Raffinose family oligosaccharides (RFOs) are of almost ubiquitous occurrence in plant seeds. They accumulate during seed development and disappear rapidly during germination. The biosynthesis of raffinose, the first member of the series, proceeds by addition of a galactosyl unit to sucrose. Galactinol, a galactosyl derivative of myo-inositol, acts as a galactosyl donor. It is synthesized from UDP-D-GALACTOSE AND MYO-INOSITOL. STACHYOSE, VERBASCOSE AND AJUGOSE, THE NEXT HIGHER RFOS, ARE EITHER SYNTHESIZED BY GALACTINOL-DEPENDENT GALACTOSYLTRANSFERASES OR BY TRANSFER OF GALACTOSYL UNITS BETWEEN TWO RFO MOLECULES. IN SEEDS, THE METABOLISM OF METHYLATED INOSITOLS, SUCH AS D-ononitol and D-pinitol, is linked with the RFO pathway. In contrast to myo-inositol, these cyclitols are galactosylated by transfer of galactosyl residues from galactinol and not from UDP-D-galactose. However, the resulting galactosyl cyclitols can replace galactinol as galactosyl donors for the biosynthesis of stachyose. These recently discovered branches of the RFO pathway are active in seeds of a range of crop species, especially in legumes. We focus here on the biochemistry and molecular biology of the enzymes of RFO and galactosyl cyclitol biosynthesis. The metabolic control and hormonal regulation of the pathway during seed development and germination is discussed. The controversial role of α-galactosidases, which are believed to hydrolyse RFOs during germination, is reviewed critically.

Lipoxygenases are widely distributed in the animal and plant kingdoms. These enzymes catalyse the hydroperoxidation of polyunsaturated fatty acids containing cis,cis-1,4-pentadiene moieties. Multiple isoenzymes, with different biochemical properties and tissue distribution, have been described for many plants. Lipoxygenases occur in vegetative tissues, but also accumulate in various seeds, and especially in leguminous seeds. Although several functions have been proposed for vegetative lipoxygenases, the roles of seed lipoxygenases remain enigmatic. In this review we discuss whether physiological functions assigned to vegetative lipoxygenases can be extended to seed isoforms.

A commercially available smoke-water solution (Seed Starter®) stimulated the germination of caryopses and intact florets of Avena fatuaL. The solution was most effective when diluted (5–50%) and presented to intact or dehulled grain that had received a short period of dry after-ripening. It was less effective when applied at full strength or to grains that had been freshly harvested. The same stimulatory effect was observed in partly after-ripened caryopses of nine different wild oat biotypes obtained from three different cropping regions of the world. When freshly harvested caryopses were re-tested with the commercial solution (100%) for just 7 days prior to placement on to distilled water, a much higher germination percentage was possible than seen with continuous smoke-water incubation. The stimulatory ability of smoke water was more closely matched to that of gibberellic acid than to potassium nitrate, which had little or no effect on freshly harvested caryopses. The smoke-water solution (5–100%) was tested on the germination of 18 other cool temperate arable weed species. All monocotyledonous species tested (viz. Avena sterilis ssp. ludoviciana L., Alopecurus myosuroides, Sorghum halepense, Phalaris paradoxa) responded positively, while those of the dicotyledonous species were either strongly stimulated (≥40%stimulation Malva neglecta), moderately stimulated (≥20% stimulation Galium aparine, Veronica persica), slightly stimulated (Polygonum persicaria, P. pennsylvanicum, Fallopia convolvulus), unaffected (P. aviculare, Sinapis arvensis, Heracleum sphondylium, Angelica sylvestris, Mercurialis annua, Veronica hederifolia) or inhibited (Lamium purpureum). The optimal concentrations required to stimulate germination of the monocotyledonous species were similar to those observed for A. fatua (5–10%). However, for the dicotyledonous species slightly stronger solutions were required (10–20%). When the unaffected species were retested using a 10-day pre-chilling treatment, smoke water showed a small promotive response in three (S. arvensis, P. aviculare and V. hederifolia) of the six species. When four different smoke-water solutions (Seed Starter®, ®, charred-wood solution and wheat-straw solution) were tested on two representative species (A. fatua and M. neglecta), three formulations were effective in promoting the germination of both species, while the fourth (charred-wood solution) was only active on A. fatua. The active concentrations were different for the four solutions. Three solutions were active in the 2–20% dilution range, while the fourth (®) was only active in the 1–2% dilution range and was inhibitory at higher concentrations. These observations are discussed in the context that smoke may play an important ecological role in the management and control of introduced weeds in native and arable communities.

Common buckwheat (Fagopyrum esculentum Moench) plants produce many flowers, but fewer seeds. Seed set is highly variable among years, between plants, and during the period of flowering within a plant or raceme. Seasonal variations suggest that temperature and water-deficit stresses are important factors for seed set. The effects of mild temperature and water-deficit stresses on seed set and seed filling were determined in planta and in vitro. An in vitro method to culture matched sets of racemes from individual plants was used for precise comparisons between experimental treatments. Buckwheat racemes form new flowers continuously during several weeks in planta. Seed set resulting in yield occurs during the first 2–3 weeks of flowering and then rapidly declines in planta independently of mild stresses. Plants grown at 18°C have 40% increased seed set, set seeds over a longer duration, and produce 40% more dry matter per seed than plants grown at 25°C. Similar patterns occurred in vitro. A 3-day water-deficit stress during the first week of flowering reduced the number of seeds by 50%without a reduction in seed size and dry weight, or the number of flowers formed in planta or in vitro. The effect of water-deficit stress continued after rewatering and subsequently was expressed as a reduction in fertility in newly formed flowers, both in planta and in vitro. Mild temperature and water-deficit stresses affected both female and male components of seed set in common buckwheat, resulting in a persistent but non-additive reduction in sink strength.

At shedding, the moisture content (MC) of Avicennia marina (Forssk.) Vierh. propagules was 65% (fresh mass basis), and there was no significant difference in the MC of four tissues (hypocotyl, cotyledons, plumule and root primordia). Viability declined as the propagules were dried below 60% MC, so that only 40%of seeds were capable of germination at 54% MC. At 47% MC all the seeds had died. The four tissues dried at the same constant rate of 0.02 g water g dwt-1 h–1 throughout this range of MCs. There was no significant depletion of the free-radical-quenching mechanisms measured. In each tissue an organic free-radical was detected by electron paramagnetic resonance (EPR). In the plumule the amplitude of the signal increased by a further 50% at MCs where viability was lost, but there was no increase in the other tissues. There was a concurrent increase in the amount of tocopherol and the activity of superoxide dismutase in the plumule. Lipid peroxidation, assessed by the amount of thiobarbituric acid-reactive substances, also increased in advance of viability loss, suggesting that propagules were experiencing oxidative stress. However, lipid peroxidation decreased at 54–57% MC, where most seeds lost viability. The results presented are consistent with a propagule reacting to oxidative stress, but overtaken by more catastrophic physical damage.

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).

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.

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.