TRANSPORT OF CATIONS FROM COTYLEDON TO SEEDLING OF THE EMBRYONIC PLANTS OF VIGNA SESQUIPEDALIS

Decrease of dry material, water, potassium and divalent cationsin the cotyledon (catabolic organ and accumulation of thesesubstances in the seedling (anabolic organ) were traced duringthe germination stage of Vigna sesquipedalis, cultured at 15°,25° and 30° in the dark on the sand with the supplyof tap water. One half of the divalent cations finally accumulatedin the seedling came from the root, whereas most of the potassiumfrom the cotyledon. Practically all the calcium in the cotyledonremained untransported, while 90% of K stored in the cotyledonwas transported into seedling. As for divalent cations otherthan Ca, 50–60% of the total divalent cations was transportable.The concentration of K, transportable dry material and transportabledivalent cations decreased linearly with the culture age. Fromthe temperature dependency of the rate of this decrease, itwas inferred that the transport of cations from cotyledon toseedling involved at least two component processes having activationenergies of approximately 5 and 16 Kcal, respectively. The rateof transport at 30° was found to be 10–20 times greaterthan that calculated from the simple diffusion model in water.Fractionation of cell inclusions in the cotyledon by the useof a centrifuge (1,500 and 16,000 rpm) suggested that the amountsof ions in the precipitable fractions, being bound to certaincell components, precisely corresponded to the untransportablefraction. ¹Main part of this work was reported at the Annual Meeting ofthe Botanical Society of Japan held at Fukuoka on Oct. 25. 1958. (Received October 16, 1961; )     

A new method in growth-electrophysiology: Pressurized intra-organ perfusion

Abstract A new experimental system was devised for the simultaneous measurement of elongation rate and the activity of the spatially separate electrogenic ion pumps of a hypocotyl segment excised from a seedling of Vigna unguiculata L. Walp. under enforced intra-organ perfusion by artificial solutions. The pathway of the perfusion medium was apoplastic space, including xylem vessels as main routes. The elongation rate of the segment was highly dependent on the perfusion pressure applied. It was possible to increase the growth rate under pressurized perfusion by 10-30 times as much as that without perfusion. Elongation rate was also dependent on respiration under perfusion, being retarded reversibly by anoxia a few minutes after the activities of the electrogenic ion pumps were stopped. Perfusion pressure had a little influence on the membrane potential (V_px) below a breakdown level (c. 130 kPa). Perfusion of mannitol or sorbitol solution of appropriate concentration reduced the elongation rate reversibly.     

Spontaneous Membrane Potential Changes Associated With the Zooid and Vacuolar Contractions In Vorticella Convallaria

SYNOPSIS Interacellular membrane potential and spontaneous changes associated with motile responses in the zooid of Vorticella convallaria Linnaeus were recorded by conventional electrophysiological technics. an all-or-none large transient depolarization (large pulse) occurs in association with a spontaneous contraction of the zooid. A small transient potential change (small pulse) was observed in association with periodic contraction of the contractile vacuole.     

Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis I. Distribution of overall ion concentration and the role of hydrogen ion in generation of potential difference

Overall concentration of free inorganic ions distributes inthe hypocotyl of a bean seedling {Vigna sesquipedalis) at aconstant level (H⁺) or decreases monotonously from the cotyledonarynode towards the base (K⁺, Na⁺, Ca⁺⁺ and Mg⁺⁺, phosphate, NO₃^–).According to our theory, this is inconsistent with the distributionof electric potential having a definite minimum in the elongatingregion. The discrepancy can not be explained by regional variancein radial potential difference or histological differentiationin passive ionic permeability of the cell membrane. Short circuitcurrent observed through a hypocotyl segment corresponded toa net flux in ions of 10–24 pEq/cm².sec. It is questionable,however, whether this is due to active ion transport, whichcan be the source of electric potential difference, or is apassive flow due to histological heterogeneity in ion concentration. In order to investigate the latter possibility, pH of sap exudingfrom stumps made at various intervals along the hypocotyl axiswas measured, since H⁺ is the ion electro-osmotically most effective.pH Values of acropetal exudates distributed along the axis closelycorresponding to the distribution of electric potential. Thissuggests that potential distribution is determined by a passiveflow of H⁺ through a specific channel in the vascular system.The fact that H⁺ production and the uptake of ions and waterare most active at the elongating zone of hypocotyl is discussedfrom a physiological point of view. (Received December 3, 1969; )     

Experiments Pertaining to the Suppression of Accessory Sperm in Fertilized Newt Eggs*

In the physiologically polyspermic eggs of the newt, Cynops pyrrhogaster, a number of accessory sperm undergo pronuclear formation along with a concomitant DNA synthesis, but degenerate after zygote nucleus formation. When denuded eggs were divided into two halves at various post-fertilization stages, the andromerogons produced before zygote nucleus formation but not after that stage cleaved at a high frequency. The accessory sperm were unable to participate in the cleavage when they were located in the half of the egg which was connected with the diploid merogon by a cytoplasmic bridge higher than 100 μm in height. The removal of the egg nucleus or the retardation of early post-fertilization nuclear events by treatment with cycloheximide resulted in the induction of multipolar cleavage. Continuous exposure of the fertilized eggs to aphidicolin showed that in the appreciable absence of the DNA synthesis many eggs underwent a first cleavage cytokinesis of a mostly abortive type, but failed to initiate the following cytokinesis at all. Cytological examinations in association with these experiments suggest that the observed suppression of accessory sperm includes the inhibition of centriolar replication under the influence of the zygote nucleus, resulting in the failure of cytasters corporating with nuclear-independent activity of cortical cytoplasm.     

Genetic differentiation and distribution routes of the bronze featherback Notopterus notopterus (Osteoglossiformes: Notopteridae) in Indochina

Mitochondrial DNA analysis was used to investigate genetic variation in the bronze featherback fish Notopterus notopterus in Indochina. Five hundred and five fish samples collected from 11 localities were separated into three genetically differentiated intraspecific groups. Chao Phraya River samples formed a distinct group. Mekong River samples were clearly separated into two different groups, namely, middle and lower Mekong groups. The lower Mekong group was closely related to Malay Peninsula group, even though the two groups are separated by a tract of ocean. F‐values (0.82–0.95) also confirmed genetic differentiation of the middle and lower Mekong groups. Although the two Mekong groups inhabit the same river basin, molecular clock calculations indicate they separated approximately 1.2 Mya, suggesting (1) evolutionary divergence before invasion of the Mekong River; (2) differences in migration routes to the river; and/or (3) differences in the timings of invasion. The complexities of historical events cannot be ignored in determinations of factors responsible for the exceptional biodiversity in the Mekong basin. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 575–582.     

The Genesis and Transmission of Epidermal Potentials of Newt Embryonic Cells in Vivo and in Vitro

The genesis and transmission of action potentials in epidermal cells of a newt ( Cynops pyrrhogaster ) embryo were investigated quantitatively in vivo during development and in vitro in the absence of nerve cells. Typical action potentials, composed of a fast spike followed by a slow action potential, can be recorded from any of the epidermal cells from Stage 24/25 to 35/36. The potential is graded with current intensity, and only the slow component induces transmission to other epidermal cells. The fast spike is found in all epidermal cells from Stage 24/25 to Stage 50; it is abolished by Stage 52. The slow potential disappears at Stage 38 just before or after hatching. The cultured epithelioid explants (epithelioid aggregate) and cultured monolayer cells taken from the presumptive epidermal tissue of the ectoderm of the pregastrula, indicate that sequential changes in the genesis of the dual action potentials are similar to those of the intact embryo. In monolayer cell culture devoid of nerve cells, the epidermal cells, also generate a two-step action potential. Such two-step potentials are characteristic of both ciliated and non-ciliated epidermal cells and occur even during mitotic activity. In contrast, cultured neural plate cells isolated from the neurula generate typical spike-like action potentials.     

Further examination of the effects of IAA and anoxia on the growth rate and the spatially separate electrogenic ion pumps in bean hypocotyl

Abstract. Measurements of V_ps and V_px were made on Vigna sesquipedalis hypocotyls in a stream of air or nitrogen during and after the application of IAA in an aerosol added to the gas stream. The lAA-induced hyperpolarization of V_ps and increase in growth rate in air was maintained for at least half an hour after the 50-min IAA treatment was terminated. Changing from air to O₂-free gas stream in the presence of IAA aerosol depolarized V_ps and V_px, and then reduced growth rate, to the same extent as in hypocotyls in which IAA and O₂ supply were terminated simultaneously. Under anoxic conditions, application of an IAA N₂-aerosol had no effect on V_ps. V_px or growth rate.