Desiccation tolerance in developing soybean seeds: The role of stress proteins

The consistent correlation between desiccation tolerance in orthodox seed tissue and an accumulation of certain "late embryogenesis abundant" (LEA) proteins suggests that these proteins reduce desiccation-induced cellular damage. The aim of the present work was to test this hypothesis. Exogenous abscisic acid (ABA) was used to elevate the level of heal-soluble LEA-like proteins in axes from immature (30 days after flowering: mid-development) seeds of soybean ( Glycine max [L.] Merrill cv. Chippewa 64). As the LEA-like proteins accumulated in response to ABA, the leakage of all elements after desiccation and subsequent rehydration markedly declined. Both LEA-like protein accumulation and the decline in desiccation-induced electrolyte leakage were apparently dependent on the presence of ABA. Both effects of ABA were inhibited by cycloheximide. Light microscopy revealed a marked effect of the ABA on cellular integrity following desiccation. Osmotic stress also caused a decrease in desiccation-induced electrolyte leakage and stimulated the accumulation of LEA-like proteins. Our data are consistent with the hypothesis that the LEA-like proteins contribute to the increase in desiccation tolerance in response to ABA, and are consistent with a general protective role for these proteins in desiccation tolerance.     

Effects of defoliation on seed protein concentration in normal and high protein lines of soybean

Two high (NC106, NC111) and two normal (NC103, NC107) seed protein concentration lines, derived from two different recurrent selection populations of soybean (Glycine max L. Merr.) were subjected to partial defoliation at beginning seed fill (R5) under outdoor pot culture and field conditions. The aim of this study was to test the hypothesis that capacity to store N in vegetative organs and/or to mobilize that N to reproductive organs is associated with the high seed protein concentration trait. Symbiotic N₂ fixation was the sole source of N in the pot experiment and the major source of N (met > 50% of the N requirement) in the low N soil used in the field experiment. Seed protein concentration and seed yield at maturity in both experiments and N accumulation and mobilization between R5 and maturity in the pot experiment were measured. The four genotypes did not differ significantly with respect to the amount of N accumulated before beginning seed fill (R5). Removal of up to two leaflets per trifoliolate leaf at R5 significantly decreased the seed protein concentration of NC107/111 but had no effect on this trait in NC103/106. Defoliation treatments significantly decreased seed yield, whole plant N accumulation (N₂-fixation) during reproductive growth and vegetative N mobilization of all genotypes. Differences in harvest indices between the high and low protein lines accounted for approximately 35% of the differences in protein concentration. The two normal protein lines mobilized more vegetative N to the seed (average. 5.26 g plant^–1) than the two high protein lines (average. 4.28 g plant^–1). The two high seed protein lines (NC106, NC111) exhibited significantly different relative dependencies of reproductive N accumulation on vegetative N mobilization, 45% vs. 29%, in the control treatment. Whereas, NC103 with normal and NC106 with high seed protein concentration exhibited similar relative dependencies of reproductive N accumulation on vegetative N mobilization, (47% vs. 45%). Collectively, these results indicate that N stored in shoot organs before R5 and greater absolute and relative contribution of vegetative N mobilization to the reproductive N requirement are not responsible for the high seed protein concentration trait.Abbreviations DAT days after transplanting - R5 fifth reproductive stage according to Fehr and Caviness, 1977 Mention of 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 may also be suitable.     

Genomic organization and evolution of the soybean SB92 satellite sequence

Repetitive DNA sequences comprise a large percentage of plant genomes, and their characterization provides information about both species and genome evolution. We have isolated a recombinant clone containing a highly repeated DNA element (SB92) that is homologous to ca. 0.9% of the soybean genome or about 10⁵ copies. This repeated sequence is tandemly arranged and is found in four or five major genomic locations. FISH analysis of metaphase chromosomes suggests that two of these locations are centromeric. We have determined the sequence of two cloned repeats and performed genomic sequencing to obtain a consensus sequence. The consensus repeat size was 92 bp and exhibited an average of 10% nucleotide substitution relative to the two cloned repeats. This high level of sequence diversity suggests an ancient origin but is inconsistent with the limited phylogenetic distribution of SB92, which is found an high copy number only in the annual soybeans. It therefore seems likely that this sequence is undergoing very rapid evolution.     

Effect of Soil Temperature and pH on Resistance of Soybean to Heterodera glycines

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a major pest of soybean, Glycine max L. Merr. Soybean cultivars resistant to SCN are commonly grown in nematode-infested fields. The objective of this study was to examine the stability of SCN resistance in soybean genotypes at different soil temperatures and pH levels. Reactions of five SCN-resistant genotypes, Peking, Plant Introduction (PI) 88788, Custer, Bedford, and Forrest, to SCN races 3, 5, and 14 were studied at 20, 26, and 32 C, and at soil pH''s 5.5, 6.5, and 7.5. Soybean cultivar Essex was included as a susceptible check. Temperature, SCN race, soybean genotype, and their interactions significantly affected SCN reproduction. The effect of temperature on reproduction was quadratic with the three races producing significantly greater numbers of cysts at 26 C; however, reproduction on resistant genotypes remained at a low level. Higher numbers of females matured at the soil pH levels of 6.5 and 7.5 than at pH 5.5. Across the ranges of temperature and soil pH studied, resistance to SCN in the soybean genotypes remained stable.     

Effects of a Mutant Strain and a Wild Type Strain of Verticillium lecanii on Heterodera glycines Populations in the Greenhouse

A wild type strain ofVerticillium lecanii and a mutant strain with increased tolerance to the fungicide benomyl were evaluated in greenhouse experiments for effects on Heterodera glycines populations. Nematodes were applied at 300 eggs and juveniles per 4,550-cm³ pot (two soybean plants in 4,990 g loamy sand per pot) and at both 300 and 10,000 eggs and juveniles per 1,720-cm³ pot (one soybean plant in 2,060 g sand per pot). With 300 nematodes added per pot, both V. lecanii strains significantly reduced nematode populations in loamy sand (fungus applied at 0.02% dry weight per dry weight loamy sand) and sand (0.006% and 0.06% fungus application rates). The mutant strain applied at 0.002% to sand also significantly reduced cyst numbers. When 10,000 nematodes were added per pot, only the mutant strain at 0.06% significantly decreased population. Various media were tested for isolation of the fungus strains from prills, loamy sand, and sand, but the fungi were recovered from few of the greenhouse pots.     

Production of a lipopeptide antibiotic, surfactin, by recombinant Bacillus subtilis in solid state fermentation

Production of a lipopeptide antibiotic, surfactin, in solid state fermentation (SSF) on soybean curd residue, Okara, as a solid substrate was carried out using Bacillus subtilis MI113 with a recombinant plasmid pC112, which contains lpa-14, a gene related to surfactin production cloned at our laboratory from a wild-type surfactin producer, B. subtilis RB14. The optimal moisture content and temperature for the production of surfactin were 82% and 37 degrees C, respectively. The amount of surfactin produced by MI113 (pC112) was as high as 2.0 g/kg wet weight, which was eight times as high as that of the original B. subtilis RB14 at the optimal temperature for surfactin production, 30 degrees C. Although the stability of the plasmid showed a similar pattern in both SSF and submerged fermentation (SMF), production of surfactin in SSF was 4-5 times more efficient than in SMF. (c) 1995 John Wiley & Sons, Inc.     

Seasonal body weight, lipid content, and impact of starvation and water stress on adult survivorship and longevity ofNezara viridula andEuschistus heros

Fresh and dry body weights (FW, DW) were greater for adult southern green stink bug,Nezara viridula (L.) than for the brown stink bug,Euschistus heros F. throughout the year in southern Brazil. FemalesN. viridula significantly increased FW and DW in late summer-early autumn, and during mid-spring; femaleE. heros did not show the same rates of increase in FW and DW. FemaleN. viridula were heavier than males, particularly during summer; however, female and maleE. heros were generally similar in weight.E. heros contained significantly greater amounts of lipid thanN. viridula, during mid-autumn to early-spring (April–September). Survivorship (%) and total longevity ofE. heros adults provided water only was greater (34.6–24.6 days, for females and males) than that forN. viridula (14.8–13.0 days); without water and food, longevity was drastically reduced (<7 days) for both species.     

Genetics of Soybean-Heterodera glycines Interactions

The soybean cyst nematode, Heterodera glycines, is one of the most economically important pathogens of soybean. Effective management of the nematode is often dependent on the planting of resistant soybean cultivars. During the past 40 years, more than 60 soybean genotypes and plant introductions (PI) have been reported as resistant to H. glycines. About 130 modern soybean cultivars registered in the United States are resistant to certain races of H. glycines. Several resistance genes have been identified and genetically mapped; however, resistance levels in many soybean cultivars are not durable. Some older cultivars are no longer resistant to certain H. glycines populations in many production areas, especially if a soybean monoculture has been practiced. Past soybean registration reports show that all resistant cultivars developed in public institutions from the mid-1960s to the present have been derived from five PIs. This narrow genetic background is fragile. To further complicate the issue, soybean-H. glycines genetic interactions are complex and poorly understood. Studies to identify soybean resistance genes sometimes have overlapped, and the same genes may have been reported several times and designated by different names. Nevertheless, many potential resistance genes in existing germplasm resources have not yet been characterized. Clearly, it is necessary to identify new resistance genes, develop more precise selection methods, and integrate these resistance genes into new cultivars. Rational deployment of resistant cultivars is critical to future sustained soybean production.     

Relationship between Meloidogyne incognita and Rotylenchulus reniformis as Influenced by Soybean Genotype

The effect of soybean genotype on competition between Meloidogyne incognita race 2 (Mi) and Rotylenchulus reniformis (Rr) was evaluated in greenhouse and microplot replacement series experiments. Soil in pots containing seedlings of ''Davis'' (susceptible to Mi) or ''Buckshot 66'' (resistant to Mi) was infested with 1,000 vermiform individuals in the following Mi:Rr ratios: 0:0, 100:0, 75:25, 50:50, 25:75, or 0:100. After 91 days, the relative nematode yields (number of nematodes in mixed culture divided by the number in nonmixed culture) of each species were calculated based on soil and root nematode populations expressed as nematodes per gram of dry root tissue. To define the relationship between the two species, calculated relative nematode yields were compared with a theoretical noncompetition model using lack-of-fit regression. In the greenhouse, Mi populations on ''Davis'' were stimulated in the presence of Rr. In microplots, low Mi and Rr population densities likely resulted from severe galling and destruction of feeder roots that probably occurred early in the season. Enhanced susceptibility to Mi was not observed on ''Buckshot 66'', which remained resistant to Mi even when colonized by Rr. Host resistance is a key factor in determining the nature of the relationship between Mi and Rr.     

Cassettes for seed-specific expression tested in transformed embryogenic cultures of soybean

Soybean (Glycine max [L.] Merrill) lectin is a seed protein that accumulates in protein bodies of cotyledons during seed development. We have constructed two expression cassettes containing the 5′ and 3′ regions of the soybean lectin gene connected by aNot I restriction site. One vector also contains the 32 amino acid signal sequence. Using polymerase chain reaction (PCR), the coding region of the β-glucuronidase (uidA) gene was inserted into theNot I site of each vector. We tested the function of the expression cassettes in transformed embryogenic cultures of soybean. Development-specific GUS expression was observed in developing somatic embryos transformed with the chimeric lectin promoter-GUS constructs as determined by histochemical assays. Our data indicate that these cassettes could be used to drive expression of foreign genes to modify embryo-specific traits of soybean as protein quality or quantity in the seed.