Many studies have compared diaspore dispersal ability and degree of dormancy in the two diaspores of dimorphic plant species. A primary goal of these studies was to determine if germination and dispersal characteristics of the two morphs fit within a high risk–low risk (bet-hedging) life-history strategy, i.e. high dispersal/low dormancy in one morph versus low dispersal/high dormancy in the other one. In a survey of 26 papers on 28 diaspore dimorphic species, we found that in 12 of the studies, which were published between 1978 and 2008, seeds were stored, and thus possibly afterripened, before they were tested for germination. The 14 papers that tested fresh seeds were published between 1963 and 2010. Failure to test fresh seeds likely resulted in misinterpretation of the diaspore dispersal/dormancy strategy in some of the species investigated. We conclude that it is imperative that fresh seeds be tested for germination in order to be certain that the correct relationship between dispersal and dormancy is elucidated, and thus that the correct interpretation is made concerning life-history strategy and bet-hedging, in dimorphic species.

The wheat transcription factor TaABF1 physically interacts with the protein kinase PKABA1 and mediates both abscisic acid (ABA)-induced and ABA-suppressed gene expression. In bombarded aleurone cells of imbibing grains, the effect of TaABF1 in down-regulating the gibberellin (GA)-induced Amy32b promoter was stronger in the presence of exogenous ABA. As these grains contained low levels of endogenous ABA, the effect of TaABF1 may also be mediated by ABA-induced activation even in the absence of exogenous ABA. Levels of TaABF1 protein decreased slightly during imbibition of afterripened grains. However, TaABF1 levels (especially in aleurone layers) were not substantially affected by exogenous ABA or GA, indicating that changes in TaABF1 protein level are not an important part of regulating its role in hormone signalling. We found that TaABF1 was phosphorylated in vivo in aleurone cells, suggesting a role for post-translational modification in regulating TaABF1 activity. Induction of Amy32b by overexpression of the transcription factor GAMyb could not be prevented by TaABF1, indicating that TaABF1 acts upstream of GAMyb transcription in the signalling pathway. Supporting this view, knockdown of TaABF1 by RNA interference resulted in increased expression from the GAMyb promoter. These results are consistent with a model in which TaABF1 is constitutively present in aleurone cells, while its ability to down-regulate GAMyb is regulated in response to ABA.

Alfalfa (Medicago sativa L.) yield is severely compromised by soil salinity, especially at the level of seedling establishment. This question was addressed by proteomics to decipher whether specific changes in protein accumulation correlate with germination performance of alfalfa seeds submitted to a salinity stress as obtained by imbibing seeds in the presence of NaCl. This study used alfalfa seeds submitted to an osmopriming invigoration treatment that proved very efficient in counteracting the negative effect of salinity stress on germination performance. Comparative proteomic analyses disclosed 94 proteins commonly characterizing the response of both the untreated control and osmoprimed seeds to the experimental salinity stress. Remarkably, many of them, representing 84 proteins, showed contrasting accumulation patterns when comparing the untreated control and osmoprimed seeds submitted to the same salt stress. Thus numerous changes observed in the proteome of the untreated control seeds imbibed in the presence of salt, and presumably accounting for the loss in seed vigour associated with salinity stress, can be substantially reversed in osmoprimed seeds undergoing this stress. These data therefore provide a biochemical understanding of the increase in seed vigour generally observed with primed seeds.

Sucrose, raffinose and stachyose accumulate as stored soluble carbohydrates in embryos during soybean [Glycine max L. (Merrill)] seed development and maturation. Raffinose and stachyose in soybean feed products are not digested by humans, chickens or pigs, resulting in flatulence and reduced nutritional value. Soybean lines selected for low raffinose and low stachyose (LRS) or low raffinose, low stachyose and low phytin (LRSP1, LRSP2) concentrations in mature seeds were compared to a CHECK line with normal raffinose, stachyose and phytin. To determine whether increasing the supply of free cyclitols to immature embryos of these lines results in increased accumulation of galactosyl cyclitols, isolated immature embryos free of maternal tissues were fed solutions containing either d-chiro-inositol, myo-inositol or d-pinitol, or a control solution without cyclitols, for 24 h. Embryos were precociously matured by slow drying for 14 d with daily transfers to stepwise lower relative humidities. Soluble carbohydrates were extracted from axis and cotyledon tissues of mature, dry embryos and analysed by high-resolution gas chromatography. Axis and cotyledons from LRS, LRSP1 and LRSP2 embryos had low concentrations of stachyose compared to CHECK embryos after feeding a control solution without cyclitols. Feeding d-chiro-inositol to isolated embryos increased fagopyritol B1 accumulation in embryos of all lines. Feeding myo-inositol increased stachyose accumulation in LRSP1 and LRSP2 cotyledons. Feeding d-pinitol increased free d-pinitol in cotyledons of all lines but increased galactopinitol A and galactopinitol B only in LRS cotyledons. Supplying additional d-chiro-inositol to immature embryos can enhance accumulation of fagopyritol B1 in mature embryos of low-raffinose and low-stachyose or low-raffinose, low-stachyose and low-phytin soybeans.

The present study was conducted to evaluate the contribution of nitric oxide (NO) to the priming effects on seed germination, seedling vigour and low-temperature tolerance of two tomato cultivars (Solanum lycopersicum, cv. Cherry and Falcato) under four different constant temperatures (10, 15, 20 and 25°C). Treatments included priming in a polyethylene glycol 6000 (PEG 6000) solution (osmopriming) or presoaking in sodium nitroprusside (SNP) solution, a donor of NO, for 24 h at 25°C. Suboptimal temperatures reduced seed germination and subsequent seedling growth, as well as amylase activity, in both cultivars, but Falcato was more sensitive to low temperature than Cherry. Both osmopriming and SNP treatments enhanced germination capacity, germination index, seedling root and shoot length, α- and β-amylase activities and sugar content under suboptimal temperatures, especially in Falcato. We observed similarities between the modes of action of the two priming treatments. Both treatments increased seed NO content, whereas their positive effects on germination and subsequent seedling growth under low-temperature stress was reversed by the addition of methylene blue (MB), a scavenger of NO. This is the first report that suggests that positive effects of priming are most likely mediated through NO signalling.

Although seed dormancy of temperate legumes is well understood, less is known about it in species that grow in subalpine/alpine areas. This study investigated dormancy and germination of four Vicia species from the Tibetan Plateau. Fresh seeds of V. sativa were permeable to water, whereas those of V. angustifolia, V. amoena and V. unijuga had physical dormancy (PY). One year of dry storage increased the proportion of impermeable seeds in V. angustifolia, but showed no effect on seed coat permeability in V. amoena or V. unijuga. Seeds of all four species also had non-deep physiological dormancy (PD), which was especially apparent in the two annuals at a high germination temperature (20°C). After 1 year of storage, PD had been lost. The hydrotime model showed that fresh seeds obtained a significantly higher median water potential [Ψb(50)] than stored seeds, implying that PD prevents germination in winter for seeds dispersed without PY when water availability is limited. After 6 months on the soil surface in the field, a high proportion of permeable seeds remained ungerminated, further suggesting that PD plays a key role in preventing germination after dispersal. Addition of fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, evened-out the differences in germination between fresh and stored seeds, which points to the key role of ABA biosynthesis in maintaining dormancy. Further, fresh seeds were more sensitive to exogenous ABA than stored seeds, indicating that storage decreased embryo sensitivity to ABA. On the other hand, the gibberellic acid GA3 increased germination rate, which implies that embryo sensitivity to GA is also involved in seed dormancy regulation. This study showed that PY, PD or their combination (PY+PD) plays a key role in timing germination after dispersal, and that different intensities of dormancy occur among these four Vicia species from the Tibetan Plateau.

Narcissus longispathus (Amaryllidaceae) is a perennial geophyte and a Mediterranean narrowly endemic species. At dispersal time, N. longispathus seeds are dormant and have underdeveloped embryos. This work aimed to determine requirements for dormancy break and germination and to compare dormancy traits with those of the two endemic Iberian congeners. Phenology of embryo growth and germination were studied by regularly exhuming seeds sown in near-natural conditions. Temperature and light requirements for embryo growth, breaking of dormancy and germination were determined by incubating seeds under controlled laboratory conditions. Mean embryo length in fresh seeds was 1.50 mm, and embryos had to grow to 3.80 mm before radicle emergence. Embryos grew to full size and seeds germinated when they were warm stratified for 2 months (optimum 1 month at 20/7°C+1 month at 15/4°C), then cold stratified at 5°C for 2 months, and finally incubated at cool temperatures (15/4°C) for 30 d. However, in seeds only subjected to either warm or cold stratification, the embryos hardly grew and did not germinate. In natural conditions, the embryos elongate in autumn–winter, and in late winter–early spring (March) almost all radicles and seedlings emerged. Velocity of embryo growth and germination percentages increased with seed storage duration. Seeds of N. longispathus have non-deep complex morphophysiological dormancy (MPD). This is the first report of such a level of MPD in Narcissus. Our data suggest that non-deep complex MPD may have been derived from intermediate complex MPD in the section Pseudonarcissi.

Invasive alien plants often occur in monospecific stands with high density in the invaded range. Production of bioactive secondary metabolites in such stands could have allelopathic effects on germination of native species. We tested this component of the novel weapon hypothesis for Heracleum mantegazzianum, a prominent invader in Europe, using seeds of 11 native herbs exposed to soil or soil extracts from invaded stands, moist seeds or seed extracts of H. mantegazzianum. There was no effect of the various treatments on germination of most species, while germination was reduced in Urtica dioica on invaded soil, in Poa trivialis with H. mantegazzianum seed extract, and negative effects of the essential oil bergapten were found in three species. In P. trivialis the results of the seed extract were not supported by the experiment with added seeds of the invasive plant. Thus, there is limited evidence for allelopathic effects of the invasive H. mantegazzianum on germination of co-occurring native herbs.