Evidence for panicle control of stomatal behaviour in water-stressed plants of pearl millet

Stomatal conductance (gs), water potential (ψ), 14C-labelled assimilate export, and abscisic acid (ABA) concentration, were measured in flag leaves hof pearl millet grown in the field in the semi-arid tropics with restricted water supply. At similar ψ, gs increased with progressive stage of development hand growth of the panicle. Flag leaves ixhibited a lower s and rate of 14C-assimilate export, and a higher concentration of ABA, at the boot stage than following panicle emergence. Panicle removal resulted in a reduction in flag leaf 14C-assimilate export when carried out at stigma emergence (panicles just fully emerged from flag leaf sheath), but not when carried out after grain set. Reduction in flag leaf s were detected about 3 days after panicle removal and were correlated with increases in ABA concentration. The increased ABA was not due to any reduction in ψ. Completely blocking assimilate export by heat girdling caused a marked increased in ABA and a reduction in gs. It is suggested that the panicle might stimulate the export of ABA from the flag leaf, so lowering the ABA concentration in the leaf gand facilitating the higher gs found, under water stress, in flowering plants

A Rapid Effect of Heat Girdling on Stomatal Conductance in Pearl Millet (Pennisetum americanum [L.] Leeke)

A heat girdle, applied to the base of flag leaves of pearl millet, caused a rapid decline in stomatal conductance (gs). Stomata began to close within minutes of girdling (with gs reaching a minimum after about 5 min) but then partly reopened before closing again 20\2-30 min from the start of treatment. The initial closing response could be deferred and initially counteracted by enclosing the leaf in a polyethylene bag. Cell death in the girdled zone appeared to be necessary for the response as mechanical pressure alone was ineffective. Only stomata «downstream» of a girdled zone (relative to the direction of xylem flow) were affected by the treatment; there was no lateral or 《backward》 transmission of a closing stimulus. No immediate differences between control and girdled leaves could be detected in bulk leaf water potential or in abscisic acid content. The rapid effects of girdling on gs are thus ascribed to a transient, localised disturbance in epidermal water relations probably induced by a temporary interruption in xylem flow

Codimension-2 surfaces and their Hilbert spaces: low-energy clues for holography from general covariance

We argue that the holographic principle may be hinted at already from low-energy considerations, assuming diffeomorphism invariance, quantum mechanics and Minkowski-like causality. We consider the states of finite spacelike hypersurfaces in a diffeomorphism-invariant QFT. A low-energy regularization is assumed. We note a natural dependence of the Hilbert space on a codimension-2 boundary surface. The Hilbert product is defined dynamically, in terms of transition amplitudes which are described by a path integral. We show that a canonical basis is incompatible with these assumptions, which opens the possibility for a smaller Hilbert-space dimension than canonically expected. We argue further that this dimension may decrease with surface area at constant volume, hinting at holographic area-proportionality. We draw comparisons with other approaches and setups, and propose an interpretation for the non-holographic space of graviton states at asymptotically-Minkowski null infinity.Comment: 13 pages, 9 eps figures. Added Section VI, improved presentation. Expanded and split the Introduction into two sections. Added Section VII. Added reference

Stomatal responses of pearl millet (Pennisetum americanum(L.) Leeke) genotypes, in relation to abscisic acid and water stress

Stomatal responses to water stress and to applied (±)-abscisic acid (ABA) were examined in genotypes of pearl millet (Pennisetum americanum (L.) Leeke) known to differ in amounts of endogenous ABA accumulating during drought. In both a pot and a field experiment, Serere 39, a genotype with a high capacity to accumulate ABA, showed a higher stomatal sensitivity to water stress than did the ‘low’ ABA accumulator, BJ 104. In the field experiment, a third genotype, B282, accumulating least amounts of ABA, also had the lowest stomatal sensitivity to water stress. There were no significant differences between these genotypes in stomatal response to applied (±)-ABA, or in the relationships between leaf conductance and levels of endogenous ABA. It is concluded that the differences in accumulation of endogenous ABA by these genotypes of pearl millet are of functional significance, and that endogenous ABA generated during a water stress which develops over days or weeks mediates stomatal responses to such stress

Stomatal responses of pearl millet (Pennisetum americanum [L.] Leeke) to leaf water status and environmental factors in the field

Factors affecting stomatal conductance (g1) of pearl millet (Pennisetum americanum [L.] Leeke), cultivar BJ 104, were examined in the field in India during the dry season. Diurnal changes in g1 were evaluated for upper expanded leaves at flowering on two occasions using plants subjected to varying degrees of water stress. Except for the most severely stressed treatment, diurnal changes in g1 closely matched changes in irradiance (I), the promotive effect of which largely overcame opposing influences on g1 of increasing atmospheric vapour pressure deficit, and decreasing leaf water and turgor potentials (Ψ, Ψp). Two main effects of water stress on g1 were evident: (i) a decrease in the amplitude of the mid-day peak in g1, and (ii) a decrease in the time over which high g1 was maintained, resulting in early (mid-day) closure and hysteresis in the relationship between g1 and I. Leaf conductance was greatest for upper leaves and decreased down the canopy. At equivalent depths in the canopy g1 was higher in flowering than in photoperiodically-retarded plants of the same age. The magnitude of water stress-induced stomatal closure increased down the plant, and was more marked in retarded than in flowering plants. Within individual stress treatments Ψ of upper leaves decreased linearly as transpiration flux increased. It is concluded that stomatal behaviour of upper leaves of pearl millet at flowering largely operates to maximize assimilation rather than to minimize water los

Stomatal Response to Water Stress and its Relationship to Bulk Leaf Water Status and Osmotic Adjustment in Pearl Millet (Pennisetum americanum [L.] Leeke)

The water potential (Ψ) at which stomata completed closure (Ψ8Lmin) was determined for pearl millet (Pennisetum americanum [L.] Leeke) at two growth stages by monitoring changes in leaf conductance (gL) and Ψ following shoot detachment. Leaf water status was evaluated concurrently using a pressure-volume (P-V) technique. In a pot experiment with young vegetative plants, Ψ8Lmin closely approximated to the estimated Ψ at zero turgor (Ψu) both for control and for drought-conditioned plants which had osmotically adjusted. However, for penultimate leaves of field-grown flowering plants, Ψ8Lmin was found to be 0.61 (irrigated plants) and 0.87 (droughted plants) MPa below Ψu. In drought-stressed field-grown plants, osmotic adjustment (characterized by a decrease in solute (osmotic) potential (Ψs ) at both full hydration and zero turgor) was insufficient to maintain a positive bulk leaf turgor potential (Ψp) once Ψ had declined to below about -1.5 MPa. It is suggested that localized adjustment by the stomatal complex in response to environmental differences, leaf ageing and/or ontogenetic change, is responsible for the uncoupling of stomatal from bulk leaf water status

Osmotic adjustment to water stress in pearl millet (Pennisetum americanum [L.] Leeke) under field conditions

Abstract. Osmotic adjustment, a mechanism whereby plants maintain positive turgor despite low water potential (ψ), was investigated in pearl millet (Pennisetum americanum [L.] Leeke) in three types of field experiment at Hyderabad, India: 1.Osmotic adjustment during the growing season was evaluated by comparing solute potential (ψs) of leaves taken at midday from irrigated and droughted plots and allowed to rehydrate in the laboratory. The degree of seasonal adjustment was also estimated by comparing observed values of ψs in the field with those expected if ψs decreased solely in proportion to water loss. Both types of assessment indicated the maximum seasonal adjustment to be about 0.2 MPa. The cultivars BJ 104 and Serere 39 differed in their capacity to adjust osmotically over the season; Serere 39 was least able to osmoregulate. 2.Measurements of diurnal variations in ψ and ψs in BJ 104 revealed osmotic adjustment during the afternoon hours. At a given value of ψ, turgor (ψp) was about 0.1 MPa higher in irrigated, and over 0.2 MPa higher in droughted plants, in the afternoon, than in the morning. 3.Osmotic adjustment of different leaves within the canopy was investigated. Upper leaves had lower ψ than basal leaves. Differences in ψ were matched by gradients in ψs, so that turgor was similar for all leaf layers

An axisymmetric evolution code for the Einstein equations on hyperboloidal slices

We present the first stable dynamical numerical evolutions of the Einstein equations in terms of a conformally rescaled metric on hyperboloidal hypersurfaces extending to future null infinity. Axisymmetry is imposed in order to reduce the computational cost. The formulation is based on an earlier axisymmetric evolution scheme, adapted to time slices of constant mean curvature. Ideas from a previous study by Moncrief and the author are applied in order to regularize the formally singular evolution equations at future null infinity. Long-term stable and convergent evolutions of Schwarzschild spacetime are obtained, including a gravitational perturbation. The Bondi news function is evaluated at future null infinity.Comment: 21 pages, 4 figures. Minor additions, updated to agree with journal versio

Comparative studies on the structure of an upland African stream ecosystem

Upland stream systems have been extensively investigated in Europe, North America and Australasia and many of the central ideas concerning their function are based on these systems. One central paradigm, the river continuum concept is ultimately derived from those North American streams whose catchments remain forested with native vegetation. Streams of the tropics may or may not fit the model. They have been little studied. The Amani Nature Reserve in the East Usambara Mountains of north-eastern Tanzania offers an opportunity to bring these naturally forested systems to the attention of the ecological community. This article describes a comparison made between two lengths of the River Dodwe in this area. The work was carried out by a group of postgraduate students from eighteen European and African countries with advice from five staff members, as part of a course organised by the Tropical Biology Association. Rigorous efforts were made to standardise techniques, in a situation where equipment and laboratory facilities were very basic, through a management structure and deliberate allocation of work to specialists in each area.The article offers a summary of invertebrate communities found in the stream and its biomass. Crabs seem to be the key organism in both sections of the streams

A Jacobi-Davidson type method with a correction equation tailored for integral operators

The final publication is available at Springer via http://dx.doi.org/10.1007/s11075-012-9656-9We propose two iterative numerical methods for eigenvalue computations of large dimensional problems arising from finite approximations of integral operators, and describe their parallel implementation. A matrix representation of the problem on a space of moderate dimension, defined from an infinite dimensional one, is computed along with its eigenpairs. These are taken as initial approximations and iteratively refined, by means of a correction equation based on the reduced resolvent operator and performed on the moderate size space, to enhance their quality. Each refinement step requires the prolongation of the correction equation solution back to a higher dimensional space, defined from the infinite dimensional one. This approach is particularly adapted for the computation of eigenpair approximations of integral operators, where prolongation and restriction matrices can be easily built making a bridge between coarser and finer discretizations. We propose two methods that apply a Jacobi–Davidson like correction: Multipower Defect-Correction (MPDC), which uses a single-vector scheme, if the eigenvalues to refine are simple, and Rayleigh–Ritz Defect-Correction (RRDC), which is based on a projection onto an expanding subspace. Their main advantage lies in the fact that the correction equation is performed on a smaller space while for general solvers it is done on the higher dimensional one. We discuss implementation and parallelization details, using the PETSc and SLEPc packages. Also, numerical results on an astrophysics application, whose mathematical model involves a weakly singular integral operator, are presented.This work was partially supported by European Regional Development Fund through COMPETE, FCT-Fundacao para a Ciencia e a Tecnologia through CMUP-Centro de Matematica da Universidade do Porto and Spanish Ministerio de Ciencia e Innovacion under projects TIN2009-07519 and AIC10-D-000600.Vasconcelos, PB.; D'almeida, FD.; Román Moltó, JE. (2013). A Jacobi-Davidson type method with a correction equation tailored for integral operators. Numerical Algorithms. 64(1):85-103. doi:10.1007/s11075-012-9656-9S85103641Absil, P.A., Mahony, R., Sepulchre, R., Dooren, P.V.: A Grassmann–Rayleigh quotient iteration for computing invariant subspaces. SIAM Rev. 44(1), 57–73 (2002)Ahues, M., Largillier, A., Limaye, B.V.: Spectral Computations with Bounded Operators. 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