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.

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.

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.

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.

Immature embryos isolated from fruits of Acer pseudoplatanus L. at various stages during a 24-week development period, showed a sharply defined transient accumulation of endogenous free ABA, with peak levels at 10 weeks postanthesis (wpa). When this ABA peak occurred isolated embryos showed a high level of germinability when incubated in sterile culture; however, germinability fell rapidly thereafter, reaching minimum values at 14 wpa before recovering as maturity approached. Halfembryos and excised embryonic axes, although showing consistently higher germinability than whole embryos, also showed a similar progressive reduction in germination capacity up to 14 wpa, followed by a recovery in germinability. This peak of free ABA in the embryo also correlated with the start of the most rapid phase of both embryo mass and volume increase. The possibility that endogenous ABA is the causal agent of this short-lived embryo dormancy in A. pseudoplatanus is discussed, as is the possibility that by suppressing precocious germination, ABA frees the embryo to initiate or accelerate its normal developmental processes.

Priming in polyethylene glycol (PEG, −1.5 MPa) for 7 d followed by drying, led to a 4–5 fold increase in mean longevity when achenes (seeds) of Ranunculus sceleratus L. were subsequently stored at 35°C and 9.2% moisture content on a fresh weight basis (67.1% equilibrium relative humidity). The increase in longevity was due to an increase in the standard deviation of the frequency distribution of individual seed lifespans (decrease in the slope of transformed survival curves) and to a lesser extent to an increase in the intercept of survival curves. Priming for 1 d resulted in a smaller but significant increase in longevity independent of whether seeds were primed in PEG, distilled water or a saturated atmosphere (100% RH).

The effects of priming were not due to the prevention of imbibition injury, and there was no evidence that the water relations of whole achenes was affected by priming. The effects of a 7 d priming treatment were dependent on the temperature and nature of the priming medium. However, no differences were recorded between corresponding treatments which were primed in PEG or distilled water. Moreover, the survival and responsivity to priming of R. sceleratus seeds was not related to dormancy status. The effects of priming on the longevity of R. sceleratus seeds are apparently unrelated to seed quality as the response of seeds previously aged for 8 d at 35°C and 7.9% moisture content was similar to that for unaged seeds.

Priming followed by drying did not increase seed longevity in the related species R. acris L. The promotive effects of priming on seed survival appear to be species specific and may be related to ecological factors.

Embryogenesis was induced on cotyledons of immature zygotic embryos of soybean (Glycine max (L.) Merrill) placed on solid medium containing 62.5 mm glutamine, soybean seed growth medium salts and vitamins, and 40 mg I−1 2,4-dichlorophenoxyacetic acid (2,4-D) plus 175 mm maltose, or 8 mg I−1 α-naphthaleneacetic acid (NAA) plus 88 mM sucrose. Somatic embryo development was continued in liquid medium containing 0.16 mg I−1 indole-3-butyric acid and 2.64 mg I−1 abscisic acid, glutamine and salts as above, and 88–438 mM sucrose in progressively increasing steps. Germination was on solid half-strength Murashige-Skoog medium. During maturation, somatic embryos mimicked zygotic embryos in colour, protein concentration, water and solute potentials, and respiration. Protein and lipid accumulated to 329 and 86 g kg−1 dry weight in somatic embryos. Fatty acid composition was similar to that of axes of mature seeds. Before desiccation, the water and solute potentials of maturing somatic embryos declined to −1.13 and −1.99 MPa while turgor increased to 0.86 MPa. Concomitantly, a 60% reduction in activity of the cytochrome oxidase pathway of respiration occurred with somatic embryo maturation at 600 g water kg−1 fresh weight. Although small (about 8 mg per embryo), 60% of the somatic embryos formed roots and shoots during germination after maturation without drying and 30% germinated after drying to 60 g water kg−1 fresh weight. In the greenhouse, somatic plantlets grew to mature plants with seeds.

Prolonged imbibition and incubation of lettuce seeds at a supraoptimal temperature induces secondary dormancy. Such seeds no longer germinate when returned to conditions optimal for germination of non-dormant seeds. The possibility that inhibitors are involved in the induction of thermodormancy was investigated.

Washing of thermodormant seeds restored germination to a small extent. However, continuous leaching of seeds during high-temperature treatment with distilled water, largely prevented the induction of thermodormancy. Such seeds were qualitatively similar to nondormant seeds, i.e. they required only light to germinate at a lower temperature and germinated in the dark if given GA3. The germination water from thermodormant seeds inhibited the germination of non-dormant lettuce seeds. The inhibition was not an osmotic effect. Absorbance in the ultraviolet region was higher in germination water from thermodormant seeds than that of non-dormant seeds. It is concluded that inhibitors are involved in the induction of thermodormancy of lettuce seeds.

Chromosome integrity and DNA polymerase activity are negatively affected by improper storage of maize seeds. We have extended our studies on the effect of improper storage on DNA metabolism by analysing the effect of hot–dry and hot–humid conditions on DNA ligase activity. An assay to measure ligase activity was established by using linearized plasmid DNA as substrate and protein extracts from maize axes. Optimal conditions were established for the in vitro assay. Enzyme activity was importantly reduced under both storage conditions. Activity recovered 6–9 h after imbibition. A model for loss of viability and vigour due to damage of DNA metabolism is proposed.