Endo-β-mannanase (EC 3.2.1.78), an enzyme that mobilizes the endosperm cell walls of the lettuce (Lactuca sativa L.) seed, increases in activity in the micropylar and lateral regions of this tissue following the completion of germination. Its complementary DNA (cDNA) sequence (LsMan1) was determined using the polymerase chain reaction (PCR) with degenerate primers. The 3‘-end of the cDNA sequence was obtained by 3‘-end rapid amplification of cDNA ends (RACE), and the 5‘-end sequence by genome walking and 5‘-end RACE. The predicted amino acid sequence from the cDNA has a high identity with endo-β-mannanases present in other species (e.g. 67% identity with coffee β-1,4-mannan endohydrolase, 62% identity with tomato fruit endo-β-mannanase). Southern blot analysis suggests the presence of several members of an endo-β-mannanase gene family in the lettuce genome. Several isoforms of the enzyme, including three major ones, were detected by isoelectric focusing. Based on Northern blot analysis, accumulation of the endo-β-mannanase mRNA occurred only after lettuce seeds had germinated, and increased thereafter, although enzyme activity persisted after transcription declined.

Changes in population hydrotime parameters were determined during stratification in Polygonum aviculare L. seeds in order to model dormancy loss. Seeds buried in pots were stored at three temperatures (1.6, 7 and 12°C) for 110 d and were exhumed at regular intervals during the storage period. Exhumed seeds were incubated at different water potentials at 15°C and germination time courses were analysed to determine hydrotime parameters. The population mean base water potential (Ψb(50)) decreased concomitantly with seed dormancy, while the hydrotime constant (θH) and the standard deviation of base water potential (θΨb) displayed only minor changes. Based on these results, a model for simulating P. aviculare seed dormancy loss in relation to low temperature was developed. The model employs Ψb(50) as an index of mean seed population dormancy status. While Ψb(50) was allowed to vary as seeds were released from dormancy, θH and θΨb were held constant. Changes in Ψb(50) were related to the time and temperature, using a previously developed thermal stratification time index (Stt), which quantifies the accumulation of thermal time units below a threshold temperature required for dormancy loss to occur. Therefore, Ψb(50) varied in relation to the accumulation of Stt according to time and temperature. Model performance showed acceptable prediction of timing and percentage of germination of seeds buried in irrigated plots, but did not accurately predict germination of seeds exhumed from rain-fed plots. Thus, environmental factors other than temperature could also be involved in the regulation of dormancy status of buried seeds under field conditions.

An early difference in net protein phosphorylation activity occurred in dormant and after-ripened wheat (Triticum aestivum L.) grains within the first hour of imbibition at 30°C. Embryos from dry, dormant and after-ripened caryopses exhibited a high degree of protein phosphorylation, particularly of four proteins (68, 54, 51 and 42 kDa). Upon hydration, protein phosphorylation activity in dormant embryos decreased within 1 h and reached minimal phosphorylation activity by 5 h. Protein phosphorylation activity in after-ripened (germinable) embryos was not suppressed and remained high during germination. If the hydrated dormant embryos were dried, protein phosphorylation activity was restored. Application of the protein phosphatase inhibitor, okadaic acid, partially overcame dormancy and slowed the decrease in phosphorylation activity. These results suggested that reduction of protein phosphorylation activity slowed the rate of germination.

Seed germination and emergence are influenced by the position of seeds in the soil bank profile. Mediterranean grasslands are heavily dependent on seed banks, as these systems are mainly composed of annual species. Seed bank germination experiments in a greenhouse were conducted to analyse the role played by burial depth on seed bank dynamics in annual Mediterranean grasslands. Specifically, they addressed two objectives: (1) to assess the ability of seeds in the shallow layer of the soil bank to emerge when they are buried at different depths, and (2) to ascertain the ability of seeds from deep layers to germinate and emerge to the surface. The study also produced a depth profile of species and seeds. The results show that: (1) all species (100%) and the majority of viable seeds (98.9%) are situated in the first centimetre, with a significant fall in the number of species and seeds in the soil bank as depth increases; (2) for the majority of species (92%) and seeds (85.4%) in the shallow bank, the emergence percentage declines significantly with burial depth; and (3) seeds that are present in deep layers need to rise to the surface in order to produce seedlings. In conclusion, the function of the seed bank in Mediterranean grasslands depends on the number of species and seeds in it, but also on the seed position in the profile and vertical movements that enable them to reach the surface.

The germination dynamics of Ilex aquifolium L. were studied in central Spain using a 3-year field sowing experiment. Ten triads of bags (n = 30 seeds per bag) were buried randomly in four different microhabitats: inside the holly woodland, along the forest edge, in open grassland and under isolated shrubs. Bags were harvested annually, and seeds were analysed for seed viability, embryo development changes and germination. Holly seeds did not germinate until the second year. Embryo development and seed germination were faster at the forest edge, with a total germination proportion of 63% of sown seeds. Germination in the holly woodland (48%), under the shrubs (46%) and in grassland (46%) were very similar. Thus, recruitment of Ilex populations in this region is not limited by requirements for germination. After the third year, the seed bank was reduced by 80–90% of the initial seeds, so it can be considered as a short-persistent seed bank. Holly seed behaviour can enhance recruitment in semi-open areas, such as forest edges. Linked to the short persistence of its seed bank, this species can be considered an intermediate strategist between mature forest specialists and early successional species. This work contributes to a deeper knowledge of the germination ecology of I. aquifolium, in an effort to determine the relative importance of germination/ dormancy processes within holly population dynamics.