Seed Germination: A Guide to the Early Stages,N.V. Obroucheva,Leiden: Backhuys, 1999

Russian Journal of Plant Physiology -     

The Physiology of Plant Integrity

The original concept of the plant integration system is presented and exemplified by the data from the studies of the regulatory controls that mediate the effects of red light (R) on the growth of etiolated maize seedlings. The integrity of higher-plant behavior depends on the functional activity and interaction of the dominant (control center). In vegetating plants as the simplest case, these centers include the shoot apex and the distal part of the root comprising the sensory tissues, the zones of the synthesis of specific hormones, and the zones of high morphogenetic and sink capacities. The system of propagating electric signals is usually devoid of the permanent generation centers. The dominant centers recognize the external and internal signals and induce the development of polarity (the bioelectric and physiological gradients), canalized connections (the conducting bundles), and oscillations. Trophic, hormonal, and electrophysiological signals of intercellular regulation are propagated along the conducting bundles and affect the intracellular membrane, metabolic, and genic control systems. The regulatory controls comprise the receptor cells recognizing the external and internal signals, the tissues of connection channels, the effector cells, and the feedback loop elements. When three-day-old etiolated maize (Zea maysL.) seedlings are treated with red light (RL), the photosignal is recognized by the phytochrome in the cells of the mesocotyl intercalary meristem; as a result, the positive biopotential is prolonged in these cells and in the coleoptilar node. An electric field (the receptor potential) thus produced would hamper, by electroosmosis, IAA transport from the coleoptile into the mesocotyl and in this way, would drastically inhibit the growth of the latter and temporarily promote the growth of the former. The primary leaves, also recognize R, as a result R promotes cell growth and the synthesis of gibberellins. The Ukhtomskii's principle of the dominant is used to interpret the plant ability for switching over its physiological systems in response to specific signals.     

Electroosmotic Phenomena in Plant Tissues

The effect of a direct electric current on electrolyte transport through plant tissues was studied by applying it to 10-mm segments of the mesocotyls of etiolated maize seedlings, similar segments of one-year linden shoots with the normal conducting system and without vascular bundles, and isolated elements of the xylem and cell wall segments. At current densities of 9–38 A/mm² (10–20 V), electrolyte solutions in plant tissues always moved toward the cathode. The results suggest that electroosmosis is one of the factors responsible for changes in solution transport through the conductive plant tissues that occur under the effect of electric current.     

Impact of magnetic field inhomogeneity on electron cyclotron radiative loss in tokamak reactors

The potential importance of electron cyclotron (EC) emission in the local electron power balance in the steady-state regimes of ITER operation with high temperatures, as well as in the DEMO reactor, requires accurate calculation of the one-dimensional (over magnetic surfaces) distribution of the net radiated power density, P _EC(ρ). When the central electron temperature increases to ∼30 keV, the local EC radiative loss comprises a substantial fraction of the heating power from fusion alphas and is close to the total auxiliary NBI heating power, P _EC(0) ≃ 0.3P _α(0) ≃ P _aux(0). In the present paper, the model of EC radiative transport in an axisymmetric toroidal plasma is extended to the case of an inhomogeneous magnetic field B(R, Z). The impact of such inhomogeneity on local and total power losses is analyzed in the framework of this model by using the CYNEQ code. It is shown that, for the magnetic field B, temperature T _e , density n _e , and wall reflection coefficient R _w expected in ITER and DEMO, accurate simulations of the EC radiative loss require self-consistent 1.5D transport analysis (i.e., one-dimensional simulations of plasma transport and two-dimensional simulations of plasma equilibrium). It is shown that EC radiative transport can be described with good accuracy in the 1D approximation with the surface-averaged magnetic field, B(ρ) = 〈B(R, Z)〉 _ms . This makes it possible to substantially reduce the computational time required for time-dependent self-consistent 1.5D transport analysis. Benchmarking of the CYNEQ results with available results of the RAYTEC, EXACTEC, and CYTRAN codes is performed for various approximations of the magnetic field.     

Influence of plasma pedestal profiles on access to ELM-free regimes in ITER

The influence of current density and pressure gradient profiles in the pedestal on the access to the regimes free from edge localized modes (ELMs) like quiescent H-mode in ITER is investigated. Using the simulator of MHD modes localized near plasma boundary based on the KINX code, calculations of the ELM stability were performed for the ITER plasma in scenarios 2 and 4 under variations of density and temperature profiles with the self-consistent bootstrap current in the pedestal. Low pressure gradient values at the separatrix, the same position of the density and temperature pedestals and high poloidal beta values facilitate reaching high current density in the pedestal and a potential transition into the regime with saturated large scale kink modes. New version of the localized MHD mode simulator allows one to compute the growth rates of ideal peeling-ballooning modes with different toroidal mode numbers and to determine the stability region taking into account diamagnetic stabilization. The edge stability diagrams computations and sensitivity studies of the stability limits to the value of diamagnetic frequency show that diamagnetic stabilization of the modes with high toroidal mode numbers can help to access the quiescent H-mode even with high plasma density but only with low pressure gradient values at the separatrix. The limiting pressure at the top of the pedestal increases for higher plasma density. With flat density profile the access to the quiescent H-mode is closed even with diamagnetic stabilization taken into account, while toroidal mode numbers of the most unstable peeling-ballooning mode decrease from n = 10?40 to n = 3?20.     

Role of Auxin in Induction of Polarity in Fucus vesiculosus Zygotes

We studied the effects of auxin (indole-3-acetic acid) on formation of the primary polarity axis in zygotes of the brown algae Fucus vesiculosusL. Within the first 2.5 h after fertilization, the zygotes release this phytohormone in the ambient medium. The treatment of developing zygotes with the inhibitor of indole-3-acetic acid transport from the cell 2,3,5-triiodobenzoic acid at 5 mg/l arrests the auxin secretion and leads to its accumulation in the cells. This causes a significant delay in zygote polarization. The treatment of zygotes with the exogenous indole-3-acetic acid at 1 mg/l stimulates cell polarization and formation of a rhizoid protuberance. When auxin was added to the medium with triiodobenzoic acid, the inhibitory effect of the latter was eliminated. It has been proposed that the content of indole-3-acetic acid in the ambient medium is a key factor in the induction of polarity of the F. vesiculosus zygotes.