西瓜种子内源β-半乳甘露聚糖酶活性与分布以及与萌发速度的关系

利用单粒种子凝胶扩散法研究了β-半乳甘露聚糖酶在西瓜种子萌发过程中的分布以及与西瓜种子萌发速率的关系。结果发现,在胚根尖突破种皮前吸胀的西瓜种子中,内源β-半乳甘露聚糖酶主要分布于种子的胚膜套中,并起到减弱外种皮和胚膜套细胞壁对胚根伸出的机械阻力的作用。对具有不同萌发速率的品种以及引发处理和未处理的西瓜种子中酶活性的检测证明,β-半乳甘露聚糖酶活性与西瓜种子萌发速度相关。固体基质引发三倍体西瓜种子过程中β-半乳甘露聚糖酶的活化和种皮阻力的减弱,是引发种子提高了萌发速度和萌发能力的原因之一。     

The use of an ELISA to quantitate the extent of 11S globulin mobilization in untreated and primed sugar beet seed lots

Seed priming (controlled imbibition) is a widely used technique for improving crop establishment, because it allows a reduction of the time to radicle emergence following seed imbibition and synchronization of individual seeds within seed lots with respect to germination timing. The major problem encountered in seed priming is the control of seed imbibition to a level permitting pre-germinative processes to proceed but that blocks radicle emergence. If not, the consequence of drying back the seeds to initial moisture content for storage purposes could be a total loss of the treated batch. This is because, as long as radicle growth has not begun, seeds may be re-dried without any permanent deleterious effects upon subsequent germination or growth. Recently, we reported the discovery of a molecular marker of sugar beet seed priming, corresponding to the basic B-subunit of the seed storage protein 11S globulin. An ELISA based upon this molecular marker has been used to analyse how different sugar beet seed lots respond to a priming treatment. The results demonstrate that this ELISA allows us to readily distinguish between the primed seeds and the corresponding untreated seeds.     

Magnetopriming circumvents the effect of salinity stress on germination in chickpea seeds

Chickpea seeds of Pusa 1053 (Mediterranean) and Pusa 256 (native) were magnetoprimed with 100 mT static magnetic field for 1 h to evaluate the effect of magnetopriming on germination of seeds under saline conditions. Enhanced rate of germination and seedling growth parameters (root and shoot length, and vigour indices) under different salinity levels indicated that magnetopriming was more effective in alleviating salinity stress at early seedling stage in Pusa 1053 as compared to Pusa 256. Dynamics of seed water absorption in magnetoprimed seeds showed increased water uptake in Pusa 1053 under non-saline as compared to saline conditions. This could have resulted in faster hydration of enzymes in primed seeds leading to higher rate of germination. Total amylase, protease and dehydrogenase activities were higher in primed seeds as compared to unprimed seeds under both non-saline and saline conditions. Production of superoxide radicals was enhanced in germinating seeds of both the genotypes under salinity irrespective of priming. Increased levels of hydrogen peroxide in germinating magnetoprimed seeds, under both the growing conditions, suggested its role in promotion of germination. Our results showed that magnetopriming of dry seeds of chickpea can be effectively used as a pre-sowing treatment for mitigating adverse effects of salinity at seed germination and early seedling growth.     

Galactomannan hydrolyzing activity develops during priming in the micropylar endosperm tip of tomato seeds

Development of galactomannan hydrolyzing activity was followed in seeds of tomato [ Lycopersicon esculentum (L.) Mill. cv. Toyonishiki] during priming and germination. The activity developed in seeds that were being primed in polyethylene glycol (-0.8 MPa). The activity was detected exclusively in the endosperm portion just adjacent to the radicle tip. Part of the activity remained active after desiccation of the primed seeds. After transfer to water, the activity in the primed seeds immediately began to increase, while in unprimed seeds the beginning of the increase in activity was delayed by about 1 day. In scanning electron microscopy, the inner surface of the cell walls of the micropylar endosperm portion appeared eroded in primed seeds that had been imbibed in water for 16 h (before germination), but not in unprimed seeds imbibed for the same period. These results support the hypothesis that galactomannan hydrolyzing enzyme, which is believed to be responsible for breakdown of tomato endosperm cell walls and hence for the weakening of mechanical restraint against radicle growth, may be involved in the improved germination of primed tomato seeds.     

Proteomic analysis of arabidopsis seed germination and priming

To better understand seed germination, a complex developmental process, we developed a proteome analysis of the model plant Arabidopsis for which complete genome sequence is now available. Among about 1,300 total seed proteins resolved in two-dimensional gels, changes in the abundance (up- and down-regulation) of 74 proteins were observed during germination sensu stricto (i.e. prior to radicle emergence) and the radicle protrusion step. This approach was also used to analyze protein changes occurring during industrial seed pretreatments such as priming that accelerate seed germination and improve seedling uniformity. Several proteins were identified by matrix-assisted laser-desorption ionization time of flight mass spectrometry. Some of them had previously been shown to play a role during germination and/or priming in several plant species, a finding that underlines the usefulness of using Arabidopsis as a model system for molecular analysis of seed quality. Furthermore, the present study, carried out at the protein level, validates previous results obtained at the level of gene expression (e.g. from quantitation of differentially expressed mRNAs or analyses of promoter/reporter constructs). Finally, this approach revealed new proteins associated with the different phases of seed germination and priming. Some of them are involved either in the imbibition process of the seeds (such as an actin isoform or a WD-40 repeat protein) or in the seed dehydration process (e.g. cytosolic glyceraldehyde-3-phosphate dehydrogenase). These facts highlight the power of proteomics to unravel specific features of complex developmental processes such as germination and to detect protein markers that can be used to characterize seed vigor of commercial seed lots and to develop and monitor priming treatments.     

The effects of re-use of polyethylene glycol priming osmotica upon the development of microbial populations and germination of leeks and carrots

Three batches of leek seeds were osmotically primed successively in the same polyethylene glycol solution in a bubble column at a seed concentration of 100 g/litre for seven days at 15°C. Three batches of carrot seeds were similarly primed in a separate solution for six days at 15°C. The concentration of microorganisms in the solutions increased rapidly during priming of the first seed batch for both seed types, but increases during priming of the second and third batches were small. The seeds were the main source of the microorganisms; priming reduced the numbers of colonies of filamentous fungi and increased those of bacteria and yeasts. The priming treatments improved the percentage germination of the three seed batches of primed carrots and reduced the mean time to germination in both species and the mean time to emergence in compost. Percentage emergence was not affected by priming except in the third batch of primed carrot seed. The presence of large numbers of microorganisms in the priming solutions did not greatly affect seed performance when the same osmoticum was used three times with leeks and twice with carrots. Priming did not affect the number of abnormal seedlings.     

The impact of different seed priming agents and priming durations on stand establishment and biochemical attributes of Stevia rebaudiana Bertoni

Stevia (Stevia rebaudiana Bertoni) is an alternative sugar crop currently gaining importance in several geographic regions of the world. Generally, crop is propagated by seeds; however, low seed germination hinders the adaptability of the crop in different cropping systems. Seed priming with different compounds improves germination of several arable crops under stressful and benign environmental conditions. This study evaluated the role of different seed priming agents and priming durations on stand establishment, allometric and yield-related traits, and steviol glycosides contents of Stevia in two different experiments. The first experiment consisted of five different seed priming agents (i.e., hydropriming with distilled water, ascorbic acid, potassium chloride, benzyl amine purine and unprimed seeds) and five priming durations (0, 8, 16, 24 and 32 h). Seed priming with potassium chloride (KCl) and benzyl amine purine (BAP) for 32 h improved stand establishment and biochemical attributes of Stevia seeds. Therefore, these two seed priming agents along with unprimed seeds were included in the second experiment to quantify their impact on allometric and yield-related traits and steviol glycosides contents. Seed priming with both KCl and BAP resulted in better allometric traits (plant height, number of leaves per plant, leaf area and chlorophyll index) compared with unprimed seeds. Similarly, seed priming with KCl resulted in higher fresh and dry biomass production of stem and leaves. Nonetheless, higher stevioside and rebaudioside A contents were recorded for the seeds primed with KCl, whereas unprimed seeds resulted in the lowest values. It is concluded that Stevia seeds must be primed with KCl for 32 h before sowing to get higher seed germination, leaf yield and steviol glycosides contents. Nonetheless, the role of KCl priming in improving abiotic stress tolerance of Stevia must be explored in the future studies.     

Hydro and halo priming: influenced germination responses in wheat Var-HUW-468 under heavy metal stress

The beneficial effect of seed priming in improving critical growth stages like seed germination and early growth phases has been accepted by Plant Physiologists for many important field crops. In the present investigation, studies were made to see the effect of heavy metal stress imposed during germination using solution of HgCl₂ in four different concentrations (0.0, 0.50, 0.75 and 1.00 mM) in Petri dishes on primed and non-primed seeds of wheat. Priming has been done with distilled water (hydro), Mg(NO₃)₂ and Ca(NO₃)₂ (halo) salts. Different germination parameters, such as germination percentage, radicle and plumule lengths, seedling emergence, soluble and insoluble sugar contents and activity of α-amylase in endosperm were studied at different study periods. Primed seeds increased all the germination parameters except insoluble sugar content in respect to non-primed control in the absence of HgCl₂. However, the use of primed seeds has shown to overcome the inhibitory effects of heavy metal stress imposed in the form of HgCl₂ solution during the period of germination. Hence, the work concludes the mitigating effects of priming under heavy metal stress.     

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.     

Seed priming for abiotic stress tolerance: an overview

Plants are exposed to any number of potentially adverse environmental conditions such as water deficit, high salinity, extreme temperature, submergence, etc. These abiotic stresses adversely affect the plant growth and productivity. Nowadays various strategies are employed to generate plants that can withstand these stresses. In recent years, seed priming has been developed as an indispensable method to produce tolerant plants against various stresses. Seed priming is the induction of a particular physiological state in plants by the treatment of natural and synthetic compounds to the seeds before germination. In plant defense, priming is defined as a physiological process by which a plant prepares to respond to imminent abiotic stress more quickly or aggressively. Moreover, plants raised from primed seeds showed sturdy and quick cellular defense response against abiotic stresses. Priming for enhanced resistance to abiotic stress obviously is operating via various pathways involved in different metabolic processes. The seedlings emerging from primed seeds showed early and uniform germination. Moreover, the overall growth of plants is enhanced due to the seed-priming treatments. The main objective of this review is to provide an overview of various crops in which seed priming is practiced and about various seed-priming methods and its effects.     

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.     

The Effects of Priming and Accelerated Ageing upon the Nucleic Acid Content of Leek Seeds and their Embryos

Using seed priming and accelerated ageing techniques, a singlelot of leek (Allium porrum) seeds was manipulated to producefour lots of seeds with different germination performance. Changesin content of the major nucleic acid species in whole seedsand embryos of two of these lots (primed and unprimed), weredetermined over the early stages of germination. The major effectof priming was an increased level of RNA species in the seedsand embryos, and this difference was maintained during germination.Comparison of nucleic acid levels in the dry seeds of thesetwo lots and two others (aged and aged then primed) indicatedthat there was no correlation with germination performance.Similar comparisons of the nucleic acid levels in the embryosof seeds imbibed for 1 d showed only a limited correlation betweenrRNA levels and germination performance. Analysis of these datasuggests that accelerated ageing has an adverse effect uponendosperm cells, which results in the degradation of their nucleicacids during priming. Furthermore, the viability of these agedseeds also falls during priming. The data also indicate thatratios of rRNA to DNA correlate with germination performanceof the four lots of seeds studied. It is proposed that sucha relationship is indicative of the efficiency of a primingtreatment, and may be useful in comparisons of naturally varyingseed lots. Key words: Leek, seed, germination, priming, nucleic acids     

Effect of Water Stress, Seed Coat Restraint, and Abscisic Acid upon Different Germination Capabilities of Two Tomato Lines at Low Temperature

Two tomato (Lycopersicon esculentum Mill.) lines with greatly different capabilities to germinate at 10°C were compared with respect to sensitivity to experimental treatments which affect the water status of the embryo. Germination rates and final percentages could be drastically changed (at 25°C) by (a) removing the mechanical constraint from the radicle tip, (b) imposing water stress by an osmoticum, (c) stress hardening of the seeds through osmotic pretreatment, and (d) inhibiting embryo expansion by abscisic acid (ABA). All treatments showed a similar difference in germination vigor between the two lines indicating that cold sensitivity is in fact a matter of water relations rather than of phase transitions in membrane lipids. Inhibition of germination by ABA was completely abolished by removing the mechanical constraint from the radicle tip. Osmotic stress of −3 bar which quantitatively replaced this constraint in inhibiting germination also restored the sensitivity to ABA. It is concluded that all these treatments act on the balance between the hydraulic extension force of the embryo radicle and the opposing force of the seed layers covering the radicle tip. The difference in cold sensitivity between the two seed lines resides either in the osmotic potential or the pressure potential of the germinating embryo.     

Hydrogen Sulfide Promotes Wheat Seed Germination and Alleviates Oxidative Damage against Copper Stress

With the enhancement of copper (Cu) stress, the germination percentage of wheat seeds decreased gradually. Pretreatment with sodium hydrosulfide (NaHS), hydrogen sulfide (H2S) donor alleviated the inhibitory effect of Cu stress in a dose-dependent manner; whereas little visible symptom was observed in germinating seeds and radicle tips cultured in NaHs solutions. It was verified that H2S or HS- rather than other sulfur-containing components derived from NaHs attribute to the potential role in promoting seed germination against Cu stress. Further studies showed that NaHS could promote amylase and esterase activities, reduce Cu-induced disturbance of plasma membrane integrity in the radicle tips, and sustain lower levels of malondialdehyde and H2O2 in germinating seeds. Furthermore, NaHs pretreatment increased activities of superoxide dismutase and catalase and decreased that of lipoxygenase, but showed no significant effect on ascorbate peroxidase. Alternatively, NaHs prevented uptake of Cu and promoted the accumulation of free amino acids in seeds exposed to Cu. In addition, a rapid accumulation of endogenous H2S in seeds was observed at the early stags of germination, and higher level of H2S in NaHS-pretreated seeds. These data indicated that H2S was involved in the mechanism of germinating seeds' responses to Cu stress.     

Improving seed germination and seedling growth of Lepidium sativum with different priming methods under arsenic stress

This study was carried out to determine the effects of seven kinds of priming, gibberellic acid (GA), salicylic acid (SA), citric acid (CA), sodium chloride (NaCl), potassium chloride (KCl), zinc (Zn) and iron (Fe) on seed germination and seedling emergence of garden cress (Lepidium sativum) under arsenic stress. Results revealed that germination percentage (GP), seed vigor index (SVI), radicle length (RL), plumule length (PL) and tolerance index (TI) were significantly decreased when arsenic stress was augmented from 0 to 100 mg L^?1. Nevertheless, primed seeds (hormo, nutri and halo-priming) increased seed germination and seedling emergence and tolerance index of L. sativum. Phytotoxicity was also reduced by priming practices. Meanwhile, priming with gibberellic acid (GA) had the most positive effects on measured traits. Generally, the order of the effect of priming treatments tested decreases by the following order: GA > CA > KCl > Fe > Zn > SA > NaCl. The result of this study is coherent with the hypothesis that under heavy metal stress, priming can develop seed germination performance and seedling emergence.     

Effects of seed priming with ascorbic acid to mitigate salinity stress on three wheat (Triticum aestivum L.) cultivars.

In this study, the effect of seed priming using ascorbic acid (ASA) on three commercial wheat cultivars i.e., Punjab-2011, Faisalabad-2008, and Ujala-2016 under salinity stress in both homogenous and heterogeneous environments has been investigated. It revealed that different levels of salinity have significantly reduced the growth attributes like percent germination, germination index, radical & plumule length, seed vigor index (In-vitro), seedling length, fresh & dry weight, and total chlorophyll content (In-vivo) with subsequent treatments. Salinity stress was induced by using NaCl in three different concentrations (100, 150, and 200 mM). Seeds of the three cultivars primed with 50, 100, and 150 mg/L ascorbic-acids have not only improved percent germination but also considerably reduced germination time and increased germination index (GI) indicating the potential for tolerating saline conditions. Seedling growth (seedling length, Fresh weight, and dry weight) of seeds primed with 50, 100, and 150 mg/L (ASA) was significantly higher than other non-primed seeds under the prevailing saline conditions. Hormonal priming with different concentrations of ascorbic acid was effective, nevertheless, the best results were obtained with 100 and 150 mg/L (ASA) concentrations. We concluded that the delay in germination and seedling growth was mainly due to excessive Na⁺ accumulation in the seeds of wheat cultivars. On the other hand, seed priming with various concentrations of ascorbic acid has proved to be effective in inducing salt tolerance in terms of germination parameters, seedling characteristics, and chlorophyll retention in the three local commercial wheat cultivars.     

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.     

Mechanism of seed priming in circumventing thermodormancy in lettuce

Lettuce (Lactuca sativa L. cv Minetto) seeds were primed in aerated solutions of 1% K₃PO₄ or water at 15°C in the dark for various periods of time to determine the manner by which seed priming bypasses thermodormancy. Seeds which were not primed did not germinate at 35°C, whereas those which were primed for 20 h in 1% K₃PO₄ or distilled H₂O had up to 86% germination. The rate of water uptake and respiration during priming were similar regardless of soak solution. Cell elongation occurred in both water and 1% K₃PO₄, 4 to 6 h prior to cell division. Both processes commenced sooner in water than K₃PO₄. Radicle protrusion (germination) occurred in the priming solution at 21 h in water and 27 h in 1% K₃PO₄.

Respiration, radicle protrusion and cell division consistently occurred sooner in primed (redried) seeds compared to nonprimed seeds when they were imbibed at 25°C. Cell division and elongation commenced after 10 h imbibition in primed (redried) seeds imbibed at 35°C. Neither process occurred in nonprimed seeds. Respiratory rates were higher in both primed and nonprimed seeds imbibed at 35°C compared to those imbibed at 25°C, although radicle protrusion did not occur in nonprimed seeds which were imbibed at 35°C. It is apparent that cell elongation and division are inhibited during high temperature imbibition in nonprimed lettuce seeds. Seed priming appears to lead to the irreversible initiation of cell elongation, thus overcoming thermodormancy.

     

Nitric oxide accelerates seed germination in warm-season grasses

The nitric oxide (NO) donor sodium nitroprusside (SNP) significantly promoted germination of switchgrass (Panicum virgatum L. cv Kanlow) in the light and in the dark at 25°C, across a broad range of concentrations. SNP also promoted seed germination in two other warm-season grasses. A chemical scavenger of NO inhibited germination and blocked SNP stimulation of seed germination. The phenolic (+)-catechin acted synergistically with SNP and nitrite in promoting seed germination. Acidified nitrite, an alternate NO donor also significantly stimulated seed germination. Interestingly, sodium cyanide, potassium ferricyanide and potassium ferrocyanide at 200 μM strongly enhanced seed germination as well, whereas potassium chloride was without effect. Ferrocyanide and cyanide stimulation of seed germination was blocked by an NO scavenger. Incubation of seeds with a fluorescent NO-specific probe provided evidence for NO production in germinating switchgrass seeds. Abscisic acid (ABA) at 10 μM depressed germination, inhibited root elongation and essentially abolished coleoptile emergence. SNP partially overcame ABA effects on radicle emergence but did not overcome the effects of ABA on coleoptile elongation. Light microscopy indicated extension of the radicle and coleoptiles in seeds maintained on water or on SNP after 2 days. In contrast, there was minimal growth of the radicle and coleoptile in ABA-treated seeds even after 3–4 days. These data indicate that seed germination of warm-season grasses is significantly influenced by NO signaling pathways and document that NO could be an endogenous trigger for release from dormancy in these species.