Using seeds to restore natural ecosystems has a greater chance of success if the seeds used are ready to germinate given appropriate environmental conditions. For Australian native Poaceae species, seed quality and dormancy can impose constraints on restoration success. In this study, germination biology of three Australian native Poaceae species, such as Cymbopogon refractus, Capillipedium spicigerum and Bothriochloa bladhii, was investigated. The seeds were exposed to different germination-enhancing chemicals (GECs, namely smoke water (SW), potassium nitrate (KNO3) or a combination (SW + KNO3)) and treated with three different seed enhancement technologies (SETs, namely seed priming, seed coating or seed cookies) then sown into two contrasting soil types (sodosol or black vertisol). Laboratory germination percentages achieved were <50% for all species, limited by dormant seeds. Incorporating GECs together with seed priming or seed coating treatment significantly increased seedling emergence rates and promoted earlier emergence as compared to the untreated control. For C. refractus and C. spicigerum, priming and/or coating with KNO3 + SW had the highest cumulative emergence. For B. bladhii, total seedling emergence was the highest (36% in both soils) for primed seeds with KNO3. Seedling emergence from seed cookies was low in all three species (<15%). Generally, soil type did not influence emergence rates for either GEC or SET. Understanding the environmental requirements needed for seed germination, together with an appropriate pre-treatment before sowing, can speed up seedling emergence and increase total emergence when using native Poaceae species for seed-based restoration.

Grass pea (Lathyrus sativus L.) has a Mediterranean origin and was spread to Western Europe, Africa and South Asia. Over time, this grain legume crop has become important in South Asia, where it is often affected by waterlogging at germination. Therefore, varieties with waterlogging tolerance of seeds at germination are needed. This study evaluated waterlogging tolerance in a grass pea diversity panel. First, morpho-agronomic traits of 53 grass pea genotypes from 7 diverse countries (Afghanistan, Australia, Bangladesh, Cyprus, Ethiopia, Greece and Pakistan) were measured in a glasshouse. Seeds of the collection were then sown into waterlogged soil for 6 days and is subsequently drained for 8 days. Finally, representative genotypes from each country of origin of the three survival patterns (described below) were then tested to identify the effect of seed priming on germination and seedling growth in waterlogged soil. Canonical analysis of six traits (seed weight, pod length, pod width, flowering time, time to maturity and seedling survival) showed that genotypes from Bangladesh and Ethiopia were similar. There was a significant variation amongst genotypes in waterlogging tolerance. Genotypes from Bangladesh and Ethiopia showed the highest percent seedling survival (54% and 47%), with an ability to germinate under waterlogging and then maintain growth from the first day of draining to the final sampling (Pattern 1). In contrast, genotypes from other origins either germinated during waterlogging, but did not survive during drainage (Pattern 2) or failed to germinate and had low seedling survival during waterlogging and drainage (Pattern 3). Priming seeds reduced seedling survival in grass pea. Despite Mediterranean origin, specific ecotypes of grass pea with greater waterlogging tolerance under warm wet conditions have been favoured in Bangladesh and Ethiopia where adaptation to extreme precipitation events at germination and seedling survival upon soil drainage is critical for successful crops.

A promising approach for the control of parasitic weeds is herbicide seed priming, which consists of soaking crop seeds in a herbicide solution such that the herbicide is later present in the crop seedling to inhibit growth of attaching parasites. This technique is effective where selectivity exists between crop and parasite; for example, varieties of imidazolinone-resistant maize. However, seed priming has not been reported for sorghum or pearl millet, two crops that are greatly affected by purple witchweed. Research was initiated to evaluate herbicides for potential use as seed priming agents in these crops. Auxin-mimic and acetolactate synthase-inhibitor class herbicides were evaluated; specifically, clopyralid, 2,4-DB, dicamba, picloram, and prosulfuron. For sorghum, immersion of seed in 0.5% (w/v) ae 2,4-DB for 5 min 1 d before planting reduced purple witchweed densities to levels 20 to 50% of nontreated controls. However, this concentration was at the threshold of crop toxicity and reduced sorghum yields in some experiments. None of the herbicides tested consistently reduced purple witchweed on pearl millet. This research illustrates both the potential and limitations of adapting seed priming technology for sorghum and pearl millet.

The basic B-subunit of the seed storage protein 11-S globulin (an 11-S-legumin type protein) is the major polypeptide in soluble protein extracts from primed sugarbeet (Beta vulgaris L.) seeds. In contrast, only a small amount of this protein is present in corresponding extracts from untreated dry mature seeds. Here, and as for all 11-S globulins described so far, the B-chain is linked to other polypeptide(s), corresponding most presumably to an acidic A-chain, through the formation of disulphide bridge(s). Polyacrylamide gel electrophoretic analyses of total and soluble protein extracts from untreated and primed seeds strongly indicate that this priming-induced solubilization of the B-chain resulted from an endoproteolytic attack on the A-chain. Microscopical immunolocalization showed a uniform distribution of the 11-S globulin B-chain over the protein bodies of the embryonic cells from the untreated seeds. For the primed seeds, however, the B-subunit of 11-S globulin diffused out of the protein bodies and invaded the cytosolic compartment. This phenomenon occurred independently of the manner of priming, being observed with hydroprimed and osmoprimed seeds, as well as with sugarbeet seeds that had been primed by a prehydration treatment. Quantitative analyses of the amounts of soluble 11-S globulin B-chain have enabled the priming of sugarbeet seeds to be optimized.

Seed germination rates are sensitive to both temperature (T) and water potential (ψ). The times to germination of seeds imbibed at suboptimal T and/or reduced ψ are inversely proportional to the amounts by which T exceeds a base temperature (Tb) and ψ exceeds a base water potential (ψb). Germination rates across a range of suboptimal T and ψ can be normalized on the basis of the hydrothermal time accumulated in excess of these thresholds. However, seeds can also progress metabolically toward germination even at T or ψ too low to allow radicle emergence to occur. Seeds preimbibed at low ψ and dried back, or primed, germinate more rapidly upon subsequent reimbibition. We show here that the increase in germination rates of tomato (Lycopersicon esculentum Mill.) seeds resulting from seed priming is linearly related to the hydrothermal time accumulated during the priming treatment. The threshold temperature (Tmin = 7.05°C) and water potential (ψmin = −2.50 MPa) for metabolic advancement were considerably lower than the corresponding thresholds for radicle emergence of the same seed lot (Tb = 11°C; ψb = −0.71 MPa), allowing the accumulation of hydrothermal priming time that is subsequently expressed as more rapid germination when T or ψ increase. The hydrothermal time model can now be applied to quantify and analyse germination rates of seeds across the entire range of suboptimal T and ψ at which metabolic progress toward radicle emergence is possible.

The effects of seed priming on germination and endo-β-mannanase activity at inhibitory and non-inhibitory temperatures in thermosensitive ‘Dark Green Boston’ (DGB) and in thermotolerant ‘Everglades’ (EVE) lettuce were investigated. A single-seed endo-β-mannanase assay was used to follow the enzyme activity during priming. Seeds were primed at 15°C in aerated solutions of polyethylene glycol (PEG) with constant light, then redried. Primed and non-primed seeds germinated 100% at 20°C. At 35°C, non-primed and primed EVE seeds germinated 100%, whereas non-primed seeds of DGB germinated only 4%. During priming, endo-β-mannanase activity increased between 24 and 48 h in EVE and between 24 and 72 h in DGB after the beginning of osmotic imbibition. Endo-β-mannanase activity persisted in primed seeds following seed drying, was detected before radicle protrusion and was present in the micropylar region in front of the radicle tip. Higher enzyme activity was observed in primed seeds and EVE compared with non-primed and DGB seeds. The results suggest that priming may overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds due to increased endo-β-mannanase activity, possibly leading to a weakening of endosperm, thus overcoming thermodormancy.

Osmotic priming reduces the longevity of Vigna radiata (mung bean) seeds during subsequent dry storage. The present study has investigated the relationship between volumetric changes, modified water sorption properties and the decrease in seed longevity after priming. Volumetric analysis of control embryos revealed two major dehydration-related volumetric contractions in the biopolymer matrix, reflecting structural reorganization in biopolymer matrix during drying. These contractions occurred at hydration from 0.29 to 0.23 g g–1 dw and from 0.18 to 0.11 g g–1 dw, respectively. Volumetric contractions were reduced significantly after priming and also occurred at higher water contents (i.e. 0.48–0.32 g g–1 dw and 0.21–0.11 g g–1 dw). Consequently, at the same water content, primed seed embryos had higher specific biopolymer volume and lower specific density than control embryos. Water sorption study showed that priming did not change the monolayer hydration value, but altered the properties of multilayer water sorption in seed axes. The analysis of water clustering function suggested that priming enhanced the water–water association in seed axes, but not in cotyledon tissues. Solid-state 1H-NMR (nuclear magnetic resonance) investigation confirmed that priming did not cause a significant change of water dynamic properties in cotyledon tissues at water contents below 0.20 g g–1 dw. The relevance of volumetric modifications of the biopolymer matrix and changes in water clustering function to the reduced seed longevity after priming is discussed. It is proposed that priming-induced increases in surface reactivity may enhance deteriorative chemical reactions in re-dried seed tissues.

The enhanced laboratory and field emergence characteristics of osmo- and halo-primed tomato seeds (cv. Pusa Ruby) were related to changes in hydration–dehydration kinetics, modified sorption properties and nuclear magnetic resonance (NMR) relaxation behaviour of humidified and imbibed seeds. Water sorption isotherms were constructed for primed and unprimed seeds by equilibrating to different water activities (aw) at 25°C. Analysis of the isotherms by the D'Arcy–Watt equation revealed that priming reduced the number of strong binding sites and the associated water content, and increased significantly the number of weak binding sites and the associated water content. This redistribution of water, which increased the availability of seed water, may be the reason for the higher speed of germination of primed seeds. The changes in transverse relaxation time (T2) of seed water and its components, measured in vivo using nuclear magnetic resonance spectroscopy, showed interesting differences between primed and unprimed seeds. With an increase in humidification time, the T2 of primed seeds could be resolved into three components with varying mobilities, while the control seeds had only two components until 10 d of humidification. During imbibition, the third component appeared after 2 and 6 h in primed and control seeds, respectively. This component disappeared after the germination process started in all treatments. The third fraction, with very low molecular mobility, which accounted for about 40% of the proton population, was assigned to hydration water of macromolecules. Hence, we propose that better performance of primed seeds may be attributed to the modifications of seed water-binding properties and reorganization of seed water during imbibition, so as to increase the macromolecular hydration water required for various metabolic activities related to the germination process.

Priming of sugarbeet (Beta vulgaris L.) seeds induces increased solubilization of the basic B-subunit of 11-S globulin (a major seed storage protein in sugarbeet). Using a sensitive single-seed ELISA, the soluble and total B-subunit contents of individual untreated and primed sugarbeet seeds were measured. With the untreated seeds, there was a 160-fold range of the soluble B-subunit content among individual seeds. The individual primed seeds also exhibited large variations in their soluble B-subunit content, yet only over a five-fold range. Furthermore, the frequency distributions of soluble B-subunit content were markedly different for the primed and untreated seed populations; the primed seed population exhibited a substantially higher median than that for the untreated seed population. In marked contrast, and as expected from results with pooled seed samples, the distributions of total B-subunit content were superimposed when comparing untreated and primed seed populations.

Correlative evidence indicates that sucrose and α-galactosyl-sucrose oligosaccharides (raffinose family oligosaccharides; RFOs) may be involved in seed longevity. Priming treatments (hydration in water or osmotic solutions followed by drying) can improve short-term seed performance but often result in reduced seed longevity. As RFOs are metabolized quickly following seed imbibition, loss of RFOs during priming could lead to more rapid deterioration in dry storage. This hypothesis was tested by measuring sucrose and oligosaccharide contents and potential longevity of primed seeds. Raffinose contents of whole lettuce (Lactuca sativa L.) seeds declined during hydration and priming and were correlated with decreased median potential viability (p50). However, this relationship was less significant when only the embryonic axes were analysed. In tomato (Lycopersicon esculentum Mill.) and impatiens (Impatiens balsamina L.) seeds, planteose was the major galactosyl-sucrose oligosaccharide and only small quantities of RFOs were present. Planteose contents declined during priming in seeds of both species, while sucrose contents increased or remained constant. Post-priming treatments that restored longevity in primed impatiens and tomato seeds were not accompanied by consistent changes in RFO or planteose contents. Our data do not rule out a role for oligosaccharides in seed longevity, but they make it unlikely that changes in oligosaccharide contents alone are responsible for the reduction in longevity due to priming or its restoration by post-priming treatments.

The relationship between initial mobilization of 11-S globulin storage protein (leading to solubilization of its B-subunit) and germination performance after priming was studied in sugarbeet (Beta vulgaris L.) seeds. Priming was conducted for 2 d either in water (hydropriming) or in –2.0 MPa polyethylene glycol-8000 (osmopriming), at various temperatures ranging from 5 to 40°C and oxygen concentrations in the atmosphere ranging from 0 to 21%. For both types of pre-treatments, the range of temperatures and the concentrations of oxygen which were effective in priming were very similar to those which allowed solubilization of the B-subunit of 11-S globulin, supporting the robustness of this protein marker for optimization of sugarbeet seed priming. Furthermore, the temperature and oxygen dependence of priming efficiency closely paralleled that for germination of the untreated seeds, reinforcing the finding that the beneficial effect of priming corresponded to the advancement of germination sensu stricto (i.e. phase II of the germination process). For priming times longer than 2 d, particularly for osmopriming, there was a very dramatic decrease in germination of the treated seeds. For instance, following a 14 d osmopriming at 25°C as much as 60% of the pre-treated seed population failed to germinate when transferred to water. This loss in germination performance quite closely paralleled degradation of LEA (late embryogenesis abundant) proteins, notably a heat-stable seed-specific protein of about 60 kDa and a seed-specific biotinylated LEA protein.

A model of seed germination is proposed which uses a variable with the units of an osmotic potential (virtual osmotic potential) to integrate the effect of a constant or a varying water potential. This differs from existing models that describe the effects of fixed water potentials on germination, or the effects of fixed priming water potentials on the subsequent germination at a fixed water potential. When a seed is sown, the virtual osmotic potential is assumed to fall at a rate that depends on the ambient water potential, and on the difference between its current and a minimum value. Radicle growth is assumed to initiate when the difference between the ambient water potential and the virtual osmotic potential exceeds a threshold. The germination of carrot and onion seeds at various fixed potentials below 0 MPa was well described by the virtual osmotic potential model. The model was also used to simulate the results of experiments in which seeds were given a single step change in water potential.