Ionic concentrations in developingPelvetia eggs
TL;DR: The correlation of these data with electrical data on the same system (Weisenseel and Jaffe) and possible physiological consequences of the ion concentration changes are discussed.
About: This article is published in Developmental Biology.The article was published on 1972-04-01. It has received 50 citations till now.
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01 Jan 1976
TL;DR: In this paper, it was shown that in biological systems the inflow of information would be specific and integrative, while the flow of energy would simply impose a more general limitation under certain conditions.
Abstract: Regulation concerns the flow of information. It can primarily be distinguished from the flow of energy. Changes in the rate of a process can take place in response to an inflow of either, but it seems likely that in biological systems the inflow of information would be specific and integrative, while the inflow of energy would simply impose a more general limitation under certain conditions.
220 citations
TL;DR: The use of Ca2+-selective microelectrodes and the fluorescent indicator Quin-2 to measure [Ca2+]cyt in rhizoids of germinating Fucus serratus zygotes is evaluated and the presence of a longitudinal gradient in the rhizoid cell is demonstrated.
Abstract: It is becoming increasingly clear that cytoplasmic Ca2+ (Ca2+cyt.) has an important role in the regulation of plant cell functions as well as in animal cells1–3. However, there is an acute lack of measurements of the cytoplasmic Ca2+ concentration ([Ca2+]cyt) in plants. Direct measurements have so far been limited to Chara and Nitella, using aequorin4, and to Haemanthus endosperm cells, using Quin-2 (ref. 5). The latter study demonstrated a gradient of [Ca2+]cyt in dividing cells. Here we evaluate the use of Ca2+-selective microelectrodes and the fluorescent indicator Quin-2 to measure [Ca2+]cyt in rhizoids of germinating Fucus serratus zygotes. This preparation is particularly attractive for such an investigation as the Fucus zygote is a well-studied developmental system and the relatively large polarized rhizoid cells are predominantly cytoplasmic with no large vacuoles. We demonstrate the presence of a longitudinal gradient of [Ca2+]cyt in the rhizoid cell. This gradient appears to be maintained by preferential Ca2+ influx in the region of the growing tip. The significance of the gradient for cell polarity is discussed.
176 citations
TL;DR: This study focuses upon the early development of the fucoid egg, a common seaweed egg that has no preformed animal-vegetal axis, and an essentially electrical hypothesis of localization, which suggests that movement in this region may act to make the local membrane leakier, which thus provides the last link in apositive feedback loop.
Abstract: We are concerned with the mechanisms of intracellular localization that contribute to development. How, for example, does an ameboid cell form a protrusion at one point and not a t another? How does a neuron initiate an outgrowth a t one point and not a t another? How is a neurite’s continued growth oriented? How does a plant egg or spore initiate an outgrowth at one point and not a t another? How are “vegetal” materials localized in one end of an animal egg so that it develops into gut, not skin? Genetic mechanisms have proven to have considerable generality; much of what is true of the genetics of bacteria is likewise true of man. Similarly, we expect morphogenetic mechanisms, in particular those of intracellular localization, to have much generality. Therefore, we have focused our study upon the early development of the fucoid egg. Unlike animal eggs, this common seaweed egg has no preformed animal-vegetal axis. The fucoid zygote is essentially apolar. Then, in the course of a day or less, it initiates growth at one pole, visibly polarizes, and divides into two quite different cells: a rhizoid, or attachment, cell a t the growth pole and a thallus cell a t its antipode (FIGURE 1). This first day of the fucoid egg’s development is a prototype of the localization process. We are further focusing our study upon an essentially electrical hypothesis of localization. According to this hypothesis, the plasma membrane in a growth region, or presumptive growth region, becomes relatively leaky to certain cations that are normally a t a much higher electrochemical potential outside of the cell than within it. These cations could include Caz+, MgZ+, Na+, and H+. The resultant movement of these cations into this region constitutes entry of an electrical current. Movement of this cation flux or current through the resistance of the cytoplasm under the leak will necessarily generate a cytoplasmicjeld that is relatively positive under the leaky portion of the membrane. This field will generate movement. It will tend to pull vesicles and other cytoplasmic constituents with a negative surface charge toward the leaky membrane region. This movement, in turn, may act to make the local membrane leakier, which thus provides the last link in apositive feedback loop. This loop would serve to establish and maintain localized growth, expansion, segregation. and other functions. Specifically, this movement could give such feedback by causing fusion of certain vesicles with the plasma membrane if these vesicles were themselves relatively leaky to particular cations or if they thus released substances that made preexisting parts of the membrane leaky. In our view, the mature nerve synapse may serve as a model of this hypothesis,
145 citations
TL;DR: Subprotoplasts prepared from different regions of rhizoid and thallus cells of Fucus zygotes displayed mechanosensitive plasma membrane channels in cell-attached patch-clamp experiments by using laser microsurgery, patterned by interactions of the cell wall, plasma membrane, and intracellular Ca2+ stores.
Abstract: Subprotoplasts prepared from different regions of rhizoid and thallus cells of Fucus zygotes displayed mechanosensitive plasma membrane channels in cell-attached patch-clamp experiments by using laser microsurgery. In excised patches, this channel was found to be voltage gated, carrying K+ outward and Ca2+ inward, with a relative permeability of Ca2+/K+ of 0.35 to 0.5, and an increased open probability at membrane potentials more positive than -80 mV. No significant difference was found in the density of this channel type from different regions of rhizoid or thallus cells. Hypoosmotic treatment of intact zygotes induced dramatic transient elevations of cytoplasmic Ca2+, initiating at the rhizoid apex and propagating in a wavelike manner to subapical regions. Localized initiation of the Ca2+ transient correlated with greater osmotic swelling at the rhizoid apex compared with other regions of the zygote. Ca2+ transients exhibited a refractory period between successive hypoosmotic shocks, during which additional transients could not be elicited and the ability to osmoregulate was impaired. Buffering the Ca2+ transients with microinjected Br2BAPTA similarly reduced the ability of rhizoid cells to osmoregulate. Ca2+ influx was associated with the initiation of the Ca2+ transient in apical regions, whereas intracellular sources contributed to its propagation. Thus, localized signal transduction is patterned by interactions of the cell wall, plasma membrane, and intracellular Ca2+ stores.
137 citations
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TL;DR: The status of the knowledge of the roles of the essential mineral elements other than univalent cations is surveyed, referring for the most part to the pertinent recent reviews, and the importance of these cations in this capacity is questionable.
Abstract: Of the many inorganic elements that higher plants absorb in ionic form from the soil or aquatic environment, only a relatively few are known to be indispensible for metabolic processes. The essential macronutrient elements other than C, H, and 0 include N, P, K, S, Ca, and Mg. The concentration of these elements in higher plants is illustrated by analyses of Zea mays showing percentages of 1.45 N, 0.20 P, 0.92 K, 0.17 5, 0.23 Ca, and 0.18 Mg in dry material (159). Another group of mineral elements generally required by plants in small quantities and referred to as micronutrient elements include Fe, Mn, B, Cu, Zn, Cl, and Mo. Several elements are required by some spe cies of higher plants and microorganisms but not by others. Cobalt is a micronutrient for some microorganisms and symbionts (71), V is essential for Scenedesmus obliquus (6), Na is needed for certain blue-green algae and halophytes (4, 37, 270), and Si is reported (131) to be indispensable for the growth of diatoms. Although B is generally required for higher plants, it has not been shown to be essential for microorganisms. Even though the micronutrient elements occur in plant tissues at con centrations ranging from less than one to a few hundred ppm of dry matter, it seems that more effort has been devoted to the elucidation of the mode of action of these than to some of the macronutrient elements, such as K, that commonly make up 1 to 2 per cent of the dry material of plants. Authors of modern textbooks often state that the specific role of K in plants is unknown. They indicate that K in some way is involved in the unique organization of protoplasm, that it functions in cellular osmotic processes, and is necessary for cell membrane permeability. That univalent cations function as acti vators for certain enzymes usually is mentioned, but the impression is left that the importance of these cations in this capacity is questionable. A de cision was made by the writers, therefore, to first survey briefly the status of our knowledge of the roles of the essential mineral elements other than uni valent cations, referring for the most part to the pertinent recent reviews. The remainder and major portion of this review will deal with the role of the
527 citations
410 citations
TL;DR: The results agree with the observations of Fenn & Cobb (1936) on mammalian muscle in showing that activity is associated with an entry of sodium ions and a somewhat smaller loss of potassium ions, and that labelled K+ and Na+ are lost exponentially from single muscle fibres.
Abstract: The aim of the experiments described here was to investigate the movements of labelled sodium and potassium ions through the surface membrane of single muscle fibres, and to determine the effect of activity on these movements. The advantages of using a single fibre are that the surface area can be measured fairly accurately and that radioactive ions have rapid access to the surface. The second point is important because frog muscle fatigues in a few minutes if stimulated at more than about 3 c/s. Activity can be maintained for long periods at low frequencies but the changes in ionic flux are then too small to be measured accurately. For this reason it is desirable to collect or apply tracer over well-defined periods lasting only a few minutes. This condition is difficult to satisfy with whole muscle. Other disadvantages of whole muscle are the variation in fibre diameter within the muscle and the difficulty of distinguishing between extracellular and intracellular sodium ions. Complications may also arise from the presence of muscle spindles, slow fibres and blood vessels. The disadvantages of the single fibre are the low counting rate associated with the small quantity of tracer inside the fibre and the difficulty of isolating fibres which will survive for long periods of time. However, since neither difficulty is insuperable it seemed desirable to attempt a quantitative analysis of ionic movements along lines similar to those followed in investigating giant nerve fibres (Keynes, 1951). The results agree with the observations of Fenn & Cobb (1936) on mammalian muscle in showing that activity is associated with an entry of sodium ions and a somewhat smaller loss of potassium ions. They also show that labelled K+ and Na+ are lost exponentially from single muscle fibres and that the movements of these ions are of the kind expected in a system in which exchange is limited by a single barrier such as the surface membrane.
219 citations
TL;DR: The fertilization reaction of echinoderm eggs (Lytechinus pictus, a sea urchin, and Dendraster excentricus) was followed with intracellular electrodes and membrane potential and K(+) activity were recorded.
Abstract: The fertilization reaction of echinoderm eggs (Lytechinus pictus, a sea urchin, and Dendraster excentricus, a sand dollar) was followed with intracellular electrodes Membrane potential and K+ activity were recorded
The unfertilized egg of Lytechinus has a membrane potential of -8 mV, inside negative Within 5 sec after the addition of sperm, a fertilization action potential develops, going to +10 mV, inside positive The time from the initial depolarization to a return to the original -8 mV is 120-150 sec The repolarization continues until a potential of -10 to -14 mV is reached, at which point it pauses for 3-4 min At 6-8 min after fertilization, a further and relatively rapid hyperpolarization begins, going to -60 to -65 mV by 15-25 min after fertilization and remaining constant at these values
The membrane potential of the unfertilized egg appears to depend on a general permeability to anions The fertilization action potential seems to reflect a prolonged influx of sodium The final depolarization to -60 mV is attributable to the development of potassium conductance
Simultaneous measurements with a K+ ion-selective electrode gives constant readings of about 240 mM K+ in the unfertilized eggs throughout the fertilization process
Similar results were obtained with Dendraster eggs The resting potential of the unfertilized eggs was -7 mV; the action potential on activation attained +18 mV; the repolarization paused at -16 to -24 mV and the final potential attained was -70 mV The electrical changes after fertilization with spermatozoa or activation with Pronase were identical
192 citations
01 Jan 1968
180 citations