A high-molecular-weight aspartyl proteinase complex, sensitive to pepstatin A was purified to near electrophoretic homogeneity from dry seeds ofjack pine (Pinus banksiana, Lamb.). Two partial activities, endo-and exo-proteinolytic, were associated with the complex, judged by the analysis of haemoglobin hydrolysis products. The high activity of this enzyme in dry jack pine seed suggests a possible function in early germination.

The growing conditions of a parent plant may affect the degree of dormancy of its seeds. This has been demonstrated in numerous species, both wild and cultivated. The evidence comes from field observations and controlled experiments. A survey of the literature shows that some well defined patterns emerge, with certain environmental factors tending to have similar effects over a wide range of species. Lower dormancy (i.e., increased germinability) is generally associated with the following environmental conditions during seed development: high temperatures, short days, red light, drought and high nitrogen levels. The effects are probably the result of changes in the quantity, mobility or activity of growth substances such as abscisic acid. The ecological implications of the phenomenon are briefly discussed.

Mature seeds of Norway maple (Acer platanoides L.) are tolerant of desiccation, at least to moisture contents of about 7% (fresh weight basis), but those of sycamore (Acer pseudoplatanus) are killed by drying below about 45% moisture content. Sycamore seeds are thus recalcitrant; while the classification of those of Norway maple as orthodox is confirmed by the fact that between 19% and 7.5% moisture content their longevity is increased in a predictable way by reduction of seed moisturecontent. However, the period of useful storage of the latter in seed banks may be much less than for many crop species. The rates of water loss to a dry environment of both fruits and seeds of sycamore are much less than those of Norway maple, suggesting a degree of desiccationavoidance in the desiccation-intolerant species. Seed physiological maturity (maximum dry weight) occurred 2–3 weeks earlier in Norway maple than insycamore, but in both species this occurred about 150–160 days after peak flowering. Tetrazolium staining is a good indicator of embryo viability in both species, correlating well with germination test results. In Norway maple both methods of viability testing indicated that whole-seed desiccation tolerance coincided with the attainment of maximum dry weight. Tetrazolium staining indicated the development of desiccation tolerance in the radicles/hypocotyls of both species approximately 2–4 weeks before physiological maturity. Possible correlation between changes in the level of embryo dormancy during development and the acquisition of desiccation tolerance are discussed.

The value of the garden pea (Pisum sativum) both as an experimental tool and food crop has led to an accumulated wealth of genetic variation. This paper describes how some of the variation may be harnessed for studying seed development. One can identify genotypic differences for maternal, embryonic and cellular components and the interaction between them. The impact of these components on processes such as cell division, partitioning and the deposition of storage products can then be assessed by utilizing new techniques such as immunocytochemistry and in situ hybridization.

The rugosus loci, which induce wrinkling of the seed, are examples of how major genes can be exploited to dissect seed development. Alleles at one of these loci, r, have been defined at both the molecular and biochemical levels. A much clearer picture can now be drawn of the pleiotropic nature of the genes, from their effects on starch composition to those on cellular development, which has implications for seed development in many species. The rugosus loci are the only ones known to affect seed development in peas. By analogy with cereal seeds, however, one would anticipate other mutants in the starch pathway which also affect the shape of the seed. Here, we report the induction of new rugosus-like mutants, compare them to starch mutants in other species and examine the ways in which they may help our understanding of starch biosynthesis and the regulation of seed development.

Low and high moisture kernels and embryos were imbibed by soaking in distilled water at 5°C and 25°C. Leaching of seeds and embryos was measured by ion conductivity of imbibition water after fixed time intervals. Imbibed kernels were placed on moist filter paper after 1 h imbibition and embryos on a solid culture medium after 15 min imbibition and germinated at 25°C. Primary root length was measured 3 days after germination.

The leakage from seeds or embryos was correlated with the velocity of water uptake but did not show its highest values when low moisture seeds or embryos were imbibed at chilling temperature. Furthermore germination was apparently not affected by imbibitional chilling of either low moisture content seeds or embryos. In one of the three genotypes tested (B73) seedlings from low moisture content seeds imbibed at 5°C showed a reduction of the primary root growth. However, this reduction was also seen in seedlings from low moisture B73 seeds imbided at 25°C and resulting in higher level of leaching. Thus, injury by imbibition of low moisture seeds appears independent of chilling temperature and not due to loss of semipermeability of membrane lipids. Our results suggest that, in the case of embryos, water inrush into the cells reaches levels injurious for membrane integrity independently of the two moisture contents and temperature considered.

The variation for protein content has been assessed in a series of pea (Pisum sativum L.) lines differing in mean seed size. The range of seed size within each genotype was manipulated by growing the plants in different environments and by altering the structure of the plant. The response of the lines in terms of seed weight to the environments and treatments was inconsistent, but 90% of the total variation was accounted for by differences between genotypes. In contrast, for percentage protein, the genetic component was much weaker with nearly half the variation being accounted for by within (residual) variation. The correlations between seed weight and percentage protein were highly genotype specific. For the largerseeded genotype, percentage protein increased with increasing seed size (r= +0.9, P < 0.01), while for the small-seeded genotype there was mid-range negative value (r = −0.5, P <0.01). It is suggested that any assessment of percentage protein in pea genotypes must take account of seed size.

Seed development and changes in germination ability and longevity were monitored in control and shaded spring barley (Hordeum vulgare L.)crops grown in two contrasting years. Shading reduced seed dry matter accumulation rates by 24–28% and delayed maturation drying slightly, but had little effect (0–2 d) on the timing of physiological maturity (end of the seed-filling period); final seed dry weights were 76–85% of controls. Moisture contents (wb) at physiological maturity were 48–55%; final mean seed dry weights in the controls were 40.9 mg(S.E. 0.6) in 1988 and 35.2 mg (S.E. 0.5) in 1989. Shading had little orno effect on germination ability or longevity in either year. Seeds fromthe first harvest were viable when dried below 15% moisture content despite being only 34% (1988) to 63% (1989) filled; desiccation promoted germination. Maximum germination achieved after forced desiccation occurredin seeds harvested 7–10 d (1989) to 11–13 d (1988) after physiological maturity, with little subsequent change during the following 14 (1988) or 27 d (1989). Longevity continued to increase during development until a maximum was reached 18–20 d (1988) to 27 d (1989) after physiological maturity (at moisture contents on the mother plant of 18–19% and 14–15%, respectively). In both years, the longevity of these seeds was greater (P<0.005) than that of seeds harvested either subsequently or earlier at physiological maturity. The results contradict the hypothesis that maximum seed quality coincides with physiological maturity and thereafter declines. Rather, maximum seed quality was attained close to when barley seed crops can be combine harvested The subsequent decline in potential longevity on the maternal plant in the field was quantitatively similar to that expected during post-harvest storage.

An expressed napin storage protein gene from Brassica rapa, BcNA1, has been cloned and sequenced. The gene is a member of a family of four to seven napin genes in B. rapa and is highly expressed in developing seeds. An expression cassette containing the DNA flanking the napin coding region of BcNA1 has been engineered and demonstrated to function appropriately, as compared with the gene's endogenous expression, in transgenic rapeseed using the β-glucuronidase reporter gene. The B. rapa BcNA1 gene and a B. napus napin gene, gNa, share extremely high nucleotide homology not only throughout their coding regions, but over a DNA locus comprising 4.3 kb. We suggest the gNa gene was contributed by the original B. rapa progenitor of the amphidiploid B. napus.

Utilization of lipid and protein storage reserves was examined during germination and early growth of somatic and excised seed embryos in vitro, and seed of interior spruce. High germination frequencies were recorded for somatic and excised seed embryos, and elongation of radicles and hypocotyls observed for both embryo types. Although elongation of the embryo types differed (i.e. somatic ≤ excised seed < seed), fresh weight gain was similar. Utilization of triglycerides in somatic embryos was more rapid than in excised seed and seed embryos, thus it appeared to be under embryo infuence. By contrast, depletion of storage proteins appeared to be influenced by the megagametophyte, with hydrolysis in somatic and excised seed embryos preceding that of the seed embryo by 2 days. Differential utilization of the storage reserves was temporally associated with differences in growth patterns of somatic and seed embryos. The evidence presented indicates that the in vitro germination medium does not entirely supplant the role of the megagametophyte during germination and early growth. The relevance of these results to artificial seed technology is discussed.

Even though the embryo of a maize (Zea mays L.) kernel contributes relatively little to total kernel weight, it is a main source of electrolytes which leach from the kernel during imbibition. Ageing of maize kernels for 18 days at 40°C and a moisture content of about 15% results in an increase of electrolyte leakage which almost exclusively originates from the embryo. The effect of ageing is most apparent after prolonged periods of imbibition. Mechanical damage increases leakage early during imbibition, the effect of damage being considerably larger for aged than for unaged kernels. The large amount of electrolytes measured after the first hour of imbibition of undamaged kernels comes mainly from the pericarp. The electrolyte content of the pericarp is variety dependent and may interfere with quality testing by conductivity measurements.

Dormant dehusked Avena sativa L. (cv. Moyencourt) caryopses germinated easily at 10°C, but their germination was poor at 25 and 30°C. Ethanol overcame their dormancy and allowed germination at the last two temperatures when given continuously at concentrations ranging from 50 to 200 mm, or at higher concentrations at the beginning of imbibition. Ethanol also promoted germination in hypoxia. Other alcohols which were good substrates for alcohol dehydrogenase (ADH: EC 1.1.1.1), such as butanol-1, propanol-1 and 2-propen-1-ol, had the same stimulatory effect as ethanol, whereas alcohols which could not be oxidized by ADH (propanol-2 and methanol) did not improve germination. Salicylhydroxamic acid (SHAM) did not alter the stimulation of germination induced by ethanol, but 4-methylpyrazole (4-MP, an inhibitor of ADH) completely abolished this stimulation. The improvement of germination by alcohols which were good substrates for ADH was always associated with an increase in oxygen uptake by caryopses, whereas alcohols which were not ADH substrates did not enhance respiration. The stimulation of oxygen uptake induced by ethanol resulted in a decrease in CO2/O2 ratio and was suppressed by 4-MP, but ATP level in embryos was not modified until after the germination of caryopses. All the results obtained seem to demonstrate that the stimulatory action of ethanol on germination of dormant oat caryopses requires its metabolism through ADH and involves an activation of glycolysis and the Krebs cycle.

Seed viability was maintained in four cultivars of oil palm (Elaeis guineensis Jacq.) during 12 months of hermetic storage at 15°C with 10–12% moisture content (embryo moisture contents of 19–21%). The viability of both these and drier seeds was reduced greatly during this period at cooler storage temperatures of 0°C and −20°C, however. For example, intact seeds at 6.1–7.4% moisture content (embryo moisture contents of 9.1–12.0%, at which freezing damage would not be expected) lost viability more rapidly at 0°C and −20°C than at 15°C. Moreover, desiccation to 4–5% moisture content (4–6% embryo moisture content) reduced seed lot viability in some but not all cultivars. The results confirm earlier reports that oil palm is not recalcitrant, but neither is it orthodox. Thus, seed storage behaviour in oil palm appears to be intermediate between these categories. Additional results are presented which suggest that the seeds of the royal palm (Oreodoxa regia HBK) may also show intermediate seed storage behaviour.

The field emergence ability of a total of 88 seed lots of spring barley (Hordeum vulgare L.) harvested serially during development in 2 years was compared, as was the size of the resultant seedlings. For seedsproduced in each year, field emergence and the mean dry weight of emerged seedlings were significantly greater for seed lots harvested some timeafter physiological maturity (end of the seed-filling period) than for those harvested at or before this developmental stage. This is compatiblewith results for the potential longevity of these lots. It is concluded that barley seed quality continues to increase after physiological maturity, and that the developing seeds attain maximum quality (however this is assessed) close to when the seed crop can be combine harvested. Positive correlations were detected between seedling emergence and seed dry weight (P<0.05) and between the mean dry weight of emerged seedlings and seed dry weight (P<0.005) among seed lots harvested close to when maximum quality was attained in four seed production environments.

Excised Helianthus annuus embryos were capable of precocious germination as early as 7 d after pollination. At this stage they were not capable of withstanding desiccation treatment. The desiccation tolerance was acquired at a stage of development which depended on the rate of water loss to which embryos were subjected. Coincident with the acquisition of tolerance to a rapid desiccation, they gained the capacity to withstand 24 h preincubation in agitated water; this acquisition could be correlated to a sharp decrease of the leaching of electrolytes, amino acids and proteins in the incubation water, suggesting that a change in membrane properties played a key role in this transition. Moreover, the acquisition of tolerance to these stresses was coincident with the increase of endogenous abscisic acid (ABA). ABA applied in vitro to young embryos induced tolerance both to desiccation and to preincubation in water: this in vitro acquisition of tolerance was again correlated with a decrease in the leakage.

Osmotic and ionic effects of NaCl were investigated in germinating wheat. Approximately isotonic solutions of NaCl and sorbitol inhibited germination and seedling growth to similar degrees. When dry kernels were pre-imbibed in salt for 24 h and then transferred to water, germination was equivalent to that of kernels imbibed continuously in water and the development of embryos was delayed to about the same extent as kernels pre-imbibed in sorbitol for 24 h. Measurements of water uptake, respiration, biosynthetic activities and rubidium uptake in embryos dissected from grains imbibed in NaCI or sorbitol for the first 24 h demonstrated that salt supplied to dry kernels closely mimicked sorbitol in counteracting the reactivation of embryo metabolism. No toxic effects of salt were observed when dry kernels were pre-imbibed in very high NaCI concentrations for 24 h and then transferred to water, even though embryo sodium contents increased considerably. Ultrastructural observations of embryo tissue further showed that salt influx into dry grains did not produce ion-specific damage in cell organization. On the other hand, salt specific effects became evident when the 24 h salt exposure was applied to kernels pre-hydrated for 24 h and, even more, for 30 h. We conclude that in wheat the inhibition of germination by salt corresponds to that induced by an osmoticum, provided that the caryopsis has not reached the stage of germination associated with active embryo expansion.

An osmotic priming treatment of 14 days in a −1.0 MPa polyethylene glycol solution improves the germination performance of a highvigour seed lot of leek (Allium porrum L., cv. Verina). Using in vivo pulse-labelling, two-dimensional polyacrylamide gel electrophoresis and fluorography, five polypeptides were found to be synthesized in embryonic tissue at 14 days of priming that were not present at 4 days of germination without prior priming. These polypeptides were still synthesized at 6 h of germination following priming. This time point lies in the 6–12 h lag phase in protein synthesis previously observed in leek embryo tissue during germination of primed seeds where there is little increase in the rate of synthesis over that seen at the end of priming. None of the polypeptides was synthesized at 2 days of germination after priming, a period of seedling growth. The five polypeptides appear to be specifically associated with the priming period. Two additional polypeptides were found in leek embryos that were synthesized at higher levels at the end of priming than during germination alone. These continued to be synthesized, at lower levels in leek embryo tissue upon germination after priming. Several polypeptides were identified in leek endosperm tissue which were synthesized at higher levels during priming than during germination and also two polypeptides whose synthesis appeared to be specific to germination.

Dormancy in rice (Oryza sativa L.) seed is imposed by certain physical and chemical factors associated with its covering structures, i.e.hull and pericarp. The nature of these germination blocks, their mode ofaction, and processes regulating the release of dormancy are not fully understood. Of nine rice cultivars studied, Ching-shi 15, Stejaree 45, PTB10, and Mahsuri are weakly dormant, and Bansphul, Benaful, Kataktara, Dular, and N22 are dormant. Release of seed dormancy in rice by various treatments, oxidative processes and enzymic changes associated with dormancy, and parallelism between natural and artificially imposed dormancy patterns were examined. The influence of the hull in imposing dormancy was stronger and more prolonged than that of the pericarp. Application of GA3 was effective in inducing germination only in weakly dormant cultivars. Dormancy was completely released in all cultivars by subjecting the seeds to moist heat treatment, by removing the hull and pericarp, and by applying GA3 after dehulling. Dormant cultivars had higher O2 uptake rate and peroxidase activity and lower amylase and dehydrogenase activities than the weakly dormant ones. Hull removal substantially decreased peroxidase activity but enhanced amylase and dehydrogenase activities. Nonanoic acid (C90), a short-chain saturated fatty acid (SCSFA), when exogenously applied to non-dormant seeds imposed dormancy. Dry heat treatment or presoaking in 0.01 m KNO3 or 0.1 m H2O2 was very effective in releasing SCSFA-imposed dormancy. Amylase activity was greatly reduced by treatments with nonanoic acid (C90) or ABA. Considering earlier reports and results of the present study, it is proposed that seed dormancy in rice is regulated both by the presence of SCSFAs and ABA in the hull and the pericarp. The relative significance of these substances in cultivars of tropical and temperate origins and its implications in terms of ecogeographic adaptability are discussed.

Instrumental neutron activation analysis (NAA) was used to quantify the amounts of K, Mg, Cl, Ca and Mn leaked into water from imbibing dry seeds, dry fruits and isolated seed parts. A number of intact monocot and dicot dry seeds or fruits were studied as were some isolated parts such as testa, endosperm and embryo. All samples studied leaked detectable amounts of the five elements measured but the amounts leaked varied greatly. In most cases K was leaked in greater amounts than the other elements while Mn was leaked least. The leakage of Ca was highest from isolated seed coats and from mericarps of three umbelliferous species. Comparisons of the amount of element leaked with the total amount of that element present in the starting material showed that leakage, especially of K, represents a substantial loss of mineral nutrient reserves. The degree of leakage of elements did not appear to be closely related to the types of organic storage reserves present.