Photosynthetic gas exchange in leaves of wheat plants supplied with silicon and infected with Pyricularia oryzae

Photosynthetic gas exchange in the leaves of wheat plants growing in a nutrient solution containing 0 or 2 mM silicon (Si) and inoculated with Pyricularia oryzae was investigated. The blast severity, the gas exchange parameters such as net carbon assimilation rate (A), stomatal conductance to water vapor (g _s), internal CO₂ concentration (C _i) and transpiration rate (E) and the concentration of pigments (chlorophyll a, chlorophyll b and carotenoids) were determined. The blast severity was reduced by 67.66 % on +Si plants compared with the ?Si plants. There were significant increases of 29.3, 17.7 and 45 % for A at 48, 72 and 96 h after inoculation (hai); 26.7 and 49 % for g _s at 48 and 96 hai; and 25.2 and 31.4 % for E at 48 and 96 hai, respectively, for +Si inoculated plants when compared with the ?Si inoculated plants. The C _i was significantly lower for +Si inoculated plants than for ?Si inoculated plants at 48, 72 and 96 hai. For inoculated plants, the concentrations of chlorophyll a and chlorophyll b were significantly higher for the +Si plants compared with the ?Si plants at 72 and 96 hai. The results of this study clearly demonstrated that the supply of Si to the wheat plants was associated with lower blast severity in parallel with improved gas exchange performance, resulting in higher energy for mounting successful defense strategies against P. oryzae infection.     

Sedimentation coefficients of self-associating species: I. Basic theory

Under the same solution conditions, the apparent weight average sedimentation coefficient, s_wa, and some quantities obtained from it can be combined with the equilibrium constant or constants, K_i, and the monomer concentration, c_I, obtained from sedimentation equilibrium, light scattering or osmotic pressure experiments on the same self-associating solute, so that the individual sedimentation coefficients, s_i, of the self-associating species, and also the hydrodynamic concentration dependence parameter,g or $\text{g}$, can be evaluated. Using two different models for the hydrodynamic concentration parameter, four different methods are presented for the evaluation of the s_i's. Methods for evaluating g or $\text{g}$, once the s_i's are known, are presented. A method for obtaining the number average sedimentation coefficient, s_N, and its application to self-associations is presented. Methods are shown for the evaluation of Z average properties, x_zc, as well as number average properties,x_Nc, of a self-associating solute from its weight average properties, x_wc.     

Determination of the effective diffusion coefficient of oxygen in gel materials in relation to gel concentration

Summary The effective diffusion coefficient of oxygen, ID_e, was determined in different gel support materials (calcium alginate, -carrageenan, gellan gum, agar and agarose) which are generally used for immobilization of cells. The method used was based upon fitting Crank's model on the experimental data. The model describes the solute diffusion from a well-stirred solution into gel beads which are initially free of solute. The effect of the gel concentration on ID_e of oxygen in the gel was investigated. The results showed a decreasing ID_e for both agar and agarose at increasing gel concentration. In case of calcium alginate and gellan gum, a maximum in ID_e at the intermediate gel concentration was observed. It is hypothesized that this phenomenon is due to a changing gelpore structure at increasing gel concentrations. The ID_e of oxygen in calcium alginate, -carrageenan and gellan gum varied from 1.5^*10^–9 to 2.1^*10^–9 m²s^–1 in the gel concentration range of 0.5 to 5% (w/v).     

Electroendosmosis correction for electrophoretic mobility determined in cells

Electroendosmosis is a complicating factor in gel electrophoresis. Determination of electroendosmotic mobility by the use of vitamin B₁₂ as a marker in agar and agarose gels at different concentrations revealed that electroendosmosis was not reduced to zero by extrapolation of observed mobility values to zero gel concentration. It is shown that a Ferguson plot of the observed values of electrophoretic mobilities yields the correct values for K_R; however the extrapolated values of electrophoretic mobility must still be corrected for electroendosmosis to obtain the true electrophoretic mobilities.     

Interactions of Elevated CO2 Concentration and Drought Stress on Photosynthesis in Eucalyptus Cladocalyx F. Muell

Response of net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (c _i), and photosynthetic efficiency (F_v/F_m) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C₈₀₀) or 380 (C₃₈₀) µmol mol^-1 CO₂ concentration under sufficient water supply or under water stress. The well-watered plants at C₈₀₀ showed a 2.2 fold enhancement of P _N without any change in g _s. Under both C₈₀₀ and C₃₈₀, water stress decreased P _N and g _s significantly without any substantial reduction of c _i, suggesting that both stomatal and non-stomatal factors regulated P _N. However, the photosynthetic efficiency of PS2 was not altered.     

Photosynthesis Parameters in Two Cultivars of Mulberry Differing in Salt Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (salt tolerant cv. S1 and salt sensitive cv. ATP) were subjected to different concentrations of NaCl for 12 d. Leaf area, dry mass accumulation, total chlorophyll (Chl) content, net CO₂ assimilation rate (P _N), stomatal conductance (g _s), and transpiration rate (E) declined, and intercellular CO₂ concentration (C _i) increased. The changes in these parameters were dependent on stress severity and duration, and differed between the two cultivars. The tolerant cultivar showed a lesser reduction in P _N and g _s coupled with a better C _i and water use efficiency (WUE) than the sensitive cultivar.     

The effect of reduced water potential on soybean mitochondria

The respiration of excised hypocotyls and of isolated hypocotyl mitochondria from soybean [Glycine max (L.) Merr., var. Wayne] was determined in various concentrations of sucrose and potassium chloride. Hypocotyl oxygen uptake declined with increasing solute concentration; no specific effects of either solute were apparent. Mitochondrial state III respiration was strongly inhibited as the solute concentrations were raised and there was in addition a specific inhibitory effect of the salt. State IV respiration, however, was unaffected by the presence of osmoticum. ADP/O ratios were also unaffected, except at high potassium chloride concentrations (470 mm). The primary effect of solutes was thus to limit the rate of substrate oxidation.     

Intrinsic perturbing ability of alkanols in lipid bilayers

The proportionality constant between the equipotency concentrations of a series of solutes and the fraction of a solute in the membrane phase is directly related to the solute to lipid mol ratio. Experimental measurements of partition coefficient and of several alkanol-induced effects show that the solute/lipid mol ratlos for a series of alkanols are not constant at their equipotency concentrations. The deviations in the solute/lipid ratios are similar in the various systems, and these deviations seem to depend primarily upon the chain length and branching in alkanols. It is suggested that such intrinsic differences in the perturbing ability of alcohols arise from a specificity of interaction between alkanols and lipid bilayer. We have correlated partition coefficients (in n-octanol, in egg phosphatidylcholine liposomes, and in dipalmitoyl phosphatidylcholine liposomes) for thirteen alkanols to the equipotency concentrations for their ability to modify the order-disorder thermotropic transition in dipalmitoyl phosphatidylcholine, ability to stimulate the hydrolysis of phosphatidylcholine in a bilayer by bee venom phospholipase A₂, and for the activation of the galactoside transport system in Escherichia coli. Significant correlation is found between equipotency concentrations for perturbing the order-disorder transition, the activation of phospholipase A₂-catalyzed hydrolysis and the activation of galactoside transport system.     

Light-harvesting in photosystem I

Improving Rubisco catalysis is considered a promising way to enhance C₃-photosynthesis and photosynthetic water use efficiency (WUE) provided the introduced changes have little or no impact on other processes affecting photosynthesis such as leaf photochemistry or leaf CO₂ diffusion conductances. However, the extent to which the factors affecting photosynthetic capacity are co-regulated is unclear. The aim of the present study was to characterize the photochemistry and CO₂ transport processes in the leaves of three transplantomic tobacco genotypes expressing hybrid Rubisco isoforms comprising different Flaveria L-subunits that show variations in catalysis and differing trade-offs between the amount of Rubisco and its activation state. Stomatal conductance (g _s) in each transplantomic tobacco line matched wild-type, while their photochemistry showed co-regulation with the variations in Rubisco catalysis. A tight co-regulation was observed between Rubisco activity and mesophyll conductance (g _m) that was independent of g _s thus producing plants with varying g _m/g _s ratios. Since the g _m/g _s ratio has been shown to positively correlate with intrinsic WUE, the present results suggest that altering photosynthesis by modifying Rubisco catalysis may also be useful for targeting WUE.     

Mesorhizobium sp. J8 can establish symbiosis with Glycyrrhiza uralensis,increasing glycyrrhizin production

Licorice (Glycyrrhiza uralensis) is a medicinal plant that contains glycyrrhizin (GL), which has various pharmacological activities. Because licorice is a legume, it can establish a symbiotic relationship with nitrogen-fixing rhizobial bacteria. However, the effect of this symbiosis on GL production is unknown. Rhizobia were isolated from root nodules of Glycyrrhiza glabra, and a rhizobium that can form root nodules in G. uralensis was selected. Whole-genome analysis revealed a single circular chromosome of 6.7 Mbp. This rhizobium was classified as Mesorhizobium by phylogenetic analysis and was designated Mesorhizobium sp. J8. When G. uralensis plants grown from cuttings were inoculated with J8, root nodules formed. Shoot biomass and SPAD values of inoculated plants were significantly higher than those of uninoculated controls, and the GL content of the roots was 3.2 times that of controls. Because uninoculated plants from cuttings showed slight nodule formation, we grew plants from seeds in plant boxes filled with sterilized vermiculite, inoculated half of the seedlings with J8, and grew them with or without 100 µM KNO₃. The SPAD values of inoculated plants were significantly higher than those of uninoculated plants. Furthermore, the expression level of the CYP88D6 gene, which is a marker of GL synthesis, was 2.5 times higher than in inoculated plants. These results indicate that rhizobial symbiosis promotes both biomass and GL production in G. uralensis.     

Effects of common components on hardness of culture media prepared with gelrite™

Summary Tissue cultures on properly solidified Gelrite media generally showed superior shoot proliferation and rooting, as well as shoot and root vigor and callus development to those on TC agar. Vitrification, or hyperhydricity, was observed in both Gelrite and agar media and minimized by increasing the gel concentrations. Rigidity of Gelrite media depended on combined levels of MS macrosalts, basal nutrient formulations, sucrose concentration, pH, and Gelrite concentration. Most MS macrosalts increased hardness of Gelrite gels; NH₄NO₃ had a decreasing effect. Rigidity of TC agar gels increased with reductions of MS macrosalts. A slightly softer Gelrite medium resulted when sucrose was excluded. Both Gelrite and agar media were softer at lower pHs and harder at higher pHs. Activated charcoal and mannitol increased gel hardness, and more noticeably of agar gels. NaCl addenda reduced rigidity, with their effects being more pronounced on Gelrite than on agar gels. Gelrite is a trademark of Kelco Division of Merck & Co. (San Diego, CA), manufacturer of the gellan gum. Phytagel is a trademark of Sigma Chemical Co. (St. Louis, MO) for repackaged Gelrite. TC agar used for comparisons in this investigation is plant tissue culture tested agar obtained from JRH Biosciences (Lenexa, KS).     

Control of Flowering in the Grapevine (Vitis vinifera L.): Formation of Inflorescences in Vitro by Isolated Tendrils

Photosynthesis, primary productivity, N content, and N₂ fixation were determined as a function of applied NH₄⁺ in peas (Pisum sativum L. cv. Alaska) which were inoculated or not inoculated with Rhizobium leguminosarum. Cabon dioxide exchange rate (CER) increased 10-fold, total N content 7-fold, and total dry weight 3-fold in 26-day-old uninoculated plants as applied NH₄⁺ was increased from 0 to 16 millimolar. In inoculated plants of the same age CER and dry weight were maximal at 2 millimolar NH₄⁺, and total N content increased between 0 and 2 millimolar NH₄⁺ but did not change significantly with higher NH₄⁺ applications. Per cent N content of uninoculated plants was significantly lower than that of inoculated plants except at the highest NH₄⁺ concentration (16 millimolar). Symbiotic N₂ fixation by inoculated plants was maximal in peas grown with 2 millimolar NH₄⁺; and apparent relative efficiency of N₂ fixation, calculated from C₂H₂ reduction and H₂ evolution, was maximal in the 2 to 4 millimolar NH₄⁺ concentration range. The capacity to fix N₂ through the Rhizobium-legume symbiosis significantly enhanced the rate and efficiency of photosynthesis and plant N content when NH₄⁺ concentration in the nutrient solution was below 8 millimolar. Above 8 millimolar NH₄⁺ concentration uninoculated plants had greater CER, N content, and dry weight.     

Carbon Dioxide and Light Responses of Photosynthesis in Cowpea and Pigeonpea during Water Deficit and Recovery

Greenhouse-grown pigeonpea (Cajanus cajan, [L.] Millsp.; cultivar UW-10) and cowpea (Vigna unguiculata, [L.] Walp.; cultivar California No. 5) were well-watered (control) or subjected to low water potential by withholding water to compare their modes of adaptation to water-limited conditions. Leaf CO₂ exchange rate (CER), leaf diffusive conductance to CO₂ (g_l), and CO₂ concentration in the leaf intercellular air space (C_i) were determined at various CO₂ concentrations and photon flux densities (PFD) of photosynthetically active radiation (400 to 700 nanometer). In cowpea, g_l declined to less than 15% of controls and total water potential (ψ_w) at midafternoon declined to −0.8 megapascal after 5 days of withholding water, whereas g_l in pigeonpea was about 40% of controls even though midafternoon ψ_w was −1.9 megapascal. After 8 days of withholding water, ψ_w at midafternoon declined to −0.9 and −2.4 megapascals in cowpea and pigeonpea, respectively. The solute component of water potential (ψ_s) decreased substantially less in cowpea than pigeonpea. Photosynthetic CER at saturation photon flux density (PFD) and ambient external CO₂ concentration (360 microliters per liter) on day 5 of withholding decreased by 83 and 55% in cowpea and pigeonpea, respectively. When measured at external, CO₂ concentration in bulk air of 360 microliters per liter, the CER of cowpea had fully recovered to control levels 3 days after rewatering; however, at 970 microliters per liter the PFD-saturated CERs of both species were substantially lower than in controls, indicating residual impairment. In stressed plants of both species the CER responses to C_i from 250 to 600 microliters per liter indicated that a substantial nonstomatal inhibition of CER had occurred. Although the sensitivity of g_l to water limitation in cowpea suggested a dehydration avoidance response, parallel measurements of CER at various C_i and PFD indicated that photosynthetic activity of cowpea mesophyll was substantially inhibited by the water-limited treatment.     

Limitation factors for photosynthesis in ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) leaves in response to moderate water stress

The levels of stomatal, mesophyll and biochemical limitations in CO₂ assimilation of ‘Bluecrop’ highbush blueberry leaves were compared at two different levels of leaf water potential. The leaf water potentials were ?1.49 and ?1.94 MPa in daily-irrigated (DI) and non-irrigated (NI) shrubs, respectively. The NI shrubs represented plants under moderate water stress. Mesophyll conductance (g _m) and chloroplastic CO₂ concentration (C _c) were estimated by combined measurements of gas exchange and chlorophyll fluorescence under various intercellular CO₂ concentrations (C _i). Net CO₂ assimilation rates (A _n) as a function of C _c were used for calculating maximum carboxylation efficiency (α _cmax) at the real sites of CO₂ assimilation. Maximum A _n (A _nmax) from the light response curves at 400 μmol mol^?1 air of ambient CO₂ concentration (C _a) were lower in the leaves of NI shrubs than in those of DI ones. However, electron transport rates were higher in the leaves of NI shrubs than in those of DI ones. The decrease in CO₂ assimilation following water stress may be caused by a decrease in g _m rather than a decrease in stomatal conductance (g _s) according to limitation analysis. Limitation rates by g _s, calculated at 400 μmol mol^?1 air of C _a in A _n-C _i curves, were not significantly different between the leaves of DI and NI shrubs. However, limitation rates by g _m from A _n-C _c curves were significantly higher in the leaves of NI shrubs than in those of DI ones. Maximum carboxylation efficiency (α _cmax) values calculated from the A _n-C _c curve, contrary to those calculated from the A _n-C _i curve, were higher in the leaves of NI shrubs than in those of DI ones. Consequently, mesophyll limitation than stomatal and biochemical limitations mainly down-regulated the photosynthesis in the leaves of ‘Bluecrop’ blueberry shrubs during moderate water stress.     

Mesophyll conductance variations in response to diurnal environmental factors in Myrcia paivae and Minquartia guianensis in Central Amazonia

Mesophyll conductance (g _m) is essential to determine accurate physiological parameters used to model photosynthesis in forest ecosystems. This study aimed to determine the effects of time of day on photosynthetic parameters, and to assess the effect of using either intercellular CO₂ concentration (C _i) or chloroplast CO₂ concentration (C _c), on maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), V _cmax. We used Amazonian saplings of Myrcia paivae and Minquartia guianensis. Photosynthetic parameters were measured using an infrared gas analyzer (IRGA); g _m was determined using both gas exchange and chlorophyll (Chl) a fluorescence and gas-exchange data alone. Leaf thickness (L _T) and specific leaf area (SLA) were also measured. Air temperature, relative humidity or understory light did not correlate with g _m and on average daily IRGA-fluorometer-determined g _m was 0.04 mol(CO₂) m^?2 s^?1 for M. paivae and 0.05 mol(CO₂) m^?2 s^?1 for M. guianensis. Stomatal conductance (g _s), g _m, electron transport rate (J _F), and light-saturated net photosynthetic rate (P _Nmax) were lower in the afternoon than in the morning. However, no effect of time of day was observed on V _cmax. L _T and SLA did not affect any of the examined parameters. IRGA-determined g _m was almost the double of the value obtained using the IRGA-fluorescence method. V _cmax values determined using C _c were about 25% higher than those obtained using C _i, which highlighted the importance of using C _c in V _cmax calculation. Decline in P _Nmax at the end of the afternoon reflected variations in g _s and g _m rather than changes in V _cmax. Diurnal variation in g _m appeared to be associated more with endogenous than with atmospheric factors.     

Properties of SDS-polyacrylamide gels highly cross-linked with N,N'-diallyltartardiamide and the rapid isolation of macromolecules from the gel matrix.

Polyacrylamide gels cross-linked with N,N′-diallyltartardiamide (DATD) are, in contrast to gels cross-linked with N,N′-methylenebisacrylamide (Bis), readily solubilized by periodic acid (Anker, H. S., 1970, FEBS Lett.7, 293), thus permitting efficient analyses of electrophoretically separated, labeled biological material. The capacities of polyacrylamide gels, cross-linked with Bis and DATD, to serve as media for electrophoretic separation of proteins, were compared. As DATD-cross-linked gels were inferior to equimolar Bis-crosslinked gels with 5% cross-linking (C_Bis = 5%) by the criteria of more pronounced swelling, markedly softer gels and, less concentrated and bended protein zones on electrophoresis and subsequent staining, gels cross-linked with different percentage CDATD were examined. The water regain of DATD-cross-linked gels, the retardation coefficients, and free mobilities of different proteins in equimolar Bis- and DATD-cross-linked gels were determined. When the DATD concentration in gels was increased to C_DATD = 27%, gels assumed physical characteristics comparable to those cross-linked with Bis at C_Bis = 5%. We report further the rapid, facile isolation of protein bands out of the gel matrix cross-linked with DATD. However, the isolation procedure results in an irreversible loss of biological activity.     

Regulation of mesophyll photosynthesis in intact wheat leaves by cytoplasmic phosphate concentrations

The effect of D-(+)-mannose, inorganic phosphate (Pi) and mannose-6-phosphate on net mesophyll CO₂ assimilation rate (A) and stomatal conductance (g_s) of wheat (Triticum aestivum L.) leaves was studied. The compounds were supplied through the transpiration stream of detached leaves from plants grown in sand in growth cabinets or glasshouses, with different concentrations of Pi (0.25, 1.0 and 4.0 mM) supplied during growth. In all cases, 10 mM D-(+)mannose caused 40–60% reduction of A within 30 min, though the time courses differed for flag leaves and the sixth leaf on the mainstem of glasshouse- and cabinet-grown plants. D-(+)Mannose had a similar effect on A in leaves having a fourfold range in total phosphate content. Effects of D-(+)mannose in reducing g_s were always slower than on A. When the CO₂ concentration in the leaf chamber was adjusted to maintain intercellular CO₂ concentration (C_i) constant as A declined after mannose supply, g_s still declined indicating that stomatal closure was not caused by changing C_i. Supplying mannose-6-phosphate at 10 and 1 mM and Pi at 5 and 10 mM concentrations caused rapid reductions in g_s and also direct reductions in A. The observed effects of mannose and Pi on assimilation are consistent with the proposed regulatory role of cytoplasmic Pi in determining mesophyll carbon assimilation that has been derived previously using leaf discs, protoplasts and chloroplasts.Abbreviations and symbols A net mesophyll CO₂-assimilation rate - C_a, C_i external (assimilation-chamber) and intercellular CO₂ concentration, respectively - g_s stomatal conductance - Man6P mannose-6-phosphate - Pi orthophosphate     

Ethylene Directly Inhibits Foliar Gas Exchange in Glycine max

Gas exchange of individual attached leaves of soybean, Glycine max (L.) Merr cv Davis, was monitored during exposure to exogenous ethylene (C₂H₄) to test the hypothesis that the effects of C₂H₄ on net photosynthesis (P_N) and stomatal conductance to H₂O vapor (g_s) are direct and not mediated by changes in leaf orientation to light. Leaflets were held perpendicular to incident light in a temperature-controlled cuvette throughout a 5.5 hour exposure to 10 microliters per liter C₂H₄. Declines in both P_N and g_s were evident within 2 hours and became more pronounced throughout the exposure period. In C₂H₄ treated plants, P_N and g_s decreased to 80 and 62%, respectively, of the rates in control plants. Because epinastic movement of the leaflets was prohibited by the cuvette, the observed declines in P_N and g_s were a direct effect of C₂H₄ rather than the result of reduced light interception caused by changing leaf angle.     

Effect of Xanthobacter,isolated and characterized from rice roots,on growth of wetland rice

With an autotrophic, N-free medium, Xanthobacter populations were isolated from the roots of wetland rice grown under field conditions. Xanthobacter populations ranged from 3.2×10⁴ to 5.1×10⁵ colony-forming units (cfu) g^-1 of root and averaged 47-fold higher on the root or rhizoplane than in the neighbouring nonrhizosphere. Characterization studies indicated dissimilarities in carbon utilization and motility among the isolated Xanthobacter strains and other recognized Xanthobacter species. Under gnotobiotic conditions, the population of one isolate, Xanthobacter sp. JW-KR1, increased from 10⁵ to 10⁷ cfu plant^-1 1 d after inoculation when a rice plant was present, but declined to numbers below the limit of detection (<10⁴ cfu assembly^-1) after 3 d in the absence of a plant. Scanning electron microscopy revealed Xanthobacter as pleomorphic forms on the rhizoplane. To assess the effect of Xanthobacter on plant growth, rice plants were grown under greenhouse conditions in plant assemblies containing sand and half-strength Hoagland's nutrient solution with and without nitrogen. Plants were either inoculated with 10⁵ cfu Xanthobacter g^-1 of sand or left uninoculated. After 40 d, plants without nitrogen showed no significant differences in top or root dry weight, plant height, root length, or number of tillers or leaves, whether the plants were inoculated or uninoculated. However, when nitrogen was added, inoculated plants had a significantly larger top dry weight (15%) and number of leaves (19%) than uninoculated plants. Under conditions of added and no added nitrogen, acetylene reduction assays showed Xanthobacter sp. JW-KR1 produced <0.1 (below detection limit) and 7 nmol C₂H₄ plant^-1 h^-1, respectively. Under the conditions studied, the results suggest that both Xanthobacter and wetland rice derive some benefits from their association.