Differences in fruit morphology among or within species might indicate differences in other regenerative traits, such as seed dormancy and germination. In species with physical dormancy (PY), environmental conditions are suggested to be responsible for dormancy break in field. Seeds of Vachellia caven have PY. This species exhibits two fruit morphs highly represented in Córdoba forests, Argentina: one is dehiscent and the other is indehiscent. In this study we performed a burial experiment with the aim to determine if the differences in V. caven fruit morphology were related to different patterns of PY break of their seeds in field conditions. We related these patterns to (1) environmental conditions that could influence the loss of PY, and (2) histological features of the lens zone. Seeds of both morphs exhibited dormancy break within 14 months of the start of the experiment, but with different patterns. The dehiscent morph showed an abrupt percentage of seeds that broke dormancy 14 months after the beginning of the experiment, probably after undergoing environmental changes similar to those suggested by the two-stage softening model. The indehiscent morph showed a gradual increase in seeds that broke dormancy, not clearly related to any of the environmental variables studied. No differences in seed coat structure of the lens zone were observed between morphs. The existence of both morphs could confer the species with higher possibilities of establishing and coping with environmental heterogeneity. Those characteristics contribute to the understanding of the success of this species in open and disturbed environments.

Raphanus raphanistrum (wild radish) is a highly competitive weed in winter crops. Integrated weed management practices and decision-making tools benefit from the ability to predict seed longevity and dormancy status in the soil seed bank, as well as time and density of emergence in the field. We wondered if unique values taken from databases could serve for modelling purposes, whatever the origins of the weed populations. We investigated dormancy and longevity of fruits buried in the soil over a four-year seed burial experiment of two highly contrasted populations that differ by their biogeographical origin (oceanic versus continental climate), their habitat (arable field versus undisturbed) and their fruit size (thick versus thin fruit wall). High viability persisted over two years, followed by a rapid reduction, especially for the ‘continental-undisturbed-thin’ population. Dormancy cycling, with dormancy at its lowest in October, was observed for the ‘oceanic-arable-thick’ population, whilst a slow decrease without clear seasonal pattern was found for the other population. These results indicate different ways of regulating seed persistence in the soil, which might be taken into account when building demographic models. These differences could be due to interactions between fruit wall thickness and the other factors; it is possible that a thicker fruit wall increases longevity by promoting dormancy by physical restriction, but depending on temperature. Thinner fruit walls would make plants display other adaptive strategies to maximize survival time in the soil seed bank. Studies involving more populations and isogenic material are needed to address this specific question.

Excised axes from cotton (Gossypium hirsutum L. cv. M-8, a double haploid) were imbibed in vitro for 3,6,9,12,18 and 24 h. Data for length, fresh and dry weight and percentage water showed that excised axes undergo a triphasic pattern of growth: an initial burst, a short lag phase and then protracted rapid growth. Analysis of protein content with SDS-PAGE, and of activities of amino-, carboxy- and endopeptidases provided data indicating a direct correlation between major axis elongation growth between 12 and 24 h and enzymatic breakdown of storage proteins (especially those of 48 kDa) by carboxy- and endopeptidase. Data for axes imbibed at 30°C and 0–5°C for 12, 18 and 24 h indicated that a reduction in length and percentage moisture in the cold occurred in parallel with reductions in carboxy- and endopeptidase activities but not in ami-nopeptidase activity. The tentative conclusion is that carboxy- and endopeptidase are probably synthesized de novo in the axis during imbibition and are important in initial breakdown of storage proteins for axial elongation growth.

Hydrothermal time (HTT) models describe the time course of seed germination for a population of seeds under specific temperature and water potential conditions. The parameters of the HTT model are usually estimated using either a linear regression, non-linear least squares estimation or a generalized linear regression model. There are problems with these approaches, including loss of information, and censoring and lack of independence in the germination data. Model estimation may require optimization, and this can have a heavy computational burden. Here, we compare non-linear regression with survival and Bayesian methods, to estimate HTT models for germination of two clover species. All three methods estimated similar HTT model parameters with similar root mean squared errors. However, the Bayesian approach allowed (1) efficient estimation of model parameters without the need for computation-intensive methods and (2) easy comparison of HTT parameters for the two clover species. HTT models that accounted for a species effect were superior to those that did not. Inspection of credibility intervals and estimated posterior distributions for the Bayesian HTT model shows that it is credible that most HTT model parameters were different for the two clover species, and these differences were consistent with known biological differences between species in their germination behaviour.

In this study, we characterized two sunflower (Helianthus annuus L.) lines with differential sensitivity to drought, the sensitive line B59 and the tolerant line B71. Using both lines, we compared the content of endogenous jasmonates (JAs) in dry and imbibed seeds from plants grown under irrigation and drought. Jasmonic acid (JA), 12-oxo-phytodienoic acid (OPDA), 11-hydroxyjasmonate (11-OH-JA) and 12-hydroxyjasmonate (12-OH-JA) were detected in dry and imbibed sunflower seeds. Seeds from plants grown under drought had a lower content of total JAs and exhibited higher germination percentages than seeds from irrigated plants, demonstrating that environmental conditions have a strong influence on the progeny. OPDA and 12-OH-JA were the main compounds found in dry seeds of both lines. Imbibed seeds showed an enhanced amount of total JAs with respect to dry seeds produced by plants grown in both soil moisture conditions. Imbibition triggered a dramatic OPDA increase in the embryo, suggesting a role of this compound in germination. We conclude that JAs patterns vary during sunflower germination and that the environmental conditions experienced by the mother plant modify the hormonal content of the seed progeny.

The cell cycle is regulated, at least partially, by protein phosphorylation, activity that is carried out by a series of calcium-independent protein kinases among which the p34cdc2 kinase plays a preponderant role. The behaviour of p34cdc2-like protein kinase(s) has been followed during germination of maize in the presence or absence of the synthetic cytokinin benzyladenine (BA). Whereas there is an increase in p34cdc2-like kinase(s) activity at 15 h of germination in the presence of BA, coinciding with a peak of Ca2+-independent kinase activity, the amount of either the transcript for p34cdc2 or of the corresponding protein(s) does not show much variation during the 0–24 h period of germination studied, whether the phytohormone is present or not. Benzyladenine stimulates the cell cycle and promotes an early mitosis during maize germination. We have found evidence that BA promotes the movement of the p34cdc2-like protein(s) to nuclei several hours before this takes place during germination of control seeds, and this may constitute part of the mechanism by which the phytohormone promotes cytokinesis in plants.

The Asteraceae with up to 30,000 species occurs on all continents except Antarctica and in all major vegetation zones on earth. Our primary aim was to consider cypselae dormancy-break and germination of Asteraceae in relation to ecology, vegetation zones and evolution. Cypselae are desiccation-tolerant and in various tribes, genera, species and life forms of Asteraceae are either non-dormant (ND) or have non-deep physiological dormancy (PD) at maturity. All six types of non-deep PD are found among the Asteraceae, and dormancy is broken by cold or warm stratification or by afterripening. Soil cypselae banks may be formed but mostly are short-lived. Much within-species variation in dormancy-break and germination has been found. Using data compiled for 1192 species in 373 genera and 35 tribes of Asteraceae, we considered ND and PD in relation to life form, vegetation zone and tribe. Senecioneae and Astereae had the best representation across the vegetation zones on earth. In evergreen and semi-evergreen rainforests, more species have ND than PD, but in all other vegetation zones, except alpine/high-latitude tundra (where ND and PD are equal), more species have PD than ND. Tribes in the basal and central grades and those in the Heliantheae Alliance have both ND and PD. The high diversity and lability of non-deep PD may have enhanced the rate of species diversification by promoting the survival of new species and/or species in new habitats that became available following globally disruptive events since the origin of the Asteraceae in the Late Cretaceous.

Seeds of Oryza sativa L. (desiccation tolerant, orthodox) completed each of five distinct stages of development approximately 7 days earlier than seeds of Porteresia coarctata (Roxb.) Tateoka (desiccation intolerant, recalcitrant), despite the fact that O. sativa plants matured under cooler conditions. Isolated embryos of O. sativa were more sensitive to rapid desiccation at 6 days post anthesis (DPA) compared with naked caryopses. More than 90% of the latter were desiccation tolerant at 8 DPA and at all stages tested the germination capacity and/or rate of germination was greater following drying. In contrast, drying resulted in a complete loss of viability in seeds of P. coarctata at all stages tested. In both species, abscisic acid (ABA) began to accumulate in embryos mid-way through development. At the respective peaks, the concentration of ABA in P. coarctata was twice that recorded in O. sativa confirming that ABA levels per se do not determine desiccation tolerance in seeds. The possibility that desiccation tolerance is linked to sensitivity to ABA is discussed.

Seed is a fertilized mature ovule, which possesses an embryonic plant. When the dry, mature seeds are subjected to imbibition, they release a wide range of organic substances, which include low molecular weight carbonyl compounds (gases and volatiles) and water-soluble organic substances (enzymes and polysaccharides). The volatile organic compounds (VOCs) are molecules of low molecular weight (300 g mol−1) and high vapour pressure (0.01 kPa at 20°C) and include diverse chemical compounds. The nature and emission kinetics of volatiles produced from seeds vary, depending on the moisture content of the seeds. Orthodox seeds stored at ‘low seed moisture content’ undergo seed deterioration, predominantly due to lipid peroxidation, initiated by autoxidation or enzymatic oxidation of unsaturated or polyunsaturated fatty acids. This peroxidation leads to emission of volatile compounds. The quantity of VOCs emitted is positively correlated with the advancement of seed deterioration. With respect to the seed germination process, exposure of seeds to ‘high moisture conditions’ leads to increased respiration, triggers glycolysis and mobilization of storage reserves, resulting in the emission of volatile metabolic products. The quantity of VOCs emitted on commencement of metabolic activity in germinating seeds depends on (1) vigour status and (2) amount of storage reserves. Since it has been established that there is a significant difference between high and low vigour seeds with respect to quantity and profile of VOCs emitted, there is great potential for utilizing the VOC profile to obtain a quick and reproducible test of vigour status of crop seeds. In order to harness the VOC profile for quick assessment of vigour status of seeds, research has to be taken up to develop standard protocols for fingerprinting of VOCs for the purpose of seed vigour assessment and to fix the standard volatile biomarker(s) specific to crop and vigour status of seeds.

There is a carboxypeptidase in mung bean seeds that is localized in the protein bodies, the same vacuoles in which seed storage proteins are sequestered. This carboxypeptidase, called carboxypeptidase I (or Cpase I) has been purified by a series of ion-exchange and gel filtration columns. The pure enzyme consists of a single polypeptide chain with a MW of 41700 by SDS-PAGE or 42000 by size-exclusion HPLC. It has a pl of 4.36 and is a serine carboxypeptidase as shown by its inactivation by phenylmethylsulfonyl fluoride, and its resistance to other proteolytic inhibitory reagents. A survey of its activity with Cbz-dipeptides shows preference for C-terminal amino acids that are large, hydrophobic residues, and a small aliphatic amino acid such as alanine, but not glycine, at the penultimate amino acid residue. Cpase I can convert a trypsin inhibitor of the mung bean to its proteolytic intermediate lacking four amino acid residues at its C-terminus. This proteolytic intermediate is detected in the mung bean cotyledons during early growth. Levels of both the activity and immunological cross-reacting forms of this enzyme start high and decrease during early growth.

The first cell cycle of Vicia faba L. seeds, which begins upon imbibition of dry seeds and is completed at the first mitosis after radicle protrusion, was characterised by the flow cytometry and immunodetection of nucleolin and tubulins in root tip meristems. Flow cytometry revealed highly synchronised profiles from the quiescent G1 phase to the late G2 phase, indicating uniform cell cycle progression within a root tip until the first mitosis. Using immunoblotting, nucleolin was detected in two distinct bands with the apparent molecular masses of 89 and 99 kD; the former was detected only in seeds imbibed at 4°C for 1 day whereas the latter was found at all stages examined, suggesting that the 89 kD nucleolin may be seed-specific. Unusual localization of nucleolin in cold-imbibed seeds, undetectable in half of the cells and present in nucleoplasm, was revealed by immunofluorescence microscopy. While α- and β-tubulin were detected at all stages and no significant changes in accumulation of the proteins were observed, few microtubules were detected at the beginning of germination when cells were still in the G1 phase, suggesting that microtubules may be depolymerized in the dry seeds.

Although it has been speculated that seeds of the gymnosperm family Podocarpaceae have an underdeveloped embryo, no detailed studies have been done to definitively answer this question. Our purpose was to determine if embryos in seeds of two species of Podocarpaceae, Podocarpus costalis and Nageia nagi, from Taiwan are underdeveloped and to examine the kind of dormancy the seeds have. Embryos in fresh seeds of P. costalis were 4.6 ± 0.5 mm long, and they increased in length by about 54% before radicle emergence (germination), demonstrating that the embryo is underdeveloped at seed maturity. Seeds germinated to >90% at 30/20, 25/15 and 25°C in light in ≤ 4 weeks, without any cold stratification pretreatment. Thus, seeds of P. costalis have morphological dormancy (MD). Embryos in fresh seeds of N. nagi were 7.4 ± 0.8 mm long and they increased in length by about 39% before radicle emergence (germination) occurred, indicating that the embryo is underdeveloped at seed maturity. Seeds germinated to < 25% at 30/20 and 25°C in light in 4 weeks but to >90% at the same temperatures in 12 weeks. Thus, most seeds of N. nagi have morphophysiological dormancy (MPD). Although underdeveloped embryos are considered to be a primitive condition in seed plants, they also occur in the most advanced orders. The occurrence of underdeveloped embryos in Podocarpaceae documents that they are not restricted to a basal clade in gymnosperms.

Germination of seeds of some summer annuals in Kentucky (eastern USA) in late-winter lead to the hypothesis that under present climate conditions the whole length of the winter cold stratification (CS) period is not required for dormancy-break of seeds of summer annuals with physiological dormancy (PD). We evaluated our data from germination phenology studies of 45 species (69 datasets) and buried-seed studies of 33 species (44 datasets). We determined time and temperature of germination after CS and percentage of the total number of hours of CS during winter (% of winter CS) seeds received prior to start of germination. In the phenology studies, mean temperature during the week of first germination for C3 and C4 species was 11.1 and 14.4°C, respectively, and % of winter CS was 80.8 and 87.4, respectively. In the buried-seed studies, % of CS for C3 and C4 species was 40.8 and 48.1, respectively, when they germinated to 25% at 20/10°C. For 32 of 33 species in the buried-seed studies, the minimum temperature at which seeds germinated decreased with increased CS; thus, seeds had Type 2 non-deep PD. The time of germination is controlled by a number of hours of CS, a decrease in minimum temperature at which seeds can germinate and a temperature increase in early spring. Seeds can germinate at relatively high temperatures as early as December and January, but they continue to be CS until spring. Temperature increases in eastern North America due to global warming are not likely to inhibit the germination of summer annuals with PD in spring.

Seeds of the narrow-endemic Solidago shortii and of the geographically-widespread S. altissima and S. nemoralis buried in December 1993 were exhumed in June 1995 and given 10 cycles of 1 day wet/5 days dry, 9 of 2/5, 8 of 3/5, 7 of 4/5 and 6 of 5/5 in light at 30/15°C; the control was kept continuously wet during the experiment. Seeds of the three species incubated on wet substrate for 3, 4 or 5 days germinated to ≥47% during the first cycle. On the other hand, seeds kept moist 2 days germinated to only 4–26% in the first cycle, and none kept moist for 1 day germinated. Cumulative germination percentages of seeds of all three species at the end of the final cycle of the 1/5 treatment were 0–4%. In the 2/5 treatment, cumulative germination percentages of S. altissima and S. shortii seeds at the end of the final cycle were 50 and 41%, respectively, but that of S. nemoralis was only 4%. For all three species, cumulative germination percentages were ≥55% at the end of the final cycle of the 3/5, 4/5 and 5/5 treatments. Control seeds of the three species germinated to 85–99% after 2 weeks, and no additional seeds germinated during the remainder of the experiment. High percentages of seeds were viable in the treatments and control at the end of the experiment; however, some seeds of S. nemoralis and S. shortii given 1/5, 2/5 and 3/5 treatments became dormant. The ecological implication of this study is that seeds of the three species will not germinate on the soil surface after brief rainfall events in summer. The germination response of the narrow endemic is similar to that of its two geographically-widespread congeners.

Osmotic and ionic effects of NaCl were investigated in germinating wheat. Approximately isotonic solutions of NaCl and sorbitol inhibited germination and seedling growth to similar degrees. When dry kernels were pre-imbibed in salt for 24 h and then transferred to water, germination was equivalent to that of kernels imbibed continuously in water and the development of embryos was delayed to about the same extent as kernels pre-imbibed in sorbitol for 24 h. Measurements of water uptake, respiration, biosynthetic activities and rubidium uptake in embryos dissected from grains imbibed in NaCI or sorbitol for the first 24 h demonstrated that salt supplied to dry kernels closely mimicked sorbitol in counteracting the reactivation of embryo metabolism. No toxic effects of salt were observed when dry kernels were pre-imbibed in very high NaCI concentrations for 24 h and then transferred to water, even though embryo sodium contents increased considerably. Ultrastructural observations of embryo tissue further showed that salt influx into dry grains did not produce ion-specific damage in cell organization. On the other hand, salt specific effects became evident when the 24 h salt exposure was applied to kernels pre-hydrated for 24 h and, even more, for 30 h. We conclude that in wheat the inhibition of germination by salt corresponds to that induced by an osmoticum, provided that the caryopsis has not reached the stage of germination associated with active embryo expansion.

In central Asia, Agriophyllum squarrosum is the first species to become established during natural succession on sand dunes. However, low germination percentages and thus poor stand establishment greatly inhibit the use of this key species in the stabilization of dunes. The aim of this review is to critically analyse published information on the seed biology of A. squarrosum with particular reference to identifying the factors limiting germination of seeds sown in the field. A conceptual model is used to illustrate the complexities of factors as well as the unknowns we found about the seed/seedling stage of the life cycle of this sand dune annual. A major result of this review is that we now know that high germination percentages can be obtained by storing freshly collected seeds dry at room temperatures for 2 to 3 months to allow dormancy break to occur via afterripening, and then storing them dry at low (e.g. 4–5°C) temperature to prevent them from entering secondary dormancy. Non-dormant seeds should be sown in the field in late spring when wind-blown sand will cover them, thus ensuring that they are in darkness, which promotes germination, at the time summer rains occur.

The heat production of seeds during germination comes from metabolism as well as hydration. Previous studies either lack continuous measurements, or are based on samples composed of more than one seed, thus failing to characterize differences among the critical phases of germination. This study examines the potential of isothermal calorimetry to characterize water uptake and metabolism in single seeds. Seeds of malting barley (Hordeum vulgare L.) and winterfat [Krascheninnikovia lanata (Pursh) A.D.J. Meeuse & Smit], two species with contrasting seed size, structure, composition and selection history, were used to determine patterns of heat production rate by isothermal calorimetry during water uptake and germination. Embryos of malting barley contributed less than 4% of total seed weight, and metabolic heat production during Phase I of germination was negligible compared to that due to hydration. Embryos accounted for 74% of seed mass for winterfat, and the majority of heat produced in Phase I was due to metabolic heat release. The total heat production rate in Phase I decreased rapidly in malting barley due to slowing of hydration reactions, but increased gradually in winterfat due to an increasing metabolic rate. The heat production rate at the end of Phase II was about twice as high in malting barley as in winterfat. This indicates a higher metabolic activity for malting barley than for winterfat seeds during germination, which may have also contributed to the rapid increase in the heat production rate of malting barley seedlings during Phase III, compared to the gradual increase in heat production rate of winterfat. The comparison between excised embryos and intact seeds indicates that the covering tissues delay radicle emergence in malting barley, but not in winterfat, due to differences in seed structure between the two species.

During the maturation of dicotyledonous seeds, organic carbon, nitrogen and sulphur are stored in protein storage vacuoles (PSVs) as storage globulins. Several studies point to the coexistence of storage proteins with proteases responsible for their degradation inside PSVs. Different mechanisms have been proposed to explain why there is no proteolysis during this period. Protein aggregation to form large supramolecular structures resistant to proteolytic attack could be the reason. However, during germination, and particularly following its completion, the globulin aggregates must undergo disintegration to allow protease attack for protein reserve mobilization. Based on the well-described concentration-dependent ability of Ca2+ and Mg2+ to promote in vitro aggregation and disaggregation of globulins, we explored a possible role for these alkaline earth cations in globulin packaging and mobilization. Ca2+ and Mg2+ measurements in purified PSVs [6.37 μmol and 43.9 μmol g− 1 dry weight (DW) of cotyledons, respectively] showed the presence of these two alkaline earth cations within this compartment. To our knowledge, this is the first time that Ca2+ and Mg2+ have been quantified in purified PSVs from Lupinus albus seeds. Considering the importance of these two alkaline earth cations inside PSVs, which represent 14.6% and 60.7% of the total seed Mg2+and Ca2+, respectively, globulin aggregation and disaggregation profiles were assayed using experimental conditions closer to those that are physiologically present (proportion of Ca2+ and Mg2+, and acidic pH). Based on: (1) the high in vivo abundance of Ca2+ and Mg2+ inside PSVs; and (2) globulin aggregation and disaggregation profiles, together with structural and physiological evidence already reported in the literature, an important physiological role for Ca2+ and Mg2+ in globulin packaging and mobilization inside PSVs is suggested.

The search for germination-specific genes has been a laborious and unrewarding task, since many of the genes expressed during germination are also expressed in embryogenesis or in other developmental stages. By using mRNA differential display of transcript populations from maize (Zea mays L.) embryo axes, germinated for different times with or without a previous osmopriming treatment, a 682 bp cDNA was isolated that was present only after 24 h germination, and absent during osmopriming or during early germination. Screening of a cDNA library using the 682 bp probe yielded a 1554 bp cDNA that contained an open reading frame coding for 436 amino acids. This gene, referred to as ZmAA9-24, was expressed in root tissues, but was not detected in shoot or leaf tissues. Expression of ZmAA9-24 occurred earlier during germination (by 15 h) if embryo axes were imbibed in the presence of cytokinins or if seeds were previously osmoprimed. The predicted protein sequence of ZmAA9-24 is 39.6% identical to the product of the recently identified Arabidopsis gene COBRA (54.5% in the central region), which appears to participate in the regulation of cell expansion, particularly in roots, and belongs to the glycosylphosphatidylinositol (GPI)-anchored protein family. ZmAA9-24 expression might be regulated by both cell expansion and the cell cycle, processes that have a central role during seed germination.

Proteomic approaches based on two-dimensional gel electrophoresis, mass spectrometry and database search are widely used to address questions about the development, physiology and quality of seeds. Identification of proteins is of great importance in proteomic analyses. For seed crops without full genome information, cross-species protein identification by mass spectrometry-driven sequence similarity search can be used. However, this approach is risky due to protein polymorphism between different species. Species-specific expressed sequence tag (EST) databases are an invaluable resource, which complements mass spectrometry data analysis for protein identification. Here, we illustrate a modified method of protein identification and characterization using species-specific EST databases and peptide mass fingerprinting with an example of protein identification. This method is reliable, supplements the existing methods, and improves the efficiency and accuracy of protein identification for seed crops for which complete genome information is not available.