Intact Barley Research Articles

Nitrogen-13 Studies of Nitrate Fluxes in Barley Roots

The short-lived radio-isotope nitrogen-13 (half-life 10 min) was used as a tracer in studying fluxes of N in the roots of intact barley plants. After supplying the plants with 13N-nitrate for 30 min, efflux of 13N into an unlabelled (wash) solution was followed under steady-state conditions for a further 10 min. Tests with ion exchange resins suggested that all of the 13N released during this period was in the form of nitrate. In addition to nitrate from a surface film of solution and from the free space of the roots, efflux from another compartment was detected, tentatively identified as the cytoplasmic nitrate pool. In plants grown with nitrate as the only external N-source, efflux from this compartment decreased with a rate constant about 0·17 min−1 (half-time ∼4 min). Adding ammonium sulphate to the wash solution alone did not significantly affect either the initial rate, or the rate constant, of efflux of 13N from these roots. However, 13N efflux decreased more rapidly (rate constant about 0·32 min−1, half-time ∼2·2 min) in roots grown in, and subsequently washed with, solution containing ammonium nitrate. In barley plants grown with 1·5 mol m−3 nitrate, the cytoplasmic nitrate pool was estimated to contain about 2% of the total nitrate in the roots, corresponding to a cytoplasmic nitrate concentration ∼26 mol m−3. Nitrate efflux was equivalent to almost 40% of nitrate influx in the roots of these plants.

Regulation of NO3− Influx in Barley

Short-term (10 minutes) measurements of plasmalemma NO(3) (-) influx (phi(oc)) into roots of intact barley plants were obtained using (13)NO(3) (-). In plants grown for 4 days at various NO(3) (-) levels (0.1, 0.2, 0.5 millimolar), phi(oc) was found to be independent of the level of NO(3) (-) pretreatment. Similarly, pretreatment with Cl(-) had no effect upon plasmalemma (13)NO(3) (-) influx. Plants grown in the complete absence of (13)NO(3) (-) (in CaSO(4) solutions) subsequently revealed influx values which were more than 50% lower than for plants grown in NO(3) (-). Based upon the documented effects of NO(3) (-) or Cl(-) pretreatments on net uptake of NO(3) (-), these observations suggest that negative feedback from vacuolar NO(3) (-) and/or Cl(-) acts at the tonoplast but not at the plasmalemma. When included in the influx medium, 0.5 millimolar Cl(-) was without effect upon (13)NO(3) (-) influx, but NH(4) (+) caused approximately 50% reduction of influx at this concentration.

Water-Stress Induced Changes in Concentrations of Proline and Other Solutes in Growing Regions of Young Barley Leaves

Riazi, A., Matsuda, K. and Arslan, A. 1985. Water-stress induced changes in concentrations of proline and other solutes in growing regions of young barley leaves.—J. exp. Bot. 36: 1716–1725. Young, intact barley Hordeum vulgare L. cv. ‘Arivat’ seedlings stressed with PEG or NaCl were measured for water status and levels of proline, sugars and inorganic cations in growing (basal 1.0 cm) and other areas of leaves. In growing regions, reductions in ψn were found within 1 h in seedlings stressed with PEG (−0.8 M Pa) but 4 h were required before proline increased and proline accounted for less than 5% of the osmotic adjustment after 24 h. Increases in proline occurred to a lesser extent in expanded mid-blade regions where osmotic adjustment was less. After one or more days stress, proline levels in basal tissues were 10 × higher than in mid-blade tissues, and proline increases in these and intervening tissues occurred without loss of turgor. When seedlings were stressed for extended periods with mild to moderate concentrations of PEG, proline elevations in basal to mid-blade areas were proportional to reductions in tissue ψ and ψn NaCl-stress led to similar responses except prohne increases per unit decrease in ψx, were 2–3 × greater than in PEG-stressed tissues. Time-course studies showed levels of inorganic cations were not altered in the growing areas during the first few h of PEG-induced stress, but glucose increased as ψx, decreased. The results showed that proline increase is not the cause but could be a consequence of osmotic adjustment, and its increase is not due to cell death. They also provided independent evidence that stress responses of growing tissues differ substantially from expanded areas in young barley leaves.

Effectiveness of New Terpenoid Derivatives, Abscisic Acid and its Methyl Ester on Transpiration and Leaf Senescence of Barley

Summary The effectiveness of the new terpenoid derivatives LAB 144 143 and LAB 173 711 in reducing water loss through transpiration in barley ( Hordeum vulgare L Cv. Union) was compared with that of abscisic acid (ABA) and ABA methyl ester. The compounds were applied in biotest systems using detached primary leaves, as well as sprayed on intact greenhouse-grown barley plants. If the compounds were applied to isolated leaves via the transpiration stream all substances reduced water consumption to nearly the same substantial extent. With the foliar treatment of detached leaves LAB 144 143, LAB 173 711 and ABA methyl ester, in the order of decreasing activity, were slightly more active than ABA. This result was paralleled by the capacity of the compounds to close the stomata. In intact barley plants, too, LAB 144 143 was the most effective antitranspirant tested. It is speculated that especially LAB 144 143 penetrates the leaf surface of barley better than the other compounds. Furthermore, the new terpenoid derivatives promoted the senescence process of barley leaf segments in the same way as ABA did. Considering the structural relationships of the new compounds to ABA and their biological spectrum of action it is suggested that LAB 144 143 and LAB 173 711 are functional analogues of ABA.

Changes in the kinetics of phosphate and potassium absorption in nutrient-deficient barley roots measured by a solution-depletion technique

From measurements of the rates of depletion of labelled ions from solution in the low concentration range, we described the phosphate and potassium uptake characteristics of the roots of intact barley plants in terms of the kinetic parameters, K m and I max (the maximum rate of uptake). In relatively young (13 d) and older (42 d) plants, cessation of phosphate supply for 4 d or more caused a marked increase in I max (up to four times), without concomitant change in K m, which remained between 5 and 7 μM. By contrast, 1 d of potassium starvation with 14-d plants caused a decline in the K m (i.e. an increased apparent affinity for potassium) from 53 μM to 11 μM, without alteration to I max. After longer periods of potassium starvation, I max increased (about two times) while the K m remained at the same low value. Growth of shoots and roots were unaffected by these treatments, so that concentrations of ions in the tissues declined after 1 d or more of nutrient starvation, but we could not identify a characteristic endogenous concentration for either nutrient at which changes in kinetic parameters were invariably induced. The possible mechanisms regulating carriermediated transport, and the importance of changes induced in kinetic parameters in ion uptake from solution and soil are discussed.

Compartmental analysis of phosphate in roots of intact barley seedlings

Elution profiles of 32P-labelled inorganic phosphate (Pi) from roots of intact barley plants were observed and were found to conform to the pattern theoretically derived for three compartments in series. An allowance was made for the movement of labelled phosphate from the cytoplasm into the root xylem. Transformations of labelled phosphate within metabolically labile organic pools seem to be invisible kinetically because their rate constants are generally higher than that for Pi efflux across the plasmalemma and tonoplast. It is concluded that compartmentation of phosphate between cytoplasm and vacuole can be explored usefully by this technique especially if used in conjunction with other methods which can measure the size of cytoplasmic organic phosphate pools.

Effects of Light and of Growth Regulators on the Reversibility of Senescence in Attached Leaves of Barley

Summary Senescence of intact barley seedlings ( Hordeum vulgare ) judged by the loss of chlorophyll, was induced by putting them in the dark. Reversal of senescence by application of light was also observed. The chlorophyll content recovered after two days in the light, but seedlings were unable to recover their initial level of pigment after four days in the dark, This suggests the onset of an irreversible stage in senescence from the fourth day. Supply of kinetin to the leaf after two or four days in the dark induces a slight increase in chlorophyll content. Whereas reversion of the senescence is obtained immediately after the dark period, the same treatment with abscisic acid accelerates the loss of chlorophylls and retards the reversion by light treatment.

Short Term Studies of Nitrate Uptake into Barley Plants Using Ion-Specific Electrodes and 36ClO3−

A computer-controlled multichannel data acquisition system was employed to obtain continuous measurements of net nitrate or chlorate uptake by roots of intact barley plants (Hordeum vulgare cv Betzes) using nitrate-specific electrodes. Plants, previously grown in solutions maintained at 10 or 200 micromolar NO(3) (-) (low N or high N conditions, respectively), were provided with 200 micromolar NO(3) (-) or ClO(3) (-) during the uptake period. Initial rates of NO(3) (-) uptake were several times higher in low N plants than in high N plants. Within 10 min, uptake in the former plants declined to a new steady rate which was sustained for the remainder of the experiment. No such time-dependent changes were evident in the high N plants. Rates and patterns of net chlorate uptake exhibited almost identical dependence upon previous nitrate provision. NO(3) (-) ((36)ClO(3) (-)) influx, by contrast, appeared to be independent of NO(3) (-) pretreatment prior to influx determination. Nitrate efflux, estimated by several different methods, was strongly correlated with internal nitrate concentration of the roots.

Carbon Dioxide Exchange in an Incompatible Barley/Powdery Mildew Combination

AbstractCO2 exchanges in intact barley leaves were studied by infra red gas analysis after inoculation with an incompatible race of powdery mildew. Net photosynthesis was inhibited, and dark and photorespiration were stimulated, by inoculation. The increase in respiratory processes was approximately equal to the change in net photosynthesis indicating that CO2 fixation, “gross photosynthesis”, was unaffected by inoculation. It is concluded that changes in net photosynthesis may be the primary cause of the reduced quantity and quality of grain in incompatible barley/mildew combinations.

Vacuolar Na/K Exchange, its Occurrence in Root Cells ofHordeum,AtriplexandZeaand its Significance for K/Na Discrimination in Roots

Using excised low-salt roots of barley and Atriplex hortensis the transport of endogenous potassium through the xylem vessels was studied. It was enhanced by nitrate and additionally by sodium ions which apparently replaced vacuolar potassium which was then available in the symplasm of root cells for transport to the shoot. Vacuolar Na/K exchange also has been investigated by measurements of longitudinal ion profiles in single roots of both species. In Atriplex roots a change in the external solution from K+ to Na+ induced an exchange of vacuolar K+ for Na+, in particular in the subapical root tissues and led to increased K+ transport and loss of K+ from the cortex. In inverse experiments a change from Na+ to K+ did not induce an exchange of vacuolar Na+; merely in meristematic tissues Na+—apparently from the cytoplasm—was extruded in exchange for K+. In roots of barley seedlings without caryopsis, as in excised roots, a massive exchange of K+ for Na+ was observed in the continuous presence of external 1-0 mM Na and 0-2 mM K. This exchange also was attributed to the vacuole and was most pronounced in the young subapical tissues. It did not occur, however, in the corresponding tissues in roots of fully intact barley seedlings. In these, the young tissues retained a relatively high K/Na ratio also in their vacuoles. Similarly, contrasting results were obtained with intact and excised roots of Zea mays L. Based on these results a scheme of the events that lead to selective cation uptake in intact barley roots is proposed. In this scheme a crucial factor of selectivity is sufficient phloem recirculation of K+ by the aid of which K+-rich cortical cells are formed near the root tip. When matured these cells are suggested to maintain a high cytoplasmic K/Na ratio due to K+-dependent sodium extrusion at the plasmalemma and due to recovery of vacuolar K+ by Na/K exchange across the tonoplast.

In Vivo Nitrate Reduction in Roots and Shoots of Barley (Hordeum vulgare L.) Seedlings in Light and Darkness

In vivo NO(3) (-) reduction in roots and shoots of intact barley (Hordeum vulgare L. var Numar) seedlings was estimated in light and darkness. Seedlings were placed in darkness for 24 hours to make them carbohydrate-deficient. During darkness, the leaves lost 75% of their soluble carbohydrates, whereas the roots lost only 15%. Detached leaves from these plants reduced only 7% of the NO(3) (-) absorbed in darkness. By contrast, detached roots from the seedlings reduced the same proportion of absorbed NO(3) (-), as did roots from normal light-grown plants. The rate of NO(3) (-) reduction in the roots accounted for that found in the intact dark-treated carbohydrate-deficient seedlings. The rates of NO(3) (-) reduction in roots of intact plants were the same for approximately 12 hours, both in light and darkness, after which the NO(3) (-) reduction rate in roots of plants placed in darkness slowly declined. In the dark, approximately 40% of the NO(3) (-) reduction occurred in the roots, whereas in light only 20% of the total NO(3) (-) reduction occurred in roots. A lesser proportion was reduced in roots because the leaves reduced more nitrate in light than in darkness.

Reversible Light-Activation of Ribulose Bisphosphate Carboxylase/Oxygenase in Isolated Barley Protoplasts and Chloroplasts

The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase displayed near-maximal activity in isolated, intact barley (Hordeum vulgare L. cv. Pennrad) mesophyll protoplasts. The carboxylase deactivated 40 to 50% in situ when protoplasts were dark-incubated 20 minutes in air-equilibrated solutions. Enzyme activity was fully restored after 1 to 2 minutes of light. Addition of 5 millimolar NaHCO(3) to the incubation medium prevented dark-inactivation of the carboxylase. There was no permanent CO(2)-dependent activation of the protoplast carboxylase either in light or dark. Activation of the carboxylase from ruptured protoplasts was not increased significantly by in vitro preincubation with CO(2) and Mg(2+). In contrast to the enzyme in protoplasts, the carboxylase in intact barley chloroplasts was not fully reactivated by light at atmospheric CO(2) levels. The lag phase in carbon assimilation was not lengthened by dark-adapting protoplasts to low CO(2) demonstrating that light-activation of the carboxylase was not involved in photosynthetic induction. Irradiance response curves for reactivation of the the carboxylase and for CO(2) fixation by isolated barley protoplasts were similar. The above results show that there was a fully reversible light-activation of the carboxylase in isolated barley protoplasts at physiologically significant CO(2) levels.

Shoot-Dependent Regulation of Sodium and Potassium Fluxes in Roots of Whole Barley Seedlings

Unidirectional fluxes and the cytoplasmic and vacuolar contents of potassium and sodium in root cells of intact barley seedlings (Hordeum vulgare L., cv. Villa) were determined by use of compartmental analysis. In addition, the net vacuolar accumulation Jn and the xylem transport cx of K+ and Na+ were measured. Both of these data were needed for the evaluation of the efflux data. Fluxes and compartmental contents of K+ and Na+ were comparable to data obtained with excised roots. The effect of the shoot-to-root ratio—as varied by partial excision of the seedlings seminal roots—on the fluxes and contents was investigated. Higher shoot-to-root ratios induced an increase in xylem transport, in plasmalemma influx, and also in the cytoplasmic content of K+ and Na+. With potassium the plasmalemma efflux was almost unaltered while the tonoplast fluxes and vacuolar content were decreased (in presence of Na+). With sodium, on the other hand, the plasmalemma efflux and the tonoplast fluxes were also increased in the plants having one root and a high shoot-to-root ratio. These changes occurred even under conditions of low humidity, when transpiration was low and guttation occurred. The latter was also increased at the high shoot-to-root ratio. The observed changes could be due to a relieved feedback control of ion fluxes by the shoot and mediated in part by a relatively higher supply of photosynthates in the plants having one root. In addition, hormonal signals were suggested to participate. In particular a possibly decreased level of cytokinins in the plants having only one root could contribute to the signal. The observed changes appear to be responses of the plant to an alteration that can occur under natural conditions when the root system is damaged.

Nitrate Uptake into Barley (Hordeum vulgare) Plants

Evidence is presented that chlorate is an extremely good analog for nitrate during nitrate uptake by intact barley (Hordeum vulgare cv. Fergus) roots. The depletion of ClO(3) (-) or NO(3) (-) from uptake media over 2 to 6 hours by seedlings was found to be dependent on combined NO(3) (-) plus ClO(3) (-) concentrations, and total anion uptake was equivalent at different NO(3) (-)/ClO(3) (-) ratios. After loading barley seedlings with (36)ClO(3) (-) for 6 hours, kinetic parameters were derived from the analysis of efflux of [(36)Cl] chlorate into unlabeled solution. On the basis of this analysis, the half times for exchange for the cytoplasmic and vacuolar phases were 17 minutes and 20 hours, respectively.Data pooled from a number of different experiments were used to calculate kinetic constants (K(m) and V(max)) for (36)ClO(3) (-) influx into barley roots at different external ClO(3) (-)/NO(3) (-) ratios, using short (10 minutes) influx times. There appeared to be no discrimination by the root cells between ClO(3) (-) and NO(3) (-). Lineweaver-Burk analysis of the interaction between nitrate and chlorate were characteristic of competitive inhibition at low nitrate concentrations (0-0.5 mm). At higher concentrations, in the range of >1 mm, similar interactions between these ions were evident.

Potassium-hydrogen ion exchange across barley roots: an introduction to chemiosmotic principles of solute transport

The chemiosmotic theories of ATP synthesis and coupled solute transport across membranes are outlined. A simple experimental system for measuring H+ transport and associated cation fluxes across root cortical cells of intact barley plants is described. This system may be explored in a variety of projects or laboratory exercises designed to introduce chemiosmotic principles.

Differences in Steady-State Net Ammonium and Nitrate Influx by Cold- and Warm-Adapted Barley Varieties

A flowing nutrient culture system permitted relatively rapid determination of the steady-state net nitrogen influx by an intact barley (Hardeum vulgare L. cv Kombar and Olli) plant. Ion-selective electrodes monitored the depletion of ammonium and nitrate from a nutrient solution after a single pass through a root cuvette. Influx at concentrations as low as 4 micromolar was measured. Standard errors for a sample size of three plants were typically less than 10% of the mean.When grown under identical conditions, a variety of barley bred for cold soils had higher nitrogen influx rates at low concentrations and low temperatures than one bred for warm soils, whereas the one bred for warm soils had higher influx rates at high concentrations and high temperatures. Ammonium was more readily absorbed than nitrate by both varieties at all concentrations and temperatures tested. Ammonium and nitrate influx in both varieties were equally inhibited by low temperatures.

The effect of the osmotic potential and specific ion concentration of the nutrient solution on the uptake and reduction of nitrate by barley seedlings

Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψπ) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized to (Ψπ) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl2 or Na2SO4. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO3. The nutrient solutions were sampled for NO3 analysis each day immediately before renewing the solutions. The accumulative loss of NO3 from the solutions was considered to be uptake whereas NO3 reduction was the difference between uptake and seedling content. Lowering the (Ψπ) of the nutrient solutions resulted in decreased concentrations of NO3 in the plant, little or no effect (except at the lowest (Ψπ) level) on uptake, and increased nitrate reductase activity. Increased rates of NO3 reduction were in particular associated with the Cl concentration of the nutrient solution.

The Interactions Between Monovalent Cations and Calcium During Their Adsorption on Isolated Cell Walls and Absorption by Intact Barley Roots

The Interactions Between Monovalent Cations and Calcium During Their Adsorption on Isolated Cell Walls and Absorption by Intact Barley Roots

A Lag Phase in Vacuolar Accumulation of Cl- Ions in Roots of Intact Barley Plants

Summary The presence of NO 3 - in the external solution appears to interfere with Cl - uptake by low-salt roots of barley plants during the second (purely vacuolar) period of uptake but not during the first period. The inference is that the interaction is located at the tonoplast. This implies that during the initial period no Cl- ions are accumulated into the vacuoles.

Comparative depressive actions of barbiturates on potassium chloride uptake by intact barley and rice seedlings

Summary The comparative depressive actions of the three barbiturates, barbital, amobarbital, and secobarbital, respectively classed as long-, medium-, and short-acting barbiturates, on potassium and chloride ion uptake by intact barley and rice seedlings were investigated. Barbital exerted the least and secobarbital the most depressive action on the uptake of both potassium and chloride ions by both types of seedlings. The functioning of the Meyer-Overton principle regarding lipid solubility in relation to drug or anaesthetic potency, observed previously in germinating angiosperm seedlings and in germinating pollen grains, was also evident in this investigation.