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Biomedical subjects

D W Rains

Publications and source records attributed to D W Rains.

At least 19 recordsLinked to original sources
PubMed1996

Effect of root perturbation and excision on nitrate influx and efflux in barley (Hordeum vulgare) seedlings.

The effects of perturbation and excision on net NO3- uptake, influx and efflux in roots of 8-day-old barley (Hordeum vulgare L.) seedlings induced with NO3- or NO2- were determined. Perturbation was simulated by mechanically striking the intact roots with a glass rod. Perturbation or excision of roots and subsequent division into small segments had little effect on NO3- influx, but briefly inhibited net uptake which recovered within a few min. While in perturbed roots net uptake rates recovered to the same level as in control roots, full recovery did not occur in excised roots. Inhibition of net uptake was due to stimulation on NO3- efflux. The recovery time and level of inhibition of net NO3- uptake and/or stimulation of efflux were a function of extent of perturbation, or the number of segments following excision, and root NO3- concentration. NO3- efflux was further stimulated when roots were perturbed after cytoplasmic NO3- had been depleted, indicating that both the plasmalemma and tonoplast may be affected. In excised roots both NO3- influx and efflux decreased with age due to depletion of energy sources. The results indicate that root perturbation and excision had no effect on NO3- influx but inhibited net uptake by stimulating efflux.

Glucose↗
PubMed1988

Determination of ammonium ion by fluorometry or spectrophotometry after on-line derivatization with o-phthalaldehyde.

A fast, sensitive, simple, and highly reproducible method for routine assay of ammonium ion (NH4+) was developed by using HPLC equipment. The method is based on the reaction of NH4+ with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol. After an on-line derivatization, the resulting NH4(+)-OPA product was quantified by using fluorometric or spectrophotometric detection. For fluorometric detection, the excitation and emission wavelengths were 410 and 470 nm, respectively. The spectrophotometric detection was made by measuring absorbance at 410 nm. Results on the effects of OPA-reagent composition and pH, reaction temperature, sample matrix, and linearity of the assay are presented. Even though it took about 2 min from the time of sample injection to the appearance of sample peak, sample injections could be overlapped at an interval of about 1 min. Thus, the actual time needed for analysis was about 1 min per assay. The method can be used in a fully automated mode by using an autosampler injector.

Chromatography, High Pressure Liquid↗
PubMed1984

Early effects of salinity on nitrate assimilation in barley seedlings.

The effect of NaCl and Na(2)SO(4) salinity on NO(3) (-) assimilation in young barley (Hordeum vulgare L. var Numar) seedlings was studied. The induction of the NO(3) (-) transporter was affected very little; the major effect of the salts was on its activity. Both Cl(-) and SO(4) (2-) salts severely inhibited uptake of NO(3) (-). When compared on the basis of osmolality of the uptake solutions, Cl(-) salts were more inhibitory (15-30%) than SO(4) (2-) salts. At equal concentrations, SO(4) (2-) salts inhibited NO(3) (-) uptake 30 to 40% more than did Cl(-) salts. The absolute concentrations of each ion seemed more important as inhibitors of NO(3) (-) uptake than did the osmolality of the uptake solutions. Both K(+) and Na(+) salts inhibited NO(3) (-) uptake similarly; hence, the process seemed more sensitive to anionic salinity than to cationic salinity.Unlike NO(3) (-) uptake, NO(3) (-) reduction was not affected by salinity in short-term studies (12 hours). The rate of reduction of endogenous NO(3) (-) in leaves of seedlings grown on NaCl for 8 days decreased only 25%. Nitrate reductase activity in the salt-treated leaves also decreased 20% but its activity, determined either in vitro or by the ;anaerobic' in vivo assay, was always greater than the actual in situ rate of NO(3) (-) reduction. When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in situ nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO(3) (-) transporter, rather than that of the NO(3) (-) reduction system, may be a critical factor to plant survival during salt stress.

Journal Article↗
PubMed1982

Simultaneous Measurement of NH(4) Absorption and N(2) Fixation by Glycine max L. : RESPONSE TO TEMPERATURE, pH, AND EXTERNAL NITROGEN CONCENTRATION.

Ammonium absorption rates by intact nodulated and unnodulated soybean plants (Glycine max [L.] Merr., Amsoy 71) were determined from the liquid phase of a mist assay chamber. From the gas phase, simultaneous measurements of acetylene reduction rates were made from nodulated plants. Ammonium absorption capacity was consistently greater in unnodulated plants.At the beginning of flowering, plant roots were sprayed with an uptake solution ranging from 0.05 to 1.0 millimolar NH(4)Cl, and root nodules concurrently were exposed to 0.12 atmosphere acetylene. The NH(4) (+) absorption system of both nodulated and unnodulated plants were nearly saturated at 0.3 to 0.5 millimolar NH(4) (+).Increasing the pH from 4.0 to 6.8 stimulated NH(4) (+) absorption rate in both flowering and preflowering nodulated and unnodulated plants. Acetylene reduction rate was not altered by short-term exposure to increased acidity. Short-term exposure to lower absorption solution temperatures from 32 degrees C to 18 degrees C did not significantly affect NH(4) (+) absorption rate in flowering nodulated or unnodulated plants. However, acetylene reduction rate increased as the absorption solution temperature increased. The Q(10) value was 1.5 for the reaction rate. Increasing external NO(3) (-) concentration from 0.1 to 5.0 millimolar NO(3) (-) did not significantly influence the kinetics of NH(4) (+) absorption or acetylene reduction rate.

Journal Article↗
PubMed1979

Influence of light and ambient carbon dioxide concentration on nitrate assimilation by intact barley seedlings.

The influence of light, dark, and ambient CO(2) on nitrate assimilation in 8- to 9-day-old barley seedlings was studied. To develop the photosynthetic apparatus fully, the seedlings were grown in nitrogen-free Hoagland solution for 5 days in darkness followed by 3 days in continuous light.The seedlings reduced nitrate and nitrite in both light and dark, although more slowly in darkness. The slower nitrate reduction in darkness was not due to decreased uptake, since the steady-state internal concentration of nitrate was doubled. The faster nitrate reduction in light was attributed to recent products of photosynthetic CO(2) fixation supplying reducing energy, possibly by shuttle reactions between chloroplasts and cytoplasm. In carbohydrate-deficient tissue, it appeared that recently fixed photosynthate could supply all of the energy required for nitrate reduction. When sufficient metabolites were present in the green tissue, light was not obligatory for the reduction of nitrate and nitrite.

Journal Article↗
PubMed1978

Simultaneous measurement of nitrogen fixation estimated by acetylene-ethylene assay and nitrate absorption by soybeans.

An apparatus was designed for simultaneous measurement of rates of N(2) fixation estimated by C(2)H(2)-C(2)H(4) assay (N(2)[C(2)H(2)] fixation) and NO(3) (-) absorption by roots of intact, nodulated soybeans (Glycine max [L.] Merr.). The principal design features include: (a) a gas-tight mist chamber in which nodulated roots can be exposed simultaneously to C(2)H(2) in the gas phase and to a liquid phase containing NO(3) (-) sprayed in a fine mist; and (b) provision for sampling the gas phase for C(2)H(4) determination, and the liquid phase for NO(3) (-) determination.We studied NO(3) (-) absorption by soybeans as affected by nodulation, NO(3) (-) concentration during assay, and previous N nutrition during growth in nutrient solution culture in controlled environment chambers. It was established that 0.5 mm NO(3) (-) nearly saturated the NO(3) (-) absorption system of both nodulated and unnodulated soybeans when the concentration dependence of NO(3) (-) absorption rate was measured just after flowering began. Nitrate absorption rates were measured after development of N stress in unnodulated plants, and during recovery from N stress in nodulated plants. The results suggested that the lower capacity for NO(3) (-) absorption of nodulated plants was a consequence of N stress during the period of nodule growth and development.Nitrogen [C(2)H(2)] fixation rates were compared in intact plants assayed in the mist chamber and in excised roots assayed in both the mist chamber and in glass jars. Excised roots had a lower N(2)[C(2)H(2)] fixation rate than intact plants. The decline observed during the first hour after shoot removal was more pronounced for glass jar-assayed excised roots than for mist chamber-assayed excised roots.We discuss the advantages of our method for assessing the capability of a nodulated legume to acquire nitrogen through both N(2) fixation and absorption and assimilation of NO(3) (-).

Journal Article↗
PubMed1978

Characteristics of sugar uptake in hypocotyls of cotton.

Uptake of sucrose and hexoses by cotton (Gossypium hirsutum L.) hypocotyl segments from free space was shown to be an active, carrier-mediated process. Separate carriers existed for hexoses and sucrose. Accumulated sugars appeared in both soluble and insoluble fractions of the tissue. At optimum temperature and pH, sucrose uptake rate versus concentration was fit by a rectangular hyperbola with V(max) of 14 micromoles per gram fresh weight per hour and K(m) of 8 mm. Sucrose was the principal sugar found in the free space in vivo, and invertase activity was essentially absent from that space except after aging.

Journal Article↗
PubMed1978

Regulation of sugar uptake in hypocotyls of cotton.

Uptake of sucrose and hexoses by hypocotyl segments of cotton (Gossypium hirsutum L.) was shown to be dependent upon sugar level in the tissue. The effect was not related to total sugar level inasmuch as a portion of previously accumulated sugar was without influence on uptake. That portion was presumed to be compartmentalized, most likely in vacuoles. Growth regulators modified the uptake pattern apparently through alterations in secondary metabolism. Uptake and incorporation were inhibited by rotenone and stimulated by light. The light effect was blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. A general model was presented for assimilate flux within sink tissues with free space as the conduit from phloem to carrier site.

Journal Article↗
PubMed1976

Nitrate absorption by barley: I. Kinetics and energetics.

The absorption of NO(3) (-) by barley (Hordeum vulgare L.) was investigated by following the disappearance of NO(3) (-). The absorption was related to several parameters: NO(3) (-) and Ca(2+) concentrations, pH, and the presence of various anions. Absorption rate increased with increasing Ca(2+) concentration, reaching a maximum at approximately 5 mm Ca(2+), and was considerably inhibited by NH(4) (+). Absorption was influenced markedly by pH, and little or not at all by anions (Cl(-), Br(-), SO(4) (2-)), and was decreased by respiratory and oxidative phosphorylation inhibitors.

Journal Article↗
PubMed1976

Nitrate Absorption by Barley: II. Influence of Nitrate Reductase Activity.

The influence of protein synthesis and nitrate reductase activity on nitrate absorption by barley (Hordeum vulgare L.) was investigated. Cycloheximide decreased nitrate absorption. Pretreatment studies showed that cycloheximide affects either energy transfer or nitrate reductase activity or both.Illumination increased plant capacity for nitrate absorption, possibly through increased energy supply and/or increased nitrate reductase activity. There was a positive correlation between nitrate reductase activity and light. Inhibiting the development of nitrate reductase activity by tungstate decreased nitrate absorption.AT LEAST TWO NITRATE TRANSPORT SYSTEMS ARE THUS PROPOSED IN BARLEY: one operating in the dark, with little nitrate reductase activity detectable; and one closely correlated with nitrate reductase activity. Total absorption is the sum of dark absorption and absorption facilitated by nitrate reductase.

Journal Article↗
PubMed1974

Characterization of cadmium uptake by plant tissue.

The uptake of cadmium by excised root tissue of barley (Hordeum vulgare L. cv. Arivat) was investigated with respect to kinetics, concentration, and interactions with various cations. The role of metabolism in Cd absorption was examined using a range of temperatures, anaerobic treatments, and chemical inhibitors. The uptake and distribution of Cd in intact barley plants was also determined. A large fraction of the Cd taken up by excised barley roots was apparently the result of exchange adsorption and was displaced by subsequent desorption with unlabeled Cd, Zn, Cu, or Hg. Another fraction of Cd which could not be displaced by desorption in unlabeled Cd was thought to result from strong irreversible binding of Cd, perhaps on sites of the cell wall. The fraction of the Cd taken up beyond that by exchange adsorption by fresh roots was a linear function of temperature, and inhibited by conditions of low oxygen and by the presence of 2,4-dinitrophenol. It was concluded that this fraction of Cd entered excised barley roots by diffusion. Diffusion, when followed by sequestering, probably accounts for the accumulation of Cd observed in intact barley plants.

Journal Article↗
PubMed1971

Investigation of respiratory and ion transport properties of aging bean stem slices.

Ion and oxygen uptake were studied on aging bean stem slices. Oxygen uptake was high immediately after slicing, decreased to a minimum at 100 minutes, and then increased again. Ion uptake per unit of O(2) uptake data suggested that metabolic energy was utilized almost exclusively for sodium transport in fresh tissue but was diverted to potassium transport as the slices aged. Oxygen and ion uptake in fresh slices was less sensitive to 2,4-dinitrophenol as compared to the aged slices, indicating major metabolic and physiological changes occurred during aging. This was further substantiated by the tissue response to cyanide and antimycin A. Oxygen uptake was decreased by cyanide (22% by 1 mm) and antimycin A (14% by 1 microgram per milliliter) in fresh slices but not in aged slices. Potassium uptake that developed during aging was sensitive to cyanide and antimycin A. The results are pertinent to understanding the role of the stem in regulating ion transport in plants.

Journal Article↗
PubMed1970

Influence of calcium on sodium and potassium absorption by fresh and aged bean stem slices.

The influence of Ca on the aging processes of bean stem (Phaseolus vulgaris) slices and on the absorption of K and Na by fresh and aged slices was investigated. In the presence of Ca, fresh tissue showed a preferential Na uptake. The preference for Na over K resulted from a differential depressive effect of Ca on absorption of these two ions. In aged tissue Na uptake was also depressed, but K absorption was accelerated, with a net result of a much greater absorption of K than Na.The presence of Ca in the aging medium promoted the development of K-absorbing capacity as well as an increase in the rate of respiration but did not influence the loss of capacity to absorb Na as tissue aged. This, along with the demonstration that protein synthesis is involved in the development of K-absorbing capacity by aging tissue, suggests that Ca may have an effect on basic physiological processes concerned with development of ion absorption by aging tissue. The influences that Ca may have on the physical and physiological aspects of ion transport are discussed.

Journal Article↗