Barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] spikelets were collected from greenhouse-grown plants at various developmental stages. Caryopses contained in a single spikelet were dormant at maturity, but dormancy was overcome when the spikelets were dry afterripened at 23 C or were treated with high temperatures, acid scarification, or punctured with a scalpel. The season at which anthesis occurred affected the length of time for afterripening. Enhanced germination due to puncturing and scarification was not related to removal of a restriction to water entry. The effectiveness of puncturing in overcoming dormancy depended on moisture content of the spikelets at the time of puncturing. Above 18% moisture content germination percentage was low regardless of the dormancy-releasing treatment.

Wild and cultivated proso millet (Panicum miliaceum L. ♯ PANMI) showed increased height and dry mass with increasing photoperiod and flowered under all photoperiods. Increasing planting density decreased height and dry mass and slowed seedhead development in both types. Shading increased plant height and decreased dry mass of both millets and increased germination compared to unshaded treatments. Planting date did not affect germination of freshly collected seed of either millet. Wild proso millet seed had a low germination rate until 8 weeks after panicle emergence, and the rate increased to 22% after 10 weeks. Germination of cultivated proso millet seed was low for 5 weeks after panicle emergence and increased to 92% after 10 weeks.

Field studies were conducted to determine the effect of emergence timing on the fitness of the next generation as represented by seed mass, maturation, and afterripening of common waterhemp cohorts. Five natural cohorts were documented both in 2009 and 2010. Different maternal environments resulting from varied cohort emergence timings did not influence seed maturation time and seed mass, but had an inconsistent effect on seed afterripening. Here are our major findings. (1) Waterhemp cohorts needed similar amounts of time to generate viable seeds (20 to 27 d after flower initiation) and the seeds produced were of similar size (2.0 to 2.35 g), and (2) waterhemp has strong primary dormancy that may be released within 4 mo during the afterripening process, depending on the dormancy level. Seeds produced by later cohorts were more sensitive to the afterripening period, suggesting more flexibility in life strategy. Seeds from the 2009 cohorts had similar afterripening patterns; newly harvested seeds had strong primary dormancy (<10% germination), which was gradually released during dry storage and reached the maximum germination (>80%) rate 4 mo after harvest (MAH). However, germination then dropped to 40% 6 and 8 MAH, suggesting the induction of secondary seed dormancy. Strong primary dormancy at harvest for 2010 seeds was sustained in dry afterripening, perhaps because of higher dormancy level, which was the result of less-favorable parental environments brought by 10 to 30 times higher population densities and 2.5 to 5 times higher accumulative precipitation than in 2009 (see Wu and Owen 2014). We also tested the soil seed-bank seed population densities for each waterhemp cohort and found that early cohorts greatly influenced the seed population densities at the soil surface level and the turnover rate of the soil seed bank. Results from this research will provide insights into better management of waterhemp, targeting a better understanding of the seed bank.

The factual evidence for aquaporins, the constituents of water channels in cell membranes and operation of water channels is reviewed in developing, maturing and germinating seeds.

Maize (Zea mays L., cv. B73 × Mo17), wheat (Triticum aestivum L., cv. Clark), and soybean (Glycine max L. Merrill, cv. Elgin 87) were grown in the field and seed samples were collected at frequent intervals for the determination of seed fresh and dry weight and water potential of excised embryos (maize and wheat) and axes (soybean). Seed water concentration declined during seed development and the concentration at physiological maturity (PM, maximum seed dry weight) was highest in soybean (550–590 g kg−1 FW), lowest in maize (326–377 g kg−1) and intermediate in wheat (437 g kg−1). The embryo/axis water potential was relatively constant during much of seed filling before decreasing rapidly as the seeds approached PM and there was little variation among species (soybean −1.52 to −1.63 MPa, maize −1.61 to −1.99 MPa and wheat −1.66 MPa). Seed water concentration when 10% of the seeds germinated (radicle ≥3 mm) was highest in soybean (514 g kg−1), lowest in maize (332 g kg−1) and intermediate in wheat (345 g kg−1) while the water potential of the embryo/axis varied from −2.07 to −2.20 MPa across the three species. There was little variation in the water potential of the embryo/axis among species at the end of seed growth (PM) or at the beginning of germination. This similarity is consistent with the suggestion that the water status of critical seed structures may play a regulatory role in seed growth and germination.

The ability to initiate radicle elongation, or germination potential, occurs in developing embryos before the completion of seed maturation. Green embryos after the walking-stick stage in developing Arabidopsis thaliana seeds germinate when excised from seeds and incubated in Murashige–Skoog (MS) medium containing 1% sucrose. Germination potential is not observed during early embryogenesis at the globular, heart and torpedo stages. Here, we describe an Arabidopsis mutant with embryos arrested at early stages of development, but still exhibiting germination potential. The mutant, termed embryo ball (eb), produced shrunken seeds containing round or irregularly shaped embryos that did not germinate. The round embryos excised from developing eb seeds were capable of growing a primary root with root hairs when incubated in media. In contrast, cotyledons were absent at the apical region of the eb embryos, although the apical region produced leaf-like structures with trichomes, indicating vegetative leaf identity. These observations suggested that morphological maturation was not essential for the induction of germination potential. The eb embryos exhibited partial desiccation tolerance that is characteristic of mature embryos at later stages of development, suggesting that cell maturation was also independent of morphological maturation. The eb mutant provides novel information on cell and tissue identity in developmental biology, as well as a useful tool to dissect the mechanisms underlying the induction of germination potential in developing seeds.

A UK seed conservation collection of Anemone nemorosa L. seeds held at the Millennium Seed Bank (MSB) showed low viability in its first post-storage test. Because achenes of A. nemorosa are naturally dispersed when they are green, we tested the hypothesis that seeds may not be fully desiccation tolerant and storable at the time of natural dispersal, and that a post-harvest treatment could increase the proportion of desiccation-tolerant seeds. Achenes harvested at the point of natural dispersal in late May in 2003 and 2004 were either placed immediately on 1% water agar at 20°C (‘laboratory’ treatment), or placed in nylon sachets and buried in leaf litter among plants growing in the wild (‘field’ treatment). Samples were withdrawn at intervals over a period of 168 d and tested for desiccation tolerance (drying to 0.059 g H2O (g DW)− 1) and longevity (controlled ageing at 60% relative humidity and 45°C). An initial increase, followed by a decline, in the proportion of seeds surviving desiccation and in the longevity of both laboratory- and field-treated samples coincided with the development of embryos from globular to heart- and then torpedo-shaped. Developmental arrest was not required for the acquisition of desiccation tolerance, and continued growth and development of the embryo resulted in a loss of desiccation tolerance, similar to that seen in orthodox seeds upon radicle emergence. Furthermore, while A. nemorosa seeds, like many from the Ranunculaceae family, might be described as having morphological or morphophysiological dormancy, this lack of developmental arrest does not fit with the usual concept of dormancy. The implications of these results for the classification systems of seed-storage behaviour and dormancy, and for the long-term conservation of seeds of A. nemorosa, are discussed.

The germination of developing seeds is very uncommon and is generally associated with deficiencies in abscisic acid (ABA) synthesis or sensitivity. This paper examines the quantitative relationship between the inhibition of precocious germination and endogenous ABA in the embryonic axis (ABAa) of hydrated soybean [Glycine max (L.) Merr.] seeds, isolated after the completion of histodifferentiation and before the beginning of dehydration, as well as the magnitude and evolution of axis sensitivity to endogenous ABA during that period. Developing seeds harvested at 25, 30, 35, 40 and 45 d after anthesis (DAA) were subjected to incubation or washing to induce changes in ABA content. ABA content was measured by radioimmunoassay, using a monoclonal antibody against free ABA. Germinability was measured as the time to 50% germination (t50). Washing and incubation induced eight- and twofold increases, respectively, in the rate of ABAa decline compared with the in planta ABAa decline. The threshold ABAa for inhibition of precocious germination (ABAc) increased slightly from 25 to 40 DAA [1.15–1.66 μg ABA (g DW)− 1]. This contrasted with the substantial decline in ABAa [10.90–2.07 μg ABA (g DW)− 1] during the same period, and indicated that sensitivity to endogenous ABA of hydrated seeds was initially high and diminished slowly during development. The relationship between (ABAa–ABAc) and t50 was linear for immature seeds incubated before and after washing. Below the ABAc, there were no differences in the t50 of 25–45 DAA seeds. The ABAa contribution to the control of precocious soybean seed germination was evident, although other potentially interacting factors were also present.

Homologues of the pea SBP65, a late embryogenesis abundant (LEA) biotinylated protein that behaves as a putative sink for the free vitamin biotin during embryo development, were characterized biochemically in various plant species, including soybean, lentil, peanut, rape, cabbage, carrot and sugarbeet. Based on sequence homologies, the genome of Arabidopsis thaliana contains a gene putatively encoding a homologue of pea SBP65. These proteins exhibit two remarkable features. First, they only accumulate in seeds, particularly during late stages of embryo development. The results strongly suggest that these seed-specific biotinylated proteins belong to the class of plant proteins called seed maturation proteins, which are presumed to play major roles in embryo development. Secondly, covalent attachment of biotin occurs at a lysine residue within a conserved motif of (V/M)GKF, which shows no resemblance to the highly conserved AMKM tetrapeptide that houses the target lysine residue in the well-characterized biotin-dependent carboxylases and decarboxylases. These findings highlight novel structural features for protein biotinylation.

Seeds of Cenchrus ciliaris L. were produced under different hydro–photo–thermal environments with and without fertilizer. Dormancy loss of spikelets and extracted caryopses was tested during dry after-ripening at 40°C and 43% equilibrium relative humidity. Caryopses had higher initial germination and lost their dormancy faster than spikelets. Dormancy of both caryopses and spikelets generally decreased with an increase of maturation temperature and fertility, whereas dormancy increased if water stress was imposed during maturation. The latter effect was smaller when the mother plants were exposed to water stress after caryopses were fully formed than when water stress cycles were applied throughout maturation. Daylength extension (to 14 or 18 h d-1) by artificial light increased dormancy of both caryopses and spikelets. The effect of long days declined when plants were exposed to natural daylight for more than 10 h d-1. The after-ripening curves were consistent with the hypothesis that dormancy periods of individual seeds are normally distributed within each seed lot. Rates of loss of dormancy were quantified by the slopes of these curves. In a given experiment, these rates were identical for caryopses but not always for spikelets that matured in diverse environments. Even for caryopses, however, the slopes varied between experiments. Therefore, the results do not support the hypothesis that a dormancy model can be applied universally to all seed lots of Cenchrus ciliaris. Methods of predicting the period of after-ripening required to achieve desired levels of dormancy for reseeding degraded rangelands are discussed.

Methanol accumulates in maturing seeds, correlating with preharvest deterioration. Since the source of methanol may be from pectin de-methylation, methanol, cell wall uronic acid, pectin methyl esterification, pectinesterase (PE; EC 3.1.1.11) activity, and neutral sugar composition and partitioning of cell wall polysaccharides were determined during soybean (Glycine max [L.] Merrill) seed development, maturation, and desiccation in planta. Axis cell wall polysaccharides were more easily solubilized, richer in uronic acid, rhamnose, and xylose, and less rich in galactose than cotyledon cell wall polysaccharides. Methanol accumulated to 9.7 μg per two cotyledons and 0.5 μg per axis; total methanol decreased to 3 μg per two cotyledons during loss of green color. Total uronic acid increased from 0.12 to 0.27 mg per axis and 0.9 to 4 mg per cotyledon between 24 and 50 days after flowering (DAF). After loss of green color, pectin methyl esterification in axes increased from 7 to 24 mole% between 50 and 60 DAF but decreased to 14 mole%by 62 DAF in latter stages of seed desiccation. In cotyledons, methyl esterification ranged from 25 to 40 mole% and was 31 mole% after desiccation. PE activity increased 100 fold in axes, including a 30-fold increase in activity after loss of green color at 46 DAF. Cotyledon PE activity was 40-fold higher than in axes at 24 DAF, declined 75% by 56 DAF, and then increased 5 fold during desiccation. Pectin methyl de-esterification by PE is sufficient to be the sole source for methanol accumulation in seed tissues during development and maturation.