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This study addresses the hypothesis that stagnation of soybean yield on the farm can be improved by selection of a physiological trait favoring carbon assimilate partitioning to terminally placed pods versus genotypes having axillary pods at close plant spacing. C was fed to source-sink units comprising a leaf, axillary/terminal pods, and petioles at upper and lower positions of the stem axis in two soybean cultivars, namely Shakujo and Enrei, at different densities of populations. The cultivars differ significantly in architecture, Shakujo bearing a few hundreds of pods in close succession to one another in a terminally placed raceme, in contrast to Enrei having axillary racemes. Pod yield per plant was higher in Enrei than in Shakujo at low density, but Shakujo out-yielded Enrei at close spacing. Population density decreased yield per plant and altered the pattern of assimilate partitioning significantly within the plants for both varieties. At high density more assimilates moved to the upper parts at the cost of the lower parts. The terminally placed pods of Shakujo were advantaged to receive assimilates under density stress. No benefit was accrued to pod filling of Enrei, however, under this condition. [ABSTRACT FROM AUTHOR]

Anthranilate synthase (AS) is a key regulatory enzyme in tryptophan (Trp) biosynthesis and is subject to feedback inhibition by Trp. The gene encoding a mutated feedback-resistant α subunit of rice AS ( OASA1D) under the control of either a soybean glycinin gene promoter or the 35S promoter of cauliflower mosaic virus for seed-specific or constitutive expression, respectively, was introduced into soybean [ Glycine max (L.) Merrill] by particle bombardment. A total of seven different transgenic lines that showed markedly increased accumulation of free Trp in their seeds were developed. The overproduction of free Trp was stably inherited in subsequent generations without any apparent detrimental effect on plant growth or reproduction. The total Trp content of transgenic seeds was also about twice that of nontransgenic seeds, whereas the amount of protein-bound Trp was not substantially affected by OASA1D expression. In spite of the marked increase in free Trp content, metabolic profiling by high-performance liquid chromatography coupled with mass spectrometry revealed little change in the amounts of other aromatic compounds in the transgenic seeds. We developed a rapid and feasible system based on farmed rainbow trout to evaluate the nutritional quality of a limited quantity of transgenic soybean seeds. Supplementation of fish food with OASA1D transgenic soybean seeds or with nontransgenic seeds plus crystalline Trp increased the growth rate of the farmed fish. These results indicate transformation with OASA1D is a reliable approach to improve the nutritional quality of soybean (or of other grain legumes) for human and animal food. [ABSTRACT FROM AUTHOR]

Particle bombardment is a common platform for soybean transformation hut tends to cause transgene silencing due to the integration of rearranged or multiple copies of transgenes. We now describe the isolation of a total of 44 independent transgenic soybean plants after transformation by particle bombardment with one of two gene constructs, pHV and pHVS. Both constructs contain the hygromycin phosphotransferase gene (hpt) as a selectable marker and a modified glycinin gene (V3-1) for evaluation of homology-dependent silencing of endogenous glycinin genes; pHVS also contains sGFP(S65T), which encodes a modified form of green fluorescent protein (GFP), as a reporter gene in the flanking region of V3-1. Fluorescence microscopy revealed that the leaves of 8 of the 25 independent transgenic plants obtained with pHVS expressed (FP; most of these (FP-positive plants also contained V3-1 mRNA and an increased glycinin content in their seeds, and they exhibited simple banding patterns on Southern blots that were indicative of a low copy number of each of the three transgenes. In contrast, most of the transgenic plants obtained with pHVS that did not express GFP, as well as most of those obtained with pHV, lacked endogenous glycinin in their seeds and exhibited more complex patterns of transgene integration. The use of a reporter gene such as sGFP(S65T) in addition to an antibiotic resistance gene may thus help to reduce the problem of gene silencing associated with direct DNA transformation systems and facilitate the recovery of transgenic plants that stably express the gene of interest. [ABSTRACT FROM AUTHOR]

Abstract: Physiological processes that modulate photosynthetic acclimation to rising atmospheric CO2 concentration are subjects of intense discussion recently. Apparently, the down-regulation of photosynthesis under elevated CO2 is not understood clearly. In the present study, the response of soybean (Glycine max L.) to CO2 enrichment was examined in terms of nitrogen partitioning and water relation. The plants grown under potted conditions without combined N application were exposed to either ambient air (38Pa CO2) or CO2 enrichment (100Pa CO2) for short (6 days) and long (27 days). Plant biomass, apparent photosynthetic rate, transpiration rate and 15N uptake and partitioning were measured consecutively after elevated CO2 treatment. Long-term exposure reduced photosynthetic rate, stomatal conductance and transpiration rate. In contrast, short-term exposure increased biomass production of soybean due to increase in dry weight of leaves. Leaf N concentration tended to decrease with CO2 enrichment, however such difference was not true for stem and roots. A close correlation was observed between transpiration rate and 15N partitioned into leaves, suggesting that transpiration plays an important role on nitrogen partitioning to leaves. In conclusion existence of a feed back mechanism for photosynthetic acclimation has been proposed. Down-regulation of photosynthetic activity under CO2 enrichment is caused by decreasing leaf N concentration, and reduced rate of transpiration owing to decreased stomatal conductance is partially responsible for poor N translocation. [Copyright &y& Elsevier]