Soybean leaf responses to threecornered alfalfa hopper petiole girdling

Specific leaf weight, percent moisture, and free sugar, starch, and amino nitrogen content of soybean (Glycine max (L.) Merrill) leaves were measured at 1, 3, 7, and 10 day(s) after petiole girdling by threecornered alfalfa hopper,Spissistilus festinus (Say) (Homoptera: Membracidae) nymphs. Leaf starch was increased at 1, 3, and 7 day(s) after girdling and largely accounted for corresponding increases in specific leaf weight and decreases in percent moisture, free sugars, and amino nitrogen. Specific leaf weight was increased at 10 days after girdling despite no increase in starch. Amino nitrogen content was decreased 10 days after girdling. When leaf dry weights were corrected for starch, free sugar content was not affected by girdling, and amino nitrogen content was reduced only at 3 and 10 days. The amino nitrogen: free sugar ratio was reduced only at 10 days after girdling. Changes in leaf starch indicated a rapid but reversible effect of girdling on leaf carbohydrate metabolism.     

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     

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     

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.     

Effect of irradiance during growth of Glycine max on photosynthetic capacity and percent activation of ribulose 1,5-bisphosphate carboxylase

The initial (in vivo) and total (activity present after preincubation with CO₂ and Mg²⁺) activities of ribulose bisphosphate carboxylase were both assayed in extracts of leaves of soybean (Glycine max) plants which had been grown under 4 different irradiance levels. The total carboxylase activity per unit leaf area decreased with decreased irradiance during growth but was not different on a dry weight basis. The initial activity as a percentage of the total activity was unchanged (approximately 95%) except in leaves of plants grown at the lowest irradiance (74%). When the plants grown at the lowest irradiance were exposed to high irradiance, the initial activity was increased to 93% of the total. Light saturated rates of photosynthesis per unit leaf area were lower and saturated at lower irradiance for plants grown at lower irradiances. Initial carboxylase activity was correlated closely (r²=0.84) with leaf photosynthesis rate on a dry weight basis.     

Soybean genotypic differences in sensitivity of symbiotic nitrogen fixation to soil dehydration

Nitrogen fixation activity by soybean (Glycine max (L.) Merr.) nodules has been shown to be especially sensitive to soil dehydration. Specifically, nitrogen fixation rates have been found to decrease in response to soil dehydration preceding alterations in plant gas exchange rates. The objective of this research was to investigate possible genetic variation in the sensitivity of soybean cultivars for nitrogen fixation rates in response to soil drying. Field tests showed substantial variation among cultivars with Jackson and CNS showing the least sensitivity in nitrogen accumulation to soil drying. Glasshouse experiments confirmed a large divergence among cultivars in the nitrogen fixation response to drought. Nitrogen fixation in Jackson was again found to be tolerant of soil drying, but the other five cultivars tested, including CNS, were found to be intolerant. Experiments with CNS which induced localized soil drying around the nodules did not result in decreases in nitrogen fixation rates, but rather nitrogen fixation responded to drying of the entire rooting volume. The osmotic potential of nodules was found to decrease markedly upon soil drying. However, the decrease in nodule osmotic potential occurred after significant decreases in nitrogen fixation rates had already been observed. Overall, the results of this study indicate that important genetic variations for sensitivity of nitrogen fixation to soil drying exist in soybean, and that the variation may be useful in physiology and breeding studies.     

结荚期短期干旱和复水对大豆（Glycine max）叶片光合和产量的影响

以大豆为研究对象,研究结荚期土壤水分的短期变动对大豆叶片光合生理生态以及最后产量形成的影响.研究发现,与叶片的水分状况相比,大豆的叶片气孔对土壤水分的匮缺更加敏感,在实验的第2天,处理组叶片气孔导度降为对照的24.9%(P＜0.01),但是叶片水势和对照相差不显著(P＞0.05);随着土壤干旱的进行,处理组叶片的净光合速率、蒸腾速率等都显著下降,但ФPSⅡ只有在第3天才出现显著的下降.复水后第3天,净光合速率比对照高24.3%(P＜0.01),表现出了明显的旱后超补偿效应;研究发现,结荚期即使短期的土壤水分干旱,也会对大豆后期的生物量的分配产生较大的影响,使处理组的豆干重降低13.9%(P＜0.01),根茎比增加35.3%(P＜0.05),收获指数减少17.4%(P＜0.05).     

Cadmium Toxicity: The effect on Macro- and Micro-Nutrient Contents in Soybean Seedlings

The effect of Cd (10, 100, and 200 M) on tissue contents of macronutrients (N, P, K, Ca, Mg) and micronutrients (Fe, Zn, Cu, Mn) was investigated in hydroponically grown soybean (Glycine max) seedlings. Concentration changes of analysed elements observed against increasing Cd accumulation indicated that acute Cd-phytotoxic effect monitored through chlorophyll content was not a consequence of nutrient deficiency.     

Soybean seedling emergence at high temperatures

Bragg and Cobb soybean [Glycine max (L.) Merr.] seeds were germinated in sand at temperatures ranging from 25 to 40°C. Emergence decreased with increasing temperature above 37°C, with virtually no emergence at 40°C. Emergence of 12 other cultivars at 38°C ranged from 25 to 95%. Foster and Coker 338 were more sensitive to high temperature than the other cultivars.     

Seasonal correlations of specific leaf weight to net photosynthesis and dark respiration of apple leaves

Specific leaf weight (SLW), net photosynthesis (P _n ), and dark respiration (R _d ) of apple leaves were monitored for an entire growing season. Leaves were sampled from the canopy interior and periphery to provide a range of SLW. Leaf P _n was linearly correlated with SLW until mid-August, when P _n began to decline. During September the relationship between SLW and P _n was a quadratic. Leaf R _d and SLW were linearly correlated throughout the season. Leaf P _n and R _d were significantly correlated through most of the season, but the relationship was not always linear. Specific leaf weight appears to be a reliable index of the previous light environment of a leaf, but use to estimate P _n is probably limited to the first half of the season, because of increased variation after mid-August.Former Graduate Research Assistant (presently Assistant Professor, Department of Horticulture and Forestry, Rutgers University, Cook College, New Brunswick, NJ 08903, USA) and Associate Professor, respectively.     

Identification of quantitative trait loci for plant height, lodging, and maturity in a soybean population segregating for growth habit

The use of molecular markers to identify quantitative trait loci (QTLs) has the potential to enhance the efficiency of trait selection in plant breeding. The purpose of the present study was to identify additional QTLs for plant height, lodging, and maturity in a soybean, Glycine max (L.) Merr., population segregating for growth habit. In this study, 153 restriction fragment length polymorphisms (RFLP) and one morphological marker (Dt1) were used to identify QTLs associated with plant height, lodging, and maturity in 111 F₂-derived lines from a cross of PI 97100 and Coker 237. The F₂-derived lines and two parents were grown at Athens, Ga., and Blackville, S.C., in 1994 and evaluated for phenotypic traits. The genetic linkage map of these 143 loci covered about 1600 cM and converged into 23 linkage groups. Eleven markers remained unlinked. Using interval-mapping analysis for linked markers and single-factor analysis of variance (ANOVA), loci were tested for association with phenotypic data taken at each location as well as mean values over the two locations. In the combined analysis over locations, the major locus associated with plant height was identified as Dt1 on linkage group (LG) L. The Dt1 locus was also associated with lodging. This locus explained 67.7% of the total variation for plant height, and 56.4% for lodging. In addition, two QTLs for plant height (K007 on LG H and A516b on LG N) and one QTL for lodging (cr517 on LG J) were identified. For maturity, two independent QTLs were identified in intervals between R051 and N100, and between B032 and CpTI, on LG K. These QTLs explained 31.2% and 26.2% of the total variation for maturity, respectively. The same QTLs were identified for all traits at each location. This consistency of QTLs may be related to a few QTLs with large effects conditioning plant height, lodging, and maturity in this population.     

Cultivar differences in leaf photosynthesis of rice bred in Japan

The grain yield of rice (Oryza sativa L.), as well as of other cereal crops, is limited to a large extent, by the supply of photosynthates produced during grain filling period. In this study, flag leaf photosynthesis (LPS) after heading was compared among 32 cultivars bred during the past century in Japan, to determine if the improvement of LPS has occurred with the breeding advance of high yielding cultivars. Measurement of LPS was made for 5 consecutive years in the paddy field, on the flag leaf of the main stem, at heading (LPS-0), and 2 weeks (LPS-2) and 4 weeks (LPS-4) after heading. LPS decreased with advance of leaf senescence from LPS-0 to LPS-2, and then to LPS-4. However, if nitrogen was top-dressed at the heading time, high LPS-2 was maintained, particularly in the newer cultivars. A significant positive correlation between LPS and the released year of cultivar was found at LPS-2, especially in the nitrogen top-dressed plot, but not at LPS-0 or LPS-4. Cultivar difference in LPS of the senescing leaves were not stable through the different years, whereas LPS-0 was stable over years, suggesting that the LPS in the senescent leaf is susceptible to the environmental variation due to the effects on leaf senescence. Cultivar difference in LPS at any stage was closely associated with mesophyll conductance to CO₂, and stomatal conductance was also associated with cultivar difference in such a high LPS as LPS-0 and nitrogen top-dressed LPS-2. Significant correlation between LPS and specific leaf weight was not observed at any stage of the flag leaf.Abbreviations CV coefficient of variation - g_m mesophyll conductance - g_s stomatal conductance - LPS apparent photosynthetic rate per unit leaf area (leaf photosynthesis) - LPS-0 LPS at heading - LPS-2 LPS at active grain filling - LPS-4 LPS at maturity of grain - NT non-top dressed plot - PPFD photosynthetic photon flux density - r_m mesophyll resistance - r_s stomatal diffusion resistance against CO₂ - r_s(H₂O) stomatal diffusion resistance against H₂O - RuBisCO ribulose-1,5-bisphosphate carboxylase/oxygenase - SLW specific leaf weight - TD nitrogen top-dressed plot     

Dynamics of Seed Protein Biosynthesis in Two Soybean Genotypes Differing in Drought Susceptibility

The dynamics of seed storage protein biosynthesis was studied under field conditions during two vegetative seasons. Two soybean (Glycine max L. Merr.) genotypes were examined: BOSA (drought tolerant) and L 121 (drought susceptible). Seed samples were taken from plants at three stages of seed maturation (50 and 70 d after flowering, and at full maturity). The earlier synthesis of the -subunit of the 7S protein occurred in the drought susceptible cultivar. We have not found such differences in the synthesis of the - and -subunits of the 7S protein. Our results did not confirm significant genotypic differences in protein composition of the mature seeds between the cultivars studied, but have pointed out to the differences in the dynamics of protein biosynthesis during seed maturation and desiccation.     

Changes of Donor and Acceptor Side in Photosystem 2 Complex Induced by Iron Deficiency in Attached Soybean and Maize Leaves

Photosynthesis in iron-deficient soybean and maize leaves decreased drastically. The quantum yield of photosystem 2 (PS2) electron transport (Φ_PS2), the efficiency of excitation energy capture by open PS2 reaction centres (F_v′/F_m′), and photochemical quenching coefficient (q_P) under high irradiance were lowered significantly by iron deficiency, but non-photochemical quenching (NPQ) increased markedly. The analysis of the polyphasic rise of fluorescence transient showed that iron depletion induced a pronounced K step both in soybean and maize leaves. The maximal quantum yield of PS2 photochemistry (Φ_po) decreased only slightly, however, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than Q_A (Ψ₀) and the quantum yield of electron transport beyond Q_A (Ψ_Eo) in iron deficient leaves decreased more significantly compared with that in control. Thus not only the donor side but also the acceptor of PS2 was probably damaged in iron deficient soybean and maize leaves. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Effect of Chilling on DNA Endoreplication in Root Cortex Cells and Root Hairs of Soybean Seedlings

Relative nuclear DNA contents in cortex parenchyma cells in root segments of 3- and 7-d-old soybean seedlings grown at 25 °C and in plants grown for 3 d at 25 °C, and then for 4 d at 10 °C, were determined with cytophotometry. Measurements revealed that in each variant the cortex cell nuclei with DNA content between 2C and 8C were in all the examined segments and nuclei with 8C – 16C DNA appeared in higher parts of roots. However, in chilled plant cells the number of 8C – 16C DNA nuclei was very low. Therefore, chilling inhibited endoreplication in comparison with plants grown at 25 °C for 7 d, and even reduced endopolyploidy level as compared to the initial seedlings, i.e. 3-d-old plants. DNA contents in root hairs grown at 25 °C (control) and in root hairs emerged at 10 °C were also determined. In controls 4C – 8C DNA nuclei predominated while in chilled plants an additional population of 2C – 4C DNA appeared. Thus a reduction of DNA synthesis was brought about by low temperature. The occurrence of an intermediate DNA contents besides those with full endoreplication cycles suggests the possibility of differential DNA replication. This suggestion seems to be supported by the lack of ³H-thymidine incorporation into root hair nuclei at the examined developmental stage both in control and chilled root hairs. The same number, but larger, chromocentric lumps in polyploid cortex cell nuclei of higher root zones, in comparison to meristematic nuclei, suggests that endoreduplication process occurred. This revised version was published online in July 2006 with corrections to the Cover Date.