Dormancy-breaking requirements and level of morphophysiological dormancy (MPD) were determined for seeds of Ilex formosana and I. uraiensis from the subtropical region, and seeds of I. rotunda from both the subtropical and tropical regions of Taiwan. We hypothesized that some Ilex species would have deep simple MPD broken by warm stratification. Germination of seeds and embryo growth was monitored at 30/20, 25/15, 20/10, 15/5°C and at 25°C. Seeds were cold-stratified and then incubated at 25/15°C, and seeds treated with GA3 and GA4 were incubated at 25/15°C. Fresh seeds reached 50% germination after 11–45 weeks of warm stratification. Pre-treatment with GA increased germination percentages of I. formosana and I. rotunda (tropical) but not I. uraiensis and I. rotunda (subtropical), while cold stratification did not promote germination of either species but increased the germination rate of I. rotunda (tropical). Embryo length in seeds of all species increased ≥710% prior to root emergence, and growth occurred during warm stratification. The positive response to GA and relatively short time for beginning of germination and to reach 50% germination indicate non-deep simple MPD in seeds of I. formosana and I. rotunda (tropical). The negative response to GA and long time for beginning of germination and to reach 50% germination indicate deep simple MPD in seeds of I. uraiensis and I. rotunda (subtropical). Thus, in both the subtropical and tropical regions of Taiwan, the seeds of Ilex species have non-deep simple and deep simple MPD that are broken by warm stratification. Furthermore, GA treatment increases the germination rate and percentage of Ilex seeds with non-deep simple MPD, and cold stratification promotes the seed germination rate of Ilex species with non-deep simple MPD in tropical region.

Viburnum is a temperate-zone genus that also occurs in mountains of South America and Malesia, and seeds of many species have morphophysiological dormancy (MPD). Information on the level of MPD in seeds of species in various clades of Viburnum potentially would increase our understanding of the evolutionary relationships between the nine levels of MPD. Our aim was to determine the level of MPD in seeds of Viburnum plicatum var. formosanum that is endemic to mountains (1800–3000 m a.s.l.) in Taiwan and a member of the Lutescentia clade. The temperature requirements for embryo growth and root and shoot emergence and response of seeds to gibberellic acid (GA) were determined. No fresh seeds germinated during 16 weeks of incubation at 15/5, 20/10, 25/15, 30/20 or 25°C. Embryo growth and root emergence occurred during moist cold stratification at 5°C or at a temperature sequence of 15/5 to 5°C. During cold stratification, embryos length increased from 0.76 ± 0.06 to 3.40 ± 0.26 mm and the embryo length:seed length ratio from 0.20 ± 0.02 to 0.68 ± 0.07. In a temperature sequence simulating field conditions, embryos grew inside seeds at 5°C, roots emerged at 15/5°C and shoots emerged at 20/10°C. The optimum temperature for embryo growth was 5°C. Neither GA3 nor GA4 was effective in promoting root emergence. We conclude that seeds of V. plicatum var. formosanum have deep complex MPD, which is a first report for Viburnum. Dormancy release during the cool season at high elevations helps to ensure that seeds germinate at the beginning of the warm season.

Understanding seed biology and onset of germination requirements is a key point for designing effective weed management programs. Gibberellins (GAs) are known to play a role in onset of germination of several species. Onset of germination often requires an increase in de novo GA content or an increase in sensitivity to GAs. Reduced germination of seeds incubated in solutions containing compounds that inhibit GA synthesis provide evidence that GAs are required to trigger germination. Trinexapac-ethyl (TE), a GA synthesis inhibitor, is frequently used as a plant growth regulator in crop production. However, to the best of our knowledge, TE has not been used to study the requirement of GAs in onset of germination. Germination studies were conducted using seeds of artichoke thistle and common teasel under a range of TE concentrations (0 to 500 μM TE), a combined solution of 125 μM TE + 100 μM GA3 for artichoke, and 250 μM TE + 100 μM GA3 for common teasel. Germination tests were conducted at 20/10 C (12-h thermoperiod) in darkness for artichoke and at constant 15 C with 12 h of light for common teasel. Germination of artichoke in 125 μM TE was reduced to 47% when compared with the check (95%), but the combined TE + GA3 solution maintained germination at 84%. Germination of common teasel in 250 μM TE was reduced to 10% when compared with the check (91%), and the combined TE + GA3 solution increased germination to 63%. These results demonstrate the utility of TE to study the role of GAs in onset of germination. This novel use of TE is a valuable option to study germination requirements of weed species, and therefore contributes to the design of weed management programs.

A population-based modelling approach was used to predict the occurrence of germination in Solanum sarrachoides (SOLSA) for different treatments. Seeds collected in Toledo (Spain) were exposed to constant temperatures, to temperatures alternating between 10 and 30°C and to gibberellins (GAs; 0, 50, 100, 150 and 1000 ppm) during a 24-h imbibition period. The following parameters were measured: base temperature (Tb), mean thermal time (θT (50)) and the standard deviation of thermal time (σθT ). The SOLSA seeds only germinated at constant temperatures when the highest GA concentration was applied. The thermal model suggests that the induction and loss of physiological dormancy following seed dispersal is achieved when temperatures vary and when a mean thermal time of 66 growing degree-days (d°C) and a Tb value of 16°C are achieved when no GA treatment was added. The concentration of GA applied under conditions of alternating temperatures has an additive effect, reducing θT (50) up to threefold, from basal level (66 d°C) to 19.40 d°C, when the 1000 ppm GA treatment was applied. In this last case, the germination was accelerated by reducing Tb to 14°C. A 5–10°C change in temperature and a range of average temperatures of 20–27.5°C promoted the germination of SOLSA seeds to the greatest extent in the absence of GA. However, these conditions are not frequently encountered in the irrigated areas of the studied region; this finding could explain the limited ability of SOLSA to expand its range within this area.

Fluctuating temperatures terminate seed dormancy in many species, including Cynara cardunculus (L.) var. sylvestris. Termination of physiological dormancy requires low ratios of abscisic acid (ABA)/gibberellins (GA). In a previous paper we have shown that physiological responses to fluctuating temperatures comprise a reduction of abscisic acid (ABA) content and sensitivity. However, a possible stimulation of GA synthesis was also suggested as part of the mechanism. That possible stimulation, as well as the identification of potential regulatory sites for ABA and GA metabolism and signalling involved in the termination of dormancy by fluctuating temperatures, are yet to be determined. In this study, we measured GA content and sensitivity in seeds incubated under constant and fluctuating temperatures. We also assessed the expression of several genes involved in ABA and GA metabolism and signalling. Our results show that fluctuating temperatures reduce ABA/GA ratios through a reduction in ABA accumulation during incubation but without altering GA synthesis as compared to that observed under constant temperatures. On the other hand, fluctuating temperatures did not increase sensitivity to GA. Fluctuating temperatures reduced the expression of CycaNCED and CycaABI5 (ABA synthesis and signalling genes) with a temporal pattern that coincides with the interruption of ABA accumulation that precedes germination of seeds incubated under fluctuating temperatures. However, fluctuating temperatures did not modify the expression of CycaCYP707A2 (ABA inactivation) as compared to that observed under constant temperatures. Consistent with our determinations of GA content and sensitivity, fluctuating temperatures did not modify the expression of GA synthesis (CycaGA3ox) and signalling genes (CycaRGL2 and CycaGAI) in relation to that observed at constant temperatures. These results show that fluctuating temperatures terminate dormancy in Cynara cardunculus seeds through an interruption in ABA accumulation and a reduction in ABA signalling exerted at the level of CycaNCED and CycaABI5 expression.

Although mature seeds of the monogeneric conifer family Cephalotaxaceae sensu stricto have underdeveloped embryos, no definitive studies have been done to classify dormancy in this family. Our primary purpose was to determine the kind of dormancy in seeds of Cephalotaxus wilsoniana and to put the results into a broad phylogenetic context for gymnosperms. The species is of horticultural and medicinal value, and information is needed on how to propagate it efficiently from seeds. Embryo growth and germination were monitored for seeds at warm, cold and warm plus cold temperatures, and germination was monitored for seeds subjected to: (1) cold →  warm →  cold →  warm; and (2) warm →  cold →  warm →  cold →  warm temperature sequences. The effects of gibberellic acids GA3 and GA4 were tested on radicle emergence in ungerminated seeds and on shoot emergence in root-emerged seeds. Germination was promoted by ≥ 36 weeks of warm stratification followed by ≥ 8 weeks of cold stratification, but only if seeds were returned to high temperatures. The underdeveloped embryo must increase in length by >120% before the radicle emerges. Neither GA3 nor GA4 was effective in promoting radicle emergence; however, both plant growth regulators increased rate (but not percentage) of shoot emergence in root-emerged seeds. We conclude that seeds of C. wilsoniana have the deep simple level of morphophysiological dormancy (MPD), C1b-C3-B1b; thus, warm stratification followed by cold stratification and then warm-temperature incubation are required for germination. In gymnosperms, MPD is known in cycads, Ginkgo and now in three families of conifers.

The transition from the dormant to the non-dormant state of a viable and mature seed can take place at low hydration by exposure to air-dry storage conditions (dry afterripening; AR). The events occurring during this loss of dormancy are of considerable physiological, ecological and agricultural interest. AR may be attributable to increased sensitivity to germination-stimulating factors and a widening of the temperature window for germination. Genetic, –omics and physiological studies on this mode of dormancy breaking provide support for a key role of the balance between gibberellin (GA) and abscisic acid (ABA) metabolism and sensitivity. Recent evidence also supports a possible role for ethylene (ET) in this complex signalling network that is necessary for AR implementation. However, hormone-independent signals, such as reactive oxygen species (ROS), nitrate () or nicotinamide adenine dinucleotide (NAD+), also appear to be involved. The way in which hormone- and non-hormone-signalling pathways affects each other (cross-talk) is still under study. This review provides updated information on the programmes that overcome seed dormancy. Thus, we have reviewed: (1) the –omic status in dry seeds; (2) the relationship between temperature and nitrate signalling and AR; (3) alterations in ABA/GA synthesis and signalling; (4) the action of hormone molecules other than ABA and GA (i.e. ET, salicylic and jasmonic acids); and (5) participation of reactive oxygen species (ROS), NAD+ and protein carbonylation. Taken together, the acquisition and implementation of dry AR involve a complex signalling network that is difficult to disentangle.

Cynara cardunculus (L.) seeds require incubation at fluctuating temperatures to terminate dormancy. In this study, we analysed the physiological mechanisms underlying such a requirement, focusing on the role of abscisic acid (ABA) and gibberellin (GA). As a conceptual framework, we considered the possibility that fluctuating temperatures and light trigger a similar set of hormonal processes after stimulus perception. To test this possibility, we (1) carried out hydrotime analysis of germination in seeds exposed to fluctuating temperatures (25/15°C) and constant temperature (20°C) with or without gibberellin (GA3) or red light; (2) determined the responses of seeds incubated at fluctuating or constant temperature to ABA, GA3, fluridone, an inhibitor of ABA biosynthesis, and paclobutrazol, an inhibitor of GA biosynthesis; and (3) determined the ABA content of seeds incubated at fluctuating or constant temperature. Incubation at 25/15°C or 20°C in the presence of GA3 reduced the mean base water potential [ψb(50)] of the population to a similar extent, compared to that observed with seeds incubated at 20°C without GA3. Irradiation with red light also reduced ψb(50) to a lesser extent than incubation in the presence of GA3. At all concentrations tested, exogenously applied GA3 did not promote germination of seeds incubated at 25/15°C. However, paclobutrazol inhibited germination, suggesting that fluctuating temperatures terminate dormancy through de novo GA biosynthesis. Fluctuating temperatures enhanced seed germination in the presence of ABA, but ABA content did not differ between seeds incubated at fluctuating and constant temperatures. This study provides clear evidence for the involvement of hormonal regulation in dormancy termination by fluctuating temperatures.

Intact seeds (seed+endocarp) from freshly harvested fruits of Prunus campanulata were dormant, and required 4–6 weeks of warm followed by 8 weeks of cold stratification for maximum germination percentage. Removing both endocarp and seed coat, however, promoted germination in a high percentage of non-stratified seeds. Treatment of intact, non-stratified seeds with gibberellic acid (GA3) was only partially effective in breaking dormancy. However, GA3 promoted germination of non-stratified seeds in which the endocarp (but not the seed coat) had been removed. The order of abscisic acid (ABA) concentration in fresh seeds was endocarp > seed coat > embryo, and its concentration in endocarp plus seed coat was about 6.2-fold higher than that in the embryo. Total ABA contents of seeds subjected to warm and/or cold moist stratification were reduced 6- to 12-fold. A higher concentration of GA4 was detected in embryos of non-dormant than in those of dormant seeds. Fluridone, a carotenoid biosynthesis inhibitor, was efficient in breaking dormancy of Prunus seeds. Paclobutrazol, a GA biosynthesis inhibitor, completely inhibited seed germination, and the inhibitory effect could be partially reversed by GA4, but not by GA3. Thus, dormancy in P. campanulata seeds is imposed by the covering layers. Dormancy break is accompanied by a decrease in ABA content of the covering layers and germination by an increase of embryonic GA4 content.

Expansins are a multi-gene family of proteins involved in changes in cell wall properties. In seeds where the embryo is completely surrounded by the endosperm, dormancy breakage requires weakening of the micropylar endosperm, increased embryo growth potential or both. Cell wall alterations are fundamental components of these processes, and expansins are thought to participate in them. Here, we explore the possible involvement of expansins in the control of germination by phytochrome in Datura ferox L. seeds. Based on the conserved sequences of known expansin genes, corresponding primers were designed to investigate the expression of expansin mRNAs by reverse transcriptase polymerase chain reaction (RT-PCR). One expansin mRNA was detected in micropylar endosperm of D. ferox, while two mRNAs were present in the embryo prior to radicle emergence. Expansin transcript content is promoted by red (R) light, both in the micropylar endosperm and the embryo; these effects of R are far-red light (FR) reversible, displaying a typical low-fluence response (LFR) in a way fully consistent with the photocontrol of germination. On the other hand, when the promotion of germination by the LFR is antagonized by exposing the seeds to continuous FR through a high-irradiance response (HIR) or by ABA, the inhibitory treatments do not affect expansin mRNA abundance. The results support the participation of expansins in the promotion of germination by LFR of phytochromes, and suggest that inhibition of germination by HIR or ABA does not include a reduction in the transcription of expansin genes.

Higher plants have several strategies to perpetuate themselves under adequate ecophysiological conditions. The production of heterogeneous seeds is one such strategy. That is, to ensure the survival of the next generation, an individual plant might produce seeds that are heterogeneous with respect to the extent of dormancy, dispersion and persistence within the seed bank. Heterogeneity can affect not only certain physiological and molecular properties related to seed germination, but also such characteristics as colour, size and shape, parameters commonly used to differentiate morphs within a heterogeneous seed population. In heterogeneous seeds, the above features determine seed behaviour and alter their mechanism of germination. In this work, emphasis is placed on the existence of seed mutants having major alterations in characteristics of the testa and hormonal response. These mutants constitute a valuable tool for elucidating the mechanism of dormancy, germination and perpetuation of seeds. Finally, ontogeny and heterogeneity are reviewed, providing the first data related to the possible hormonal control of heterogeneity in seeds. These results raise the hypothesis that one of the factors triggering differences in germination among heterogeneous seeds may be an alteration in the signalling and action mechanism of ethylene and abscisic acid (ABA).

The objectives of this study were (i) to evaluate the relative involvement of fructans from leaf sheaths and from elongating leaf bases to regrowth after defoliation of Lolium perenne L. by following fructan exohydrolase (FEH), sucrose-sucrose fructosyl transferase (SST) and invertase (INV) activities and (ii) to examine whether gibberellins could be implicated in regulation of FEH activity. In stubble, 36% of fructans are located in leaf bases and 64% in leaf sheaths. During the first phase of regrowth, the depletion of carbohydrates was mainly due to the decline of fructans, which represented 76% and 50% of the carbohydrates mobilized from leaf sheaths and elongating leaf bases respectively. Despite a decrease in protein content, FEH activity increased 2·5-fold in leaf sheaths and six-fold in elongating leaf bases, so that the fructan-hydrolysing activity was four times higher in growing leaves than in leaf sheaths, 2 d after defoliation. INV activity also increased, whereas the pattern of SST activity was inversely related to the variations of both hydrolysing activities. SST activity, which is highest in growing leaves, declined approximately threefold in leaf sheaths and elongating leaf bases at the beginning of regrowth.

The increase in activity of FEH in stubble was strongly inhibited by an inhibitor of the biosynthesis of gibberellin, uniconazole. FEH activity was decreased to c. 67%, 45% and 33% of the level in nontreated plants 24, 48 and 72 h following defoliation, respectively. The inhibition could be overcome by a subsequent treatment with gibberellic acids (GAs). For the first time, data are provided to support the view that GAs might play a role in the regulation of FEH activity, and the implication of this result is discussed.