Establishing the large scale osmotic priming of onion seeds by using enriched air

Onion seeds were primed in polyethylene glycol solutions (PEG) (-1.5 MPa) for 14 days at 15°C on filter paper and in bubble columns containing 50 g seed litre^-1 PEG using air or enriched air (75% O₂/25% N₂) to aerate and suspend the seeds. Compared with untreated seeds, priming seeds in bubble columns using enriched air increased the percentage seed germination but it did not when air was used, or when seeds were primed on filter paper. Mean germination times (t_m) were significantly reduced in all cases but the reduction was greatest using enriched air and least using air. The spread of germination times was significantly reduced only for seeds primed in enriched air. Drying seeds following priming reduced the percentage germination compared with untreated seeds, but only significantly for those primed in bubble columns using air. Drying also increased the mean germination times by 1.5 to 1.8 days (relative to primed seed which had not been dried). Seeds primed in enriched air were least affected. This increased time is that typically required for water re-imbibition after drying. Priming with enriched air followed by drying gave the same number of normal seedlings as untreated seeds.     

Drought resistance in rice seedlings conferred by seed priming

Seed priming is a method by which seeds are subjected to different stress conditions to impart stress adaptation in seedlings germinating and growing under stressful situations. Drought stress is a major reason behind failure of crops. We studied the effects of hydropriming, dehydration priming (induced by PEG), and osmopriming (induced by NaCl and KH₂PO₄) on subsequent germination, growth and anti-oxidant defense mechanisms of 2-week-old rice seedlings under continuing dehydration stress. Unprimed seeds grown in PEG showed significantly lower germination and growth along with significantly higher reactive oxygen species (ROS) and lipid peroxidation levels. Among the priming methods, 5 % PEG priming was found to be the best in terms of germination and growth rate along with the lowest amount of ROS and lipid peroxidation (malondialdehyde [MDA]) values. MDA levels were reduced significantly by all of the priming methods. Hence, reduction of lipid peroxidation may be a key factor underlying the drought tolerance produced by the priming treatments. Glutathione peroxidase (GPX) activity seemed to bear an excellent correlation with oxidative stress resistance through seed priming. The PEG priming produced minimum peroxidative damage and superior germination and growth rate along with efficient GPX activity, overexpressed MnSOD and maintenance of HSP70 expression in normal as well as in drought condition. Therefore, in PEG-primed seeds the existence of robust protective mechanisms is definitely indicated.     

Effects of osmotic priming and ageing on the germination and emergence of carrot and leek seed

Carrot and leek seed was osmotically primed in polyethylene glycol solution (273 g/kg water and 342 g/kg water respectively) for 10, 14 or 17 days before accelerated ageing for 0, 24, 48, 72 or 96 h. Priming reduced the germination time compared with non-primed seed. Accelerated ageing increased germination and emergence times and decreased percentage germination and emergence to a greater extent for the primed seeds than for non-primed seeds in both species. Primed and dried but non-aged seed from both species was stored at 10°C for 12 months. There was no loss of viability and improvements in germination time due to priming were maintained throughout the storage period for all the priming treatments in leek, and for the 10 and 14 day priming treatments in carrot. Carrot seed primed for 17 days lost some viability after 12 months storage compared with non-stored seed.     

Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. I. Laboratory germination

Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for 2 weeks at 15 °C. Priming reduced the mean germination times (recorded at 15 °C) of all seed lots (compared to the untreated control) by 3–4 days in carrot, 6–10 days in celery and 3–5 days in onion. The largest reductions in mean germination time occurred in the slowest-germinating seed lots. There were highly significant interactions between priming and cultivars, and between priming and seed lots within cultivars for each species. Drying back the primed seeds at 15 °C increased the mean germination times (compared to primed seed which had not been dried) by 0·6 day in carrot and 1·4 days in celery, and there was no interaction with cultivars or seed lots. The corresponding increase for onion was either 1·0 or 1·8 days, according to the cultivar, but this variation was largely attributable to differences in time taken for the dried seeds to re-imbibe. Seeds dried back at 30 °C germinated 0·2·0·7 day (depending on the species) later than those dried at 15 °C. Percentage germination was not affected by either priming or drying back. Priming reduced the spread of germination times in all cultivars. For primed and dried-back seed, the spread of germination times was larger than that of primed seed in certain cultivars, but was always smaller than that of untreated seeds.     

Catalase is a key enzyme in seed recovery from ageing during priming

Ageing induces seed deterioration expressed as the loss of seed vigour and/or viability. Priming treatment, which consists in soaking of seeds in a solution of low water potential, has been shown to reinvigorate aged seeds. We investigate the importance of catalase in oxidation protection during accelerated ageing and repair during subsequent priming treatment of sunflower (Helianthus annuus L.) seeds. Seeds equilibrated to 0.29 g H₂O g⁻¹ dry matter (DM) were aged at 35 °C for different durations and then primed by incubation for 7 days at 15 °C in a solution of polyethylene glycol 8000 at −2 MPa. Accelerated ageing affected seed germination and priming treatment reversed partially the ageing effect. The inhibition of catalase by the addition of aminotriazol during priming treatment reduced seed repair indicating that catalase plays a key role in protection and repair systems during ageing. Ageing was associated with H₂O₂ accumulation as showed by biochemical quantification and CeCl₃ staining. Catalase was reduced at the level of gene expression, protein content and affinity. Interestingly, priming induced catalase synthesis by activating expression and translation of the enzyme. Immunocytolocalization of catalase showed that the enzyme co-localized with H₂O₂ in the cytosol. These results clearly indicate that priming induce the synthesis of catalase which is involved in seed recovery during priming.     

Effect of priming treatments on seed germination and seedling growth in bamboo [Dendrocalamus strictus (Roxb.) Nees]

Instances of flowering of bamboo species Dendrocalamus strictus are few and far between which are taken as opportunity by nurserymen to collect seeds for propagation. Germination of seeds is reported to be poor. Therefore, different seed priming treatments were applied to D. strictus seeds collected from Ranchi in order to obtain uniform and high germination. Under laboratory conditions, dehusking of seeds before sowing ensured cent percent germination. Seed priming with KNO₃ 1% solution resulted in 80.4% increase in germination followed by hydropriming by 16 h (73.1% increase). In field conditions, dehusked seeds gave 23.0% germination without any priming treatment. Priming treatment with KNO₃ 1% gave the highest rise in germination (39.1%) followed by hydropriming for 16 h (26.1%). Seeds with their seed coats intact could give germination of 9.5% when germinated without any treatment. A rise of 115.8% in germination was obtained by priming with KNO₃ 1% (final germination count 20.5%). The next best treatment was hydropriming for 16 h (final germination 18.5%, a rise of 94.7%). KNO₃ 1% also induced the earliest and the most rapid germination. When seedlings germinated in laboratory were transferred to soil, all seedlings from all treatments established successfully without any mortality whatsoever. Therefore, it is recommended that seeds should be primed for 8 h with 1% KNO₃ and germinated in laboratory or in farm house under normal atmospheric condition before transplanting the seedlings to soil.     

Oxygen-dependent aging of seeds

When seeds of soybeans (Glycine max Amsoy var.) or safflower were stored under high O₂ concentrations, their per cent germination declined rapidly. For example, soybean seeds stored under 7.7 atmospheres O₂ pressure at 25°C and 17% moisture lost all viability within 22 days, whereas under 7.7 atmospheres N₂, the per cent germination remained greater than 80%. Germination decreased continually in O₂ pressures ranging from 0 to 7.7 atmospheres. High levels of O₂, moisture, or temperature each acted independently to cause losses of germination, but when applied simultaneously, these factors acted synergistically. Soybean seeds were also aged under conditions of high temperature (44°C) and humidity (100% RH), which have been routinely used to accelerate aging. Under these conditions, no O₂ dependence of seed death was observable.

Increased lipid oxidation was not detected in seeds that had lost germination ability due to high O₂ treatment. Seeds of two safflower varieties that contained either high oleic or high linoleic fatty acid compositions were subjected to high O₂ treatment. Although the lipid of the high oleic variety is markedly more stable to oxidative degradation, we detected no significant difference in the O₂ tolerance of these seeds.

     

In vivo assay of nitrate reductase in cotton leaf discs: effect of oxygen and ammonium

Factors affecting nitrate reduction by leaf discs of cotton (Gossypium hirsutum L.) were investigated. When incubated in 30 mm nitrate, discs reduced nitrate much more slowly under air or O₂ than under N₂. Inhibition by O₂ did not occur at nitrate levels of 100 mm or greater. Treatment with arsenate had little effect under N₂ but stimulated nitrate reduction under air. Similarly, ammonium inhibited nitrate reduction, with the inhibition being partially relieved by arsenate. Uptake of nitrate was unaffected by ammonium. The NAD/NADH ratio increased in response to both oxygen and ammonium. The effects of these treatments on nitrate reduction can be explained by competition with nitrate for NADH generated by glycolysis.     

氧化铈纳米颗粒种子引发对盐胁迫下辣椒种子萌发及幼苗生长的影响

氧化铈纳米颗粒(CeO₂NP_S),因具有较强的自由基清除能力和抗氧化酶特性,已被证明可提高植物的耐盐性,但其对辣椒种子引发作用和机制尚不明确。为揭示CeO₂NP_S种子引发处理辣椒对盐胁迫下的萌发及幼苗生长的影响,以辣椒品种(Capsicum annuum)茂蔬360为试验材料,设置了7个CeO₂NP_S浓度(0、0.05、0.1、0.2、0.3、0.4、0.5 mmol·L^-1),以未引发处理组为对照,研究不同浓度CeO₂NP_S种子引发处理后对盐胁迫下辣椒种子萌发、幼苗生物量和生理生化指标的影响。结果表明:(1)0.5 mmol·L^-1 CeO₂NP_S种子引发处理后的种子,其可溶性蛋白质、脯氨酸含量和过氧化氢酶(CAT)活性、抗坏血酸(AsA)含量和AsA/DHA比值显著提高,超氧阴离子(O₂^-)含量显著降低; 盐胁迫下,该处理种子的发芽率、发芽势、发芽指数、活力指数最大。(2)0.4 mmol·L^-1 CeO₂NP_S种子引发处理的幼苗在盐胁迫下的鲜重、干重和根长最大,幼苗的可溶性蛋白质、AsA含量和AsA/DHA比值均显著提高。综上认为,CeO₂NP_S引发处理不仅可通过降低种子水势、促进贮藏物质代谢和提高抗氧化能力提高种子在盐胁迫下的发芽率,还可在苗期通过增强蛋白合成和抗坏血酸-谷胱甘肽循环(AsA-GSH)促进盐胁迫下幼苗的生长。     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VI. INFLUENCE OF PRIMING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL DURING SEED DEVELOPMENT

Seed priming (imbibition in water or osmotic solutions followedby redrying) generally accelerates germination rates upon subsequentre-imbibition, but the response to priming treatments can varyboth within and among seed lots. Seed maturity could influenceresponsiveness to priming, perhaps explaining variable primingeffects among developmentally heterogeneous seed lots. In thecurrent study, muskmelon (Cucumis melo L.) seeds at two stagesof development, maturing (40 d after anthesis (DAA)) and fullymature (60 DAA), were primed in 0?3 M KNO₃ for 48 h at 30 ?C,dried, and imbibed in polyethylene glycol 8000 solutions of0 to –1?2 MPa at 15, 20, 25, and 30 ?C. Germination sensitivitiesto temperature and water potential () were quantified as indicatorsof the influence of seed maturity and priming on seed vigour.Germination percentages of 40 and 60 DAA control seeds weresimilar in water at 30 ?C, but the mean germination rate (inverseof time to germination) of 40 DAA seeds was 50% less than thatof 60 DAA seeds. Germination percentages and rates of both 40and 60 DAA seeds decreased at temperatures below 25 ?C. Reductionsin also delayed and inhibited germination, with the 40 DAAseeds being more sensitive to low than the 60 DAA seeds. Primingsignificantly improved the performance of 40 DAA seeds at lowtemperatures and reduced , but had less effect on 60 DAA seeds.Priming lowered both the minimum temperature (T_b) and the minimum (_b) at which germination occurred. Overall, priming of 40 DAAseeds improved their germination performance under stress conditionsto equal or exceed that of control 60 DAA seeds, while 60 DAAseeds exhibited only modest improvements due to priming. Asthe osmotic environment inside mature fruits approximates thatof a priming solution, muskmelon seeds may be ‘primed’in situ during the late stage of development after maximum dryweight accumulation. Key words: Cucumis melo L., seed priming, germination, vigour, development, temperature     

Germination, respiration, and adenylate energy charge of seeds at various oxygen partial pressures

The effect of O₂ partial pressure on the germination and the respiration of 12 cultivated species was studied. The reciprocal of the time necessary to observe rootlet emergence in 50% of the seeds was used to approach the germination rate. The maximum germination and respiration rates were reached in most seeds at O₂ pressures close to that of air. Decreasing the O₂ pressure produced a gradual decrease of the germination rate. The seeds could be classed in two groups according to their response to low O₂ pressures. Group I includes lettuce, sunflower, radish, turnip, cabbage, flax, and soybean: at O₂ pressures close to 2 kilopascals, the germination in this group was stopped and the adenylate energy charge was lower than 0.6. Group II includes rice, wheat, maize, sorghum, and pea. The germination rate of these seeds was also gradually decreased by lowering the O₂ partial pressure but germination still occured, very slowly, at 0.1 kilopascal; the adenylate energy charge remained higher than 0.6. These differences in the germination rates and adenylate energy charge values could not be explained by differences in the sensitivity of respiration to O₂.     

Effects of soaking seeds in exogenous vitamins on active oxygen metabolism and seedling growth under low-temperature stress

This study investigated the influence of the exogenous application of vitamin B2 (V_B2), B12 (V_B12), biotin (V_H), and nicotinic acid (V_PP) on oxygen production in maize (Zea mays L.) seedlings at 5 °C for day 1, 3, 5 and 7. The seeds were soaked in V_B2, V_B12, V_H, and V_PP solutions for 24 h at the concentration of 100 mg/L, and control was soaked in distilled water. A total of 50 seeds were used for each treatment in germination boxes was repeated three times. The germination box was placed in a hypothermic incubator for 1, 3, 5, and 7 days in the dark at 5 °C, then moved to a plant growth room and kept for seven days. Compared with the V_H and V_PP treatments, the V_B2 and V_B12 treatments had higher thiobarbituric acid reactive substances, proline, and soluble sugars. The V_B2 and V_B12 treatments also increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) than other treatments. The V_B2 and V_B12 treatments reduced the contents of hydrogen peroxide (H₂O₂^–), superoxide anion (O₂^–), and the damage of reactive oxygen species (ROS) to cells, increased the stability of the cell membrane and the content of cell osmoregulation substances. Moreover, V_B2 and V_B12 had higher seedling growth, germination rate, and index. Treatments V_B2 and V_B12 could promote maize seed germination and growth under low-temperature stress. Exogenous vitamins in crop production can be a valuable tool for protecting plants against low-temperature stress.     

Effects of seed burial on germination,protein mobilisation and seedling survival in Dodonaea viscosa

Ecological restoration of disturbed areas requires substantial knowledge of the germination of native plants and the creation of novel methods to increase seedling establishment in the field. We studied the effects of soil matrix priming on the germination of Dodonaea viscosa seeds, which exhibit physical dormancy. To this end, we buried both pre‐scarified (in H₂SO₄, 3 min) and non‐pre‐scarified seeds in the Parque Ecológico de la Ciudad de México. After seeds were unearthed, they were post‐scarified for 0, 2, 6 and 10 min and their germination percentages compared to the germination of a control batch of laboratory‐stored seeds. For both control and unearthed seeds, the protein pattern was determined in the enriched storage protein fraction in SDS‐PAGE gels stained with Coomassie blue. Percentage germination increased as the scarification time increased. Pre‐scarification significantly increased percentage germination of post‐scarified seeds in relation to the control and non‐pre‐scarified seeds. In seeds unearthed from the forest site, the buried pre‐scarified seeds had relatively high percentage germination, even in the absence of post‐scarification treatment. A 48‐kDa protein was not found in unearthed, pre‐scarified seeds nor in the control germinated seeds, indicating that mobilisation of this protein occurred during soil priming. Burying seeds for a short period, including the beginning of the rainy season, promoted natural priming, which increased protein mobilisation. Functionally, priming effects were reflected in high percentage seedling survival in both the shade house and the field. Seed burial also reduced the requirement for acidic post‐scarification.     

Effects of Helminthosporium victoriae Toxin on Germination and Aleurone Secretion by Resistant and Susceptible Seeds

Oat seeds of cultivars susceptible and resistant to Helminthosporium victoriae were held for various times in pathogen-produced, host-specific toxin solutions; control seeds were in water. Seeds were then washed thoroughly and incubated on moist paper, or dried and stored for 2-3 weeks before germination was attempted. In both cases, germination of susceptible seeds was prevented by previous exposure to toxin for 1 hour or more. Control seeds and treated resistant seeds grew normally. Toxin did not affect O₂ uptake or loss of carbohydrates from seeds for the first 12 hours of imbibition. After 12 hours, toxin-treated susceptible seeds had higher respiration and lost more carbohydrates than did control seeds. Experiments with embryoless seeds showed that toxin blocked synthesis and secretion of α-amylase by susceptible but not by resistant aleurone cells. Resting aleurone cells were exposed briefly to toxin, then dried and stored until all toxin was gone. Susceptible aleurone cells treated in this way failed to produce α-amylase following exposure to gibberellic acid, while controls and resistant treated aleurone tissues produced amylase. Susceptibility or resistance to toxin appears to be expressed in resting and metabolically active tissues.     

EFFECT OF HIGH PRESSURE ON GERMINATION OF SEEDS (MEDICAGO SATIVA AND MELILOTUS ALBA)

An increase in percentage germination is obtained with seeds of Medicago sativa exposed for 1 to 10 minutes at 2000 atmospheres hydraulic pressure at 20°C., dried, and germinated after 30 days; and from seeds of Melilotus alba under the same conditions of pressure, when exposed for 5 to 30 minutes, dried, and germinated 30 days later. Exposures to 500 atmospheres pressure was less advantageous for germination; the vitality of seeds normally germinating was more rapidly destroyed than the hard impermeable seeds rendered permeable by the pressure treatment. At 0°C., it required approximately 2½ times the exposure to 2000 atmospheres for seeds of Medicago sativa, and approximately 5 times the exposure for seeds of Melilotus alba, as it did at 20°C.     

Prehydration and Priming Treatments that Advance Germination also Increase the Rate of Deterioration of Lettuce Seeds

The influence of prehydration in water or priming in –1.5 MPa polyethylene glycol 8000 solution for various periods,followed by redrying, on germination rate and longevity of lettuce(Lactuca sativa L.) seeds (achenes) was determined during controlleddeterioration at 10% moisture content (fresh weight basis) and40°C. Short prehydration treatments (up to 1 h) had littleeffect on either germination rate or longevity, but significantlyimproved root growth rates. Increasing durations of prehydrationor priming reduced the mean time to germination by up to 61%relative to untreated seeds, but also reduced mean seed longevityby as much as 84% Prehydration and priming altered the relationshipsbetween germination rate and viability and between normal andabnormal seedlings during ageing. Prehydration in abscisic acidor at a temperature inhibitory to germination did not preventthe reduction in longevity under controlled deterioration conditions.While prehydration or priming treatments effectively acceleratesubsequent germination rates of lettuce seeds, the redried seedsare nonetheless highly susceptible to deterioration in storage. Key words: Lettuce, Lactuca sativa L., seed priming, seed deterioration, germination rate     

Dormancy removal of apple seeds by cold stratification is associated with fluctuation in H2O2, NO production and protein carbonylation level

Reactive oxygen (ROS) and nitrogen (RNS) species play a signaling role in seed dormancy alleviation and germination. Their action may be described by the oxidative/nitrosative “window/door”. ROS accumulation in embryos could lead to oxidative modification of protein through carbonylation. Mature apple (Malus domestica Borkh.) seeds are dormant and do not germinate. Their dormancy may be overcome by 70–90 days long cold stratification. The aim of this work was to analyze the relationship between germinability of embryos isolated from cold (5 °C) or warm (25 °C) stratified apple seeds and ROS or nitric oxide (NO) production and accumulation of protein carbonyl groups. A biphasic pattern of variation in H₂O₂ concentration in the embryos during cold stratification was detected. H₂O₂ content increased markedly after 7 days of seeds imbibition at 5 °C. After an additional two months of cold stratification, the H₂O₂ concentration in embryos reached the maximum. NO production by the embryos was low during entire period of stratification, but increased significantly in germination sensu stricto (i.e. phase II of the germination process). The highest content of protein carbonyl groups was detected after 6 weeks of cold stratification treatment. Fluctuation of H₂O₂ and protein carbonylation seems to play a pivotal role in seed dormancy alleviation by cold stratification, while NO appears to be necessary for seed germination.     

Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Decoated pepper (Capsicum annuum L. cv Early Calwonder) seeds germinated earlier at 25°C, but not at 15°C, compared to coated seeds. The seed coat did not appear to impose a mechanical restriction on pepper seed germination. Scarification of the endosperm material directly in front of the radicle reduced the time to germination at both 15°C and 25°C.

The amount of mechanical resistance imposed by the endosperm on radicle emergence before germination was measured using the Instron Universal Testing Machine. Endosperm strength decreased as imbibition time increased. The puncture force decreased faster when seeds were imbibed at 25°C than at 15°C. The reduction in puncture force corresponded with the ability of pepper seeds to germinate. Most radicle emergence occurred at 15°C and 25°C after the puncture force was reduced to between 0.3 and 0.4 newtons.

Application of gibberellic acid₄₊₇ (100 microliters per liter) resulted in earlier germination at 15°C and 25°C and decreased endosperm strength sooner than in untreated seeds. Similarly, high O₂ concentrations had similar effects on germination earliness and endosperm strength decline as did gibberellic acid₄₊₇, but only at 25°C. At 15°C, high O₂ concentrations slowed germination and endosperm strength decline.

     

Acute and chronic ozone exposure temporarily affects seed germination in alpine plants

This study was the first to investigate the direct effects of anomalous concentrations of ozone mediated by summer heat waves on seed germination in alpine plants. During germination, the seeds were exposed to three peaks of O₃ concentration (125 ppb for 5 and 10 days; 185 ppb for 5 days), derived from measurements taken close to the species growing site. High O₃ concentration delayed the first germination time, increased the mean germination time, and reduced the germination percentage during and immediately after the treatment, but, in most cases, effects were weak and had almost vanished three weeks after the treatments. In few cases, chronic exposure to O₃ (125 for 10 days’ treatment) enhanced seed germination compared to the control, suggesting that ozone may induce antioxidant and DNA-repair mechanisms or dormancy-breaking effects in hydrated seeds. Although seed mortality increased during O₃ treatments in four species, the effect of O₃ on seed germination is mostly limited to the period of exposure, indicating that it is unlikely to produce permanent negative effects on seeds, during the germination phase. Our results show that the direct effect of O₃ on seeds of alpine plants may have minor impacts on plant reproductive performance during seed germination.