Seed germination of Grand Rapids lettuce (Lactuca sativa L.) was inhibited at 38°C (thermoinhibition). Thermoinhibition was totally relieved by a combination of 100% oxygen and 10 mg I−1 kinetin, to a lesser extent by a combination of oxygen and ethylene but not at all by oxygen plus GA3. The combination of oxygen with kinetin or ethylene was more effective in preventing thermoinhibition than a combination of all three hormones and CO2 in air. The beneficial effect of oxygen plus kinetin was not related to either increased production of CO2 or ethylene by the seeds. In air, germination was partially inhibited by 2-aminoethoxyvinyl glycine (AVG) or 2,5-norbornadiene (NBD) and totally inhibited by AVG plus NBD. Oxygen plus kinetin almost completely alleviated their inhibitory effects. It was concluded that oxygen plus kinetin caused seeds to bypass an ethylene requirement for germination or increased the sensitivity of seeds to ethylene. In air at 38°C, seeds exhibited a high level of ethanolic fermentation, while in oxygen plus kinetin they respired aerobically. At 38°C in air, contents of ATP and total adenylates were reduced, while in seeds treated with oxygen plus kinetin these contents were similar or higher than in 25°C controls. A similar response was also observed for adenylate energy charge. It was concluded that part of the mechanism of thermoinhibition could be the failure of ATP content to reach a sufficient level to satisfy the requirement for germination at 38°C. It appeared possible that the prevention of thermoinhibition by oxygen plus kinetin could be related to increased ATP content in seeds caused by this treatment.

The contents of the cytokinins zeatin (Z), zeatin riboside (ZR), and isopentenyladenine (IPA), the combined contents of gibberellins1 + 3 (GA), and the contents of indoleacetic acid (IAA) and abscisic acid (ABA) were measured during the development of the desiccation-sensitive seeds of Avicennia marina (Forssk.) Vierh. During the stage of histodifferentiation the amounts of these plant growth regulators (PGRs) were measured on whole fruits. During the phase of seed growth and reserve accumulation measurements were made on the embryonic axis, cotyledons and pericarp separately. Patterns in the amounts of PGRs present during histodifferentiation were similar to those reported for desiccation-tolerant seeds and it suggested that this process is under similar ‘hormonal’ control in A. marina as in orthodox seeds. Very high contents of cytokinins, particularly ZR, were present in both axes and cotyledons during reserve accumulation. This is thought to be related to the nature of the reserves accumulated (soluble sugars), rather than to the phenomenon of desiccation sensitivity. With the exception of ABA, embryonic contents of PGRs were relatively high at seed shedding, consistent with the rapid germination of this highly recalcitrant seed. ABA contents in the embryo were low during reserve accumulation, but concentrations in the pericarp increased throughout this development stage. ABA in the perticap could act to prevent precocious germination. The low concentrations of ABA in the embryo could be related to the desiccation-sensitivity of the seeds of A. marina.

Total protein content and amounts of albumin, legumin and vicilin have been determined for pea seeds from lines near-isogenic except for genes at the rugosus loci, r and rb (RR/RbRb; rr/RbRb; RR/rbrb; rr/rbrb). Seeds with the wildtype, round-seeded phenotype (RR/RbRb) had less protein on a total seed dry-weight basis than any of the wrinkled-seeded lines and this protein had a lower proportion of albumin. The lines which had recessive alleles at both r and rb loci had the highest proportion of protein and the highest proportion of albumin. The roundseeded peas possessed nearly two-fold more legumin than the double recessive line, with proportions for the two single recessive lines falling in between these extremes. Vicilin levels were similarfor all four near-isogenic lines. SDS-PAGE analysis of the isolated albumin, legumin and vicilin fractions revealed no significant differences between the four lines. Differential scanning calorimetry of protein extracts showed that all the wrinkled-seeded near-isolines possessed legumin fractions with diminished thermal stability relative to that from the roundseeded, wild-type line.

Chemically-induced mutants were also analysed for protein content and composition. These mutants have previously been shown to display great variation in starch and lipid levels. Total protein varied from 20.3% to 37.9%; however, relative proportions of albumin, legumin and vicilin were similar in all mutant lines. SDS-PAGE analysis identified two mutant pea lines which possessed a legumin A-chain of 65 000 Mr as well as the typical 45 000 Mr form. Differential scanning calorimetry of protein extracts indicated that the legumin in all mutants had lower enthalpies of denaturation than the legumin in the round-seeded parent.

The mutant pea lines possess exceptional variation with respect to starch, lipid and protein which raises opportunities for their use in the food and animal feedstuff industries.

It has been proposed that gibberellic acid (GA3) promotes germination by overcoming restrictions in sugar production and utilization in afterripening-responsive dormant caryopses. While their germination rates were similar, germination commenced sooner in afterripened wild oat (Avena fatua L.) caryopses than in dormant caryopses treated with GA3 and dormant excised embryos treated with GA3 plus fructose (Fru). Limited germination occurred in dormant excised embryos cultured with GA3 alone. Carbohydrate concentrations were measured over time in dormant caryopses and excised embryos whose germination was induced with GA3 and GA3 plus Fru. The concentration of sucrose (Suc) in the endosperm declined prior to germination of dormant GA3-treated caryopses. Raffinose (Raf) family oligosaccharides in the embryos of dormant GA-treated caryopses remained relatively constant prior to and shortly after the onset of germination. In contrast, Raf family oligosaccharides in the embryos of afterripened caryopses declined prior to germination. Together this suggests Raf family oligosaccharide utilization is not associated with germination per se. Increased starch levels, which occurred in dormant excised embryos treated with Fru and GA3 plus Fru, were associated with dormancy because similar effects were not apparent in afterripened embryos cultured with Fru. An initial decline in the concentration of Raf family oligosaccharides in dormant embryos cultured with GA3 or GA3 plus Fru seems to be a result of the excision process. GA3 appears to stimulate the germination of dormant embryos by enhancing the uptake or utilization of Fru. It appears that GA3 and afterripening-induced changes in carbohydrate utilization in dormant caryopses are different.

The effect of natural and artificial seed ageing has been compared in terms of physiological and biochemical responses of several maize genotypes. The physiological parameters were: viability, germinability, emergence in sand and dry matter accumulation. The biochemical parameters were: DNA synthesis and DNA polymerase activity. A close and direct relationship was found between seed deterioration and DNA metabolism in all maize materials which responded to ageing according to their genetic constitution; i.e., vigorous genotypes suffered less severe damage or recovery was faster than in the low-vigour genotypes. Coordination of events at appropriate times would seem a critical factor for proper seed germination.

The development of (1→3,1→4)-β-glucan 4-glucanohydrolase (EC 3.2.1.73) has been examined in germinating wheat (Triticum aestivum cv. Millewa) grain, and in isolated aleurone layers and scutella. Activity is first detected in extracts of intact grain 2–3 days after the initiation of germination and thereafter increases until 6 days. In isolated aleurone layers, (1→3,1→4)-β-glucanase activity is secreted for up to 4 days. Treatment of aleurone layers with gibberellic acid (GA3) results in a 2-fold enhancement of secreted enzyme for the first 2 days, but activity decreases after 2 days. (1→3,1→4)-β-Glucanase secretion from GA3-treated aleurone layers clearly precedes the secretion of amylase and (1→4)-β-xylanase. Small but significant levels of cellulase are secreted from aleurone layers after GA3 treatment. Isolated scutella also secrete (1→3,1→4)-β-glucanase but GA3 has little apparent effect on secretion patterns from this tissue. Proteins secreted from excised aleurone layers and scutella, together with those in homogenates of intact, germinated grain, have been examined by Western blot analysis, using monoclonal antibodies against barley (1→3,1→4)-β-glucanases as probes. In each case the wheat (1→3,1→4)-β-glucanase is recognised only by the monoclonal antibody that is specific for barley isoenzyme El.

Ageing causes a delay in the onset of DNA replication in seeds. Aerated hydration for 8 h, a treatment to invigorate seeds, resulted in a reduction of about 12 h in the time difference in the onset of DNA synthesis between unaged and aged embryos of brassica seed. This effect is consistent with a recovery process occurring during aerated hydration of the seed involving the repair of accumulated DNA damage. The occurrence of hydroxyurea-resistant 3H-thymidine incorporation in aged Brussels sprouts embryos during the period 16–32 h from the start of hydration supports this interpretation.

A novel method has been devised to extract poly (A+)RNA from seed tissues. The advantages of this technique include the speed of extraction and the elimination of the hazardous phenol:chloroform extraction step which usually precedes oligo (dT)-cellulose column chromatography. Instead, the crude supernatant, containing a high concentration of SDS and salts to effectively inhibit RNase activity, is passed directly over the oligo (dT)-cellulose column. The resultant isolated poly (A+)RNA is of high yield and purity and is suitable for in vitro translation and Northern blot analysis.

The premise of this paper is that the chemical potential of water strongly influences aging reactions in seeds, and that there will be an optimal chemical potential of water for seed longevity. If this is true, the optimum moisture content for storage and the optimal drying protocols should vary with the storage temperature, but should be predictable from water sorption isotherms. Isotherms for pea, soybean and peanut are given for temperatures between 65° and −150°C. Relative humidity/moisture content relationships were determined directly for temperatures between 5° and 50°C using saturated salt solutions. At extreme temperatures, isotherms were calculated from heat capacity measurements using differential scanning calorimetry or extrapolations of van't Hoff analyses. The family of isotherms was used to predict optimum moisture contents at storage temperatures between 65°C and −150°C. The optimal moisture contents for these three species are consistently shown to increase as the storage temperature is lowered.

Wheat (Triticum aestivum L) seeds contain a proteinaceous α-amylase inhibitor. We estimated the amount of the inhibitor that can bind to α-amylase rather than the total amount of the inhibitor, using an ELISA method. During 48 h of imbibition, the amount of the inhibitor did not change, while α-amylase activity increased rapidly. These results suggest that α-amylase synthesized de novo does not bind to the inhibitor. To examine further the interaction between α-amylase and its inhibitor, we localized immunohistochemically both α-amylase and the inhibitor in germinating seeds. In the embryo, we observed α-amylase only in the scutellar epithelial cells at 24 h after the start of imbibition, and later in the scutellar parenchyma cells. The inhibitor, on the other hand, was present between the scutellar parenchyma cells of the embryo at 0 h and 24 h after the start of imbibition, and disappeared later. α-amylase is separated from the inhibitor in the embryo. In the endosperm, we detected α-amylase in the aleurone cells at 24 h after the start of imbibition and later in the starchy endosperm. The inhibitor was present in the aleurone cells and starchy endosperm of the dry seed. During imbibition, the inhibitor in the starchy endosperm disappeared from the area to which α-amylase was secreted. It appears that α-amylase in the starchy endosperm also does not interact with the inhibitor. The aleurone cells are the only place that α-amylase can come into contact with the inhibitor. But, early secretion of α-amylase from the aleurone cells after imbibition started, and rapid disappearance of the inhibitor in the aleurone cells suggest that the α-amylase inhibitor does not work as an effective inhibitor of the endogenous α-amylase synthesized following germination.