The great majority of seed proteins that are stored in the vacuole prior to desiccation are transported via the Golgi apparatus. In this organelle they are separated from other products of the secretory pathway. Evidence is accumulating that the mechanism for segregation of storage proteins is different from that of soluble proteins destined for lytic vacuoles: it rarely seems to require short targeting propeptides at the N- or C-terminus. Instead, the three-dimensional conformation of the protein appears to be a critical factor, leading to self-assembly into osmiophilic aggregates. Also unusual is that this process starts immediately after entry into the Golgi apparatus, i.e. at the cis-cisternae, rather than at the trans-pole where acid hydrolases are packaged into clathrin-coated vesicles. Storage protein aggregates accumulate into so-called “dense” vesicles at the periphery of the cisternae and are transported towards the trans-pole of the Golgi apparatus by cisternal progression. Before the dense vesicles are released, clathrin-coated vesicles form at their surface; however, the function of the latter remains the object of speculation. In other eukaryotes, delivery of Golgi-derived lumenal products to the vacuole does not occur directly, but via a pre-vacuolar compartment. There is evidence that this is also the case for plants, and in developing pea cotyledons the pre-vacuolar compartment takes the form of a large multivesicular body. Ultimately this appears to fuse in toto with the protein storage vacuole.

Peroxiredoxins are thiol–requiring antioxidants found in organisms ranging from bacteria to humans. They can be divided into two subgroups with either one or two conserved cysteine residues. In plants, 1–Cys peroxiredoxins have been identified in a number of grasses and cereals, and in the dicotyledonous species Arabidopsis thaliana. In contrast to other antioxidants, the 1–Cys peroxiredoxin genes are expressed solely in seeds, and only in the parts of the seeds surviving desiccation, i.e. the embryo and the aleurone layer. The expression pattern is characteristic of late embryogenesis–abundant genes. The PER1 protein of barley is present in high concentrations in the nucleus at the onset of desiccation. 1–Cys genes are expressed in a dormancy–related manner in mature seeds, in that transcript levels are high in imbibed dormant seeds, but disappear upon germination of their non–dormant counterparts. 1–Cys transcript levels can be up–regulated by ABA and osmotic stresses and suppressed by gibberellic acid. Two hypotheses have been put forward on the function of 1–Cys peroxiredoxins in seed physiology. First, these proteins might protect macromolecules of embryo and aleurone cells against damaging reactive oxygen species during seed desiccation and early imbibition. And second, seed peroxiredoxins might play a role in the maintenance of dormancy. These hypotheses are discussed, taking into account present knowledge of the biochemistry and molecular biology of peroxiredoxins.

The first cell cycle of Vicia faba L. seeds, which begins upon imbibition of dry seeds and is completed at the first mitosis after radicle protrusion, was characterised by the flow cytometry and immunodetection of nucleolin and tubulins in root tip meristems. Flow cytometry revealed highly synchronised profiles from the quiescent G1 phase to the late G2 phase, indicating uniform cell cycle progression within a root tip until the first mitosis. Using immunoblotting, nucleolin was detected in two distinct bands with the apparent molecular masses of 89 and 99 kD; the former was detected only in seeds imbibed at 4°C for 1 day whereas the latter was found at all stages examined, suggesting that the 89 kD nucleolin may be seed-specific. Unusual localization of nucleolin in cold-imbibed seeds, undetectable in half of the cells and present in nucleoplasm, was revealed by immunofluorescence microscopy. While α- and β-tubulin were detected at all stages and no significant changes in accumulation of the proteins were observed, few microtubules were detected at the beginning of germination when cells were still in the G1 phase, suggesting that microtubules may be depolymerized in the dry seeds.

The raffinose family of oligosaccharides (RFO) is present in relatively high levels in grain legume seeds. They are considered to be antinutritional compounds because they are, at least in part, believed to be responsible for causing flatulence in humans, which is the single most important factor in deterring people from including more legume seeds in their diet. The RFO also have important functions within the plant. They serve as transport metabolites in many legumes and have been proposed to play a positive role in cold acclimatisation and in conferring desiccation tolerance during seed maturation. These responses to environmental stresses are believed to result from the RFO acting as protecting agents for membrane bound-proteins. We have screened 70 pea lines from the test array of the John Innes Pisum germplasm collection, and lines were selected which had unusual RFO composition. The soluble sugars within these lines were quantified using High Performance Anion Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD), and variants were identified which were deficient in verbascose and one with a reduced level of raffinose. These selected lines are being used in a crossing programme designed to study the genetics of the RFO pathway and to produce new material to test the effect of specific RFO on the plant’s responses to the environment and on the diets of humans and animals.

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.

The relationships among water content, relative humidity and temperature were documented in both seeds and excised embryos of Coffea spp. using water sorption isotherms. Isotherms were constructed at 5, 15 and 25°C and calculated for lower temperatures. There were no apparent differences in sorption characteristics among whole seeds of several cultivars of C. arabica and among different species of Coffea. Excised embryos of genetically diverse Coffea germplasm also exhibited similar sorption characteristics, though there were substantial differences observed between embryos and whole seeds. The shape of isotherms of coffee seed tissues was intermediate to the reverse sigmoidal shape observed for orthodox seeds and the monotonic shape observed for desiccation intolerant plant tissues. The heats of sorption calculated for RH ≤ 25% for whole seeds of Coffea spp. were similar to orthodox seeds. In contrast, the heats of sorption calculated in the same RH range for excised embryos were intermediate between those of orthodox and recalcitrant embryos. Our observations are consistent with earlier observations that desiccation sensitivity or poor longevity is linked with low levels of water sorption at relative humidities less than 25%. An explanation for this remains elusive.

The effects of temperature, oxygen availability and salinity on seed germination in a population of Zostera marina L. from the Fleet, a tidal lagoon in southern England, were investigated in the laboratory. The fate of seeds under natural conditions was also monitored throughout the year from core samples and from seed samples buried in the sediment layer in nylon sachets. Supported with temperature, salinity and oxygen level measurements at the study site, field data confirmed that following seed dispersal in September/October, the majority of seeds germinated in the Fleet during the winter and early spring. In the laboratory, seeds germinated more rapidly and to a higher final percentage under anaerobic conditions compared to aerobic conditions. Under anaerobic conditions, rapid, near complete germination was possible at full salinity (30 g l-1) or when the salinity was reduced by 50%(15 g l-1). Under aerobic conditions, seeds germinated more rapidly at lower salinity. The effects of temperature were strongly dependent on the presence or absence of oxygen. Under anaerobic conditions, there was a pronounced optimum constant temperature for germination around 6°C, corresponding closely to the average water temperature recorded during the period mid-October to the end of March. On the other hand, under aerobic conditions, very low levels of germination were recorded at low temperatures. These findings support previously published evidence that seeds of Z. marina are well adapted to germinate in anaerobic sediments and that water temperature is the key environmental variable that determines the timing of germination under natural conditions. Previous misuse of dormancy terms to describe seed populations of Z. marina is discussed.

We tested whether seed mass and shape are good predictors of seed persistence in the soil of subhumid temperate montane grasslands of central Argentina. We plotted seed mass against variance of seed dimensions of 71 herbaceous species and obtained information on their persistence in the soil from a previous experiment on germinable seed banks. We identified a certain seed mass/shape combination beyond which no seed was persistent in the soil, with the exception of the annual Tagetes minuta. Our results confirmed the patterns previously reported for British species: small and compact seeds tend to persist in the soil for a longer time than big and elongated or flattened seeds. We suggest that the value of seed mass and shape as predictors of persistence in the soil can be extended beyond the British flora to herbaceous floras from other humid temperate regions.