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.

A common feature of desiccation-tolerant organisms, such as orthodox seeds, is the presence of large quantities of sugars, especially di- and oligosaccharides. These sugars may be one component of the suite of adaptations that allow anhydrobiotes to survive the loss of most of their cellular water. This paper describes the physical effects of dehydration on cellular ultrastructure, with particular emphasis on membranes, and explains quantitatively how sugars and other solutes can influence these physical effects. As a result of dehydration, the surfaces of membranes are brought into close approach, which causes physical stresses that can lead to a variety of effects, including demixing of membrane components and fluid-to-gel phase transitions of membrane lipids. The presence of small solutes, such as sugars, between membranes can limit their close approach and, thereby, diminish the physical stresses that cause lipid fluid-to-gel phase transitions to occur during dehydration. Thus, in the presence of intermembrane sugars, the lipid fluid-to-gel phase transition temperature (Tm) does not increase as much as it does in the absence of sugars. Vitrification of the intermembrane sugar solution has the additional effect of adding a mechanical resistance to the lipid phase transition; therefore, when sugars vitrify between fluid phase bilayers, Tm is depressed below its fully hydrated value (To). These effects occur only for solutes small enough to remain in very narrow spaces between membranes at low hydration. Large solutes, such as polymers, may be excluded from such regions and, therefore, do not diminish the physical forces that lead to membrane changes at low hydration.

To determine whether seeds of the weedy shrub Wigandia urens, from the Valley of Mexico, undergo natural priming when buried in soil, comparative experiments were performed with seeds: (1) harvested directly from the plants; (2) buried in three natural habitat conditions; and (3) laboratory primed with polyethylene glycol. Seeds were sown in a growth chamber and in a shade house. Final germination percentages, emergence, germination and emergence rates, survival and initial growth were determined. Burial and priming enhanced the germination and emergence parameters evaluated in the laboratory and in the shade house. Effects of treatments on survival were not significantly different. Nevertheless, burial improved emergence and mean survival, and induced differences in specific leaf area of seedlings that could have ecological significance. Heat-stable proteins were extracted and electrophoresed. Proteins formed in W. urens seeds during burial had molecular weights (14–21 kDa) similar to those reported for late embryogenesis abundant (LEA) proteins induced by priming in other species. Nevertheless, the presence and abundance of proteins expressed (14–23, 36 and more than 45 kDa) differed among control, primed and buried seeds. During soil burial, molecular and physiological responses were induced that were similar to the effects of priming.

Cucurbita maxima Duch. cv. Warted Hubbard, which produces large fruits with many seeds, was used as a test system to study changes in several mineral nutrients during seed formation. Developing embryos increased markedly in weight, size and oil content. Energy dispersive X-ray (EDX) analysis was carried out on mineral nutrient storage globoids in developing Cucurbita cotyledons from 4 to 9 weeks after pollination. Phosphorus peak-to-background (p/b) and potassium p/b ratios increased slightly after the fourth week, while magnesium p/b ratios remained unchanged. The calcium p/b ratio was statistically higher at 4 weeks than in the subsequent weeks. Traces of iron and zinc were found in most of the globoids at all fruit ages. The zinc p/b ratio was higher in globoids at 4 weeks than at 9 weeks. Traces of manganese were detectable in only 18% of the globoids at 4 weeks and not detectable in any globoids at 9 weeks. The frequency of the small globoids of 0.25 μm in diameter was the highest at 4 weeks and was zero at 9 weeks. The frequency of the larger globoids increased progressively from 4 to 9 weeks. As the spherical globoids increased in size and hence in volume, there was a 6.4-fold increase in the embryo phytic acid, which is the main component of globoids. On a whole embryo basis, P content increased 4.5-fold, K 3.3-fold, Mg 5.4-fold and Ca 3.2-fold from the fourth to the ninth week.

Cell cycle activities are initiated following imbibition of non-dormant seeds. However, it is not known whether cell cycle related events other than DNA replication also remain suppressed in imbibed dormant seeds. The objective of this study was to demonstrate that the transitions between the non-dormant and dormant (both primary and secondary) states are reflected in cell cycle events, such as DNA replication and the changing patterns of the microtubular cytoskeleton involved in the processes of growth and development. The present studies were conducted on seeds from tomato (Lycopersicon esculentum cv. Moneymaker) that possessed primary dormancy or were manipulated to attain secondary dormancy. In addition, a non-dormant abscisic acid (ABA)-deficient mutant, sitw, was used. DNA replication, as measured by flow cytometry, and β-tubulin accumulation, analysed by immunoblotting, were compared with immunocytological studies of active DNA synthesis and microtubular cytoskeleton formation. It is shown that the depth of dormancy, which distinguishes primary and secondary dormancy, may depend on the progression of the cell cycle prior to the induction of dormancy.

Abstract A partial cDNA fragment (1.1kb) of protease C1, an enzyme that initiates the proteolytic degradation of the β-conglycinin storage proteins in the soybean (Glycine max [L.] Merrill. cv. Amsoy 71) through limited action at Glurich regions, has been cloned by reverse transcription-polymerase chain reaction (RT-PCR). The sequence was extended toward the 5' end by another 314 bases. The nucleotide sequence shows that protease C1 belongs to the subtilisin family of serine proteases. The sequence encompasses the critical Asp, His and Ser residues of the catalytic triad, as well as the Asn at the binding site. Northern analysis shows the presence of a 2.5kb mRNA not only in seedling cotyledons, but also in developing seeds. The developing seeds, and even dry seeds, exhibit phenylmethylsulfonyl fluoride (PMSF) and EDTA-sensitive protease activity that only cleaves the α- and α'-, but not the β-subunits, of soybean β-conglycinin. The discrete proteolytic intermediates produced are of the same sizes as those produced by pure enzyme, as are the final 50 kDa and 48 kDa products. The activity is also sensitive to inhibition by synthetic poly-L-Glu, all characteristics of purified protease C1. These data suggest that protease C1, or an enzyme very similar to it, is synthesized in a form that is active in vitro. Because seeds do accumulate β-conglycinin and because there is very little evidence of the proteolytic products of protease C1 action in extracts of dry seeds, one can surmise that the protease C1 is not particularly active in vivo during seed maturation. GenBank lists the sequence of the 1.1kb fragment with accession number AAD02075.

Patterns of dormancy and smoke responsiveness in artificially buried seeds were investigated in eight native plant species from the species-rich mediterranean-type climate zone of south-western Australia. A comparison was made between germination and viability behaviour of shelf- and field-soil-stored seed, with and without smoke treatment, at least every 3 months. These comparisons corresponded with each of the four seasons. The species chosen germinated with the aid of smoke under field or glasshouse conditions (termed ‘dormant’; n = 4) or produced low and variable germination under glasshouse conditions with smoke (termed ‘deeply dormant’; n = 4). Three trends were observed in viability of soil-stored seeds over 450 d: no decline, gradual decline or late-onset decline. In addition, various germination responses to soil burial and aerosol smoke were observed. Burial was not required for optimal germination in Anigozanthos manglesii. However, for all other species tested, maximum germination was observed only following a period of burial. This was manifested in a germination response without smoke after a short period of burial (Stylidium affine and Conospermum triplinervium) or a longer period of burial (Conostylis neocymosa, Hibbertia commutata, Leucopogon conostephioides, Stirlingia latifolia and Stylidium crossocephalum). Smoke treatment led to high germination in buried seed of S. affine, S. crossocephalum and H. commutata. The patterns of germination detected in this limited number of species indicate that a variety of mechanisms may exist, both temporally and spatially, in south-western Australian species, and support further research of this type for horticulture and land restoration.

A model has been developed to simulate the annual dormancy cycle of seeds of light-requiring species in the seed bank and the germination of exhumed seeds after irradiation. Simulation of dormancy and germination is based on a physiological model concerning the action of phytochrome in the seed. Dormancy is related to the amount of a hypothetical phytochrome receptor, which fluctuates in an annual pattern. Relief of dormancy is equivalent to an increase in the amount of receptor, and induction of dormancy is equivalent to a decrease in the amount of receptor. Annual changes in temperature are the driving force for annual changes in the amount of phytochrome receptor in seeds that are buried in the seed bank. From the average amount of phytochrome receptor in the seeds of a population, the model calculates the germination percentage that is reached when a seed sample from the population is exhumed, irradiated and incubated at a given temperature in darkness. In the model, relief of dormancy results in a widening of the range of temperatures over which germination can occur, and induction of dormancy results in a narrowing of this range. Model parameters were estimated by fitting the model to data from a burial experiment with seeds of Polygonum persicaria L., Chenopodium album L. and Spergula arvensis L. At regular time intervals during 3 years, subsamples of these seeds were exhumed and tested for germination in the laboratory. The simulation model gave a good description of the observed cyclic changes in germinability of exhumed seeds.

Soybean (Glycine max (L.) Merr.) seeds with elevated or reduced percentages of palmitate and elevated percentages of stearate were compared with seeds of typical composition in tests for germination, seedling growth rate and leachate conductivity. In general, seeds with altered compositions did well in these physiological tests, but their vigour tended to be negatively correlated with the percentages of stearate and palmitate in various lipid classes.