Seed germination implies an expansion process restarting the growth of the embryonic axis (Ax) and which is completed by radicle emergence through the seed covering layers. In developing soybean seeds, abscisic acid in Ax (ABAa) mainly inhibits Ax growth. Additionally, the expression of the EXP1 gene at the elongation zone (EZ) was found to be involved in the promotion of mature soybean Ax growth, which increased during water incubation and which was repressed by exogenous ABA. This work aimed to evaluate (1) the ABAa and EXP1 levels at the EZ and (2) the role of the seed coat (SC) in developing soybean seed germination. Whole seeds (Se), embryos (Em) and Ax at 25–45 d after anthesis (DAA) germinated in vitro, and germination performance increased with DAA. ABAa decreased in planta from 25 DAA until its critical non-inhibitory threshold (ABAc) at around physiological maturity (45 DAA). At earlier ages, the ABAc was reached during the in vitro incubation. Concomitantly, EXP1 transcripts accumulated with age into the pool of long-lived mRNAs and were up-regulated during incubation. Additionally, isolated Ax germinated faster, took up more water and increased its water potential more rapidly during incubation than Ax in Se. Also, a lower osmotic gradient was required to germinate at 45 DAA, when ABAa was no longer inhibitory. Simultaneously, the pressure to protrude SC through the micropylar area increased from 25 to 45 DAA. These results support the role of ABAa and EXP1 in controlling Ax growth and the SC in delaying radicle protrusion.

Fatty acid (FA) levels and profiles are vital for soybean oil quality, while cytokinins (CKs) and abscisic acid (ABA) are potent regulators of plant growth and development. Previous research suggested associations between FA biosynthesis and hormonal signalling networks; however, hormonal regulation of FA accumulation during soybean (Glycine max) seed maturation has never been measured. We analysed hormone and FA profiles obtained from HPLC-(ESI)-MS/MS and GC-FID screening during soybean seed maturation. A multilayered data processing approach, involving heat-maps, principal component analysis (PCA), correlation and multiregression models, suggested a strong relationship between hormone metabolism and FA/oil accumulation during seed maturation. Most strikingly, positive correlations were found between the levels of CK ribosides [transZeatin riboside (tZR), N6-isopentenyladenosine (iPR)] at the early stages of SM (R5-R6) and C18:0, C18:2 and oil content at the R8 stage. Moreover, multiple regression models revealed functional linkages between several CK derivatives and FA and oil content in mature seeds. To further test the significance of hormone regulation in FA metabolism, plants of two soybean accessions with contrasting hormone and FA profiles were sprayed with exogenous ABA and transZeatin (tZ) during the seed-filling period (R5-R6). Depending on the hormone type and concentration, these treatments distinctly modified biosynthesis of all tested FAs, except for C18:0. Most remarkably, tZ (50 nM) promoted production of C16:0, C18:1, C18:2, C18:3, and oil accumulation in maturing seeds. Overall, the results indicate impactful roles for ABA and CKs in FA accumulation during SM and represent a further step towards understanding FA biosynthesis, and potential improvements of soybean oil profiles.

The regulation of plasma membrane H+-ATPase was considered in imbibing Vicia faba seeds, a distinctive feature of which is germination by cell elongation, whereas the mitotic activity starts later. The enzyme activation is known to precede germination because it provides H+ ion efflux from the cytoplasm to cell walls which favours their modification and loosening, being the prerequisites of cell elongation commencement. The presence of an enzyme in imbibing embryo axes was confirmed immunochemically. H+ ion efflux was recorded with a pH-meter as acidification of ambient solution by the embryonic axes for 5 min. The activation of the enzyme and its subsequent activity are regulated in different ways. Enzyme activation is hydration-driven, it starts when water content increases up to the threshold level of 55% (fresh weight basis). This value was confirmed by imbibition in the presence of the osmoticum polyethylene glycol 6000, at various osmotic potentials. The activation does not depend on indolylacetic or abscisic acid treatment. Hydration-triggered activation of the enzyme favours rapid seed germination and its correspondence to the soil water potential. Enzyme activity after its activation is inhibited by 60–70% by 10−5–10−7 M abscisic acid, whereas indolylacetic acid exerted no effect. The regulation of plasma membrane H+-ATPase activity is presumably accomplished by the interaction of the enzyme with 14-3-3 proteins and endogenous fusicoccin, present in imbibing axes.

During soybean seed germination, the expansive growth potential of the embryonic axes is driven by water uptake while cell wall loosening occurs in cells from the elongation zone (EZ). Expansins are regarded as primary promoters of cell wall remodelling in all plant expansion processes, with the expression profiles of the soybean expansins supporting their cell or tissue specificity. Therefore, we used embryonic axes isolated from whole seed and focused on the EZ to study seed germination. Using a suite of degenerate primers, we amplified an abundantly expressed expansin gene at the EZ during soybean embryonic axis germination, which was identified as EXP1 by in silico analyses. Expression studies showed that EXP1 was induced under germination conditions in distilled water and down-regulated by abscisic acid (ABA), which inhibits soybean germination by physiologically restraining expansion. Moreover, we also identified a time window of ABA responsiveness within the first 6 h of incubation in water, after which ABA lost control of both EXP1 expression and embryonic axis germination, thus confirming the early role of EXP1 in the EZ during this process. By contrast, EXP1 levels in the EZ increased even when germination was impaired by osmotically limiting the water availability required to develop the embryonic axes’ growth potential. We propose that these higher EXP1 levels are involved in the fast germination of soybean embryonic axes as soon as water availability is re-established. Taken together, our results show strong EXP1 expression in the EZ and postulate EXP1 as a target candidate for soybean seed germination control.

The timing of the germination of seeds is highly responsive to inputs from the environment. Temperature plays a key role in the control of germination, with low temperatures acting to stimulate this developmental transition in many species. In Arabidopsis, extensive gene expression changes have been reported at the whole seed level in response to cold, while much less is known about their spatial distribution across the diverse cell types of the embryo. In this study we examined the spatiotemporal patterns of promoter activity and protein abundance for key gibberellic acid (GA) and abscisic acid (ABA) factors which regulate the decision to germinate both during a time course of germination and in response to cold. Low temperature stimulated the spatial relocalization of these factors to the vasculature. The response of these seeds to dormancy-breaking stratification treatments therefore stimulates the distribution of both positive (GA) and negatively acting (ABA) components to this same cell type. This altered spatial pattern persisted following the transfer of seeds to 22°C, as well as after their rehydration, indicating that this alteration is persistent. These observations suggest that the vasculature plays a role in the low temperature-mediated stimulation of germination in this species, while novel cell types are recruited to promote germination in response to stratification.

Dynamics of abscisic acid (ABA) and indole-3-acetic acid (IAA) contents were followed in developing barley caryopses of the ABA-deficient mutant AZ34 and its parental cultivar Steptoe. Distribution of these hormones and HvPIP2 aquaporins (AQPs) was studied with the help of immunohistochemical methods in the roots and coleorhiza of developing embryos. In Steptoe, maturation of the caryopsis was accompanied by vast accumulation of ABA, while this hormone accumulated more slowly in the caryopsis of AZ34 and its content was lower than in Steptoe. Accumulation of ABA was accompanied by a decline in IAA level in the developing caryopsis, the process being delayed in AZ34 in accordance with the slower accumulation of ABA. ABA accumulated to high levels in the coleorhiza cells of Steptoe, while the effect was absent in AZ34. The high level of ABA was likely to be important for maintaining the barrier function of the coleorhiza, preventing germination of seminal roots and enabling seed dormancy, while the absence of ABA accumulation in coleorhiza of AZ34 may be responsible for the initiation of root germination inside the caryopsis. The abundance of HvPIP2 AQPs in the seminal roots was higher at the beginning of maturation of Steptoe caryopsis and declined afterwards, while the levels of APQs increased later in AZ34 in accordance with the delay in ABA accumulation. These results suggest the importance of ABA accumulation in coleorhiza for preventing precocious growth of seminal roots, and suggest regulation of IAA and aquaporin levels by this hormone during maturation of embryos.

We used two sunflower genotypes displaying pericarp-imposed dormancy at high incubation temperatures (i.e. 30°C) to investigate the role of the pericarp as a limitation to oxygen availability to the embryo (hypoxia), and its impact on embryo abscisic acid (ABA) content and sensitivity to ABA. Results showed that both genotypes displayed very different oxygen threshold values for inhibition of embryo germination when incubation was performed at 30°C. Expression of dormancy in one genotype was therefore related to exacerbated embryo sensitivity to hypoxia, whereas in the other genotype, the pericarp appeared to act as a more severe restraint to oxygen entry. Increased sensitivity to hypoxia was, in part, related to increased sensitivity to ABA, but not to alterations in ABA metabolism. The activity of pericarp-microbial communities (bacteria and fungi) at high temperatures was also assessed as a potential determinant of hypoxia to the embryo. Oxygen consumption in pericarps incubated at 30°C was attenuated with antibiotics, which concomitantly promoted achene germination. In agreement with the observed more severe oxygen deprivation to the embryo exerted by the pericarp, the bacterial load in the pericarp was significantly higher in the commercial hybrid than in the inbred line; however, the application of antibiotics strongly reduced the bacterial colony counts for each genotype. Different bacterial and fungal communities, assessed through their profiles of carbon-source utilization, were determined between genotypes and after treatment with antibiotics. This work highlights the relationship between enhancement of sensitivity to hypoxia with incubation temperature and seed dormancy expression, and suggests that microbial activity might be part of the mechanism through which hypoxia is imposed.

The wheat bZip transcription factor TaABF1 mediates both abscisic acid (ABA)-induced and ABA-suppressed gene expression. As levels of TaABF1 protein do not change in response to ABA, and TaABF1 is in a phosphorylated state in vivo, we investigated whether TaABF1 could be regulated at the post-translational level. In bombarded aleurone cells, a TaABF1 protein carrying phosphomimetic mutations (serine to aspartate) at four sites (S36D, S37D, S113D, S115D) was three to five times more potent than wild-type TaABF1 in activating HVA1, an ABA-responsive gene. The phosphomimetic mutations also increased the ability of TaABF1 to downregulate the ABA-suppressed gene Amy32b. These findings strongly suggest that phosphorylation at these sites increases the transcriptional regulatory activity of TaABF1. In contrast to the activation observed by the quadruple serine to aspartate mutation, a single S113D mutation completely eliminated the ability of TaABF1 to upregulate HVA1 or downregulate Amy32b. Thus phosphorylation of TaABF1 can either stimulate or inhibit the activity of TaABF1 in regulating downstream genes, depending on the site and pattern of phosphorylation. Mutation of S318 and S322 (in the bZIP domain) eliminated the ability of TaABF1 to activate HVA1, but had no effect on the ability of TaABF1 to downregulate Amy32b, suggesting that TaABF1 represses Amy32b expression through a mechanism other than direct DNA binding. An important step towards understanding how ABA and gibberellin (GA) signals are integrated through TaABF1 phosphorylation to regulate downstream gene expression is to clarify the effects of those hormones on the expression of specific genes. In contrast to some other ABA-induced genes, we found that HVA1 induction by ABA or TaABF1 is not inhibited by GA.

This work presents the results of physiological studies developed to understand modifications linked to the reduction of seed dormancy provoked by domestication processes. The experiments performed compared wild and domesticated Cucurbita subspecies and their hybrids developed by reciprocal crossings. Seeds of two accessions of the wild subspecies presented dormancy, but it was largely reduced in seeds from the domesticated genotype, and partially reverted in hybrids, especially in those obtained when the domesticated genotype was used as the mother plant. In addition, naked embryos of all subspecies did not display dormancy when incubation was performed at 28°C, but embryo germination was progressively reduced only in the wild genotype under decreasing incubation temperatures (22 and 16°C). In the embryos, abscisic acid (ABA) concentrations were similar in both domesticated and wild subspecies, whereas in the seed coat, it was threefold higher in the wild subspecies. The naked embryos from the wild subspecies were far more responsive to ABA than those from the domesticated subspecies. These results indicate that dormancy in the wild subspecies is imposed by the seed coat tissues and that this effect is mediated by their high ABA content and the sensitivity of the embryos to ABA. These physiological aspects were apparently removed by domestication along with the temperature-dependent response for germination.

Tubers of yellow nutsedge (Cyperus esculentus L.) were collected over a 2-yr period to investigate the variation in abscisic acid (ABA) and total phenols throughout the year. The amount of ABA increased gradually from the end of the summer to November when it reached the highest level (6.81 μg/g fresh wt of tubers). This coincided with the onset of dormancy of the tubers in the field. In April, when a maximum of tubers showed sprouting, no free ABA was detected in tuber extracts. These data seem to indicate that free ABA is, in part at least, responsible for the dormant state of tubers. No obvious relation was seen between the state of dormancy of the tubers and their total phenolic content. It is unlikely that the phenolics as a group have one specific role in regulating dormancy of the tubers, but is possible that individual classes, or individual phenols, may possess significant activity.

The effect of various growth regulators on seedling field bindweed (Convolvulus arvensis L. # CONAR) growth and control with herbicides was evaluated. Fourteen growth regulators were applied at 0.38 to 380 g/ha 7 days before herbicide application in greenhouse, growth chamber and field studies. Field bindweed seedlings pretreated with growth regulators were more effectively controlled by herbicides compared to those not pretreated in greenhouse evaluations. Abscisic acid [[R-(Z,E)]-(+)-5-(1-hydroxy-2,6-6-trimethyl-4-oxo-2-cyclohexane-1-yl)-3-methyl-2,4-pentadicenoic acid] (ABA), ancymidol [a-cyclopropyl-a-(p-methoxyphenyl)-5-pyrimidine methanol], cycloheximide {3-[2-(3,5-dimethyl-2-oxocylohexyl)-2-hydroxyethyl]glutarimide}, ethylenediamine tetraacetic acid [N,N′-1,2-ethanediyl-bis-(N-(carboxymethyl) glycine] (EDTA), and 1-naphthaleneacetic acid (NAA) increased field bindweed stem length. Ancymidol and gibberellic acid [ent-3α,10,13-trihydroxy-20-norgibberell-1,16-diene-7,19-dioc acid 19,10-lactone] (GA) increased root weight, and GA increased root length. Cycloheximide, ethephon [(2-chloroethyl)phosphonic acid] and MH (1,2-dihydro-3,6-pyridazinedione) decreased field bindweed root weight. Ancymidol, GA and IAA (indole-3-acetic acid) increased the number of shoots per plant of seedling field bindweed. Dicamba (3,6-dichloro-2-methoxybenzoic acid) efficacy was enhanced following field bindweed preconditioning with ethephon and IAA. Ancymidol and cycloheximide applied as pretreatments increased glyphosate [N-(phosphonomethyl)glycine] activity on seedling field bindweed. Ancymidol and IAA pretreatment improved field bindweed control with triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}. Herbicide-growth regulator combination treatments that increased field bindweed control in greenhouse and growth chamber studies did not increase top growth control in the field.

Substituted quinolinecarboxylic acids, including quinclorac (BAS 514H), are a new class of highly selective auxin herbicides, which are chemically similar to naturally occurring compounds isolated from plants and soils. Quinclorac is used in rice to control important dicot and monocot weeds, particularly barnyardgrass. The herbicide has also been developed for application in turfgrass areas, spring wheat, and chemical fallow. Quinclorac is readily absorbed by germinating seeds, roots, and leaves and is translocated in the plant both acropetally and basipetally. By mimicking an auxin overdose, quinclorac affects the phytohormonal system in sensitive plants. The compound stimulates the induction of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and thus promotes ethylene biosynthesis. In susceptible dicots, increased levels of ethylene trigger an accumulation of abscisic acid (ABA), which, as part of the intrinsic auxin activity of quinclorac, plays a major role in growth inhibition and the induction of epinasty and senescence. In sensitive grasses, such as barnyardgrass species, large crabgrass, broadleaf signalgrass, and green foxtail, quinclorac leads particularly to an accumulation of tissue cyanide, formed as a co-product during increased ACC and ethylene synthesis. This causes phytotoxicity characterized by the inhibition of root and particularly shoot growth with tissue chlorosis and subsequent necrosis. These effects were not observed in tolerant rice and a resistant biotype of barnyardgrass. No significant differences in uptake, translocation, or metabolism of quinclorac between resistant and sensitive grasses were found. Hence, a target-site-based mechanism of selectivity is suggested. The induction process of the ACC synthase activity plays the primary role in the selective herbicide action of quinclorac. This is a common effect of auxin herbicides and auxins, which lead to the accumulation of cyanide and/or ABA depending on the plant species and tissues, the compound concentration in the tissue, and their biological activity.

Induction of germination in dormant barnyardgrass seeds by wounding was investigated. Previous research indicated that a volatile compound was emitted during imbibition of wounded caryopses. When wounded caryopses were submerged in agar, total germination and speed of germination were stimulated, and the stimulation was dependent upon the concentration of agar. A twofold increase in germination occurred in 1% agar versus water, and a fivefold increase with caryopses placed in 5% agar. When wounded caryopses were imbibed, there was a fourfold increase in respiration over that of intact caryopses after 1 h. This increased rate of respiration of wounded caryopses continued for 7 h, while there was a gradual increase in respiration of intact caryopses. Carbon dioxide induced intact dormant caryopses to germinate but was not effective in stimulating germination of the seed (spikelet). High levels of abscisic acid found in the hulls of dormant seeds may have prevented the action of carbon dioxide. These results suggest that increased respiration resulting from wounding provides elevated levels of carbon dioxide in the microenvironment of the seed, thus stimulating germination. Removal of the hulls is necessary for germination even in high levels of carbon dioxide.

Applications of glyphosate [N-(phosphonomethyl)glycine] to the leaves of pea (Pisum sativum L. ‘Burpee's Blue Bantam’), sunflower (Helianthus annuus L. ‘Mammoth’), and bean (Phaseolus vulgaris L. ‘Red Kidney’) reduced transpiration in all three species. The reduction varied with species and concentration applied. Eight-day-old bean leaves responded earlier than leaves on older plants. However, after 29 h, there was no difference in transpiration rates with seedling age, since treated leaves on both ages investigated were transpiring at about one-half the rate of control leaves. Addition of surfactant to the solution shortened the time interval between treatment and transpirational response but did not affect the final transpiration rate as compared to glyphosate without surfactant. The effect of glyphosate on transpiration was not due to changes in water availability or to the surface of the leaf that was treated. It is suggested that these results can give some insight into uptake, translocation, and mode of action of glyphosate.

Fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone} and R-4-0244 [1-(m-trifluoromethylphenyl)-3-chloro-4-chloromethyl-2-pyrrolidone], herbicides that block carotenoid synthesis, increase the sensitivity of corn (Zea mays L. ‘Merit’) to exogenously-applied gibberellic acid (GA). Increase in shoot length due to the application of GA to imbibing corn seeds was considerably enhanced by simultaneously applying either fluridone or R-40244. Fluridone was more active in this respect than R-40244.

Dark germination of light-requiring lettuce seeds (Lactuca sativa L. ‘Grand Rapids’) was stimulated by SAN 9789 [4-chloro-5-(methylamino-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] and to a minor degree by BASF 13761 [4-chloro-5-methoxy-2-phenyl-3(2H)-pyridazinone] and BASF 44521 [4-chloro-5-methoxy-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], but not by’ pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], SAN 9785 [4-chloro-5-(dimethylamino)-2-phenyl-3 (2H)-pyridazinone], SAN 9774 [5-amino-4-chloro-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], or SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone]. SAN 9789 stimulation was inhibited by cis-4-cyclohexene-1,2-dicarboximide (CHDC), and abscisic acid (ABA) at 1 × 10-4 M. Red light nullified the inhibitory effect of CHDC (1 × 10-4 M) but not the inhibitory effect of ABA (1 × 10-4 M) on SAN 9789 stimulated germination. Gibberellic acid (GA3) and kinetin (6-furfurylaminopurine) increased the germination stimulatory effect of SAN 9789 in darkness. Temperatures above 25 C decreased the effect of SAN 9789, with a temperature of 35 C completely inhibiting germination. The inhibitory effect of CHDC was strongly decreased at temperatures below 20 C. SAN 9789-induced germination in darkness was always the same (25 to 26% units increase in germination) even though the red light-stimulated germination differed with the seed batch.

Experiments were conducted to investigate the effects of shading on and location of the mother plant on germination and hormone content of Palmer amaranth seed. Increasing the shading from 0 to 87% decreased germination of fresh, viable seeds in dark from 25 to 12%. Abscisic acid (ABA) content of seeds from plants in 0% shade increased from 13.3 ng g−1 dry seed to 19.1 ng g−1 dry seed with 87% shade. Shading of the mother plant did not influence the 1,000-seed weight of Palmer amaranth. Seeds that matured in the top and middle third of the mother plant had 67 to 78% greater germination than those that matured in the bottom third of the mother plant. Endogenous gibberellic acid (GA) content of seeds did not differ between locations on the mother plant; however, the ABA content of seeds produced on the bottom third of the plant was 46 and 59% higher than the ABA content of seeds produced at the middle and top third of the plant, respectively. Endogenous ABA or GA content of seeds and 1,000-seed weight had no relationship with seed germination over and above the treatment effects. This research suggests that shading and plant location can influence germination of fresh, viable seeds of Palmer amaranth, which will be a dormancy strategy for seed dispersal over time.

Hydrilla is one of the most serious aquatic weed problems in the United States, and fluridone is the United States Environment Protection Agency (USEPA)-approved herbicide that provides relatively long-term systemic control. Mature (6-wk-old) and young (freshly planted from 10-cm apical shoot apices) hydrilla were grown in 540 L fiberglass vaults under short- (natural 8 to 10 hr light/14 to 16 hr dark photoperiod) or long- (artificially extended 16 h light/8 h dark photoperiod) day greenhouse conditions. Fluridone treatments of 0, 1, 5, and 10 µg L−1 were applied after 2 wk and maintained within each population and photoperiodic regime throughout the study. Short days promoted subterranean turion formation, but this effect was reduced by long days and 5 and 10 µg L−1 fluridone. Fluridone caused a reduction in chlorophyll and carotenoid levels but the effect on anthocyanin content was variable. Short days caused elevated anthocyanin, and this effect was diminished by fluridone. Fluridone reduced the abscisic acid content of mature apical stems and was higher under short days in younger plants. These studies provide further evidence that fluridone can be used as a fall herbicide application to reduce turion production.

Seed dormancy is a critical factor in determining seed persistence in the soil and can create oilseed rape (Brassica napus L.) volunteer problems in subsequent years. A 3-year field trial in south-west Germany investigated the effects of seed maturity on primary dormancy and disposition to secondary dormancy of ten oilseed rape varieties (lines) in 2009 and 2010, and of five imidazolinone-tolerant varieties (hybrids) in 2014. Fresh seeds were sampled weekly from about 30 d after flowering (DAF) until full maturity and tested for dormancy on the day of seed collection. Primary dormancy decreased from a high level of 70−99% at 30−40 DAF to 0−15% after 7−14 d, coinciding with embryo growth and depending on variety and year. For some oilseed rape varieties, 30−50% primary dormancy was still present in mature seeds. Depending on variety, disposition to secondary dormancy was nearly zero at the early stage of seed development, increased to its highest level during development, and decreased afterwards. Some varieties maintained a high level of secondary dormancy at maturity or during the entire seed development period. The correlation between primary dormancy and secondary dormancy was significantly positive at early seed development (r = 0.95, 50 DAF), but declined in mature seeds. Environmental conditions during ripening are also expected to affect dormancy dynamics. The deeper insights into dormancy formation of oilseed rape provide the possibility to improve harvest time and harvest method, and to better assess the potential for volunteer oilseed rape in following crops.

Knowledge about the hormonal control of grain dormancy and dormancy loss is essential in wheat, because low grain dormancy at maturity is associated with the problem of pre-harvest sprouting (PHS) when cool and rainy conditions occur before harvest. Low GA (gibberellin A) hormone sensitivity and high ABA (abscisic acid) sensitivity were associated with higher wheat grain dormancy and PHS tolerance. Grains of two PHS-tolerant cultivars were very dormant at maturity, and insensitive to GA stimulation of germination. More PHS-susceptible cultivars were less sensitive to ABA inhibition of germination, and were either more GA sensitive or germinated efficiently without GA at maturity. As grain dormancy was lost through dry afterripening or cold imbibition, grains first gained GA sensitivity and then lost ABA sensitivity. These changes in GA and ABA sensitivity can serve as landmarks defining stages of dormancy loss that cannot be discerned without hormone treatment. These dormancy stages can be used to compare different cultivars, seed lots and studies. Previous work showed that wheat afterripening is associated with decreasing ABA levels in imbibing seeds. Wheat grain dormancy loss through cold imbibition also led to decreased endogenous ABA levels, suggesting that reduced ABA signalling is a general mechanism triggering dormancy loss.