germinating enzymes during germination were investigated in maize seeds exposed to static magnetic fields of 100 and 200 mT for 2 and 1 h respectively by nuclear magnetic resonance (NMR) spectroscopy. The magnetically-exposed seed showed higher water uptake in phase II and III than unexposed seed. The longitudinal relaxation time T1 of seed water showed significantly higher values and hence greater molecular mobility of cellular water in magnetically-exposed seeds as compared to unexposed. Component analysis of T2 relaxation times revealed the early appearance of hydration water with least mobility and higher values of relaxation times of cytoplasmic bulk water and hydration water in magnetically-exposed over unexposed seeds. Activities of alpha-amylase, dehydorgenase and protease during germination were higher in magnetically-exposed seeds as compared to unexposed. The quicker germination in magnetically-exposed seeds might be due to greater activities of germination related enzymes, early hydration of membranes as well as greater molecular mobility of bulk and hydration water fractions.     

The differential antioxidant capacity of watermelon flesh at different maturity stages and its inhibitory effects on seed aging may explain the significance of fruit flesh colors

Fruit can use different skin colors to attract animals for seed dispersal. Interestingly, however, many fruits such as watermelon, which has a green outer rind, also have colored flesh. The potential reasons underlying this phenomenon were investigated here. White (low maturity), pink (medium maturity), and red-fleshed (high maturity) watermelons were collected and their flesh antioxidant capacities were compared by evaluating Fe³⁺ reducing power and DPPH radical scavenging capacity. Results showed that the antioxidant capacity of fruit flesh at different maturity stages was highest in red flesh, lower in pink flesh, and lowest in white flesh. Moreover, extracts of these flesh samples were obtained and the germination rate and lipid peroxidation of aged seeds, which were pre-treated with these extracts during the artificial aging process, were investigated. This showed that the extracts can significantly increase germination rate, but decrease lipid peroxidation of aged watermelon seeds, with the greatest changes observed with red-flesh extracts and the smallest with white flesh. Dimethyl thiourea, a specific scavenger of free radicals and reactive oxygen species, had a similar effect on the germination rate and lipid peroxidation of aged seeds. Combining previously reported results and our findings, we propose a hypothetical model in which pigment biosynthesis results in the enhancement of antioxidant capacity to illustrate the physiological significance of flesh color on seed aging and germination.     

A Comparison of Changes in the Germination Responses and Phospholipid Composition of Naturally and Artificially Aged Tomato Seeds

The changes in germinability and phospholipid content of naturallyand artificially aged tomato seeds, variety Kingley Cross, werecompared. Subsequent low temperature pre-sowing treatment (LTPST)was unable to prevent decreases in the germination capacityof aged samples, but significantly improved germination rates.However, in contrast to previous studies on artificial ageingusing the variety Moneymaker, losses of total phospholipid werenot always well correlated with decreased germinability. Totalphospholipid levels in naturally aged seeds were largely unaffectedby pre-sowing treatment, but the proportion of phosphatidylcholinewas greatly increased. These results strongly suggest that lossesof phospholipid are coincidental rather than causative eventsin the loss of seed viability during ageing, and that the patternof changes depends on the type of ageing experienced by theseeds. Controlled deterioration, seed ageing, tomato seeds, seed treatment, phospholipids     

Water Content and the Conversion of Phytochrome Regulation of Lettuce Dormancy

In an effort to determine which biological reactions can occur in relation to the water content of seeds, the regulation of lettuce seed dormancy by red and far red light was determined at various hydration levels. Far red light had an inhibiting effect on germination for seeds at all moisture contents from 4 to 32% water. Germination was progressively stimulated by red light as seed hydration increased from 8 to 15%, and reached a maximum at moisture contents above 18%. Red light was ineffective at moisture contents below 8%. Seeds that had been stimulated by red light and subsequently dried lost the enhanced germinability if stored at moisture contents above 8%. The contrast between the presumed photoconversion of phytochrome far red-absorbing (Pfr) to (Pr) occurring at any moisture content and the reverse reaction occurring only if the seed moisture content is greater than 8% may be explained on the basis of the existence of unstable intermediates in the Pr to Pfr conversion. Our results suggest that the initial photoreaction involved in phytochrome conversion is relatively independent of water content, while the subsequent partial reactions become increasingly facilitated as water content increases from 8 to 18%.     

Seed Germination Traits of Loquat (<i>Eriobotrya japonica</i> Lindl.) as Affected by Various Pre-Sowing Treatments (Cutting of Cotyledons,Removal of Perisperm,Moist Chilling and/or Exogenous Application of Gibberellin)

The purpose of this study was to investigate the effects of various presowing treatments on the germinability (final germination percentage) and germination rate of loquat seeds in order to increase seedling production in nurseries (applied research) as well as provide answers for important physiological issues related to loquat seeds and their seed coat (basic research). Three experiments were carried out with various pre-sowing treatments. These treatments included full or partial removal of seed coat (perisperm), partial cutting of cotyledons as well as moist chilling at 5°C for 13 days and/or soaking the seeds in water or 250 ppm gibberellic acid (GA3) solution for 24 h. According to the results, cotyledons excision resulted in delayed germination, regardless of the presence or absence of the seed coat in comparison with the decoated seeds that demonstrated the highest germination rate amongst them. In addition, even the partial excision of seed coats affected positively both the germinability and the germination rate, compared to the control-intact seeds. Furthermore, control-intact seeds had a higher germination percentage when exposed to moist chilling independently of the application or not of gibberellin; while the combination of gibberellin application and moist chilling improved both the percentage and the rate of germination of decoated seeds. In conclusion, the role of perisperm (seed coat) in the germination procedure of loquat seeds seems to be important, indicating the existence of seed coat-imposed dormancy on loquat seeds. Finally, the existence of a mild endogenous embryo-dormancy on loquat is also discussed.     

Germination Responses of Taraxacum platycarpum Seeds to Temperature

Abstract Germination responses of Taraxacum platycarpum seeds to temperature were examined under laboratory conditions to investigate the emergence-season choice mechanism of the seeds. Almost all the newly collected seeds were non-dormant. Under constant temperature conditions, maximum percentage germination (approximately 90%) was attained at temperatures 6–16°C, where simple linear relationships were observed between the temperature and the rates of germination, i.e. the reciprocals of the time taken to germinate by seed subpopulations with 10–80% germination. Thermal time required for germination of the subpopulations ranged from 600 Kh (degree Kelvin × hours) to 1500 Kh with a relatively constant base temperature of about 2.5°C. Lower limit temperature for germination was slightly below 6°C. Higher limit temperature for germination has the normal distribution with the mean ±SD of 19±2.5°C. Pre-exposure of imbibed seeds to temperatures higher than the higher limit temperature for germination, 25 and 30°C, had no effect on the germinability and the rate of germination at a circa-optimum temperature. Moist chilling treatment at 4°C caused an increase in the variation of germination rate within the seed population, but no evidence for dormancy-inducing or breaking effects was obtained.     

Aging in Pinus sylvestris L. seeds: changes in viability and lipids

Aging of Scots pine seeds (Pinus sylvestris L.) leads to changes in seed quality, such as loss of germinability, delayed growth and abnormality in developing seedlings. The knowledge of biochemical changes responsible for these aging processes is plentiful in some seeds, which are of world-wide interest, but for pine seeds these studies are rare. The aim of the present study, was to analyse pine seeds of varying ages in order to identify biochemical changes occurring in aged pine seeds, and to see if a correlation existed between these results and traditionally used seed-quality parameters, such as germinability and electrolyte leakage.     

The physiology of seed hydration and dehydration, and the relation between water stress and the control of germination: a review

Abstract Current interest in seed hydration treatments for the improvement of level, rate and uniformity of germination or field emergence has revealed how little is known of the physiology of germination control under water stress. This review surveys briefly the responses of seeds held at different hydration levels, from normal germination in a free water supply to seed activation without germination under slight moisture stress, seed deterioration at greater moisture stress and the damage that can be caused to seeds in very dry conditions, as well as the responses to subsequent dehydration. Inhibition of germination, though not of seed activation, at certain levels of water stress is likened to various forms of dormancy, and the mechanism governing the initiation of cell elongation is suggested as the possible key to control over germination. Several lines of evidence on cell membrane integrity and action, and their responses to external factors, point to the role that the membrane may play in cell elongation (and hence germination) control, and membrane integrity may also be associated with the transition between seed deterioration at one hydration level and seed activation and repair at slightly higher hydration levels. Seed activation without germination is also considered in an ecological context.     

The prevention of dehydration injury in celery seeds by polyethylene glycol, abscisic acid, dark and high temperature

Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion.     

Phospholipid composition and fatty acid peroxidation during ageing of Acer platanoides seeds

Seeds of Norway maple ( Acer platanoides L.) differing in water content (10, 20 and 30%) were stored for 6 weeks at 20 to 30°C. During this period changes in phospholipids and fatty acids as well as in seed viability and germination capacity were studied. A considerable decrease in the phospholipid content was observed, which depended on the water content in the seeds and was related to the decrease of the seed germination capacity. The level of linoleic (18:2) and linolenic (18:3) acids in the phospholipid fraction decreased considerably in the course of the accelerated seed ageing. The results obtained suggest that phospholipid degradation and peroxidation of unsaturated fatty acids, followed by membrane destruction, play a considerable role in maple seed ageing.