Reid G. Palmer

Soybean susceptibility to manufactured nanomaterials with evidence for food quality and soil fertility interruption

Based on previously published hydroponic plant, planktonic bacterial, and soil microbial community research, manufactured nanomaterial (MNM) environmental buildup could profoundly alter soil-based food crop quality and yield. However, thus far, no single study has at once examined the full implications, as no studies have involved growing plants to full maturity in MNM-contaminated field soil. We have done so for soybean, a major global commodity crop, using farm soil amended with two high-production metal oxide MNMs (nano-CeO2 and -ZnO). The results provide a clear, but unfortunate, view of what could arise over the long term: (i) for nano-ZnO, component metal was taken up and distributed throughout edible plant tissues; (ii) for nano-CeO2, plant growth and yield diminished, but also (iii) nitrogen fixation—a major ecosystem service of leguminous crops—was shut down at high nano-CeO2 concentration. Juxtaposed against widespread land application of wastewater treatment biosolids to food crops, these findings forewarn of agriculturally associated human and environmental risks from the accelerating use of MNMs.

GENOMES, MULTIPLE ORIGINS, AND LINEAGE RECOMBINATION IN THE GLYCINE TOMENTELLA (LEGUMINOSAE) POLYPLOID COMPLEX: HISTONE H3-D GENE SEQUENCES

Abstract Relationships among the various diploid and polyploid taxa that comprise Glycine tomentella have been hypothesized from crossing studies, isozyme data, and repeat length variation for the 5S nuclear ribosomal gene loci. However, several key questions have persisted, and detailed phylogenetic evidence from homoeologous nuclear genes has been lacking. The histone H3‐D locus is single copy in diploid Glycine species and has been used to elucidate relationships among diploid races of G. tomentella, providing a framework for testing genome origins in the polyploid complex. For all six G. tomentella polyploid races (T1—T6), alleles at two homoeologous histone H3‐D loci were isolated and analyzed phylogenetically with alleles from diploid Glycine species, permitting the identification of all of the homoeologous genomes of the complex. Allele networks were constructed to subdivide groups of homoeologous alleles further, and two‐locus genotypes were constructed using these allele classes. Results suggest that some races have more than one origin and that interfertility within races has led to lineage recombination. Most alleles in polyploids are identical or closely related to alleles in diploids, suggesting recency of polyploid origins and spread beyond Australia. These features parallel the other component of the Glycine subgenus Glycine polyploid complex, G. tabacina, one of whose races shares a diploid genome with a G. tomentella polyploid race.

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

SummaryThe 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.

Irreproducibility of the soybean pollen-tube pathway transformation procedure

The interest in developing tissue culture-independent genetic transformation methods for plants has been growth. The pollen-tube pathway transformation technique is one method; however, this method is controversial because it is difficult to duplicate and produces insufficient molecular evidence to confirm transformation. Our objective was to evaluate the robustness of the soybean pollen-tube pathway technique (Glycine max L. Merr.). Solutions of purified DNA constructs carrying abar marker gene and agus reporter gene or a gene of interest (npk1) were applied to severed styles of flowers 6–8 h after self-pollination. The experiment was repeated 3 summers in the field, in which 4 DNA constructs and 7 soybean genotypes were tested. A total of 4793 progeny seeds were harvested from 5590 individually treated soybean flowers. All seeds were germinated and screened for transformants with herbicide spray, histochemical GUS assay, and Southern blot analysis. Although 2% of progenies showed partial resistance to the herbicide, no positive plants were identified from GUS assay and Southern analysis. Our results indicate that soybean pollen-tube pathway transformation is not reproducible.

Inheritance of two independent isozyme variants in soybean plants derived from tissue culture

SummarySoybean [Glycine max (L.) Merr.] plants were regenerated via somatic embryogenesis from nine soybean cultivars. Our objective was to identify and characterize genetically novel mutations that would further our understanding of the soybean genome. Variant isozyme patterns were observed in two independent tissue culturederived lines. Genetic analyses were conducted on these two isozyme variants, and they were heritable. No variant isozyme patterns were evident in control (parental) soybean lines. In the cultivar BSR 101, a mutation of Aco2-b (aconitase) to a null allele was detected. The Aco2-bn mutant, Genetic Type T318, had not been previously observed in soybean. In the Chinese cultivar Jilin 3 (PI 427.099), a chlorophyll-deficient plant was identified that also lacked two mitochondrial malate-dehydrogenase (Mdh null) isozyme bands. These two mutant phenotypes, chlorophyll-deficient and Mdh null, were found to cosegregate. The Jilin 3 mutant, Mdh1-n (Ames 1) y20 (Ames 1) Genetic Type T317, was allelic to three chlorophyll-deficient, Mdh1 null mutants [Mdh1-n (Ames 2) y20 (Ames 2) (T323), Mdh1-n (Ames 3) y20 (Ames 3) (T324), and Mdh1-n (Ames 4) y20 (Ames 4) (T325)] previously identified from a transposon-containing soybean population, and to a chlorophyll-deficient, Mdh1 null mutant [Mdh1-n (Urbana) y20 (Urbana) k2, Genetic Type T253] which occurred spontaneously in soybean. The recovery of two isozyme variants from progeny of 185 soybean plants regenerated from somatic embryogenesis indicates the feasibility of selection for molecular variants.

Conditional lethality involving a cytoplasmic mutant and chlorophyll-deficient malate dehydrogenase mutants in soybean.

SummaryConditional lethality in soybean, Glycine max (L.) Merr., occurred in F2 plants when cytoplasmicchlorophyll mutant Genetic Type T275 was the female parent and when either nuclear mutants T253 or T323 plants were the male parents. Mutant T253 [Mdh1-n (Urbana) y20 (Urbana) k2] is missing two of three mitochondrial malate dehydrogenase isozymes [Mdh1-n (Urbana)] and has yellowish-green leaves [y20 (Urbana)] and a tan-saddle pattern seed coat (k2). Mutant T323 [Mdh1-n (Ames 2) y20 (Ames 2)] also is missing two of three mitochondrial malate dehydrogenase isozymes [Mdh1-n (Ames 2)] and has yellowishgreen leaves [y20 (Ames 2)], but has yellow seed coat (K2). Mutants T275, T253, and T323 are viable both in the field and glasshouse. The genotypes cyt-Y2 Mdh1-n (Urbana) y20 (Urbana) k2/Mdh1-n (Urbana) y20 (Urbana) k2 and cyt-Y2 Mdh1-n (Ames 2) y20 (Ames 2)/Mdh1-n (Ames 2) y20 (Ames 2) are conditional lethals. These genotypes are lethal under field conditions, but plants survive in reduced light under shadecloth in the glasshouse. We do not know if their interaction with cyt-Y2 is due to Mdh1-n, y20, or Mdh1-n y20. The reciprocal cross (cyt-Y2 as male parent) gives viable genotypes. These conditional lethal genotypes should be useful for studies on the interaction between organelle and nuclear genomes.

Reply to Lombi et al.: Clear effects of manufactured nanomaterials to soybean

Lombi et al. (1) have two concerns with our study (2): (i) nano-ZnO may not reach soils in “neat” form as it does in other Zn forms, which are already regulated; and (ii) the nano-CeO2 concentrations we used are much larger than predicted from exposure modeling. They assert that we should have studied different materials, at different concentrations, as determined by “proper assessment of the pathways.” This point does not change the importance of what we researched and reported: If these manufactured nanomaterials (MNMs) occur in soil at the concentrations studied, then the reported outcomes are possible. Indeed, our findings, which elucidate the key processes involved, will be essential for interpretation of future exposure assessments.