A comparison of the effects of carbon dioxide concentration and temperature on respiration, translocation and nitrate reduction in darkened soybean leaves

BACKGROUND AND AIMS: Respiration of autotrophs is an important component of their carbon balance as well as the global carbon dioxide budget. How autotrophic respiration may respond to increasing carbon dioxide concentrations, [CO(2)], in the atmosphere remains uncertain. The existence of short-term responses of respiration rates of plant leaves to [CO(2)] is controversial. Short-term responses of respiration to temperature are not disputed. This work compared responses of dark respiration and two processes dependent on the energy and reductant supplied by dark respiration, translocation and nitrate reduction, to changes in [CO(2)] and temperature. METHODS: Mature soybean leaves were exposed for a single 8-h dark period to one of five combinations of air temperature and [CO(2)], and rates of respiration, translocation and nitrate reduction were determined for each treatment. KEY RESULTS: Low temperature and elevated [CO(2)] reduced rates of respiration, translocation and nitrate reduction, while increased temperature and low [CO(2)] increased rates of all three processes. A given change in the rate of respiration was accompanied by the same change in the rate of translocation or nitrate reduction, regardless of whether the altered respiration was caused by a change in temperature or by a change in [CO(2)]. CONCLUSIONS: These results make it highly unlikely that the observed responses of respiration rate to [CO(2)] were artefacts due to errors in the measurement of carbon dioxide exchange rates in this case, and indicate that elevated [CO(2)] at night can affect translocation and nitrate reduction through its effect on respiration.     

The effect of carbon dioxide concentration on respiration of growing and mature soybean leaves

Soybean plants were grown continuously at 350 and 700cm³m^?3 CO₂ at constant temperature. Respiration rates of third trifoliolate leaves were measured at the growth CO₂ concentration for the whole dark period from 5d before through to 5d after full area expansion. The short-term response of respiration rate to the measurement CO₂ concentration was also determined at each age. Respiration rates per unit of dry mass declined with age and were significantly less at a given age or RGR in leaves grown and measured at the elevated CO₂. The difference in respiration rate was largest in mature leaves and resulted from the different measurement CO₂ concentrations. The respiratory costs of the tissue synthesis, estimated from the elemental composition of the tissue, did not differ substantially between CO₂ treatments. The response of respiration rate to carbon dioxide concentration was not strongly affected by the form of nitrogen supplied. Maintenance respiration calculated by subtracting growth respiration from total respiration was negative in rapidly growing leaves for both CO₂ treatments. This indicates that CO₂ efflux in the dark does not accurately reflect the average 24 h rate of energy expenditure on growth and maintenance for soybean leaves.     

Response of respiration of soybean leaves grown at ambient and elevated carbon dioxide concentrations to day-to-day variation in light and temperature under field conditions

BACKGROUND AND AIMS: Respiration is an important component of plant carbon balance, but it remains uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated [CO(2)] under field conditions. The hypothesis that respiration of leaves of soybeans grown at elevated [CO(2)] is increased is tested; and the effects of photosynthesis and acclimation to temperature examined. METHODS: Net rates of carbon dioxide exchange were recorded every 10 min, 24 h per day for mature upper canopy leaves of soybeans grown in field plots at the current ambient [CO(2)] and at ambient plus 350 micromol mol(-1) [CO(2)] in open top chambers. Measurements were made on pairs of leaves from both [CO(2)] treatments on a total of 16 d during the middle of the growing seasons of two years. KEY RESULTS: Elevated [CO(2)] increased daytime net carbon dioxide fixation rates per unit of leaf area by an average of 48 %, but had no effect on night-time respiration expressed per unit of area, which averaged 53 mmol m(-2) d(-1) (1.4 micromol m(-2) s(-1)) for both the ambient and elevated [CO(2)] treatments. Leaf dry mass per unit of area was increased on average by 23 % by elevated [CO(2)], and respiration per unit of mass was significantly lower at elevated [CO(2)]. Respiration increased by a factor of 2.5 between 18 and 26 degrees C average night temperature, for both [CO(2)] treatments. CONCLUSIONS: These results do not support predictions that elevated [CO(2)] would increase respiration per unit of area by increasing photosynthesis or by increasing leaf mass per unit of area, nor the idea that acclimation of respiration to temperature would be rapid enough to make dark respiration insensitive to variation in temperature between nights.     

Entropy budgets of soybean and bur oak leaves at night

From energy budgets of soybean [ Glycine max (L.) Merr. cv. Chippewa] and bur oak ( Quercus macrocarpa ) leaves at night, entropy fluxes into or out of leaves are calculated. The absorbed entropy balances with the emitted entropy; this is not the case for leaves during the day and for an animal at night. On the assumption that the entropy in leaves is at steady state, entropy production in leaves becomes small and almost zero. Since entropy production is a measure of activity in organisms, the activity in leaves is small at night; this is in contrast to leaves during the day. Thus, a large portion of the activity in leaves is "on" in the daytime and "off" at night. Most of the activity in leaves may be triggered by solar radiation.     

Polyamine translocation following photoperiodic flowering induction in soybean

Radioactivity translocation after [¹⁴C]-spermidine application over the third trifoliate leaf of soybean plants ( Glycine max . [L.] Merr, cv. Williams) was checked during the first 72 h of short day (SD) treatment to study the involvement of polyamines (PAs) in photoperiodic flowering induction. PAs and/or their metabolites were translocated from the supplied leaf to all parts of the plant. Radioactivity reached its highest concentration in the upper portion of the stem, i.e. the apical bud and the youngest leaf. After the beginning of the first inductive night, the detected radioactivity showed two peaks of maximal concentration. The first arose after the first inductive night, coinciding with the proper flowering induction process; the second one arose after the third inductive night, coinciding with the first morphological symptoms of the transition of vegetative meristems to the reproductive condition. Soluble free PAs showed a different balance in the apical bud of SD-induced plants compared with LD-non induced control plants. Soluble conjugated PAs were detected as traces. It is suggested that under flowering inductive conditions, PAs play a different role according to the stage of the flowering process. Thus, their translocation from the leaves to the axillary and apical buds might be related, in a first step, to the fact that they were part of the complex mechanism of the flowering signal, and in a second step, to the flower transition of vegetative buds.     

Growth at elevated carbon dioxide concentration reduces hydraulic conductance in alfalfa and soybean

Hydraulic conductances of alfalfa and soybean plants grown in controlled environment chambers at the current ambient carbon dioxide concentration and at twice the current ambient concentration were determined from measurements of transpiration rate and leaf and stem water potentials in the growth conditions. Growth at elevated carbon dioxide concentration reduced both transpiration rate and hydraulic conductance from the soil to the leaf in both species. Hydraulic conductance from the soil to the base of the stem was also lower at elevated carbon dioxide in soybean, but not alfalfa. These measurements identified the stem to leaf hydraulic pathway as a major target of the carbon dioxide effect in both species. The conductance of excised stem segments was much less in plants grown at elevated carbon dioxide in soybeans.     

Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity

The hypothesis that elevated [CO(2)] alleviates ureide inhibition of N(2)-fixation was tested. Short-term responses of the acetylene reduction assay (ARA), ureide accumulation and total non-structural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soybean. The plants were exposed to ambient (360 micromol mol(-1)) or elevated (700 micromol mol(-1)) [CO(2)]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N(2)-fixation activity under both ambient and elevated [CO(2)] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO(2)] as compared with that under elevated [CO(2)]. Under ambient [CO(2)] conditions, ARA was less than that under elevated [CO(2)] 1 d after ureide treatment. Under ambient [CO(2)], the application of ureide resulted in a significant accumulation of ureide in all plant tissues, with the highest concentration increases in the leaves. However, application of exogenous ureide to plants subjected to elevated [CO(2)] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO(2)] compared with those under ambient [CO(2)]. For both [CO(2)] treatments, the application of ureide induced a significant decrease of TNC concentrations in the leaves and nodules. For both leaves and nodules, a negative correlation was observed between TNC and ureide levels. Results indicate that product(s) of ureide catabolism rather than tissue ureide concentration itself are critical in the regulation of N(2)-fixation.     

The effect of methionine, ethylene and polyamine catabolic intermediates on polyamine accumulation in detached soybean leaves

In the present study we determined the effects of methionine, intermediates of polyamine catabolic pathways and inhibitors of either ethylene biosynthetic or polyamine catabolic pathways on polyamine accumulation in soybean leaves. Inhibitors to SAM decarboxylase and spermidine synthase, methylglyloxal-bis-(guanylhy-drazone) and cyclohexylamine, respectively, suggest that methionine may provide aminopropyl groups for the synthesis of polyamine via S-adenosylmethionine (SAM). Results from experiments that utilized a combination of compounds which altered either ethylene or polyamine biosynthesis, namely, aminoethoxyvinyl glycine, CoSO₄, 2,5-norbornadiene, and CuSO₄, suggest the two pathways compete for a common precursor. However, exogenous addition of ethylene (via ethephon treatments) had little or no effect on polyamine biosynthesis. Likewise, polyamine treatments had little or no effect on ethylene biosynthesis. These data suggest that there are few or no inhibitory effects from the end products of one pathway on the synthesis of the other. Data from leaves treated with metabolic intermediates in the catabolic pathway of polyamines and inhibitors of enzymes in the catabolic pathway, i.e. aminoguanidine, hydroxyethyldrazine and gabaculine, suggest that the observed increases in polyamine titers were not due to decreased catabolism of the polyamines. One catabolic intermediate, γ-aminobutyric acid (GABA), elevated putrescine, spermidine and spermine by 12-, 1.4-, and 2-fold, respectively, Ethylene levels decreased (25%) in GABA-treated leaves. This small decrease in ethylene could not account for such large increase in putrescine titers. Further analysis demonstrated that the GABA-mediated polyamine accumulation was inhibited by difluoromethylarginine, an inhibitor of arginine decarboxylase, but not by difluoromethylornithine, an inhibitor of ornithine decarboxylase. These data suggest that GABA directly or indirectly affects the biosynthesis of polyamines via arginine decarboxylase.     

Unusual regulatory properties of sucrose-phosphate synthase purified from soybean (Glycine max) leaves

Sucrose-phosphate (SPS) from source leaves of soybean ( Glycine max (L.) Merr. cv. Ransom II) was purified 74-fold to a final specific activity of 1.8 U (mg protein)¹. The partially purified preparation was free from phosphoglucoseisomerase (EC 5.3.1.9), pyrophosphatase (EC 3.6.1.1), phosphoenolpyruvate-phosphatase (EC 3.1.3.-), phosphofructokinase (EC 2.7.1.11), and uridine diphosphatase (EC 3.6.1.6), and was used for characterization of the kinetic and regulatory properties of the enzyme. The enzyme showed hyperbolic saturation kinetics for both fructose-6-phosphate (K_m=0.57 m M ) and UDPGlucose (UDPG) (K_m=4.8 m M ). The activity of SPS was inhibited by the product UDP. In vitro this inhibition could be partially overcome by the presence of Mg²⁺. Inorganic orthophosphate was only slightly inhibitory (35% inhibition at 25 m M phosphate). Glucose-6-phosphate (up to 20 m M ) had no effect on activity, and did not show any significant interaction with phosphate inhibition. A range of potential effectors was tested and had no effect on SPS activity: Glucose-1-phosphate, fructose-1, 6-bisphosphate, α-glycero-phosphate, dihydroxyacetone-phosphate, 3-phosphoglyceric acid, (all at 5 m M ), sucrose at 100 m M and pyrophosphate at 0.1 m M . The apparent lack of allosteric regulation of soybean SPS makes this enzyme markedly different from SPS previously characterized from spinach and maize.     

Relative growth rates of leaves from soybean grown under drought-stressed and irrigated field conditions

Abstract. The relative growth rates and leaf area were graphed against leaf area, normalized with respect to final leaf area, to assess the applicability of the Lockhart cell wall expansion equation to soybean, Glycine max (L.) Merr., leaf development under field conditions. For leaves that had completed more than 20% of their growth, relative growth rates decreased linearly with an increase in the normalized leaf area, indicating that these leaves were undergoing strictly expansive growth. Drought stress significantly decreased the relative growth rate of these larger leaves. Small leaves which had completed less than 20% of their growth, were found to have highly variable relative growth rates. The large variability in relative growth rates indicated that the Lockhart cell wall expansion equation was inadequate to evaluate the growth of these young leaves. Drought stress had virtually no influence on the relative growth rates observed in the small leaves.     

The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings

Soybean ( Glycine max cv. Clark) was grown at both ambient (ca 350 μmol mol⁻¹) and elevated (ca 700 μmol mol⁻¹) CO₂ concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40°C) for 17–22 days after sowing to determine the interaction between temperature and CO₂ concentration on photosynthesis (measured as A, the rate of CO₂ assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO₂ as temperature increased from 25 to 35°C (i.e. optimal growth rates). At 40°C, primary leaves failed to develop and plants eventually died. In contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO₂ concentration. For whole plants, increased CO₂ stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO₂ for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO₂ as temperature increased. Results from the present study suggest that self-shading could limit the response of CO₂ assimilation rate and the growth response of soybean plants if temperature and CO₂ increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO₂ at the whole plant level.     

Responses of soybean to oxygen deficiency and elevated root-zone carbon dioxide concentration

Root flooding is damaging to the growth of crop plants such as soybean (Glycine max L.). Field flooding for 3 d often results in leaf chlorosis, defoliation, cessation of growth and plant death. These effects have been widely attributed solely to a lack of oxygen in the root-zone. However, an additional damaging factor may be CO(2), which attains levels of 30 % (v/v) of total dissolved gases. Accordingly, the effects of root-zone CO(2) on oxygen-deficient soybean plants were investigated in hydroponic culture. Soybean plants are shown to be very tolerant of excess water and anaerobiosis. No oxygen (100 % N(2) gas) and low oxygen (non-aerated) treatments for 14 d had no effect on soybean survival or leaf greenness, but plants became severely chlorotic and stunted when the roots were exposed to no oxygen together with CO(2) concentrations similar to those in flooded fields (equilibrium concentrations of 30 %). When root-zone CO(2) was increased to 50 %, a quarter of soybean plants died. Those plants that survived showed severe symptoms of chlorosis, necrosis and root death. In contrast, rice (Oryza sativa L.) plants were not affected by the combination of no oxygen and elevated root-zone CO(2.) A concentration of 50 % CO(2) did not affect rice plant survival or leaf colour. These results suggest that the high susceptibility of soybean to soil flooding, compared with that of rice, is an outcome of its greater sensitivity to CO(2).     

A recessive soybean cyst nematode allele for incompatibility with soybean PI 88287

The objective of this research was to characterise the degree of dominance of a soybean cyst nematode (Heterodera glycines) allele for incompatibility which interacts with a recessive soybean (Glycine max) allele for incompatibility to prevent the formation of cysts. Crosses of inbred nematode populations were made and the F, and F, populations evaluated for the numbers of cysts they could produce on several soybean lines. The nematode gene for avirulence interacts with the one recessive gene for resistance in soybean line PI 88287 and also appears to be recessive. This is the first example of a recessive-recessive gene-for-gene interaction; genes for avirulence and resistance are usually dominant. The difficulties of doing definitive genetic studies with cyst nematodes are discussed.     

Altered night-time CO2 concentration affects the growth, physiology and biochemistry of soybean

Soybean plants (Glycine max (L.) Merr. c.v. Williams) were grown in CO₂ controlled, natural-light growth chambers under one of four atmospheric CO₂ concentrations ([CO₂]): (1) 250 μmol mol^–1 24 h d^–1[250/250]; (2) 1000 μmol mol^–1 24 h d^–1[1000/1000]; (3) 250 μmol mol^–1 during daylight hours and 1000 μmol mol^–1 during night-time hours [250/1000] or (4) 1000 μmol mol^–1 during daylight hours and 250 μmol mol^–1 during night-time hours [1000/250]. During the vegetative growth phase few physiological differences were observed between plants exposed to a constant 24 h [CO₂] (250/250 and 1000/1000) and those that were switched to a higher or lower [CO₂] at night (250/1000 and 1000/250), suggesting that the primary physiological responses of plants to growth in elevated [CO₂] is apparently a response to daytime [CO₂] only. However, by the end of the reproductive growth phase, major differences were observed. Plants grown in the 1000/250 regime, when compared with those in the 1000/1000 regime, had significantly more leaf area and leaf mass, 27% more total plant dry mass, but only 18% of the fruit mass. After 12 weeks of growth these plants also had 19% higher respiration rates and 32% lower photosynthetic rates than the 1000/1000 plants. As a result the ratio of carbon gain to carbon loss was reduced significantly in the plants exposed to the reduced night-time [CO₂]. Plants grown in the opposite switching environment, 250/1000 versus 250/250, showed no major differences in biomass accumulation or allocation with the exception of a significant increase in the amount of leaf mass per unit area. Physiologically, those plants exposed to elevated night-time [CO₂] had 21% lower respiration rates, 14% lower photosynthetic rates and a significant increase in the ratio of carbon gain to carbon loss, again when compared with the 250/250 plants. Biochemical differences also were found. Ribulose-1,5-bisphosphate carboxylase/ oxygenase concentrations decreased in the 250/ 1000 treatment compared with the 250/250 plants, and phosphoenolpyruvate carboxylase activity decreased in the 1000/250 compared with the 1000/1000 plants. Glucose, fructose and to a lesser extent sucrose concentrations also were reduced in the 1000/250 treatment compared with the 1000/1000 plants. These results indicate that experimental protocols that do not maintain elevated CO₂ levels 24 h d^–1 can have significant effects on plant biomass, carbon allocation and physiology, at least for fast-growing annual crop plants. Furthermore, the results suggest some plant processes other than photosynthesis are sensitive to [CO₂] and under ecologically relevant conditions, such as high night-time [CO₂], whole plant carbon balance can be affected.     

Effects of ferulic acid on L-malate oxidation in isolated soybean mitochondria

The effects of ferulic acid on L-malate oxidation in mitochondria isolated from soybean (Glycine max L.) seedlings were investigated. Oxygen uptake and the products of L-malate oxidation were measured under two conditions: pH 6.8 and 7.8. At acidic pH, the activity of the NAD+-linked malic enzyme (L-malate:NAD+oxidoreductase [decarboxylating] EC 1.1.1.39) was favoured, whereas at alkaline pH a predominance of the L-malate dehydrogenase activity (L-malate:NAD+oxidoreductase EC 1.1.1.37) was apparent. Ferulic acid inhibited basal and coupled respiration during L-malate oxidation either at acidic or alkaline pH, reducing also the amounts of pyruvate or oxaloacetate produced. The results suggest that the site of ferulic acid action is situated at some step that precedes the respiratory chain. An interference with the L-malate entry into the mitochondria could be an explanation for the effects of ferulic acid, but the possibility of a direct inhibition of both enzymes involved in L-malate oxidation cannot be ruled out. This revised version was published online in August 2006 with corrections to the Cover Date.     

Protein synthesis at low temperatures in two soybean cultivars differing by their cold sensitivity

The effect of low temperatures (14°C/8°C, day/night) on polypeptide synthesis in leaves of two soybean ( Glycine max [L.] Merr.) cvs (Verdon and Maple Arrow) differing in cold sensitivity was investigated. The two cultivars were initially characterized in terms of cold tolerance according to their growth at the young plant stage at 14°C/8°C. Verdon was found to be more tolerant than Maple Arrow. In vivo [³⁵S]-methionine labeled polypeptides were resolved by two-dimensional electrophoresis. Autoradiograms were computer analyzed to evidence and quantify significative changes occurring after 5 days at 14°C/8°C, and to compare the response of the two cultivars. Most of the observed changes were quantitative. The two cultivars essentially exhibited a common modified polypeptide pattern in response to cold temperatures, but the changes were quantitatively more pronounced in the most tolerant cultivar. Computer analysis of two-dimensional electrophoresis gels allowed, for the first time, characterization of cultivar differences in terms of protein pattern under cold conditions.     

Inhibition of sulphur redistribution into new leaves of vegetative soybean by excision of the maturing leaf

When soybean plants are pulsed with [³⁵S]sulphate, label is subsequently redistributed from the roots to the leaves. This confounds studies to measure the redistribution of label from leaves. Accordingly, soybean plants ( Glycine max [L.] Merr. cv. Stephens) were grown in 20 μ M sulphate and a small portion of the root system (donor root) was pulsed with [³⁵S]sulphate for 24 h. After removing the donor root, the plants were transferred into unlabelled solution, either without sulphate (S20→SO) or with 20 μ M sulphate (S20→20) (intact plants). Also at this time, the expanding leaf (L3) was excised from half of the plants in each treatment (excised plants). Immediately after the pulse, only ca 15% of the label occurred in the roots and ca 40% in the expanding leaf, L3, mostly in the soluble fraction. In intact S20→20 plants, ³⁵S-label was exported from the soluble fraction of L3, mostly as sulphate, whilst L4 and L5 imported label. Similar responses occurred in S20→SO plants except that export of label from L3 was more rapid. Excision of L3 from S20→S20 plants inhibited labelling of leaves L4-L6 but not total sulphur, whereas in S20→SO plants, excision of L3 inhibited the import of both total sulphur and ³⁵S-label in leaves L4, L5 and L6. The data suggest that the soluble fraction of almost fully expanded leaves is an important reserve of sulphur for redistribution to growing leaves. The ³⁵S-label in the root system exhibited fluctuations consistent with its proposed role in the recycling of soluble sulphur from the leaves.     

Nonstructural carbohydrates of soybean plants grown in subambient and superambient levels of CO2

Photosynthesis Research - Elevated carbon dioxide (CO2) concentration increases plant photosynthesis, biomass and carbohydrate accumulation. Since plants have grown in low CO2 (200 to 300 µmol...     

Effects of canopy shade on the lipid composition of soybean leaves

The effect of canopy shade on leaf lipid composition was examined in soybeans ( Glycine max cv. Young) grown under field conditions. Expanding leaves were tagged at 50, 58 and 65 days after planting (DAP) in plots with either a high (10 plants m⁻¹ row) or low (1 plant m⁻¹ row) plant density. At 92 DAP, light conditions ranged from a pho-tosynthetic photon flux density (PPFD) of 87% of full sun with a far-red/red (735 nm/645 nm) ratio of 0.9 at upper canopy leaves to extreme shade where the PPFD was 10% of full sun with a far-red/red ratio greater than 6. Highly shaded leaves in the high plant density treatment accumulated triacylglycerol (TG) up to 25% of total leaf lipid, a 2.4-fold increase in TG on a chlorophyll basis compared to leaves in the upper canopy. Although total polar lipid content was reduced up to 50% in shaded leaves, shade had little affect on the lipid content or composition of thylakoid membranes. Shade did not affect leaf chlorophyll content. Therefore, the changes in leaf lipid composition were not related to senescence. These findings suggest that conditions of low irradiance and/or a high FR/R ratio cause a shift in carbon metabolism toward the accumulation of TG, a storage lipid. Eighteen-carbon fatty acid desaturation was also affected in highly shaded leaves where a reduction in linolenic acid (18:3) content was accompanied by a proportional increase in oleic (18:1) and linoleic (18:2) acids.