Osmotically induced proton extrusion from carrot cells in suspension culture.

Addition of 200 mm of a polyol to anthocyanin containing carrot (Daucus carota L.) cells in suspension culture decreased turgor pressure to zero and induced hyperpolarization of the membrane potential and acidification of the medium due to H(+) extrusion. These changes were shown to be slightly affected by vanadate. In parallel, a decrease in intracellular ATP and total adenylate concentrations were observed. However, when the osmoticum was NaCl acidification of the medium occurred in the absence of considerable changes in intracellular ATP concentration. These results are interpreted as indicating that a drop of turgor, by addition of a polyol, triggers a proton extrusion activity which is only slightly inhibited by vanadate but apparently ATP utilizing. The observed decrease in ATP level occurs without a change in respiration rate and is accompanied by a drop in total adenylate pool. However when NaCl is the osmoticum it is assumed that Delta(muH+) is enhanced through a Na(+)/H(+) antiporter. The difference between the two types of osmotica as related to their ability to penetrate through the cellular membrane is discussed.

Changes in Membrane Potential as a Demonstration of Selective Pore Formation in the Plasmalemma by Poly-l-Lysine Treatment.

A technique which allows determination of solute pool concentrations in the cytosol was developed exploiting the interaction between a polycation and the anionic sites of the plasmalemma. It was shown that treatment of Nicotiana tabacum, cv Xanthi, cells in suspension culture with an appropriate concentration of poly-l-lysine induced pore formation selectively in the plasmalemma. The data presented in this paper shows that the plasmalemma of all the cells was affected while the tonoplast remained undamaged. This conclusion is based on the facts that treatment of the cells with the minimum amount of poly-l-lysine which just abolishes the electrogenic potential (similarly to carbonyl cyanide-p-trifluormethoxyphenylhydrazone and NaN(3)) induces the leakage of only a small fraction of the K(+) present in the cells. These effects of poly-l-lysine differ from the effects of polymyxin B which induces total leakage of low molecular weight solutes (R. Weimberg, H. R. Lerner, A. Poljakoff-Mayber 1983 J Exp Bot 34: 1333-1346) and therefore affects also the tonoplast.Membrane potential was determined using the partition of the lipophilic cation tetraphenylphosphonium. The electrogenic component of the membrane potential was estimated using carbonyl cyanide-p-trifluormethoxyphenylhydrazone and azide. Poly-l-lysine treatment was used to measure K(+) compartmentation in Nicotiana cells grown in a NaCl-containing medium.

Kinetics of toluene-induced leakage of low molecular weight solutes from excised sorghum tissues.

The relationship between toluene concentration and the rate of leakage of solutes from toluene-treated roots and leaves of Sorghum bicolor, L. Moench, was studied to determine the effect of toluene on plant cell membranes. A threshold concentration of 0.2% toluene was needed to induce leakage. Maximal leakage rates were obtained with 0.5% toluene. Low molecular weight solutes, such as amino acids, sugars, and inorganic ions, leaked from treated tissue, while macromolecules, such as protein were retained. The rates at which the low molecular weight solutes diffused from treated cells decreased with increasing molecular weight. At 25 degrees C, treatment of roots and leaves with 0.5% toluene resulted in the quasi-quantitative leakage of solutes within 180 minutes. At 1 degrees C, roots and leaves differed in their response to toluene. The rates of leakage from roots at 1 degrees C were much lower and the total amounts much smaller than at 25 degrees C, while in leaves the difference between the two temperatures was very small.The procedure of treating tissues with 0.5% toluene for 180 minutes at 25 degrees C proved to be a rapid and simple technique for quantitative extraction of water-soluble, low molecular weight solutes from plant cells into the extracting medium while macromolecular constituents are retained inside the cells.

Does salinity induce early ageing of pea root tissue?

The effect of salinity on ageing of pea roots was studied. The distance from the apex at which differentiation of xylem elements occurred and the relative increase in the function of pentose phosphate pathways were taken as parameters for maturation or ageing.Pea seeds (Pisum stivum L.) of the varieties Alaska and Dan were used in these experiments. The seeds were germinated and grown in vermiculite moistened with Hoagland's solution or Hoagland's solution containing either 96 or 120 mM NaCl. In Alaska roots salinity induced differentiation in a lower section of the root than in controls, and the increase in the function of the pentose phosphate pathway paralleled the advance of maturation. Salinity apparently induces earlier ageing in Alaska roots. This is not the case in Dan roots which tolerate slightly higher salinity levels than Alaska.

Induction of "pore" formation in plant cell membranes by toluene.

Treatment with aqueous toluene-ethanol has been shown to induce "pore" formation in plant cell membranes. The evidence is as follows: [List: see text]While the principal experimental material was roots of Atriplex nummularia Lindl., the fact that similar results were also observed with leaves of Pisum sativum L. and with the alga Chlorella pyrenoidosa Chik. suggests that the phenomenon is general.Although the phenomenon of pore induction is qualitatively similar to that in microorganisms, the pores induced appear to be smaller. It is proposed that induced leakage could be the basis for the development of simple and rapid methods for plant biochemical studies.

Effect of Salinity on Respiratory Pathways in Root Tips of Tamarix tetragyna.

Oxygen uptake in the presence of exogenous glucose was lower in Tamarix root tips grown in saline media than in those grown in Hoagland solution. This effect was not overcome by raising the external glucose concentration.Glucose uptake and CO(2) evolution were depressed in the presence of NaCl. This effect was observed also when roots were exposed to salinity only during growth but not during uptake. Increasing the external concentration of glucose from 0.01 to 1 mm induced only a 10-fold increase in glucose uptake and CO(2) evolution. However, (14)C evolved in CO(2) as percent of (14)C absorbed, remained constant at all salinity treatments, and was similar at both glucose concentrations.Salinity above 120 mm NaCl increased the percentage of absorbed glucose oxidized via the pentose phosphate pathway, but did not affect the glycolytic pathway. At the same time, salinity depressed the glucose-6-P dehydrogenase, pyruvate kinase, and oxidative phosphorylation. These effects become most evident at a salinity level of about - 10 atm (240 mm), a concentration which is rarely exceeded in the root zone of the natural habitat of the plants.We concluded that Tamarix is reasonably well adapted to the conditions of its habitat, and that salinity affects its root metabolism differently than it does that of pea roots.

Malic dehydrogenase from tamarix roots: effects of sodium chloride in vivo and in vitro.

Soluble and mitochondrial malic dehydrogenases (MDH) were isolated from root tips of the halophyte Tamarix tetragyna L. grown in the presence and absence of NaCl. The activity of the enzymes isolated from root tips grown in the presence of NaCl was lower than that of the enzymes isolated from roots grown in absence of NaCl. The mitochondrial MDH was much more sensitive to salinity than the soluble MDH. The soluble enzyme from roots grown in NaCl had a higher Km for malate and lower Km for NAD than enzyme from the control roots. Addition of NaCl in vitro at 72 mM significantly stimulated the reductive activity of soluble MDH, while higher NaCl concentrations (240 mM and above) depressed enzyme activity. The inhibition of enzyme activity by various salts was found to be in the order MgCl(2) > NaCl = KCl > Na(2)SO(4). Mannitol at equiosmotic concentrations had no effect. Substrate inhibition, typical for oxaloacetate oxidation, was not observed at high NaCl concentrations in vitro and high substrate concentrations neutralized the inhibitory effect of NaCl. Increased coenzyme concentrations had no effect. In vitro NaCl increased the Km for malate and oxaloacetate already at relatively low concentrations. At the same time NaCl decreased the Km for NAD and NADH. The inhibitory effect of NaCl on enzyme activity seems not to be due to the effect on the Km alone. Soluble and mitochondrial MDH had different responses to pH changes, mitochondrial MDH being more sensitive. Mitochondrial MDH released from the particles had a similar response to that of the entire particles. Changes of pH modified the effect of NaCl on enzyme activity. It was postulated that NaCl apparently induces conformational changes in the enzyme.

Content of adenosine phosphate compounds in pea roots grown in saline media.

The levels of ATP, ADP and AMP, the activity of phosphatases, and the ability for oxidative phosphorylation were studied in roots of pea (Pisum sativum) plants grown in media salinized either with NaCl or Na(2)SO(4). In response to salinity, the ATP level in the roots decreased, whereas the ADP level increased slightly. As a result, the ADP:ATP ratio in the tissue increased with increasing salinity in the growth medium. The AMP level in the tissue was not affected by salinity.Phosphatase activity (using p-nitrophenyl phosphate and ATP as substrates), in the soluble and in the mitochondrial fractions from roots grown in NaCl-salinized media, was considerably higher than in the control roots. In the mitochondrial fraction of the roots grown in Na(2)SO(4)-salinized media, such an increase was not observed.The phosphorylating activity of mitochondria was depressed by the two types of salinity, but was more sensitive to NaCl salinity. In mitochondrial suspensions prepared from roots exposed to salinity, practically no phosphorylation could take place if nicotinamide adenine dinucleotide was omitted from the reaction mixture; but even when added, the restoration of phosphorylative ability was not complete. Addition of NaCl to the reaction mixture did not affect the activity of the phosphatases. Addition of Na(2)SO(4) to the reaction mixture depressed, in some cases, the activity of the acid phosphatase. Phosphorylative activity was affected, however, by both types of salinity: presence of either NaCl or Na(2)SO(4) at - 1 atm in the reaction mixture increased phosphorylative activity, and higher concentrations (-3 and -5 atm) depressed it.

The effect of water stress on mitochondria of root cells: a biochemical and cytochemical study.

Water loss from root cells of Zea mays induced by exposure to severe water stress, caused a reduction in the respiratory rate (O(2) consumption) and at the same time an increase in activity of the mitochondrial cytochrome oxidase (histochemical oxidation of diaminobenzidine). The connections between these changes and the changes in the fine structure of the mitochondria occuring in the stressed roots are discussed.

The effect of salinity on the malic dehydrogenase of pea roots.

Effect of salinity on malate dehydrogenase activity was studied.Pea root tips contain 2 different malate dehydrogenases. One is located in the particulate, mitochondrial fraction, the other in the soluble, cytoplasmic fraction. Both can act when coupled with either NAD or NADP.Growing plants in Na(2)SO(4) salinated medium did not affect the pattern of the malate dehydrogenases in the root tips. Growing plants in NaCl salinated media resulted in the appearance of a new, third isoenzyme. This new isoenzyme was located in the cytoplasmic fraction.Salinity of both types, when present in growth medium, induced increases in the NADP coupled activity of the mitochondrial malate dehydrogenase. The NAD coupled activity, however, was depressed except in the cytoplasmic fraction of plants grown in media salinated with NaCl to 1 atmosphere. Addition of either of the salts to assay media of enzymes, isolated from plants grown in non salinated substrate, did not have any significant effect.

Effect of substrate salinity on the ability for protein synthesis in pea roots.

THE EFFECT OF SALINITY ON INCORPORATION OF AMINO ACIDS INTO ROOT TIP PROTEIN IS APPARENTLY OF DUAL NATURE: in presence of salts the uptake is depressed and the normal metabolic pathways are disturbed. If the roots were grown at high salt concentration, uptake and incorporation are affected even if they are carried out in the absence of salt. NaCl and Na(2)SO(4) affect uptake, incorporation, and metabolism of (14)C leucine in different ways. There are also preliminary indications that in pea roots grown at different types of salinity, different proteins may be synthesized. Kinetin was found to inhibit incorporation of amino acids into non stressed and Na(2)SO(4) stressed roots, but promotes uptake and incorporation of amino acids into protein in NaCl stressed tissue. It seems that there are some pronounced differences between the effects of NaCl and Na(2)SO(4) salinities on the metabolism of pea root tissue.

Plastic films on plants as antitranspirants.

Plastic-film-type antitranspirants are more permeable to water vapor than to carbon dioxide. Photosynthesis in treated plants is reduced to the same or greater extent than transpiration, except under conditions of stress, when photosynthesis in treated plants is greater than in controls. This exception is attributed to reduction of stress, as the selective permeability of the films to gases would tend to produce the reverse effect.