Kiyoshi Katou

Synchrony between flower opening and petal-color change from red to blue in morning glory, Ipomoea tricolor cv. Heavenly Blue

Petal color change in morning glory Ipomoea tricolor cv. Heavenly Blue, from red to blue, during the flower-opening period is due to an unusual increase in vacuolar pH (pHv) from 6.6 to 7.7 in colored epidermal cells. We clarified that this pHv increase is involved in tonoplast-localized Na+/H+ exchanger (NHX). However, the mechanism of pHv increase and the physiological role of NHX1 in petal cells have remained obscure. In this study, synchrony of petal-color change from red to blue, pHv increase, K+ accumulation, and cell expansion growth during flower-opening period were examined with special reference to ItNHX1. We concluded that ItNHX1 exchanges K+, but not Na+, with H+ to accumulate an ionic osmoticum in the vacuole, which is then followed by cell expansion growth. This function may lead to full opening of petals with a characteristic blue color.

A mechanism of respiration-dependent water uptake enhanced by auxin

SummaryThere are many contradictory observations on the mechanohydraulic relation of growing higher plant cells and tissues. Graphical analysis of the simultaneous equations which govern irreversible wall yielding and water absorption has made more comprehensive the understanding of this relation when relative growth rate is plotted against turgor pressure. It suggests that some respiration-dependent and auxin sensitive process might regulate the difference of osmotic potential between cells and water source. Based on anatomical and electrophysiological knowledge of the pea stem xylem, we propose the wall canal system as the mechanism of respiration-dependent water uptake which is sensitive to auxin. This system consists of the xylem apoplastic walls, the xylem proton pumps, active solute uptake system and cell membranes. In the simplest case, third-order simultaneous differential equations are involved. Numerical analysis showed that net uptake of solutes enables water to be taken up against an opposing gradient of water potential. The behaviour of this wall canal system describes well the mechano-hydraulic relation of enlarging plant cells and tissues. Recent typical, but incompatible, interpretations of this relation are critically discussed based on our model.

Effect of infection by Phytophthora infestans on the membrane potential of potato cells

The membrane potential (Ψm) of potato cells (cultivar Rishiri) infected by incompatible and compatible races of Phytophthora infestans was measured, while the infection process of the measured cells was observed under a microscope. The passive (Ψd) and respiration dependent electrogenic (Ψp) components of Ψm were also analysed using the anoxia method. Cytoplasm often gathered around the inserted microelectrode and sometimes disturbed the measurement. However, it was shown that the experimental system was suitable for the long-term measurement of fm during the infection process. At the moment of penetration of the host cell wall by both the incompatible and compatible races, no signal such as an action potential was observed in the Tm. Infection by the incompatible race caused little change of Tm for a while after penetration, but |Ψd| then began to decrease. |ΨP| did not decrease, but rather increased and apparently compensated for the decrease in |Ψd|, resulting in little or slow reduction of |Ψm|. Later |Ψp| also decreased and Ψm began to depolarize gradually and at about one to several hours after penetration, rapid depolarization took place to reach a steady level of −45 to −55 mV before the cell content became granulated. In some instances, slow and steady depolarization was followed by cell death. Ψd and Ψp of the uninfected cell did not change for more than 10 h after the beginning of the measurement. The compatible race had no effect on either Ψp or Ψd at least within 24 h infection.

A mechanism of respiration-dependent water uptake in higher plants

where V is the volume o f the symplasts (m3), L is the relative hydraulic conductance o f the tissue (Pa -1 s 1), is the solute reflection coefficient o f the membrane, C i and C X are the osmotic concentra t ion within the symplast and the xylem vessels respectively (mole m 3), R is the gas constant ( Jmole l K--l), T is absolute temperature (K), and pi and P• are cell turgor pressure and hydrostat ic pressure in the xylem vessels respectively (Pa). Compar i son of water permeabilities between synthetic and natural membranes suggests that o f natural membranes must be unity for physiological solutes (OscHMAN et al. 1974). On the other hand, the relative rate o f tissue enlargement has been shown to depend on irreversible wall yielding;

A model for radial water transport across plant roots

SummaryA model based on the canal theory (Katou andFurumoto 1986 a, b) is proposed for the absorption of solute and water at the root periphery. The present canal model in the periphery and the model which was previously proposed for the exudation in the stele (Katouet al. 1987), are organized into a model for radial transport across excised plant roots, in the light of anatomical and physiological knowledge of maize roots. The canal equations for both canals are numerically solved to give quite a good explanation for the observed exudation of maize roots. It is found that the regulation of solute transport has a primary importance in the regulation of water transport across excised roots. The internal cell pressure of the symplast adjusts the water absorption at the root periphery to the water secretion into the vessels. There seems no need for this explanation of the radial water transport across roots to assume cell membranes with low reflection coefficient or variable water permeability. It would seem that the apoplast wall layers play a crucial role in metabolic control of water transport in roots as well as in hypocotyls.

Symplast as a Functional Unit in Plant Growth

Publisher Summary This chapter presents biophysical studies on the attraction center of the elongating stem based on the integrated activities of constituent cells. It discusses the physiological anatomy of the cowpea hypocotyl, based mostly on the results obtained through electrophysiological methods. The regulatory mechanism of the elongation growth of the hypocotyl is also examined. The hypocotyl of cowpea grows in the early stage of the germination period followed by epicotyl growth in the later stage. The meristematic region, the elongating region, and the matured region are arranged, in order of cell age, along the axis from the cotyledonary node toward the base. During the germination period of cowpea, the germ as an embryonic organ develops under the supply of nutrient materials from the cotyledon, which is already in a physiologically aged state, and ceases growth within the germination period. The cells in the elongating region actively attract nutrient materials from the cotyledon and may simultaneously receive regulatory signals. Such a region is called an “attraction center.” The stem may be regarded as multiple layers of disk-like symplasts penetrated by vascular bundles. The symplasts are arranged chronologically along the germ axis. The symplast situated in a semi-macroscopic stratum plays an indispensable role in the integration of molecular, subcellular, and cellular activities into stem elongation.

A model for water transport in the stele of plant roots

SummaryThe mechanism of water movement across roots is, as yet, not well understood. Some workable black box theories have already been proposed. They, however, assumed unrealistic cell membranes with low values of σ, or were based on a poor anatomical knowledge of roots. The role of root stele in solute and water transport seems to be especially uncertain. An attempted explanation of the nature of root exudation and root pressure by applying the apoplast canal theory (Katou andFurumoto 1986 a, b) to transport in the root stele is given. The canal equations are solved for boundary conditions based on anatomical and physiological knowledge of the root stele. It is found that the symplast cell membrane, cell wall and net solute transport into the wall apoplast are the essential constituents of the canal system. Numerical analysis shows that the canal system enables the coupled transport of solutes and water into a xylem vessel, and the development of root pressure beyond the level predicted by the osmotic potential difference between the ambient medium and the exudate. Observations on root exudation and root pressure previously reported seem to be explained quite well. It is concluded that the movement of water in the root stele although apparently active is essentially osmotic.

CHANGES OF THE MEMBRANE POTENTIAL AT THE TIME OF FERTILIZATION IN THE SEA URCHIN EGG WITH SPECIAL REFERENCE TO THE FERTILIZATION‐WAVE

An experimental device was developed from the work of Uehara and Sugiyama (1969), in order to study the electrical phenomena accompanying the fertilization‐wave in the sea urchin egg.

Mechanism of pressure-induced water flow across plant roots

SummaryPressure-induced non-linear water flow across plant roots was analyzed theoretically. The double-canal model of radial water transport shown lately explained accurately the observed non-linear water flow in maize roots. The driving force rather than the hydraulic permeability caused the non-linear flow of water. The conclusion was drawn that non-linearity in pressure-induced water flow was an inherent property of the apoplast canal system in roots. Net solute transport plays a primary part for water transport.

Effects of hyphal wall components of Phytophthora infestans on membrane potential of potato tuber cells

Abstract The effect of the hyphal wall component (HWC) of Phytophthora infestans on the membrane potentials (Ψm) of cells in the aged cut surface of potato tuber tissue (cv. Rishiri) were investigated. Within a few minutes of the application of HWC (3 mg ml−1), cellular depolarization occurred. Initially, depolarization was rapid. After a mean depolarization of about 25 mV, the Ψm reached an asymptotic plateau. HWC reduced the oxygen dependent electrogenic potential difference (∣Ψd∣) by about 60%, but exerted little effect on the passive potential difference (∣Ψd∣). In a later stage, ∣Ψd∣ also decreased very gradually. The extent of the HWC effect was not always the same, possibly owing to the heterogeneity of potato cells in their reactivity or accessibility to HWC. There was no difference in the activity on Ψm of HWC isolated from compatible or incompatible races. Results showed that the effect of HWC on the membrane potential of potato cells was different from that of infection by P. infestans.