Dormant line M73 wild oat caryopses were utilized to develop a system for the culture of excised embryos, to evaluate whether embryo dormancy exists, and to investigate the physiological basis for breaking dormancy. Dormant embryos cultured on N6 medium solidified with 0.25% Bacto agar displayed 70% germination in 2 d compared with approximately 20% for the other gelling agents. The non-plant-based gelling agent gellum at a concentration of 0.25% was selected for further experiments on breaking dormancy after it was determined that concentrations ≥ 0.5% decreased the rate of germination. Amending N6 medium with concentrations of 0.1 to 10 μM gibberellic acid (GA) increased the rate and extent of germination. Embryos treated with 0 to 0.01 μM GA required 6 d to attain 90% germination. Germination of dormant embryos on N6 medium without GA suggested that either true embryo dormancy did not exist in M73 or some constituent of the N6 medium promoted breaking of dormancy. Subsequent experiments indicated that the 88 mM sucrose was the constituent in the N6 medium responsible for breaking dormancy. Concentrations of sucrose from 40 to 200 mM were effective in breaking dormancy. Ten μM GA increased the rate and extent of germination of embryos cultured with 88 to 200 mM sucrose. At 88 mM, fructose, maltose, glucose, and sucrose all broke embryo dormancy. Fructose was the most active soluble sugar for breaking embryo dormancy, promoting nearly 100% germination in 4 d. As with sucrose, there was an interaction between GA and the soluble sugars in breaking dormancy. Ten μM GA with 88 mM fructose provided nearly 100% germination in 1 d. Amylose, but not amylopectin or pullulan, may substitute for soluble sugars. However, with 10 μM GA amylose, amylopectin and pullulan were equally effective in breaking dormancy. Breaking dormancy of embryos on N6 medium was independent of temperatures from 12 to 24 C in the presence of GA, but in its absence the optimum was 12 C. Application of GA to dormant caryopses significantly increased and decreased the level of glucose and sucrose, respectively, in the embryo. Gibberellic acid had a similar effect on glucose and sucrose in the endosperm tissue, except the differences were not significant at all times after treatment. The change in carbohydrate metabolism, especially in embryo tissue, may be important when considered in context with the observation that soluble sugars and GA act independently in breaking dormancy in excised M73 embryos. Breaking wild oat embryo dormancy with GA may be mainly a substitution for sugar requirement.

Glyphosate [N-(phosphonomethyl)glycine] was applied in the spring and fall to leafy spurge (Euphorbia esula L. # EPHES) in the field at rates of 0.14 to 4.48 kg ai/ha. Fall applications of glyphosate at rates of 0.56 to 4.48 kg/ha stimulated axillary branching and caused an increase in the number of stems/m2 by the end of the following summer in a dense population. This was a result of shoot growth from buds on the crown region of the root system. The absorption and translocation of 14C-glyphosate applied to leaves of mature leafy spurge plants were evaluated at prebloom, full-bloom, and senescence phenological stages. Approximately 81% of the 14C-glyphosate applied to the leaves of senescing plants was absorbed. There was a decrease in the proportion of 14C translocated out of the treated leaf when applications were made after full bloom. Translocation of 14C to the treated stem, nontreated stems, root crown, and roots did not differ with phenological stage in 1983. Translocation and concentration of 14C in most plant parts in 1985 differed with phenological stage. Translocation to the crown buds as a percentage of the 14C absorbed was highest at the senescence stage. At senescence and before soil freezing, leafy spurge crown buds demonstrate transient but active elongation toward the soil surface. This active development may account for the enhanced translocation of 14C into the crown buds.

Root buds of leafy spurge (Euphorbia esula L. # EPHES) were found to be quiescent during most of the growing season due to correlative inhibition rather than innate dormancy. Excised root buds taken from plants that were fully flowering showed reduced elongation, indicating a period of innate dormancy. This innate dormancy could be eliminated by chilling plants for 8 days at 4 C. Root buds from plants showing late summer regrowth were no longer innately dormant. IAA (indole-3-acetic acid) and NAA (1-napthaleneacetic acid) completely inhibited the growth of excised leafy spurge root buds at concentrations of 10−3 and 10−5 M, respectively. A significant increase in root bud elongation was produced by 1 mM TIBA (2,3,5-triiodobenzoic acid) applied to stem and root tissue. These data provide further evidence for the involvement of IAA in correlative control of root bud growth in leafy spurge.

Dormancy is a critical factor for the survival and persistence of weedy species. Contemporary approaches can be used to identify genes that regulate dormancy directly or indirectly to elucidate key mechanisms, signals, and pathways. Several domesticated plant species have been used as model systems to mark quantitative trait loci (QTL) that affect dormancy in seeds and vegetative propagules directly. A few weedy species have also been used to mark QTL and to determine dormancy genes using microarray analysis. Given the number of serious weeds worldwide and the role that dormancy plays in their persistence, developing fundamental knowledge on dormancy is an important step toward developing new strategies for weed management. This paper describes current research and outlines some weeds that might be candidates for dormancy investigations using molecular genetic and genomics approaches. An underlying theme in the selection of weeds for dormancy investigations is their relation to crop species and the ability to adapt existing resources to investigate dormancy in weedy plants.

In vitro fertilized (IVF) human embryos have a high incidence of developmental arrest before the blastocyst stage, therefore characterization of the molecular mechanisms that regulate embryo development is urgently required. Post-transcriptional control by microRNAs (miRNAs) is one of the most investigated RNA control mechanisms, and is hypothesized to be involved actively in developmental arrest in preimplantation embryos. In this study, we extracted total RNA from mouse 2-cell and 4-cell embryos. Using a miRNA microarray, 192 miRNAs were found to be differentially expressed in 4-cell embryos and 2-cell embryos; 122 miRNAs were upregulated and 70 were downregulated in 4-cell embryos. The microarray results were confirmed by real-time quantitative RT-PCR for six miRNAs (mmu-miR-467h, mmu-miR-466d-3p, mmu-miR-292–5p, mmu-miR-154, mmu-miR-2145, and mmu-miR-706). Cdca4 and Tcf12 were identified as miR-154 target genes by target prediction analysis. This study provides a developmental map for a large number of miRNAs in 2-cell and 4-cell embryos. The function of these miRNAs and the mechanisms by which they modulate embryonic developmental arrest require further study. The results of this study have potential applications in the field of reproductive medicine.

Many research questions focused upon seed dormancy and germination remain unanswered due to problems created by inappropriate assumptions concerning the design and implementation of experiments. Lack of attention to the genetic background and growing conditions required for seed production and subsequent storage may compromise an investigator's ability to pool data or assimilate data trends due to variability in seed performance from year to year. Seed aging events during the afterripening process can be mistaken for those involved in the transition from the dormant to nondormant state. After imbibition, inaccurate criteria for and scoring of the germination event may lead to confusion of seed vs. seedling physiology and biochemistry. In addition, a sufficient number and proper spacing of data points during timecourse experiments are required to properly stage a sequence of events. Studies comparing dormant vs. nondormant seeds must be supplemented with kinetic experiments examining the effect of a dormancy-breaking treatment upon the transition between the dormant and nondormant states. In comparisons of the relative efficacy of various dormancy-breaking chemical treatments, the physical properties of substances under evaluation (e.g. lipophilicity) should be considered. In addition, since many dormancy-breaking chemicals are toxic to vegetative growth, there is a danger of introducing pharmacological artifacts that confuse interpretation of the results obtained. These toxic properties also necessitate the use of viability tests during construction of dose-response curves to avoid confusing seed death with dormancy. Seed scientists must also avail themselves of the extensive literature on developmental arrest in other organisms, which may generate fresh ideas for experimentation.

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.

The phenomenon of dormancy extends beyond the boundaries of the plant kingdom. While plant biologists typically associate dormancy-breaking treatments only with seeds, buds or tubers, these chemicals and environmental stimuli have much broader activity as general terminators of developmental arrest in other, non-plant species. The activation of growth by these treatments is associated with signal transduction processes, metabolic upregulation and changes in gene expression, in addition to other events that may or may not be species specific. The study of both the classic and current developmental arrest literature beyond the boundaries of plant biology may be helpful in generating useful ideas and analogies for meaningful experimental progress towards understanding seed dormancy.

Crude extract specific activities of thymidylate synthase, dUTPase, thymidine kinase and dihydrofolate reductase were high during the development of Caenorhabditis elegans, the dauer larva activities being similar to those previously determined in Trichinella spiralis and T. pseudospiralis muscle larvae (with the exception of thymidine kinase, not detected in Trichinella). High thymidylate synthase expression in developmentally arrested larvae, demonstrated also at the mRNA and protein levels, is in agreement with a global cell cycle arrest of dauer larvae and indicates this unusual cell cycle regulation pattern can be shared by developmentally arrested larvae of C. elegans and the two Trichnella species. Hence, the phenomenon may be characteristic for developmentally arrested larvae of different nematodes, rather than specific for the parasitic Trichinella muscle larvae. Endogenous C. elegans thymidylate synthase was purified and its molecular properties compared with those of the recombinant protein, expression of the latter in E. coli cells confirming the NCBI database sequence identity.