Interactions among leaf photosynthetic rates,flowering and pod set in soybeans

The seasonal maximum in photosynthetic CO₂ exchange rate (CER) and the cessation of leaf expansion in soybeans (Glycine max (L.) Merr) accompany fruiting under normal agricultural conditions. To investigate whether these phenomena were obligatively tied together, we caused early flowering of long-season varieties by imposing artificial short-day treatments. Comparisons of CER and leaf area between vegetative (long-day treatment) and fruiting (short-day treatment) plants of long-season cultivar confirmed the relationship of these phenomena. The same comparisons made between a long-season and a short-season cultivar, both at the same daylength, also confirmed the relationship.     

Nitrogen and carbon partitioning in soybean under variable nitrogen supplies and acclimation to the prolonged action of elevated CO2

This study was conducted to determine reciprocal effects of low to high doses of nitrogenous fertilizer (N₃₀, N₄₀, N₅₀, N₆₀ and N₇₀ — 30, 40, 50, 60 and 70 kg ha⁻¹ respectively) and CO₂ enriched environment on C and N partitioning in soybean (Glycine max (L.) Merril cv JS-335). Plants were grown from seedling emergence to maturity inside open top chambers under ambient, AC (350±50 mol mol⁻¹) and elevated, EC (600±50 mol mol⁻¹) CO₂ and analyzed at seedling, vegetative, flowering, pod setting and maturity stages. Soybean responded to both CO₂ enrichment and N supply. Leaves, stem and root reserves at different growth stages were analyzed for total C and N contents. Consistent increase in the C contents of the leaf, stem and root was observed under EC than in AC. N contents in the different plant parts were found to be decreased under EC-grown plants specially at seedling and vegetative stage despite providing N doses to the soil. Significant increase observed for C to N dry mass ratio under EC in the root, stems and leaves at seedling and vegetative stage was decreased in the middle and later growth stages possibly due to combined impact of N doses to the soil and increased N₂ fixing activities due to EC conditions. Critical analysis of our findings reveals that the composition and partitioning of C and N of soybean under variable rates of N supply and CO₂ enrichment alter according to need under altered metabolic process. These changes eventually may lead to alteration in uptake of not only N but other essential nutrients also under changing atmosphere.     

Differential responses to K deficiency among soybean cultivars

The seed yield per unit of potassium applied differed for five soybean cultivars which were grown to maturity under different K regimes in a glasshouse. Whereas Dodds was the most responsive cultivar to moderate increases in K supply, the cultivar Bragg was the most efficient in its ability to produce seed with low levels of available K; Lee and Forest were the least efficient cultivars while Bossier and Dodds were of intermediate efficiency. The basis for the efficiency of cv. Bragg was that the growth of its tops, as indicated by mature stem weights and its roots, were less affected by reduced K supply than those of other cultivars. This enabled it to produce more pods under K-deficient regimes, resulting in a greater seed yield per plant. The percentage reduction in oil/protein ratios in the seed of the five cultivars under moderate K deficiency correlated closely with reductions in seed yield. However, changes in this ratio were poorly related to the K percentages in the seed. All cultivars experienced an impairment of plant senescence under K deficiency as evidenced by a reduction in leaf abcission and a delay in pod maturity. The existence of genetic diversity in K-use efficiency means that breeding programmes could utilize K-efficient germplasm in developing new cultivars for soils not naturally high in potassium.     

Seasonal variations in apparent photosynthesis among plant stands of different soybean cultivars

The CO₂- and H₂O-exchange rates between soybean canopies and the atmosphere were measured in three mobile chambers (4 m³). Each chamber stopped at 8 or 9 plots (3.1-m² ground area) every 25 min. Diurnal and seasonal CO₂-exchange rates (CER) of 13 soybean (Glycine max (L.) Merr.) cultivars are summarized here. The oldest two cultivars, released in 1927 and 1932, had the lowest CER values. The CER usually decreased in the afternoon (23.4 vs 27.8 mol CO₂ m^-2 s^-1 at 1.6 mmol photons m^-2 s^-1), except shortly after rainfall. During a drought, these reductions occurred earlier in the day and were more pronounced. We present evidence for a nonstomatal component of the CO₂ flux-reaction system causing CER reductions during a water stress. Daytime CER values were not correlated with temperature (24–34° C), but nighttime values were (15–25° C, r=0.85,* n=41).     

Overcoming drought-induced decreases in soybean leaf photosynthesis by measuring with CO2-enriched air

Soybean [Glycine max (L.) Merr. cv. Williams 82 and A3127] plants were grown in the field under long-term soil moisture deficit and irrigation to determine the effects of severe drought stress on the photosynthetic capacity of soybean leaves. Afternoon leaf water potentials, stomatal conductances, intercellular CO₂ concentrations and CO₂-assimilation rates for the two soil moisture treatments were compared during the pod elongation and seed enlargement stages of crop development. Leaf CO₂-assimilation rates were measured with either ambient (340 l CO₂ l^–1) or CO₂-enriched (1800 l CO₂ l^–1) air. Although seed yield and leaf area per plant were decreased an average of 48 and 31%, respectively, as a result of drought stress, leaf water potentials were reduced only an average of 0.27 MPa during the sampling period. Afternoon leaf CO₂-assimilation rates measured with ambient air were decreased an average of 56 and 49% by soil moisture deficit for Williams 82 and A3127, respectively. The reductions in leaf photosynthesis of both cultivars were associated with similar decreases in leaf stomatal conductance and with small increases in leaf intercellular CO₂ concentration. When the CO₂-enriched air was used, similar afternoon leaf CO₂-assimilation rates were found between the soil moisture treatments at each stage of crop development. These results suggest that photosynthetic capacity of soybean leaves is not reduced by severe soil moisture deficit when a stress develops gradually under field conditions.Abbreviations C_i intercellular CO₂ concentrations - A_a rates of CO₂ assimilation measured with ambient air - A_e rates of CO₂ assimilation measured with CO₂-enriched air - g_s stomatal conductances - RuBPCase ribulose-1,5-bisphosphate carboxylase     

Elevated CO2 reduces field decomposition rates of Betula pendula (Roth.) leaf litter

The effect of elevated atmospheric CO₂ and nutrient supply on elemental composition and decomposition rates of tree leaf litter was studied using litters derived from birch (Betula pendula Roth.) plants grown under two levels of atmospheric CO₂ (ambient and ambient +250 ppm) and two nutrient regimes in solar domes. CO₂ and nutrient treatments affected the chemical composition of leaves, both independently and interactively. The elevated CO₂ and unfertilized soil regime significantly enhanced lignin/N and C/N ratios of birch leaves. Decomposition was studied using field litter-bags, and marked differences were observed in the decomposition rates of litters derived from the two treatments, with the highest weight remaining being associated with litter derived from the enhanced CO₂ and unfertilized regime. Highly significant correlations were shown between birch litter decomposition rates and lignin/N and C/N ratios. It can be concluded, from this study, that at levels of atmospheric CO₂ predicted for the middle of the next century a deterioration of litter quality will result in decreased decomposition rates, leading to reduction of nutrient mineralization and increased C storage in forest ecosystems. However, such conclusions are difficult to generalize, since tree responses to elevated CO₂ depend on soil nutritional status.     

Comparison of somatic embryogenesis and embryo conversion in commercial soybean cultivars

Six commercially important soybean cultivars and one control cultivar were compared for differences in induction-efficiency of somatic embryogenesis, primary embryo yield, and embryo conversion. Cotyledons from immature seeds of similar developmental stage for all soybean cultivars were used for embryo induction. The experiments utilized a Latin square design to exclude the effect of differential lighting and position due to plate location in the growth chamber on the embryogenesis process. Results indicated that the efficiency of embryo induction and yield of primary somatic embryos were genotype-dependent. In contrast, no dependence on genotype was observed for the conversion of embryos to form roots and shoots. The percentage of cotyledons that gave a positive embryogenic response ranged from 26 to 89% for the soybean cultivars tested. The average number of primary globular-stage embryos per responding cotyledon after one month on induction medium ranged from 6 to 13 among the seven cultivars. Conversion frequencies for all genotypes ranged from 27 to 45%.     

Soybean leaf hydraulic conductance does not acclimate to growth at elevated [CO2] or temperature in growth chambers or in the field

Background and Aims

Leaf hydraulic properties are strongly linked with transpiration and photosynthesis in many species. However, it is not known if gas exchange and hydraulics will have co-ordinated responses to climate change. The objective of this study was to investigate the responses of leaf hydraulic conductance (K_leaf) in Glycine max (soybean) to growth at elevated [CO₂] and increased temperature compared with the responses of leaf gas exchange and leaf water status.

Methods

Two controlled-environment growth chamber experiments were conducted with soybean to measure K_leaf, stomatal conductance (g_s) and photosynthesis (A) during growth at elevated [CO₂] and temperature relative to ambient levels. These results were validated with field experiments on soybean grown under free-air elevated [CO₂] (FACE) and canopy warming.

Key results

In chamber studies, K_leaf did not acclimate to growth at elevated [CO₂], even though stomatal conductance decreased and photosynthesis increased. Growth at elevated temperature also did not affect K_leaf, although g_s and A showed significant but inconsistent decreases. The lack of response of K_leaf to growth at increased [CO₂] and temperature in chamber-grown plants was confirmed with field-grown soybean at a FACE facility.

Conclusions

Leaf hydraulic and leaf gas exchange responses to these two climate change factors were not strongly linked in soybean, although g_s responded to [CO₂] and increased temperature as previously reported. This differential behaviour could lead to an imbalance between hydraulic supply and transpiration demand under extreme environmental conditions likely to become more common as global climate continues to change.     

CO2 exchange characteristics during dark-light transitions in wild-type and mutant Chlamydomonas reinhardii cells

A burst of net CO₂ uptake was observed during the first 3–4 min after the onset of illumination in both wild-type Chlamydomonas reinhardii in which carbonic anhydrase was chemically inhibited with ethoxyzolamide and in a mutant of C. reinhardii (ca-1-12-1C) deficient in carbonic anhydrase activity. The burst was followed by a rapid decrease in the CO₂ uptake rate so that net evolution often occurred. After a 2–3 min period of CO₂ evolution, net CO₂ uptake again increased and ultimately reached a steady-state, positive rate. From [¹⁴CO₂]-tracer studies it was determined that CO₂ fixation proceeded at a nearly linear rate throughout the period of illumination. Thus, prior to reaching a steady state, there was a rapid accumulation of inorganic carbon inside the cells which apparently reached a supercritical concentration and the excess was excreted, causing a subsequent efflux of CO₂. A post illumination burst of net CO₂ efflux was also observed in ethoxyzolamide-inhibited wild type and ca-1 mutant cells, but not in the unihibited wild type. [¹⁴CO₂]-tracer experiments revealed that this burst was the result of a collapse of a large internal inorganic carbon pool at the onset of darkness rather than a photorespiratory post-illumination burst. These results indicate that upon illumination, chemical or genetic inhibition of carbonic anhydrase initially causes an accumulation of excess inroganic carbon in C. reinhardii cells, and that unknown regulatory mechanisms correct for this imbalance by first excreting the excess inorganic carbon and then, after several dampened oscillations, achieving an equilibrium between bicarbonate uptake, bicarbonate dehydration, and CO₂ fixation.     

Recombination rates of soybean varieties from different periods of introduction and release

Theory predicts that selection for adaptability during the short term also favors selection for a reduced recombination rate in the population. The objective of this study was to test whether the cyclic short-term selection which has taken place in soybean breeding programs in the USA since the introduction of the crop has measurably reduced recombination frequencies. Thirteen soybean varieties separated into four different release periods (prior to 1940, 1940–1954, 1955–1969, after 1970) were evaluated for their recombination frequencies within three locus pairs. Recombination frequencies among the individual varieties ranged from 7.6 to 24.1 % at thep ₁ r locus pair, from 20.9 to 30.1 % at thelnp ₂ locus pair, and from 28.7 to 41.6% at thedt ₁ l ₁ locus pair. Recombination frequencies were significantly different among varieties within a release period for thep ₁ r andlnp ₂ locus pairs, but recombination frequencies did not differ among release periods for any locus pair. Thus, apparently, plant breeders have developed soybean varieties with improved adaptation without influencing recombination rates.     

Photosynthesis at ambient and elevated humidity over a growing season in soybean

Daytime rates of net photosynthesis of upper canopy leaflets of soybeans were compared on 17 days for leaflets exposed to air at the ambient humidity and at a higher humidity. Leaflets at the higher humidity had higher rates of net photosynthesis on 16 of the 17 days. The daily total of net photosynthesis of leaflets at the higher humidity was on average 1.32 times that for leaflets at ambient humidity. A strong limitation of net photosynthesis by ambient humidity was found throughout the growing season.     

Leaf cavity CO2 concentrations and CO2 exchange in onion,Allium cepa L.

Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO₂ that accumulates within their leaf cavities. Leaf cavity CO₂ concentrations ranged from 2250 L L^–1 near the leaf base to below atmospheric (<350 L L^–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO₂ concentrations with minimum values near midday and maximum values at night. Conductance to CO₂ from the leaf cavity ranged from 24 to 202 mol m^–2 s^–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO₂ was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO₂ concentrations and conductance values or as measured directly by ¹⁴CO₂ labeling experiments. The photosynthetic responses to CO₂ and O₂ were measured to determine whether onion leaves exhibited a typical C₃-type response. A linear increase in CO₂ uptake was observed in intact leaves up to 315 L L^–1 of external CO₂ and, at this external CO₂ concentration, uptake was inhibited 35.4±0.9% by 210 mL L^–1 O₂ compared to 20 mL L^–1 O₂. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO₂ and greatly restrict the refixation of leaf cavity CO₂ by photosynthetic tissue.Abbreviations C_a external CO₂ concentration - C_i intercellular CO₂ concentration - CO₂ compensation concentration - PPFR photosynthetic photon fluence rate     

大豆microRNA基因GmMIR160A负调控植物叶片衰老进程

:叶片衰老是受内外多种因子影响的遗传发育进程.生长素、细胞分裂素和乙烯等多种植物激素是调 控叶片衰老的重要内部因子,它们通过长或短距离运输形成叶片组织内特定的区域分布和浓度梯度,从而直 接或间接参与植物叶片衰老过程.分子遗传学表明,细胞分裂素和乙烯分别是叶片衰老的抑制子和正调节 子,而生长素如何参与叶片衰老的分子机制目前还不清晰.植物体内成熟小分子RNA 由小RNA 基因转录 并通过特定酶加工形成的２１~２３bp的双链RNA分子.这些小分子通过不完全配对方式抑制其靶基因转录 和/或表达,参与植物生长发育多个过程,然而这类小RNA 分子如何调控植物叶片衰老发育过程目前则还鲜 有报告.大豆是重要的油料作物,具有典型的单次结实性衰老特征.研究大豆叶片衰老具有重要的科学意义 和深远的应用价值.该文采用实时荧光定量PCR(qPCR)技术分析大豆(Glycinemax)microRNA基因Gm- MIR１６０A 的表达模式,发现大豆第一复叶中GmMIR１６０A 表达受外源生长素和黑暗处理的诱导,暗示该基 因是生长素快速响应的叶片衰老相关基因.为进一步探究GmMIR１６０A 在大豆叶片发育中的功能,构建了 肾上腺皮质激素(Glucocorticoid,GR)类似物地塞米松(Dexamethasone,DEX)诱导表达GmMIR１６０A 双元表 达载体并通过农杆菌介导的子叶节方法转化野生型大豆.通过抗性筛选和基因组PCR 鉴定并结合表型分 析,共获得了４株诱导表达的稳定遗传转基因植株(株系OXＧ３、OXＧ５、OXＧ７和OXＧ８).GmMIR１６０A 过表达 植株根、茎、叶、花和果实在形态学上与野生型相比无显著差异,但叶片的叶绿素含量增加、最大光量子效率 (Fv/Fm)增强.进一步分子分析发现,转基因大豆叶片中GmARFs 和衰老标记基因(GmCYSP１)表达明显下 降,表明大豆Gma-miR１６０通过抑制靶基因GmARFs 的表达来负调控植物叶片的衰老进程.该文揭示了生 长素通过小分子RNA调控叶片发育一条新途径,为研究植物激素调控植物叶片衰老提供了新的思路.     

Effect of plant genotype and nitrogen fertilizer on symbiotic nitrogen fixation by soybean cultivars

Summary Isotopic as well as non-isotopic methods were used to assess symbiotic nitrogen fixation within eight soybean [Glycine max (L.) Merr.] cultivars grown at 20 and 100 kg N/ha levels of nitrogen fertilizer under field conditions.The¹⁵N methodology revealed large differences between soybean cultivars in their abilities to support nitrogen fixation. In almost all cases, the application of 100 kg N/ha resulted in lower N₂ fixed in soybean than at 20 kg N/ha in the first year of the study. However, N₂ fixed in one cultivar, Dunadja, was not significantly affected by the higher rate of N fertilizer application. These results were confirmed by measurements of acetylene reduction activity, nodule dry weight and N₂ fixed as measured by the difference method. Further proof of differences in N₂ fixed within soybean cultivars and the ability of Dunadja to fix similar amounts of N₂ at 20 and 100 kg N/ha was obtained during a second year experiment. Dunadja yield was affected by N fertilizer and produced larger yield at 100 kg N/ha than at 20 kg N/ha. This type of cultivar could be particularly useful in situations where soil N levels are high or where there is need to apply high amounts of N fertilizer.The present study reveals the great variability between legume germplasms in the ability to fix N₂ at different inorganic N levels, and also the potential that exists in breeding for nitrogen fixation associative traits. The¹⁵N methodology offers a unique tool to evaluate germplasms directly in the field for their N₂ fixation abilities at different N fertilizer levels.     

Physiological comparisons of two soybean cultivars differing in canopy photosynthesis. II. Variation in specific leaf weight,nitrogen, and protein components

Cultivar differences in canopy apparent photosynthesis (CAP) have been observed in soybean (Glycine max (L.) Merr.) but little is known about the physiological mechanisms which are responsible for such differences. This study was initiated to determine if variation in ribulose 1,5-bisphosphate carboxylase (RuBPCase) and soluble protein exists among cultivars which differ in CAP during reproductive growth. In addition, the relationship between specific leaf weight (SLW) and leaf protein was examined. Two Maturity Group VI cultivars, Tracy (high CAP) and Davis (low CAP), were grown in the field during 1979, 1980, and 1981 and in a greenhouse experiment. Leaves located at two canopy positions (topmost, fully expanded leaf and eighth node from the top) in 1979 and three canopy positions (those mentioned, plus the fourth node from the top) in 1980 and 1981 were sampled. Leaves at the two upper canopy positions exhibited greater SLW, RuBPCase m^–2, and soluble protein m^–2 than found at the eighth node down. Photosynthetic capacity of leaves at inner canopy regions was therefore affected by both light penetration into the canopy and leaf protein status. Over the three year period, the SLW was 23 percent and the soluble protein m^–2 leaf 21 percent greater in Tracy than in Davis. Although the trend in RuBPCase m^–2 leaf was not significant, it was consistently greater in Tracy in the field and greenhouse. No cultivar differences were observed when the proteins were expressed on a unit of leaf dry weight. The quantity of RuBPCase per unit leaf area was positively correlated with SLW with significant partial correlation coefficients of 0.62, 0.67, 0.35, and 0.82 for 1979, 1980, 1981, and the greenhouse study, respectively. Since these cultivars have similar leaf area indices during September, the greater SLW of Tracy is translated into more photosynthetic proteins per unit ground area and higher CAP rate.Abbreviations AP Leaf Apparent Photosynthesis - CAP Canopy Apparent Photosynthesis - DAP Days After Planting - DTT Dithothreitol - HEPES N-2-hydroethylpiperazine N-2 ethanesulfonic acid - LAI Leaf Area Index - LSD Least Significant Difference - PPFD Photosynthetic Photon Flux Density - PVP-40 Polyvinylpolypyrroledone (molecular weight, 4000) - RuBPCase Ribulose 1,5-bisphosphate Carboxylase - SLW Specific Leaf Weight     

Physiological comparisons of two soybean cultivars differing in canopy photosynthesis. I. Variation in vertical 14CO2 labelling and dry weight partitioning

Differences in canopy apparent photosynthesis (CAP) among soybean [Glycine max (L.) Merr.] genotypes have been shown to be correlated to seed yields. Since the physiological basis for such differences in CAP is unknown, two cultivars known to differ in CAP, Tracy and Davis, were studied during the 1978–1980 growing seasons. The CAP and dry weights of component plant parts were determined. In 1978 and 1979, ¹⁴CO₂ uptake by vertical leaf strata was determined and specific leaf weight (SLW) and leaf area index (LAI) were determined for corresponding strata in 1979 and 1980. Measurements were taken on several dates during reproductive growth. With the exception of CAP, all measurements (¹⁴C uptake, dry weights) were made in layers within the canopy. CAP on some dates were significantly higher in Tracy than in Davis and integrated CAP values from a certain growth period, labeled as R5 to R7, averaged 16 percent higher in Tracy for the three years studied. No differences in the relative recovery of ¹⁴C from different layers of leaves in the canopy were found. This indicates that variations in canopy structure or leaf orientation did not play a major role in the CAP differences between cultivars. The differences seem related to variations in leaf dry weights. Overall, Tracy exhibited 13.5, 19.2, and 13.2 percent greater leaf dry weights than Davis during 1978, 1979, and 1980, respectively. These differences in leaf dry weight seem largely due to a differences in the SLW. Data from these experiments indicate that differences in soybean CAP values were associated with differences in SLW.Abbreviations CAP Canopy Apparent Photosynthesis - CER Carbondioxide Exchange Rates - EST Eastern Standard Time - LAI Leaf Area Index - LSD Least Significant Difference - POPOP 1,4-bis-[2(5-phenyloxazdyl)]-benzene - PPO 2,5-diphenyloxazole - SLW Specific Leaf Weight     

Transformation of soybean via particle bombardment of embryogenic suspension culture tissue

Summary Embryogenic suspension culture tissue of soybean (Glycine max Merrill.) was bombarded with particles coated with plasmid DNAs encoding hygromycin resistance andβ-glucuronidase (GUS). One to two weeks after bombardment, embryogenic tissue was placed in a liquid proliferation medium containing hygromycin. Four to six weeks after bombardment, lobes of yellow-green, hygromycin-resistant tissue, which began as outgrowths on brown clumps of hygromycin-sensitive tissue, were isolated and cultured to give rise to clones of transgenic embryogenic material. In vivo GUS assays of hygromycin-resistant clones showed that the early outgrowths could be negative, sectored, or positive for GUS activity. Transgenic, fertile plants could be routinely produced from the proliferating transgenic embryogenic clones. Southern hybridization analyses confirmed stable transformation and indicated that both copy number and integration pattern of the introduced DNA varied among independently transformed clones. Hybridization analysis of DNA from progeny plants showed genetic linkage of multiple copies of introduced DNA. An average of three transgenic clones were obtained per bombardment making this procedure very suitable for transformation of soybean.     

Lectin in five soybean cultivars previously considered to be lectin-negative

Hemagglutinating proteins were isolated by affinity chromatography from seeds of each of five cultivars of soybeans (Clycine max (L.) Merr.) previously reported to lack detectable lectin (S.P. Pull et al., 1978; Science 200, 1277). Quantities were between 1,000 and 10,000 times less than that found in the seeds of the reference cultivar, Chippewa. The sensitivity of the hemagglutinating assay was 0.05 g ml^-1. Hemagglutinating activity was demonstrated in affinity-purified fractions from bulk seeds and seeds from individual plants in two cultivars, 30–70% ammonium-sulfate-precipitable fractions of seeds from individual plants of all five cultivars, and in whole crude extracts of individual seeds from each cultivar. In all instances, hemagglutinating activity was inhibited by galactose, anti-soybean agglutinin (SBA), and lectin-binding polysaccharide produced by Rhizobium japonicum. Affinity-purified lectin from seeds of a single Columbia plant was labeled with fluorescein isothiocyanate (FITC) and observed by fluorescence microscopy to bind to R. japonicum cells with specificity, intensity and localization indistinguishable from FITC-SBA. Lectins from distinguishable from FITC-SBA. Lectins from three cultivars in sufficiently high concentration for study had molecular properties very similar to Chippewa SBA.Abbreviations FITC fluorescein isothiocyanate - IgG immunoglobulin G - SBA soybean agglutinin