Somatic embryogenesis from cultured epicotyls and primary leaves of soybean [Glycine max (L.) Merrill]

Summary Regeneration of several varieties of soybean [Glycine max (L.) Merrill] by somatic embryogenesis from cultured epicotyls and primary leaves has been demonstrated. Somatic embryogenesis was induced from epicotyls and primary leaves when cotyledon halves with the intact zygotic embryo axes were cultured on Murashige and Skoog (MS) medium supplemented with 10 mg 1⁻¹ (45.2 μM) 2,4-D. Stable, continuously proliferating globular embryo cultures (GEC) were established from small groups of somatic embryos on MS medium supplemented with 20 mg 1⁻¹ (90.5 μM) 2,4-dichlorophenoxyacetic acid (2,4-D). Rapid multiplication of shoot tips from germinating somatic embryos was achieved on Cheng’s basal medium (CBO) containing 2.5 mg 1⁻¹ (11.3 μM) 6-benzyladenine. Fertile plants were obtained from individual somatic embryos and in vitro propagated adventitious shoot bud cultures.     

Soluble carbohydrate content of soybean [Glycine max (L.) merr.] somatic and zygotic embryos during development

Summary Somatic and zygotic embryos of soybean cv. Jack were analyzed for soluble carbohydrate, total lipids, and protein during development. Zygotic embryos accumulated trace amounts of fructose, galactose, and galactinol., whereas somatic embryos contained only trace amounts of galactose. Somatic embryos accumulated much higher glucose levels than zygotic embryos. Both somatic and zygotic embryos contain low levels of sucrose, myoinositol, and pinitol. Raffinose and stachyose accumulated in the late developmental stages of zygotic embryos, but only stachyose was found to accumulate in the late stage somatic embryos. Zygotic embryos contained low total lipid levels up to 50 d after flowering (DAF) and then the levels increased to 16% by 55 DAF and 21% at 65 DAF. Somatic embryos had low levels of total lipids throughout development with the maximum of only 4.7%. Soybean zygotic embryos contained about 40% protein throughout development, while the protein concentration of somatic embryos decreased from 44% to 25% as maturation approached. These studies demonstrate that the composition of Jack zygotic embryos is similar to that described for other cultivars during development while the somatic embryo composition and size is markedly different. The low somatic embryo germination often noted might be due to the abnormal development as shown by a composition different from that of mature zygotic embryos. The low concentration of the raffinose series sugars might be especially important factors.     

Effect of 2,4-dichlorophenoxyacetic acid concentration on somatic embryogenesis and heritable variation in soybean [Glycine max (L) merr.]

Summary The frequency and quality of embryogenic response from cotyledons of immature zygotic soybean embryos varied with 2,4-dichlorophenoxyacetic acid (2,4-D) concentration in the culture medium. The frequency of variants among progeny of regenerated plants decreased with an increase of 2,4-D concentration. Teratogenic effects on embryo morphology and development were greatest at 22.5μM 2,4-D and decreased with increasing 2,4-D. At the lowest 2,4-D concentration tested, 22.5μM, morphologically abnormal, cotyledonary-stage somatic embryos were produced. Ten percent or less of these embryos converted to plants. Over the nine genotypes tested, 40% of the families derived from plants regenerated under a low 2,4-D concentration manifested heritable variation. In contrast, embryogeny was suppressed at the globular stage by the highest 2,4-D concentration tested, 200μM. Eighty to one-hundred percent of the embryos organized under this latter 2,4-D level converted to plants. Only 3% of the families from the progeny of plants regenerated under a high 2,4-D concentration exhibited heritable variation. This is Journal Paper No. J-14217 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2974. The mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture or Iowa State University and does not imply its approval to the exclusion of other products that may be suitable. This work was supported, in part, by American Soybean Association grant no. 400-46-73-15-2763.     

Screening of soybean, Glycine max L.) Merrill, lines for somatic embryo induction and maturation capability from immature cotyledons

Summary Seventeen breeding lines of soybean, Glycine max (L.) Merrill, and cv. Jack, from relative maturity groups 0.3–7.5 were assessed for their ability to undergo somatic embryogenesis. The goal of this study was to determine which lines had high embryogenic capacity. We also sought to understand the relationship between relative maturity and embryogenesis. Embryos from immature cotyledons were initiated on solid MS medium with varying levels of 2,4-dichlorophenoxyacetic acid (2,4-D). Qualitative and quantitative measures of initiation, proliferation, differentiation, and maturation were recorded. The breeding lines differed significantly with respect to percent induction, number of embryos induced, and quality of induced embryos. After 1 mo, of proliferation, two early maturing lines, the control, Jack, and NK-5, had the best overall performance. High percent response of proliferating embryos was positively associated with lower maturity groups. Relatively high concentrations of 2,4-D (compared with that used in prolifcrating medium, e.g., 226 μM; 50 mg l⁻¹) in the initiating medium reduced numbers of embryo clusters per cotyledon initiated and percent initiation, and the concentration of 2,4-D affected the proliferation of somatic embryos in a breeding line-dependent manner. The breeding lines differed significantly in the time to produce mature somatic embryos. There was a positive correlation between immature embryo quality and number of differentiated somatic embryos produced. Retired.     

Fatty acid composition of soybean (Glycine max (L.) merr.) somatic embryos

Summary Somatic embryos from four soybean cultivars were matured for 30 and 45 d. Success of embryo germination was evaluated for each length of maturation. The percentage of somatic embryos undergoing successful germination, as defined by rooting and shoot emergence, was greater for embryos matured 45 d than for embryos matured 30 d. Therefore, embryos matured for 45 d are probably physiologically more mature than embryos matured for 30 d. Relative percentages of fatty acids comprising oils and lipids of somatic embryos were determined for each length of maturation and for each cultivar. Variation in relative percentages of palmitic acid, oleic acid, and linoleic acid was affected by length of maturation. However, these changes were genotype dependent. A significant interaction between the cultivars Clark and Maple Arrow and stage of maturation was observed for levels of oleic acid. No other interactions were observed. These data suggest that if changes in relative percentages of certain fatty acids are associated with soybean somatic embryo maturation the changes are genotype dependent. This is journal paper No. J-12870 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2763. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture and does not imply its approval to the exclusion of other products that also may be suitable. This research was supported in part by grants from the American Soybean Association Development Foundation and the Iowa Soybean Promotion Board.     

Embryogenic response of multiple soybean [Glycine max (L.) merr.] cultivars across three locations

Summary Nine soybean [Glycine max (L.) Merr.] cultivars representing midwestern, mid-south, and southern US growing regions were evaluated at each of three locations (Athens, GA; Lexington, KY; and Wooster, OH) using uniform embryogenic induction and proliferation protocols in order to evaluate the portability of soybean somatic embryogenic protocols to different locations. The experimental design minimized variation between locations by having all cultivars present at all locations on all days. A quantitative weighted score for primary embryo induction was developed on average embryo number per explant and was used to describe non-embryogenic, poorly embryogenic, moderately embryogenic, and highly embryogenic responses. Ranking of cultivars remained similar across all locations, indicating a uniform transportability of the protocol, at least as far as embryo induction is concerned. Continued proliferation of embryogenic cultures was also measured using a repetitive growth measure but few meaningful conclusions could be made due to the high level of variability including inconsistent growth of cultures between each subculture. Overall, several cultivars were identified as being uniformly embryogenic or non-embryogenic at the primary induction phase at all locations, and we predict that those embryogenic cultivars could be used by any laboratory for high-efficiency induction of embryogenesis. The best of these cultivars, ‘Jack’, was uniformly responsive across all locations and should be selected as the genotype most likely to yield positive results when attempting to culture and genetically engineer soybeans via embryogenic protocols.     

Mapping QTLs for tissue culture response in soybean (Glycine max (L.) Merr.)

Hempseed is rich in polyunsaturated fatty acids (PUFAs), which have potential as therapeutic compounds for the treatment of neurodegenerative and cardiovascular disease. However, the effect of hempseed meal (HSM) intake on the animal models of these diseases has yet to be elucidated. In this study, we assessed the effects of the intake of HSM and PUFAs on oxidative stress, cytotoxicity and neurological phenotypes, and cholesterol uptake, using Drosophila models. HSM intake was shown to reduce H₂O₂ toxicity markedly, indicating that HSM exerts a profound antioxidant effect. Meanwhile, intake of HSM, as well as linoleic or linolenic acids (major PUFA components of HSM) was shown to ameliorate Aβ42-induced eye degeneration, thus suggesting that these compounds exert a protective effect against Aβ42 cytotoxicity. On the contrary, locomotion and longevity in the Parkinson’s disease model and eye degeneration in the Huntington’s disease model were unaffected by HSM feeding. Additionally, intake of HSM or linoleic acid was shown to reduce cholesterol uptake significantly. Moreover, linoleic acid intake has been shown to delay pupariation, and cholesterol feeding rescued the linoleic acid-induced larval growth delay, thereby indicating that linoleic acid acts antagonistically with cholesterol during larval growth. In conclusion, our results indicate that HSM and linoleic acid exert inhibitory effects on both Aβ42 cytotoxicity and cholesterol uptake, and are potential candidates for the treatment of Alzheimer’s disease and cardiovascular disease.     

In vitro root induction by 24-epibrassinolide on hypocotyl segments of soybean [Glycine max (L.) Merr.]

Soybean hypocotyl segments were treated in the dark with 24-epibrassinolide (BR) at a range of concentrations for different durations. The maximum effect on adventitious root induction, both in terms of number and length was obtained at very low concentration (0.0001 ppm) of BR applied for 8 h. Higher concentrations were supraoptimal unless applied for a shorter period (4 h). BR was ineffective when applied at low concentration in continuous light.     

Soybean [Glycine max (L.) merrill] embryogenic cultures: The role of sucrose and total nitrogen content on proliferation

Summary To improve proliferation of soybean cultures in liquid medium, the effects of sucrose; total inorganic nitrogen; content of No₃ ⁻, NH₄ ⁺, Ca²⁺, PO₄ ³⁻, K⁺; NH₄ ⁺/NO₃ ⁻ ratio; and medium osmotic pressure were studied using cv. Jack. Sucrose concentration, osmotic pressure, total nitrogen content, and ammonium to nitrate ratio were found to be the major factors controlling proliferation of soybean embryogenic cultures. Growth decreased linearly as sucrose concentration increased from 29.7 mM to 175.3 mM. A sucrose concentration of 29.2 mM, a nitrogen content of 34.9 mM, at 1 to 4 ammonium to nitrate ratio were found to be optimal for the fastest proliferation of soybean embryogenic cultures. There was no significant effect on proliferation of cultures when concentrations of NH₄ ⁺, Ca²⁺, PO₄ ³⁻, and K⁺ were tested in the range of 3.50 to 10.50, 1.02 to 3.06, 0.68 to 2.04, and 22.30 to 36.70 mM, respectively. The relative proliferation of embryogenic cultures of four soybean genotypes was evaluated in Finer and Nagasawa medium and in the new medium formulation. Despite genotype-specific differences in growth, the genotypes tested showed a biomass increase in the new formulation equal to 278, 269, 170, and 251% for Chapman, F138, Jack, and Williams 82, respectively, relative to their growth on standard FN medium. Due to its lowered sucrose and nitrogen content, we are referring to the new medium as FN Lite.     

Maturation and germination of somatic embryos as affected by sucrose and plant growth regulators in soybeans Glycine gracilis Skvortz and Glycine max (L.) Merr.

The effects of sucrose on maturation and of plant growth regulators on germination of soybean somatic embryos were investigated for the purpose of developing an efficient culture method for plant recovery. Somatic embryos produced on medium with a low sucrose concentration (5 gl^-1), less than 1 mm in length, 0.6 mg in fresh weight, and green in color, were grown for 2 weeks on MS medium containing 5 gl^-1 or 30 gl^-1 sucrose and then for another 5 weeks on MS medium containing 5–90 gl^-1 sucrose. The highest increase in fresh weight of somatic embryos was obtained in the treatment of transferring from 30 gl^-1 sucrose (2 weeks) to 60 gl^-1 (5 weeks). With the increase in fresh weight, the somatic embryos gradually changed color from green to yellow, and finally to white, when they stopped growth. Soybean seed storage proteins (-conglycinin and glycinin) were accumulated in somatic embryos under tissue specific and stage specific control analogous to that in zygotic embryos. Exogenous gibberellic acid was effective in promoting precocious germination of premature soybean somatic embryos, but was not necessary for the germination of mature somatic embryos. The efficiency of somatic embryo germination was as high as 77% from semi-wild soybean and 60–64% from cultivated soybeans, showing that the plant regeneration system developed in this study was efficient and practical.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BR brassinolide - GA₃ gibberellic acid - IBA indolebutyric acid - NAA -naphthaleneacetic acid - PAGE polyacrylamide gel electrophoresis - SDS Sodium Lauryl Sulfate     

Indole butyric acid induces regeneration of phenotypically normal apricot (Prunus armeniaca L.) plants from immature embryos

A prerequisite for most transformation systems is an efficient and reliable method to regenerate phenotypically normal plants. Immature embryos or cotyledons were cultured at three developmental stages (stage 1, 2 and 3, PF=3, 30–60, and 100, respectively) from two unrelated apricot genotypes, Zard and NJA82. Explants were cultured on MS media supplemented with either BA or TDZ at four concentrations (0, 0.5, 5.0 or 20 M) and 2,4-D at 0 or 1 M. Stage 1 embryos cultured on MS medium without growth regulators formed embryoid-like structures. Shoot primordia induction was greatest with stage 2 cotyledons on media containing 5–20 M TDZ and 1 M 2,4-D, although shoot morphology was abnormal, especially with the highest level of TDZ. In another factorial experiment, stage 2 cotyledons were cultured on media containing TDZ (0, 5, 7.5, 10, 15 or 20 M) in combination with either no auxin, 1 M 2,4-D, 1 M IBA, or 5 MIBA. Regeneration percentages of 80% or more were observed on media containing 1–5 M IBA and 5–10 M TDZ. The medium containing 5 M IBA and no TDZ exhibited the highest frequency of phenotypically normal plantlet regeneration.Abbreviations BA 6-benzylaminopurine - IBA indole-3-butyric acid - 2,4-D 2,4 dichlorophenoxyacetic acid - 2iP 2-isopentenyladenine - MS Murashige and Skoog basal medium - NAA 1-naphthaleneacetic acid - PF percent fill [(embryo length/seed length) × 100] - TDZ thidiazuron [N-phenyl-N(1,2,3,-thidiazol-5-yl)-urea] - WPM McCown's woody plant medium     

Cryopreservation of the SB-M photosynthetic soybean [Glycine max (L.) Merr.] suspension culture

Summary The photosynthetic cell suspension culture of soybean [Glycine max (L.) Merr. cv. Corsoy] (SB-M) was successfully cryopreserved in liquid nitrogen using a preculture and controlled freezing to −40° C (two-step) freezing method. The effective method included a preculture treatment with gradually increasing levels of sorbitol added to the 3% sucrose already present in the medium. The cells were then placed in a cryoprotectant solution [10% DMSO (dimethylsulfoxide) and 9.1% sorbitol, or 10% DMSO and 8% sucrose], incubated for 30 min at 0° C, cooled at a rate of 1° C/min to −40° C, held at −40° C for 1 h, and then immersed directly into liquid nitrogen. The cells were thawed at 40° C and then immediately placed in liquid culture medium. The cell viabilities immediately after thawing were 75% or higher in all cases where cell growth resumed. The original growth rate and chlorophyll level of the cells was recovered within 40 to 47 d. If the sorbitol level was not high enough or the preculture period too short, growing cultures could not be recovered. Likewise, survival was not attained with cryoprotectant mixtures consisting of 15% DMSO, 15% glycerol, and 9.1% sucrose or 15% glycerol and 8% sucrose. The successful method was reproducible, thus allowing long-term storage of this and certain other unique photosynthetic suspension cultures in liquid nitrogen.     

Rhizobium inoculant for soybean [Glycine max (L.) Merrill] in Mekong Delta

Summary Rhizobial inoculation trials were conducted in an acid heavy clay soil in Mekong Delta, Viet Nam, using peat based inoculants produced locally and the commercial granular product of Nitragin CCo., Wisconsin, USA. The pH of these soils ranged from 4.5 to 5.1. Two soybean cultivars, MTD₆ and MTD₁₀, were tested as host plants. There were no significant differences between locally made inoculant treated plants and the uninoculated controls in both cultivars. But, the Nitragin inoculation improved all plant characteristics examined in both cultivars. Grain yields of Nitragin inoculated plants of cultivar MTD₆ and cultivar MTD₁₀ were 6.5 and 5.5 times as much as those of the controls; protein content of grain increased 11 and 16 percent, respectively. Well nodulated plants had shorter life cycles, flowering durations, and days to flowering. The Rhizobium symbiosis resulted in an additional 153 kg grain-N/ha. These studies show that a surface coated commercial multistrain inoculant can be used to successfully grow soybeans in the acid, heavy clay soils of the Mekong Delta.     

Identification of QTL underlying somatic embryogenesis capacity of immature embryos in soybean (Glycine max (L.) Merr.)

High embryogenesis capacity of soybean (Glycine max (L.) Merr.) in vitro possessed potential for effective genetic engineering and tissue culture. The objects of this study were to identify quantitative trait loci (QTL) underlying embryogenesis traits and to identify genotypes with higher somatic embryogenesis capacity. A mapping population, consisting of 126 F_5:6 recombinant inbred lines, was advanced by single-seed-descent from cross between Peking (higher primary and secondary embryogenesis) and Keburi (lower primary and secondary embryogenesis). This population was evaluated for primary embryogenesis capacity from immature embryo cultures by measuring the frequency of somatic embryogenesis (FSE), the somatic embryo number per explant (EPE) and the efficiency of somatic embryogenesis (ESE). A total of 89 simple sequence repeat markers were used to construct a genetic linkage map. Six QTL were associated with somatic embryogenesis. Two QTL for FSE were found, QFSE-1 (Satt307) and QFSE-2 (Satt286), and both were located on linkage group C2 that explained 45.21 and 25.97% of the phenotypic variation, respectively. Four QTL for EPE (QEPE-1 on MLG H, QEPE-2 on MLG G and QEPE-3 on MLG G) were found, which explained 7.11, 7.56 and 6.12% of phenotypic variation, respectively. One QTL for ESE, QESE-1 (Satt427), was found on linkage group G that explained 6.99% of the phenotypic variation. QEPE-2 and QESE-1 were located in the similar region of MLG G. These QTL provide potential for marker assistant selection of genotypes with higher embryogenesis.     

Selection of transgenic meristematic cells utilizing a herbicidal molecule results in the recovery of fertile transgenic soybean [Glycine max (L.) Merril] plants at a high frequency

Imazapyr is a herbicidal molecule that concentrates in the apical meristematic region of the plant. Its mechanism of action is the inhibition of the enzymatic activity of acetohydroxyacid synthase, which catalyses the initial step in the biosynthesis of isoleucine, leucine and valine. The selectable marker gene, ahas, was previously isolated from Arabidopsis thaliana and contains a mutation at position 653 bp. Combining the use of imazapyr, the ahas gene and a multiple shooting induction protocol has allowed us to develop a novel system to select transgenic meristematic cells after the physical introduction of foreign genes. In this study, we describe a protocol to obtain a high frequency of fertile transgenic soybean plants that is variety-independent. Received: 14 June 1999 / Accepted: 8 October 1999     

A novel Agrobacterium rhizogenes-mediated transformation method of soybean [Glycine max (L.) Merrill] using primary-node explants from seedlings

A novel Agrobacterium rhizogenes-mediated transformation method using a primary-node explant from Dairyland cultivar 93061 was developed for soybean using the disarmed Agrobacterium strain SHA17. Transformed plants regenerated from explants inoculated with SHA17 were fertile and phenotypically normal. In a comparative experiment, regeneration frequencies were not significantly different between explants inoculated with A. rhizogenes strain SHA17 and Agrobacterium tumefaciens strain AGL1; however, a 3.5-fold increase in transformation efficiency [(number of Southern or TaqMan-positive independent events/total number of explants inoculated) × 100] was found for explants cocultured with SHA17 compared to AGL1 (6.6 and 1.64%, respectively). Southern analysis of 48 T₀ plants suggested that 37.5, 23, and 39.6% of the T₀ plants contained 1, 2, and 3 or more T-DNA fragments integrated into the genome, respectively. Additionally, T₁ progeny analysis of 8 independent events resulted in typical Mendelian inheritance of T-DNA genes. Of seven T₀ plants that had two or more T-DNA fragments, six contained multiple loci segregating in T₁ progenies. Further analysis of four lines confirmed the presence of PAT, GUS, and/or DsRED2 proteins in transgenic plants that were encoded on the T-DNA into the T₂ generation.     

Regeneration of fertile plants from protoplasts of soybean (Glycine max L. Merr.): genotypic differences in culture response

Fourteen soybean (Glycine max L.) genotypes were evaluated for their regenerability from protoplasts using a procedure previously descibed for the cultivar Clark 63. Protoplasts were isolated from immature cotyledon tissue and were cultured in liquid or agarose gelled KP8, MS or B5 medium with different sugars. Significant differences were observed in plating efficiency, which was as high as 63% in Jack and A-2396, and as low as 38% in X-3337. Upon regular dilution with K8 medium, 1–2 mm diameter colonies were formed in 5–6 weeks with all the genotypes tested. These colonies were then transferred onto MSB (MS salts; Murashige & Skoog, 1962 + B5 organics; Gamborg et al., 1968) medium with 0.5 mg l^–1 each of 2,4-D, BA and KN and 500 mg l^–1 CH for further growth. Once the colonies had become green, compact and nodular, and were 8–10 mm in size, they were transferred to regeneration medium. Upon regular subculturing, calli of six genotypes; A-2396, Chamberlain, Heilong-26, Jack, Resnick and XP-3015 developed shoots, with the regeneration frequency being highest 27% in Jack (52 calli out of 192 produced 8–12 shoots). The regenerated shoots from different genotypes were elongated and rooted. So far, sixty three complete plants have been obtained, including twelve A-2396, nineteen Chamberlain, fifteen Jack, nine Resnick and eight XP-3015. A total of thirty five plants have been transplanted into pots in the greenhouse. Sixteen have set seeds and others are producing flowers and pods.Abbreviations BA 6-benzyladenine - CH casein hydrolysate - 2,4-D 2,4-dichlorophenoxyacetic acid - FDA fluorescein diacetate - GA₃ gibberellic acid - IBA indolebutyric acid - KN kinetin - MES 2[N-morpholino] ethane sulfonic acid - NAA naphthaleneacetic acid - TH thidiazuron - ZT zeatin     

Apical proliferation of embryogenic tissue of soybean [Glycine max (L.) Merrill]

Somatic embryos and embryogenic tissues were initiated from immature zygotic embryos of soybean [Glycine max (L.) Merrill cv. Fayette]. Zygotic embryos were placed on a medium containing 40 mg/l of 2,4-dichlorophenoxyacetic acid and 6% sucrose. Somatic embryos were first seen 4 weeks after cultures were initiated. Following transfer, secondary somatic embryos proliferated directly from the apical or terminal portions of the older primary somatic embryos. Single somatic embryos or clusters of embryos were seen growing directly from the top of older somatic embryos. Light microscopy revealed that these embryos were of surface or subsurface origin. The apical soybean somatic embryo tissue may represent cotyledonary tissue (which has been shown to be most responsive) at a very young and manipulatable state.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - NAA naphthaleneacetic acid Salaries and research support were provided by state and federal funds appropriated to OARDC-OSU. Journal Article No. 131-87     

Carbohydrate oxidation by leucoplasts from suspension cultures of soybean (Glycine max L.)

The aim of this work was to discover how leucoplasts from suspension cultures of soybean (Glycine max L.) oxidize hexose monophosphates. Leucoplasts were isolated from protoplast lysates on a continuous gradient of Nycodenz with a yield of 28% and an intactness of 80%. Incubation of the leucoplasts with ¹⁴C-labelled substrates led to ¹⁴CO₂ production, that was dependent upon leucoplast intactness, from [U-¹⁴C]glucose 6-phosphate, [U-¹⁴C]glucose 1-phosphate, [U-¹⁴C] fructose 6-phosphate and [U-¹⁴C]glucose+ATP, but not from [U-¹⁴C]fructose-1,6-bisphosphate or [U-¹⁴C]triose phosphate. The yield from [U-¹⁴C]glucose 6-phosphate was at least four times greater than that from any of the other substrates. When [1-¹⁴C]-, [2-¹⁴C]-, [3,4-¹⁴C]-, and [6-¹⁴C]glucose 6-phosphate were supplied to leucoplasts significant ¹⁴CO₂ production that was dependent upon leucoplast intactness was found only for [1-¹⁴C]glucose 6-phosphate. It is argued that soybean cell leucoplasts oxidize glucose 6-phosphate via the oxidative pentose phosphate pathway with very little recycling, and that in these plastids glycolysis to acetyl CoA is negligible.S.A.C. thanks the Science and Engineering Research Council for a research studentship.     

Effect of ammonium- and nitrate-nitrogen nutrition on aluminium tolerance of soybean (Glycine max L.)

Ammonium-nitrogen supply increased Al tolerance (parameter root elongation rate) of soybean (Glycine max L.) plants compared to nitrate-nitrogen supply when grown at constant pH in solution culture. This protective effect of ammonium against Al could only partially be attributed to lowered activity of monomeric aluminium species in the ammonium solution. For ammonium and nitrate-grown plants the relationship between Al concentration in the root tips and total length could be described by the same regression equation. The higher Al tolerance of soybean plants grown in the presence of ammonium was due to restricted ad/absorption of Al which resulted from competition with positively charged Al species for binding sites in the apoplast. Induction of higher symplastic Al tolerance is unlikely because preculture with ammonium decreased rather than increased aluminium tolerance of the plants.