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Future soybean [Glycine max (L.) Merr.] cultivars with elevated or reduced concentrations of isoflavones may be required to satisfy the food market. Climate influences isoflavone concentration making their prediction problematic. Our research examined the associations between precipitation and temperature during a growing season with the isoflavone concentration in the harvested seed. We grew 14 cultivars across 12 years, at one location and calculated climate parameters for readily identifiable growth stage intervals (GSI). We correlated the climate parameters within each GSI with seed daidzein, genistein and total isoflavone (TIF) concentrations. We found that cumulative precipitation from the mid-vegetative to the flowering period was correlated with daidzein and TIF concentration. Mean daily average T during early vegetative development was positively correlated with daidzein and TIF concentration and this was largely a result of higher minimum daily T. Accumulated heat stress T greater than 27 °C during seed development was significantly correlated with a reduction in genistein and TIF, but not daidzein concentration. Accumulated cold stress T's less than 20, 15 and 17 °C during seedling emergence were significantly correlated with higher seed daidzein, genistein and TIF concentrations, respectively in all short-season cultivars tested. Cold stress T during seedling emergence could be used to predict seasonal changes in isoflavone concentrations.

Isoflavones are naturally occurring compounds found in soybean [Glycine max (L.) Merr.]. Soybean isoflavone, as a quantitative trait, is subject to significant genotype x environment interaction, which makes breeding for this trait difficult. Thirty F 4:7 soybean lines, derived from crosses of 'RCAT Angora' x CK-01 and 'Heinong 35' x RCAT Angora were classified within each population as high, intermediate, or low isoflavone. The lines, parents, and two maturity checks were grown in four locations in 2005 and six locations in 2006 across Ontario and Quebec, Canada. Isoflavone content of the mature seed was determined by near-infrared reflectance. The effects of genotype, environment, and the genotype x environment (G x E) interaction were significant. Consistently performing genotypes from the two populations were identified by several stability parameters. Genotype-genotype x environment (GGE) biplot demonstrated an ability to provide information on both the genotypes and the environments in which they were evaluated. The identification of genotypes with consistent placement in either the high- and low-isoflavone classes suggested that breeding for relative isoflavone content in soybean is possible, although breeding for absolute stability remains a challenge, given the large environmental influence on soybean isoflavone levels.

Soybean, Glycine max (L.) Merr., seeds contain isoflavones, compounds with potential human health benefits. This study investigated the association of seed and agronomic traits with isoflavone level in a genetically diverse group of soybean genotypes to provide more information for cultivar development. F4:7 lines derived from several crosses were grown in four locations in 2005 and six locations in 2006 across Ontario and Quebec. Seed protein, oil and isoflavone contents were measured using near-infrared reflectance (NIR) on a plot basis. Seed yield was determined at 13% moisture and days to maturity (R8) were recorded. GGE genotype-by-trait biplots were generated to describe the relationships among all variables. Isoflavone content was not correlated with yield, indicating that potential exists for development of high or low isoflavone cultivars without sacrificing yield. Isoflavone content was negatively correlated with protein content; however, high isoflavone lines were identified with moderate protein content. Isoflavone content was correlated with maturity, suggesting that delayed planting and/or the use of later maturing varieties could be a successful strategy to increase isoflavone content. The results of this study support the potential for the development of either high or low isoflavone soybean cultivars with acceptable agronomic and seed quality traits.Key words: Soybean, isoflavone, protein, oil, yield, maturity

Soybean [Glycine max (L.) Merr.] seeds contain a high concentration of the isoflavones daidzein and genistein, which are considered to be compounds beneficial to human health. Our objective was to determine the influence of breeding and selection for yield on the isoflavone concentration of short-season cultivars. A collection of 14 historical cultivars released from 1934 to 1992 was grown at Ottawa for 12 yr under identical cultural conditions. Seed samples, taken at harvest, were examined using near-infrared reflectance in conjunction with traditional chemical methods to measure the concentration of daidzein, genistein, and total isoflavones (TIF). A linear regression equation developed based on the changes across time of cultivar release was used to determine the improvement rates for various soybean parameters. Across the 58 yr of breeding history, yield and oil concentration increased by 0.43 and 0.24% per year, respectively, while protein concentration decreased by 0.15% per year. Across the same time period daidzein, genistein, and TIF increased by 1.04, 1.47, and 0.98% per year, respectively. Moderate broad sense heritabilities of 43, 45, and 44% were calculated for the aforementioned isoflavones. Genotype main effects + genotype x environment interaction biplots revealed that recent cultivars with high isoflavone concentration were more prone to environmental influence than older cultivars. In the short-season region, plant breeders should be aware that selecting for higher yield may indirectly select for higher isoflavone concentration.

Soy protein isolates (SPI) were prepared from 12 soybean lines grown in Harrow, Ontario and by-products (fibers and wheys) from SPI making were saved. The identification and quantification of soluble sugars in defatted flours, fibers and wheys were carried out using high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) and with a colorimetric method for uronic acids. Defatted flours and fibers were acid hydrolyzed, then analyzed by HPAEC-PAD for monosaccharide composition. The results showed varietal differences in the carbohydrate composition suggesting different applications for these defatted flours and their SPI by-products.

This study focussed on the evaluation of thermal denaturation at three different stages during soy protein isolation and the effect of subunit composition on the formation of heat-induced soy protein gels. Soy protein isolates (SPI) were prepared from 12 high protein lines, Harovinton variety and 11 derived null-lines which lacked specific glycinin (11S) and β-conglycinin (7S) protein subunits. Protein denaturation during SPI processing was monitored by differential scanning calorimetry (DSC). The results showed that hexane extraction of oil from soybean flours at 23 °C or 105 °C did cause changes in protein conformation. Rheological measurements showed that lines with different subunit compositions and 11S:7S ratio had distinctive gelation temperatures and resulted in gels with different network structures. All lines formed particulate gels at 11% protein. The 11S:7S ratio was not correlated to final stiffness, measured as the storage modulus G′, of SPI gels. Lower gelation temperatures were usually observed for 7S-rich lines. The absence of A3 and the combination of A1, A2 and A4 subunits of 11S fraction may suggest the formation of stiffer gels. A more detailed study of the frequency dependence of G′ for the various networks formed also indicated that differences in subunit composition influenced the network structures.

Soymilk was made from 10 soybean [Glycine max (L.) Merr.] lines grown at three locations for 2 years, using an 18:1 water/soy protein ratio. Tofu was made with either glucono-delta-lactone (GDL) or calcium sulphate dihydrate (CS). Genotype and year effects were substantially greater than location effects on soybean protein content and seed composition; soymilk and tofu yield, solids levels, and pH; and tofu colour, hardness, and firmness. Genotype by location and genotype by year interaction effects were minor relative to the genotype and year effects. Yield of soymilk, GDL tofu, and CS tofu, which averaged 7.39 l, 6.29 kg, and 6.15 kg per kg soybeans, respectively, were all positively correlated with seed protein and stachyose, and negatively correlated with seed oil, free sugar, sucrose and remainder content. Seed protein was positively correlated with tofu hardness and firmness, while seed oil, free sugar, sucrose, and remainder content were generally negatively correlated with tofu quality parameters. Results of stepwise regression analysis showed that seed protein was the major determinant of soymilk yield and solids content, while soymilk yield was, in turn, the major factor determining GDL tofu yield. Procedures used in making soymilk and tofu play a major role in determining which seed component has a major effect on soymilk and tofu yield and quality.

The effects of long-term and transient exposure to elevated CO 2 concentrations on photosynthetic gas exchange and ethylene release by tomato leaves were investigated. The net CO 2 assimilation rate was enhanced when leaf tissue grown at ambient (35 Pa CO 2 ) levels was assayed at 100 Pa CO 2 . Leaf tissue grown at high (130 Pa) CO 2 exhibited a lower net CO 2 assimilation rate at high CO 2 levels than leaf tissue grown at ambient (35 Pa) CO 2 . This decrease in CO 2 exchange rate in response to growth at high CO 2 is typical of C 3 species

Current evidence indicates that ethylene is a volatile by-product of amino acid metabolism. Ethylene synthesis is linked with nitrogen metabolism through methionine and S-adenosylmethionine and as a volatile emission may serve as a non-destructive probe of amino acid turnover during photosynthesis and photorespiration. Very little is known about the relationship between ethylene and CO2 gas exchange in photosynthetic tissue. CO2 enhances the rate of ethylene release from leaf tissue in the light (1–5) and it has been proposed (3) that ethylene synthesis and/or metabolism may be moderated by photosynthetic and respiratory processes in photosynthetically competent leaves through changes in the internal CO2 concentrations.

Petioles of the celery-leaved buttercup, Ranunculus sceleratus L., elongate when the leaf blades are submerged. This elongation has been correlated with a rise in internal C 2 H 4 levels. Treatment with C 2 H 4 in air will also enhance petiole growth. The submergence-induced growth is inhibited in the presence of CoCl 2 solutions. Cobalt treatment does not inhibit petiole elongation when the leaves are exposed to C 2 H 4 in air or when the tissues are submerged in C 2 H 4 -saturated CoCl 2 solutions. Thus, the physiological effect of CoCl 2 is completely mitigated by treatment with C 2 H 4 . Cobalt can directly inhibit C 2 H 4 production by leaf tissue. There is no evidence of the effect being dependent on changes in CO 2 metabolism.

The effects of ethylene evolved from ethephon on leaf and whole plant photosynthesis in Xanthium strumarium L. were examined. Ethylene-induced epinasty reduced light interception by the leaves of ethephon treated plants by up to 60%. Gas exchange values of individual, attached leaves under identical assay conditions were not inhibited even after 36 hours of ethylene exposure, although treated leaves required a longer induction period to achieve steady state photosynthesis. The speed of translocation of recently fixed 11C-assimilate movement was not seriously impaired following ethephon treatment; however, a greater proportion of the assimilate was partitioned downward toward the roots. Within 24 hours of ethephon treatment, the whole plant net carbon exchange rate expressed on a per plant basis or a leaf area basis had dropped by 35%. The apparent inhibition of net carbon exchange rate was reversed by physically repositioning the leaves with respect to the light source. Ethylene exposure also inhibited expansion of young leaves which was partially reversed when the leaves were repositioned. The data indicated that ethylene indirectly affected net C gain and plant growth through modification of light interception and altered sink demand without directly inhibiting leaf photosynthesis.

Woodrow, L., Thompson, R. G. and Grodzinski, B. 1988. Effects of ethylene on photosynthesis and partitioning in tomato, Lycopersicon esculentum Mill.—J. exp. Bot. 39: 667-684. The extended period of ethylene release from ethephon (2-chloroethylphosphonic acid) after application to intact tomato plants has provided a model system in which the effects of ethylene on photosynthetic metabolism and carbon partitioning has been studied. Ethylene release from leaf tissue after ethephon treatment was 10 times greater than that from untreated control leaves. The specific activity of 14C2H4 released from [14C] ethephon remained constant over several days demonstrating that the ethylene was derived from the applied ethephon. The ethephon-treated plants exhibited extreme epinasty of the leaves and 24 h after application the flower buds in the first visible cluster had abscised, leaf expansion at the apex had ceased and developing adventitious roots were visible on the lower stem. Rates of steady-state photosynthesis, respiration, photorespiration and transpiration were the same in treated and control leaves 24 h after ethephon application. Both treated and control leaves partitioned similar proportions of newly-fixed 14C from 14C02 into neutral (46-4%), acidic (14 0%), basic (5 0%) and insoluble (34 0%) leaf fractions under steady-state conditions. The speed of 11 C-assimilate movement in the stems of control plants (3-62 ± 0-42 cm min "1 towards the apex and 403 ±015 cm min-1 towards the roots) was more rapid than in the ethephon-treated plants (2-90±0-31 cm min"1 upwards and 2-59±0-22 cm min-1 downwards). Furthermore, in the control plants 20 0 + 5-4% of the 14C exported to the plant from the source leaf was transported towards the developing flower cluster and young leaves. Twenty-four hours after ethephon application only 6-5 ± 1-7% of the exported 14C was translocated towards the shoot. Contrary to some reports ethylene did not affect steady-state gas exchange processes while carbon partitioning was significantly altered indicating that ethylene effects on photosynthetic carbon metabolism are indirect and not due to direct effects on photosynthetic processes per se. Key words— Ethylene, photosynthesis, partitioning. Correspondence to: Department of Horticultural Science, University of Guelph, Guelph, Ontario NIG 2W1, Canada.

Glycine decarboxylation and serine synthesis were studied in pea (Pisum sativum L.) leaf discs, in metabolically active intact chloroplasts, and in mitochondria isolated both partially by differential centrifugation (i.e. ;crude') and by further purification on a Percoll gradient. Glycolate, glyoxylate, and formate reduced glycine decarboxylase activity ((14)CO(2) and NH(3) release) in the crude green-colored mitochondrial fractions, and in the leaf discs without markedly altering serine synthesis from [1-(14)C]glycine. Glycolate acted because it was converted to glyoxylate which behaves as a noncompetitive inhibitor (K(i) = 5.1 +/- 0.5 millimolar) on the mitochondrial glycine decarboxylation reaction in both crude and Percoll-purified mitochondria. In contrast, formate facilitates glycine to serine conversion by a route which does not involve glycine breakdown in the crude mitochondrial fraction and leaf discs. Formate does not alter the conversion of two molecules of glycine to one CO(2), one NH(3), and one serine molecule in the Percoll-purified mitochondria. In chloroplasts which were unable to break glycine down to CO(2) and NH(3), serine was labeled equally from [(14)C]formate and [1-(14)C]glycine. The maximum rate of serine synthesis observed in chloroplasts is similar to that in isolated metabolically active mitochondria. Formate does not appear to be able to substitute for the one-carbon unit produced during mitochondrial glycine breakdown but can facilitate serine synthesis from glycine in a chloroplast reaction which is probably a secondary one in vivo.

Ethylene gas is a normal product of plant metabolism and is considered to be an important co-regulator of many developmental processes. In higher plants ethylene biosynthesis proceeds from methionine through S-adenosylmethionine (SAM) to 1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene (Yang, 1982). SAM functions as a methyl donor in many biochemical reactions in living tissue and is not restricted to the ethylene biosynthetic pathway. ACC however appears to have a unique role as the immediate precursor of ethylene. Green leaf tissue normally has a low endogenous ethylene production rate (20–200 pmoles/gm fr wt/h) and until recently studies with mature leaf tissue have been primarily concerned with leaf senescence and the role of ethylene in this process. Interest in leaf tissue has been increased by the observation that photosynthesis can play a role in ethylene metabolism (Gepstein, Thimann, 1980; de Laat et al., 1981; Grodzinski et al., 1982a,b; 1983; Horton et al., 1982). Several studies earlier suggested that light inhibits ethylene production in photosynthetically active leaf tissue when compared to rates obtained in the dark (Gepstein, Thimann, 1980; de Laat et al., 1981). However when leaf tissue is illuminated and the CO2 levels within the experimental system are maintained above the compensation point this inhibition is not apparent in either C3 or C4 plants (Grodzinski et al., 1982a,b;1983). Interestingly in the light ethylene release from Cl tissue never exceeds that in the dark even under conditions of high t02. The major inhibitory effect attributed to light is due to the depressed CO2 levels which are a result of the balance of photosynthetic and respiratory activity within the tissue (Grodzinski et al., 1982a). The difference between C3 and C4 plants may reflect the different carboxylation patterns in These two types and the relative ability to regulate internal CO2 concentrations. The amount of carbon flowing through the ethylene pathway is very small (pmoles carbon/mg Chl/h) in comparison to the flow through the major metabolic pathways (pmoles carbon/mg Chl/h). Ethylene metabolism and the resultant physiological effects may be subject to the many processes that can significantly modify the internal CO2 environment of the tissue. Ethylene release is responsive to changes in external CO2 concentration over the range extending from 0.0 to 0.10% which includes normal ambient levels (Woodrow, 1982; Woodrow and Horton, in preparation). Furthermore, a significant production of CO2 within the tissue from a photorespiratory intermediate (eg. glycolate) could represent a homeostatic mechanism by which internal CO2 pools may regulate ethylene metabolism. This would parallel the proposed role for photorespiration as a means of dissipating reducing energy under photo-oxidative conditions.

The stimulatory effect of CO2 on ethylene evolution from photosynthetically active excised and intact leaf tissue of both C3 and C4 plants is now well documented (Dhawan, Bassi, and Spencer, 1981; Fuhrer, 1983; Grodzinski, Boesel, and Horton, 1982a, b; 1983; Grodzinski, 1984; Kao and Yang, 1982; Woodrow and Grodzinski, 1987). The range of CO2 concentrations over which ethylene release is most responsive, 50 to 1500 ul L−1, coincides with those encountered by leaf tissue in sealed greenhouse environments under conditions of CO2 depletion or CO2 enrichment (Porter and Grodzinski, 1985; Woodrow and Grodzinski, 1987). Interestingly the current global CO2 levels and the predicted future elevated concentrations also fall within this range. Because the stimulation of ethylene release by elevated CO2 is direct and readily reversible (Grodzinski et al., 1982a, b; 1983) in both C3 and C4 plants we originally suggested that CO2 may stimulate the synthesis of ACC or ethylene and/or affect the retention and metabolism of ethylene (Grodzinski et al., 1982a,b). Nilsen and Hodges (1983) and Fuhrer (1985) also present data which support the concept of retention as a mechanism of the CO2 effect. Alternately Kao and Yang (1982) favour the view that the ACC to ethylene conversion step is directly affected by CO2. Incubations of leaf tissue at high CO2 concentrations have also resulted in increased ethylene-forming enzyme content (Philosoph-Hadas, Aharoni, and Yang, 1986).