Determinant of photosynthetic capacity in rice leaves under ambient air conditions

At the grain-filling stage, net photosynthetic rate (P _N), stomatal conductance (g _s), and ribulose-1,5-bisphosphate carboxylation efficiency (CE) were correlated in order to find the determinant of photosynthetic capacity in rice leaves. For a flag leaf, P _N in leaf middle region was higher than in its upper region, and leaf basal region had the lowest P _N value. The differences in g _s and CE were similar. P _N, g _s, and CE gradually declined from upper to basal leaves, showing a leaf position gradient. The correlation coefficient between P _N and CE was much higher than that between P _N and g _s in both cases, and P _N was negatively correlated with intercellular CO₂ concentration (C _i). Hence the carboxylation activity or activated amount of ribulose-1,5-bisphosphate carboxylase/oxygenase rather than g_s was the determinant of the photosynthetic capacity in rice leaves. In addition, in flag leaves of different tillers P _N was positively correlated with g _s, but negatively correlated with C _i. Thus g _s is not the determinant of the photosynthetic capacity in rice leaves.The study was supported by the State Key Basic Research and Development Plan (No.G1998010100).     

Quantal charge redistributions accompanying the structural transitions of sodium channels

Asymmetric displacement currents, I _g , associated with the gating of nerve sodium channels have been recorded in cell-attached macropatches of Xenopus laevis oocytes injected with exogenous mRNA coding for rat-brain-II sodium channels. The I _g properties were found to be similar to those of gating currents previously observed in native nerve preparations. I _g fluctuations were measured in order to ascertain the discreteness of the conformational changes which precede the channel opening. The autocorrelation of the fluctuations is consistent with a shot-like character of the elementary I _g contributions. The variance of the fluctuations indicates that most of the gating-charge movement that accompanies the activation of a single sodium channel occurs in 2 to 3 brief packets, each carrying an equivalent of about 2.3 electron charges.     

A distinctive phenotype in the common-<Emphasis Type="Italic">A</Emphasis> heterokaryon of <Emphasis Type="Italic">Coprinus cinereus</Emphasis>

The homobasidiomycete Coprinus cinereus, unlike Schizophyllum commune, is not known to exhibit an obvious heterokaryotic phenotype in common-A matings. In the present study we found that progeny isolated from a fruit-body collected in the field exhibit a distinctive mycelial development in common-A matings. Genetic analysis suggested that the common-A heterokaryotic phenotype is brought about by a nuclear factor(s) other than the mating type genes. Received: March 30, 2001 / Accepted: October 1, 2001     

Uninucleate spores of Phycomyces

Summary Under most culture conditions only 0.3% of the vegetative spores of Phycomyces blakesleeanus are uninucleate. On an acidified minimal medium, the uninucleate fraction can be raised up to 4.5% of the spores. The spore population can be fractionated in a gradient under gravity (1xg) yielding fractions that contain over 80% uninucleate spores. These uninucleate spores are fully viable. When the spores to be fractionated are obtained from a heterokaryotic mycelium, the uninucleate fraction produces homokaryotic mycelia.     

Effects of trypsin upon EPR signals arising from components of the donor side of Photosystem II

EPR signals from components functioning on the electron donor side of Photosystem II (PS II) have been monitored in PS II membranes isolated from spinach chloroplasts after treatment with trypsin at pH 7.5 and pH 6.0. The following information has been obtained. (1) The multiline manganese signal, the g = 4.1 signal and Signal II_slow are lost with trypsin treatment at pH 7.5, but not at pH 6.0. (2) At pH 7.5 the multiline S₂ signal and the g = 4.1 signal are lost with approximately the same dependency on the incubation time with trypsin. At pH 6.0 trypsin treatment is known to block electron transfer between Q_A and Q_B (the first and the second quinone electron acceptors, respectively) allowing only a single turnover to occur. Under these conditions both the g = 4.1 signal and the multiline signal are induced by illumination at 200 K and their amplitudes are almost the same as in untreated samples. These results are interpreted as indicating that the g = 4.1 signal arises from a side path donor or from S₂ itself rather than a carrier functioning between the S states and the reaction center as previously suggested. (3) Cytochrome b-559 is converted to its oxidized low-potential form by trypsin treatment at both values of pH. At pH 6.0 the S-state turnover still occurs indicating that the presence of reduced high-potential cytochrome b-559 is not necessary for this process.     

Element content and expression of genes of interest in guard cells are connected to spatiotemporal variations in stomatal conductance

Element content and expression of genes of interest on single cell types, such as stomata, provide valuable insights into their specific physiology, improving our understanding of leaf gas exchange regulation. We investigated how far differences in stomatal conductance (g_s) can be ascribed to changes in guard cells functioning in amphistomateous leaves. g_s was measured during the day on both leaf sides, on well-watered and drought-stressed trees (two Populus euramericana Moench and two Populus nigra L. genotypes). In parallel, guard cells were dissected for element content and gene expressions analyses. Both were strongly arranged according to genotype, and drought had the lowest impact overall. Normalizing the data by genotype highlighted a structure on the basis of leaf sides and time of day both for element content and gene expression. Guard cells magnesium, phosphorus, and chlorine were the most abundant on the abaxial side in the morning, where g_s was at the highest. In contrast, genes encoding H⁺-ATPase and aquaporins were usually more abundant in the afternoon, whereas genes encoding Ca²⁺-vacuolar antiporters, K⁺ channels, and ABA-related genes were in general more abundant on the adaxial side. Our work highlights the unique physiology of each leaf side and their analogous rhythmicity through the day.     

Epidermal conductance in different parts of durum wheat grown under Mediterranean conditions: the role of epicuticular waxes and stomata

Abstract. Epidermal (non-stomatally-controlled) conductance from the fourth leaf, first node leaf, flag leaf and ear of durum wheat (Triticum turgidum var durum L.) grown under Mediterranean field conditions has been measured, along with leaf stomatal frequency and the amount and distribution of epicuticular waxes. Measurements were carried out on varieties and land-races from the Middle East, North Africa, ‘Institut National de la Recherche Agricole’ (INRA) and ‘Centra Internacional de Mejora de Maiz y Trigo’ (CIMMYT). Significant differences were observed among genotypes in the epidermal conductances (g_e) of the four organs. For each of the four organs tested, genotypes from the Middle East and CIMMYT showed higher g_e. values than those from North Africa and INRA. Ears showed epidermal conductances that were more than four times higher than those of leaves when g_e. values were expressed per unit dry weight. The amount of epicuticular waxes was higher in the fourth leaves, intermediate in the first node and flag leaves and lower in the ears. For each organ, g_e differences among genotypes were unrelated with the amount of epicuticular waxes. Removal of epicuticular waxes by dipping the organs into chloroform significantly increased the epidermal conductance for the fourth and first node leaves and the ear. However, this did not occur for the flag leaf. For the fourth leaf, g_e of intact leaves and g_e of leaves in which epicuticular waxes were removed were unrelated (r = -0.265). The regression coefficient of this relation for the first node and flag leaves showed values of 0.666 and 0.650 (P > 0.05), respectively, and values were even higher in the ear (r > m 0.892, P > 0.01). Scanning electron microscope analysis showed that wax bloom decreased from the fourth leaf to the flag leaf, whereas the extent of amorphous wax increased. Wax bloom in leaves consisted mainly of deposits of thin wax plates. In the ears and the adaxial surface of flag leaves, fibrillar waxes predominated. In the first node and flag leaves, the wax deposits on the adaxial side cover the surface of the leaf more densely and uniformly than those on the abaxial side. There was no significant correlation between g_e and total stomatal density, or between g_e and either adaxial or abaxial stomatal density for any sample of the three different leaves. The contribution of epicuticular waxes plus total stomatal frequency only explained 42.4, 11.8, 28.3 and 16% of g_e (per unit leaf area) variations for the fourth leaf, first node leaf, flag leaf and the combined variation of the three leaves together, respectively. From these results, it is concluded that complex interrelationship between different morphophysiological characteristics probably control g_e differences among genotypes and that these interrelationships differ for each different plant part.     

Folded chromosomes in non-cycling yeast cells

Folded chromosomes from stationary phase or ammonia-starved yeast (Saccharomyces cerevisiae) cells can be isolated as compact structures, distinct and separable by sedimentation from the folded chromosomes of pre-replicative (G₁) and post-replicative (G₂) nuclei. Such cells are in a dormant or non-cycling (G₀) stage. The folded genome from such cells is referred to as theg ₀ form and has a sedimentation velocity of about 1700S. Sedimentation analysis of mixed G₀ and G₁ and G₂ lysates indicates that theg ₀ structure is not an artifactual breakdown product of theg ₁ org ₂ structures. A comparison of the proteins fromg ₀ versusg ₁ andg ₂ structures by gel electrophoresis has revealed differences in about 10–11 non-histone and perhaps 2 histone proteins. Entry into the G₀ stage, and emergence into G₁ after G₀ arrest, are accompanied by an ordered transition fromg ₂ tog ₁ tog ₀, and fromg ₀ tog ₁ tog ₂ forms, respectively. Hence, entry into G₀ and re-emergence from G₀ can be considered as differentiative processes, not normally part of the cell cycle, and accompanied by specific changes in the tertiary organization of the genome.     

Crossover of a high-spin (S=7/2, 3/2) to a low-spin (S=1/2) iron-selenium cluster in FA and FB of photosystem I on rebinding of PsaC onto P700-FX cores

 PsaC is a tightly bound ferredoxin in the Photosystem I (PS I) reaction center which contains two [4Fe-4S] clusters named F_A and F_B. We recently proposed that the mixed-ligand F_B cluster in C14D_PsaC and the mixed-ligand F_A cluster in C51D_PsaC exist in a spin state of S=3/2, and that a spin state crossover to S=1/2 occurs when the PsaC mutants are rebound onto P700-F_X cores. Since EPR signals from a highly rhombic S=3/2 spin state can be difficult to study, wild-type PsaC was reconstituted with iron and selenium to introduce an easily detected S=7/2 spin state similar to that shown for Clostridial ferredoxin. When the unbound [4Fe-4Se] PsaC was chemically reduced, a sharp derivative resonance was found at g=5.171 attributed to the excited ±3/2 doublet from an S=7/2 spin multiplet. An additional peak was found at g=5.616 attributed to the superimposed ±1/2 and ±3/2 doublets from a highly rhombic S=3/2 spin multiplet, and an axial set of resonances found around g=2.0 attributed, in part, to a classical S=1/2 spin state. When the [4Fe-4Se] PsaC was rebound onto P700-F_X cores, the spin population derived from the S=7/2 and 3/2 spin states was negligible. Illumination of the rebuilt PS I complex at 15 K resulted in two rhombic sets of resonances, one with g values of 2.043, 1.941 and 1.854, diagnostic of F_A, and the other with g values of 2.067, 1.941 and 1.878, diagnostic of F_B. Chemical reduction with sodium dithionite at pH 10.5 or photoaccumulation by freezing during illumination resulted in a set of resonances with g values of 2.046, 1.938, 1.920 and 1.883, characteristic of a spin-coupled F_A ^–/F_B ^– pair. The spin state crossover in this iron chalcogenide cluster is the first known to be induced by protein-protein association and reinforces the hypothesis that an S=3/2 to 1/2 crossover occurs in the PS I-rebound mutants C14D_PsaC and C51D_PsaC. Received: 6 August 1996 / Accepted: 28 December 1996     

On modelling the variability of interspike intervals during epileptic unit activity

In spite of the fact that the participation of well defined ionic particles in generating convulsive unit discharges is established, there is a gap between the data on ionic movements and on first-order statistics of firing patterns. Our aim was to tight this gap by studying the effectiveness of functionally separated electrical conductances of membrane during the generation of consecutive interspike interval histograms (IIHs) of unitary discharges. On account of the non-stationarity of the process curve fitting analysis which based on the simple modifications of the integrate-and-fire model has been implemented in the sequential interspike interval histogram procedure (SIIH). The experimental data were recorded from cat cortex treated with 3-Aminopyridine (3-Ap) by glass microelectrodes during nembutal anesthezia. Assuming the normal distribution of input parameters it is concluded, that the efficiency of the fluctuations of the active spike-generating conductance g _g and the passive diffusional conductance g _l may increase during the generation of the unimodal IIHs and the first mode of the bimodal IIHs. The simple conductance coupling g _l =a·g _g +b may participate in g _l activation, moreover, the reciprocally coupled mechanism g _g =c/g _l may be driven by g _l activation (a, b, c are the coupling constants). A temporal separation of processes governed by g _g or g _l respectively was observed. The timeindependent occurrences of the reciprocally coupled conductance processes may be involved in the unit activities represented by the prolonged IIHs and second modes of the bimodal IIHs.     

Optimal stomatal conductance in relation to photosynthesis in climatically contrasting Eucalyptus species under drought

Models of stomatal conductance (g_s) are based on coupling between g_s and CO₂ assimilation (A_net), and it is often assumed that the slope of this relationship (‘g₁’) is constant across species. However, if different plant species have adapted to different access costs of water, then there will be differences in g₁ among species. We hypothesized that g₁ should vary among species adapted to different climates, and tested the theory and its linkage to plant hydraulics using four Eucalyptus species from different climatic origins in a common garden. Optimal stomatal theory predicts that species from sub‐humid zones have a lower marginal water cost of C gain, hence lower g₁ than humid‐zone species. In agreement with the theory that g₁ is related to tissue carbon costs for water supply, we found a relationship between wood density and g₁ across Eucalyptus species of contrasting climatic origins. There were significant reductions in the parameter g₁ during drought in humid but not sub‐humid species, with the latter group maintaining g₁ in drought. There are strong differences in stomatal behaviour among related tree species in agreement with optimal stomatal theory, and these differences are consistent with the economics involved in water uptake and transport for carbon gain.     

Fluorescence properties of the allenic carotenoid fucoxanthin: Implication for energy transfer in photosynthetic pigment systems

The fluorescence spectrum of an allenic carotenoid, all-trans-fucoxanthin isolated from a brown alga, has been reported for the first time. This carotenoid is known to function efficiently as a primary photosynthetic antenna pigment in marine algae. The emission bands were located around 630, 685 and 750 nm in CS₂ at 20°C, absorption bands being located at 448, 476 and 505 nm. The energy difference between the 0-0 bands of absorption and emission spectra was about 3900 cm^-1 and location of the emission maximum was less sensitive to the polarizability of solvents than that of the absorption maximum. These clearly indicate that the emission originates from the optically forbidden singlet state (2A_g). This is in contrast to other carotenoids whose emission is assigned to 1B_u state, probably due to the symmetric structure of the conjugated double bond responsible for the absorption in the visible region. A rapid internal conversion from 1B_u to 2A_g state might be facilitated by distorted structure of the conjugated double bond of fucoxanthin. The energy level responsible for the emission is almost identical to the Q_y level of the acceptor molecule (Chl a), thus we propose an energy transfer pathway from the optically forbidden 2A_g state of the carotenoid to the Q_y transition of Chl a in algal pigment systems.     

Mechanisms of very fast oscillations in networks of axons coupled by gap junctions

Because electrical coupling among the neurons of the brain is much faster than chemical synaptic coupling, it is natural to hypothesize that gap junctions may play a crucial role in mechanisms underlying very fast oscillations (VFOs), i.e., oscillations at more than 80 Hz. There is now a substantial body of experimental and modeling literature supporting this hypothesis. A series of modeling papers, starting with work by Roger Traub and collaborators, have suggested that VFOs may arise from expanding waves propagating through an “axonal plexus”, a large random network of electrically coupled axons. Traub et al. also proposed a cellular automaton (CA) model to study the mechanisms of VFOs in the axonal plexus. In this model, the expanding waves take the appearance of topologically circular “target patterns”. Random external stimuli initiate each wave. We therefore call this kind of VFO “externally driven”. Using a computational model, we show that an axonal plexus can also exhibit a second, distinctly different kind of VFO in a wide parameter range. These VFOs arise from activity propagating around cycles in the network. Once triggered, they persist without any source of excitation. With idealized, regular connectivity, they take the appearance of spiral waves. We call these VFOs “re-entrant”. The behavior of the axonal plexus depends on the reliability with which action potentials propagate from one axon to the next, which, in turn, depends on the somatic membrane potential V _s and the gap junction conductance g _gj . To study these dependencies, we impose a fixed value of V _s , then study the effects of varying V _s and g _gj . Not surprisingly, propagation becomes more reliable with rising V _s and g _gj . Externally driven VFOs occur when V _s and g _gj are so high that propagation never fails. For lower V _s or g _gj , propagation is nearly reliable, but fails in rare circumstances. Surprisingly, the parameter regime where this occurs is fairly large. Even a single propagation failure can trigger re-entrant VFOs in this regime. Lowering V _s and g _gj further, one finds a third parameter regime in which propagation is unreliable, and no VFOs arise. We analyze these three parameter regimes by means of computations using model networks adapted from Traub et al., as well as much smaller model networks.     

The association behavior of beta-lactamases in polyethylene glycol solution

The β-lactamases (EC 3.5.2.6) from Bacillus licheniformis 749/C, Enterobacter cloacae P99, and TEM plasmid RP4 are studied in 10–14% (w/v) polyethyleneglycol (PEG) 8000 solutions at pH 6.5 by x-ray scattering and in 18% PEG by equilibrium sedimentation. Although all three enzymes crystallize with twofold crystal symmetry from PEG 8000, it is not possible in this study to prove that dimerization occurs; however, both techniques give evidence for association above 1% (w/v) protein concentration. For the B. lichen., P99, and TEM enzymes, a dimerization of at most 0, 5, and 10% (v/v), respectively, account for the variation of radii of gyration R_g with concentration, after accounting for the effects of nonideality. Apparent R_g were 3–5% smaller in PEG solution than in PEG-free solution. Enhanced ordering of the molecules in PEG solution or the presence of a PEG-depleted hydration shell around the enzymes can account for the observation of reduced R_g values. Accordingly, values of the partial specific volume (defined at constant chemical potential of PEG) indicate considerable PEG exclusion and are consistent with the ability of high M_r PEGs to induce crystallization of these enzymes.     

EPR of Cu Prion Protein Constructs at 2 GHz Using the g⊥ Region to Characterize Nitrogen Ligation

A double octarepeat prion protein construct, which has two histidines, mixed with copper sulfate in a 3:2 molar ratio provides at most three imidazole ligands to each copper ion to form a square-planar Cu²⁺ complex. This work is concerned with identification of the fourth ligand. A new (to our knowledge) electron paramagnetic resonance method based on analysis of the intense features of the electron paramagnetic resonance spectrum in the g_⊥ region at 2 GHz is introduced to distinguish between three and four nitrogen ligands. The methodology was established by studies of a model system consisting of histidine imidazole ligation to Cu²⁺. In this spectral region at 2 GHz (S-band), g-strain and broadening from the possible rhombic character of the Zeeman interaction are small. The most intense line is identified with the M_I = +1/2 extra absorption peak. Spectral simulation demonstrated that this peak is insensitive to cupric A_x and A_y hyperfine interaction. The spectral region to the high-field side of this peak is uncluttered and suitable for analysis of nitrogen superhyperfine couplings to determine the number of nitrogens. The spectral region to the low-field side of the intense extra absorption peak in the g_⊥ part of the spectrum is sensitive to the rhombic distortion parameters A_x and A_y. Application of the method to the prion protein system indicates that two species are present and that the dominant species contains four nitrogen ligands. A new loop-gap microwave resonator is described that contains ∼1 mL of frozen sample.     

Entropy and the complexity of graphs: I. An index of the relative complexity of a graph

The structural information content (Rashevsky, 1955; Trucco 1956a, b)I _g (X) of a graphX is defined as the entropy of the finite probability scheme constructed from the orbits of its automorphism groupG(X). The behavior ofI _g on various graph operations—complement, sum, join, cartesian product and composition, is examined. The principal result of the paper is the characterization of a class of graph product operations on whichI _g is semi-additive. That is to say, conditions are found for binary operations o and ∇ defined on graphs and groups, respectively, which are sufficient to insure thatI _g (X o Y)=I _g (X)+I _g (Y)−H _XY , whereH _XY is a certain conditional entropy defined relative to the orbits ofG(X o Y) andG(X) ∇G(Y).     

Mitochondrial ATP Synthase: A Bioinformatic Approach Reveals New Insights About the Roles of Supernumerary Subunits <Emphasis Type="Italic">g</Emphasis> and A6L

The mitochondrial ATP synthase is a membrane protein complex which couples the proton gradient across the mitochondrial inner membrane to the synthesis of ATP from ADP + P_i. The complex is composed of essential subunits for its motor functions and supernumerary subunits, the roles of which remain to be elucidated. Subunits g and A6L are supernumerary subunits, and the specific roles of these subunits are still matters of debate. To gain insight into the functions of these two subunits, we carried out the alignment and the homolog search of the protein sequences of the subunits and found the following features: Subunit g appears to have isoforms in animals, and the transmembrane domain of the animal subunit g contains a completely conserved acidic residue in the middle of a helix on the conserved side of the transmembrane helix. This finding implicates the conserved acidic residue as important for the function of subunit g. The alignment of A6L protein sequences shows a conserved aromatic residue at the N-terminal domain with which the N-terminal MPQL sequence comprises a unique MPQLX₄Ar motif that can signify the protein A6L. The conserved aromatic residue may also be important for the function of A6L.     

Photosynthesis,transpiration, and water use efficiency of <Emphasis Type="Italic">Leymus dasystachys</Emphasis> on the Hunshandake desert

Net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) declined from upper leaves to the lower ones during dry and rainy seasons, indicating that long-term carbon budget should take into account P _N variations for different leaf types. Relatively greater P _N in the dry season suggested that this species is more able to maintain higher P _N under drought, but the relatively higher E in the dry season might reduce water use efficiency (P _N/E) for the species. Significant correlations between P _N and g _s indicated that g _s may be the critical factor for P _N variability in the desert region.     

Control of transpiration from the upper canopy of a tropical forest: the role of stomatal, boundary layer and hydraulic architecture components

Concurrent, independent measurements of stomatal conductance (g_s), transpiration (E) and microenvironmental variables were used to characterize control of crown transpiration in four tree species growing in a moist, lowland tropical forest. Access to the upper forest canopy was provided by a construction crane equipped with a gondola. Estimates of boundary layer conductance (g_b) obtained with two independent methods permitted control of E to be partitioned quantitatively between g_s and g_b using a dimensionless decoupling coefficient (Ω) ranging from zero to 1. A combination of high g_s (c. 300–600 mmol m^?2 s^?1) and low wind speed, and therefore relatively low g_b (c. 100–800 mmol m^?2 s^?1), strongly decoupled E from control by stomata in all four species (Ω= 0.7–0.9). Photosynthetic water-use efficiency was predicted to increase rather than decrease with increasing g_s because g_b was relatively low and internal conductance to CO₂ transfer was relatively high. Responses of g_s to humidity were apparent only when the leaf surface, and not the bulk air, was used as the reference point for determination of external vapour pressure. However, independent measurements of crown conductance (g_c), a total vapour phase conductance that included stomatal and boundary layer components, revealed a clear decline in g_c with increasing leaf-to-bulk air vapour pressure difference (V_a because the external reference points for determination of g_c and V_a were compatible. The relationships between g_c and V_c and between g_s and V_s appeared to be distinct for each species. However, when g_s and g_c were normalized by the branch-specific ratio of leaf area to sapwood area (LA/SA), a morphological index of potential transpirational demand relative to water transport capacity, a common relationship between conductance and evaporative demand for all four species emerged. Taken together, these results implied that, at a given combination of LA/SA and evaporative demand scaled to the appropriate reference point, the vapour phase conductance and therefore transpiration rates on a leaf area basis were identical in all four contrasting species studied.     

An enzyme rate equation for the overall rate of reaction of gel-immobilized glucose oxidase particles under buffered conditions. II. Two limiting substrates

The overall rate of reaction of gel-immobilized glucose oxidase particles in buffered media has been investigated theoretically under two substrate diffusion limited conditions by the numerical solution of the diffusion equations. It has been found that the Enzyme Rate Equation (Atkinson and Lester), Biotechnol. Bioeng., 16 , 1299 (1974), together with an analytical solution which describes the asymptotic conditions associated with a large particle size, provides an adequate estimation of the values resulting from the numerical solution outside the region of the parameter space defined by 0.4 < M_g′, M₀′ < 10. When the dimensionless parameter (B₀′/B_g′)(M_g′²/M₀′²) is greater than unity the overall rate of reaction is limited principally by the external concentration and when the parameter has a value less than unity, by the external oxygen concentration. The results are generally applicable to enzymes whose kinetics are similar to those of glucose oxidase or for which the equation describing glucose oxidase kinetics provides an adequate curve-fit of experimental data.