A recombinant protein (approximately 38 kDa by SDS/PAGE), induced by expression in Escherichia coli of a cDNA encoding a 1-aminocyclopropane-1-carboxylate oxidase (ACO) isolated from embryonic axes of Cicer arietinum, was recognized by an antibody raised against an apple ACO. A monoclonal antibody, obtained from recombinant ACO of chick-peas, was used for immunolocalization experiments in the embryonic axes of chick-pea seeds. The results indicate that most of the ACO was present in the apoplast of the cell wall. No evidence of this protein in the vacuole was detected. During germination of C. arietinum seeds, the production of ethylene was induced in the embryonic axis; its highest value was reached when radicle emergence occurred. At this moment there was an accumulation of 1-aminocyclopropane-1-carboxylate (ACC), transcription of ACO mRNA, as well as maximal ACO activity. In the post-germinative period the activity of the last step of ethylene biosynthesis decreased. This decrease was eliminated by indole-3-acetic acid (IAA), which caused significant transcription of ACO mRNA. It is suggested that gene expression of ACO may be induced by auxins and spermine (Spm) and inhibited by abscisic acid (ABA).

Schismus arabicus is a common annual grass occurring in the Negev Desert of Israel. Under unpredictable distribution and very small amounts of rain, as well as massive seed predation, this species has developed complementary sets of survival strategies that are influenced by biotic and abiotic environmental factors. One of these strategies is the phenotypic germination plasticity due to distinct caryopsis size groups. These groups occur in different percentages in the seed population, according to plant age at the time of seed development and maturation, but are not influenced by photoperiod. The size of the tiny, dust-like caryopses has an influence on the range of temperatures required for germination, the speed of germination and the final germination percentage reached between 5 and 30°C. These survival characteristics contribute to making S. arabicus one of the most common annual plant species in large areas of the Saharo-Arabian deserts and Irano-Turanian regions.

A developmentally regulated, novel β-amylase gene (ESDbamy) from Hordeum vulgare L. has 76% amino acid similarity with a previously described barley β-amylase. However, the 3' -end sequences of these β-amylases were different. The glycine-rich repeats, which are signature sequences of endosperm-type β-amylases, are absent in this novel ESDbamy gene. ESDbamy is highly expressed in the caryopsis during early development; however, it is not expressed in other tissues. Early seed development-specific (ESD) β-amylase mRNA levels and enzyme activities were higher in a shrunken endosperm mutant, seg8, than in the wild type. Seg8 has defective endosperm development, reduced starch synthesis and elevated monosaccharide concentrations

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.

The effects of seed priming on germination and endo-β-mannanase activity at inhibitory and non-inhibitory temperatures in thermosensitive ‘Dark Green Boston’ (DGB) and in thermotolerant ‘Everglades’ (EVE) lettuce were investigated. A single-seed endo-β-mannanase assay was used to follow the enzyme activity during priming. Seeds were primed at 15°C in aerated solutions of polyethylene glycol (PEG) with constant light, then redried. Primed and non-primed seeds germinated 100% at 20°C. At 35°C, non-primed and primed EVE seeds germinated 100%, whereas non-primed seeds of DGB germinated only 4%. During priming, endo-β-mannanase activity increased between 24 and 48 h in EVE and between 24 and 72 h in DGB after the beginning of osmotic imbibition. Endo-β-mannanase activity persisted in primed seeds following seed drying, was detected before radicle protrusion and was present in the micropylar region in front of the radicle tip. Higher enzyme activity was observed in primed seeds and EVE compared with non-primed and DGB seeds. The results suggest that priming may overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds due to increased endo-β-mannanase activity, possibly leading to a weakening of endosperm, thus overcoming thermodormancy.

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.

The relationship between seed mass variation and germinability in ten Abutilon theophrasti Medic. plants from a single agricultural population was examined under controlled environmental conditions. Seeds were collected in the autumn of 1995 and dry-stored in paper bags at 4°C until the start of trials in the spring of 1998. For each plant, between 549 and 1000 randomly selected seeds were separated into seven mass fractions based on individual seed mass, with classes ranging from <6.0 to >11.0mg. Subjecting the seeds to a cold stratification (4°C) period for 7d followed by a 21-d alternating day/night (25/14°C) temperature and 14-h photoperiod regime, resulted in 75% overall germination, 24% dormancy and 1% non-viable seeds. The majority of the seeds germinated within 7d of being exposed to the alternating temperature/light regimes. There was a significant (P < 0.001) difference in mean seed mass between the ten plants, with mean mass ranging from 8.8 to 9.6mg. For nine of the ten plants, the greatest proportion of seeds occurred in the 9.0–9.9mg mass fraction, while the lowest proportion of seeds was generally found within the 6.0–6.9mg mass fraction. Most seeds (96%) having a mass below 6.0mg were non-viable and, of the viable seeds, none germinated. There was a significant (P < 0.0001) relationship between seed mass and total germination, but not rate of germination. Germination peaked for seed mass fractions comprising the greatest proportion of total seeds (8.0–9.9mg) and was lowest for seeds with high or low mass. There was a weak trend of lower germinability for heavier seeds (>10.0mg) compared with lighter seeds. Maternal source had a significant effect (P < 0.05) on total germination and germination rate. Findings from this study suggest that intrapopulation variation in Abutilon theophrasti seed mass and its influence on germinability of seeds may play a significant role in maintaining a variable germination pattern and persistent seed bank in this troublesome annual agricultural weed

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.

Metabolic heat and CO2 production rates were measured by microcalorimetry during germination of two melon (Cucumis melo L.) accessions, Noy Yizre’el (a cold-sensitive cultivar) and Persia 202 (a cold-tolerant breeding line), differing in their ability to germinate at low temperature (14°C). In seeds that were imbibed at either 14 or 25°C, both heat production rates (φ) and CO2 evolution rates (RCO2) WERE HIGHER IN PERSIA 202 COMPARED TO NOY YIZRE’EL. AT 14°C, Φ AND RCO2of intact Noy Yizre’el seeds remained close to zero and germination was inhibited, but metabolic activity increased with time in decoated seeds (testa removed) and most embryos germinated. The presence of the testa had less effect on metabolic activity or germination of Persia 202 seeds at 14°C. The ratio of φ/RCO2(calorespirometric ratio) is an indication of the substrate being utilized for respiration, with lower values (∼455 kJ mol–1) associated with carbohydrate substrates and higher values (∼800 kJ mol–1) associated with lipid substrates. Removal of the testae of Noy Yizre’el seeds increased φ/RCO2 at 14°C, suggesting that improved oxygen supply to the embryo promotes a shift from carbohydrate to lipid respiratory substrates associated with germination. Consistent with this interpretation, when the hilum apertures of the seed coats were sealed with silicone, φ, RCO2 and φ/RCO2of Noy Yizre’el seeds remained low and germination was inhibited at 25°C, while in Persia 202 seeds the same treatment had relatively little effect on φand RCO2, φ/RCO2approached the value expected for lipid respiratory substrates (700 kJ mol–1), and germination occurred. This confirms earlier anatomical work indicating that the testae of Persia 202 seeds were more porous than were those of Noy Yizre’el seeds, contributing to the greater tolerance of Persia 202 seeds to low temperatures. Abscisic acid (ABA) was also inhibitory to melon seed germination; imbibition of seeds at 25°C in 250 μM ABA decreased φ and RCO2, and φ/RCO2 remained lower than in control seeds in both genotypes. This effect of ABA on metabolic activity could be a cause or consequence of inhibition of germination.

Previous studies on several floras have shown that species with small, rounded seeds tend to accumulate persistent seed banks in the soil, while species with larger, less compact seeds do not. The suggested underlying mechanism is predation. Small seeds experience less predation and are more likely to become buried, which itself offers significant protection from predation by vertebrates. The relationship between seed size and shape and persistence in the soil was examined for the flora of the Arasbaran Protected Area in northwest Iran. Seed size was related to persistence in the soil in Iran in the same way as in most other floras examined, but seed shape was not. It is suggested that predation prevents persistence of large seeds in most floras. Where large-seeded persistent species predominate, for example in Australia and (to a lesser extent) in New Zealand, other factors may interfere with the relationship between seed size and predation.

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.