Light, temperature and nutrients as factors in photosynthetic adjustment to an elevated concentration of carbon dioxide

The short-term stimulation of the net rate of carbon dioxide exchange of leaves by elevated concentrations of CO₂ usually observed in C₃ plants sometimes does not persist. Experiments were conducted to test whether the patterns of response to the environment during growth were consistent with the hypotheses that photosynthetic adjustment to elevated CO₂ concentration is due to (1) feedback inhibition or (2) nutrient stress. Soybean [Glycine max (L.) Merr. cv. Williams] and sugar beet (Best vulgaris L. cv. Mono Hye-4) were grown from seed at 350 and 700 μl^? CO₂, at 20 and 25°C, at a photon flux density of 0.5 and 1.0 mmol m^?2 S^?1 and with three nutrient regimes until the third trifoliolate leaf of soybean or the sixth leaf of sugar beet had finished expanding. Net rates of CO₂ exchange of the most recently expanded leaves were then measured at both 350 and 700 μl 1^?1 CO₂. Plants grown at the elevated CO₂ concentration had net rates of leaf CO₂ exchange which were reduced by 33% in sugar beet and 23% in soybean when measured at 350 μl 1^?1 CO₂ and when averaged over all treatments. Negative photosynthetic adjustment to elevated CO₂ concentration was not greater at 20 than at 25°C, was not greater at a photon flux density of 1.0 than at 0.5 mmol m^?2 S^?1 and was not greater with limiting nutrients. Furthermore, in soybean, negative photosynthetic adjustment could be induced by a single night at elevated CO₂ concentration, with net rates of CO₂ exchange the next day equal to those of leaves of plants grown from seed at the elevated concentration of CO₂. These patterns do not support either the feedback-inhibition or the nutrient-stress hypothesis of photosynthetic adjustment to elevated concentrations of CO₂.     

Protoplasts as tools in cell biology

Studies of plant protoplasts using both fluorescent dyes and electron dense probes have demonstrated endocytosis in plants. Ultrastructural work with soybean protoplasts using cationized ferritin (CF) revealed an endocytotic pathway from coated pits at the plasma membrane to coated vesicles, the partially coated reticulum, Golgi bodies, multivesicular bodies and finally the vacuole. Endocytosis may be responsible for membrane retrieval from the cell surface or degradation of elicitors or toxins during host-pathogen interactions. Immunofluorescence studies of dividing plant protoplasts have provided new information about the preprophase band (PPB) of microtubules and the shape of spindles. Studies of PPBs in soybean protoplast cultures permitted detailed examination of PPB development and an assessment of the usefulness of the PPB index for identifying morphogenic cultures. In multinucleate protoplasts the size and number of PPBs were apparently not controlled by nuclear number. Research with conifer protoplasts resulted in the discovery of new features of gymnosperm spindles.     

Nitrate fluxes in soybean seedling roots and their response to amino acids: an approach using 15N

This study was undertaken to determine which of the two NO₃^? fluxes (influx or efflux) across plasma membranes of root cells is the target of those amino acids which have been shown to inhibit net NO₃^? uptake (Muller & Touraine 1992, Journal of Experimental Botany 43 , 617–623). Parallel experiments were performed to mea-sure either the time course of ¹⁵NO₃^? release from roots of soybean seedlings previously labelled with this isotope into non-labelled solution, or the time course of ¹⁵N accumulation from labelled ¹⁵NO₃^? solution in non-labelled seedlings. Focusing on the fate of ¹⁵NO₃^? in the cytoplasmic compartment, a model is developed to describe the time courses of the accumulation and release of tracer across the plasma membranes of root cells. Both time courses can be described by the sum of an exponential plus a linear term. In our material, the linear part of the accumulation time course is obscured by the NO₃^? fluxes exiting the cytoplasm, and the curve thus appears to be quasilinear over several minutes. However, we show that the use of the net tracer accumulation rate during this time period as an estimate of NO₃^? influx does not provide accurate estimates of influx and efflux. By contrast, ¹⁵NO₃^? efflux analysis permits calculation of the unidirectional fluxes across plasma membranes of root cells and the kinetic parameters of the cytoplasmic NO₃^? pool. Under our experimental conditions, efflux accounted for 30 to 50% of influx, and the cytoplasmic NO₃^? content was found to be in the 70–400nmol g^?1 fw range. Using this methodology, the effect of amino acid accumulation on unidirectional fluxes of nitrate was then examined. Pretreatments of the seedlings with an amino acid which has been shown to inhibit net NO₃^? uptake led to concomitant decreases in net accumulation rates of ¹⁵NO₃^? and of reduced ¹⁵N in roots and total ¹⁵N in cotyledons. NO₃^? influx was markedly inhibited by these treatments, while NO₃^? efflux remained essentially unaffected, or even decreased. It is concluded that the target of the regulation of NO₃^? uptake by phloemtranslocated amino acids is the influx system.     

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.