Effect of Exogenous Glycinebetaine on Na+ Transport in Barley Roots

Ahmad, N., Wyn Jones, R. G. and Jeschke, W. D. 1987. Effectof exogenous glycinebetaine on Na⁺ transport in barley roots.—J.exp. Bot. 38: 913–921. A comparison has been made of the kinetics of 22Na⁺ uptake intoexcised barley roots and roots pre-loaded with glycinebetaine.The elevated intracellular glycinebetaine or a metabolic consequencethereof increased the Na⁺ influx, and the effect was relatedto the level of internal glycinebetaine and or Na⁺ [Cl^–].The quasi-steady-state Na⁺ influx at the tonoplast rather thanthe plasmalemma influx was apparently influenced by glycinebetaineloading. The tonoplast fluxes and vacuolar Na⁺ content wereconsistently higher in glycinebetaine-loaded roots than unloadedroots. A membrane-modifying role of glycinebetaine in relationto ion compartmentation is discussed. Key words: Excised roots, glycinebetaine, Na⁺, ion fluxes, barley     

52Fe Translocation in Barley as Monitored by a Positron-Emitting Tracer Imaging System (PETIS): Evidence for the Direct Translocation of Fe from Roots to Young Leaves via Phloem

The real-time translocation of iron (Fe) in barley (Hordeumvulgare L. cv. Ehimehadaka no. 1) was visualized using the positron-emittingtracer ⁵²Fe and a positron-emitting tracer imaging system (PETIS).PETIS allowed us to monitor Fe translocation in barley non-destructivelyunder various conditions. In all cases, ⁵²Fe first accumulatedat the basal part of the shoot, suggesting that this regionmay play an important role in Fe distribution in graminaceousplants. Fe-deficient barley showed greater translocation of⁵²Fe from roots to shoots than did Fe-sufficient barley, demonstratingthat Fe deficiency causes enhanced ⁵²Fe uptake and translocationto shoots. In the dark, translocation of ⁵²Fe to the youngestleaf was equivalent to or higher than that under the light condition,while the translocation of ⁵²Fe to the older leaves was decreased,in both Fe-deficient and Fe-sufficient barley. This suggeststhe possibility that the mechanism and/or pathway of Fe translocationto the youngest leaf may be different from that to the olderleaves. When phloem transport in the leaf was blocked by steamtreatment, ⁵²Fe translocation from the roots to older leaveswas not affected, while ⁵²Fe translocation to the youngest leafwas reduced, indicating that Fe is translocated to the youngestleaf via phloem in addition to xylem. We propose a novel modelin which root-absorbed Fe is translocated from the basal partof the shoots and/or roots to the youngest leaf via phloem ingraminaceous plants.     

The Influence of Plant Nitrogen Status on NO2 Uptake, NO2 Assimilation and on the Gas Exchange Characteristics of Barley Plants Exposed to Atmospheric NO2

Barley plants were grown in nutrient solution at two contrastingnitrate concentrations to produce plants of low or high nitrogen(N) status. Leaves were then exposed continuously to either0.3 mm³ dm^–3 NO₂ or clean air, with the roots and rootingmedium isolated from the polluted air. Uptake of NO₂ was measuredin two ways; as depletion from an air stream containing thegas and using ¹⁵N-labelled NO₂. Results from the two methodsagreed well and demonstrated that the flux of NO₂ into the leavesof N-deficient barley was lower than that of N-sufficient plants.Nevertheless, the relative contribution of¹⁵N derived from ¹⁵NO₂to the N status of the plant was greater in the plants suppliedwith low nitrate. A major factor in regulating NO₂ uptake bybarley leaves appeared to be stomatal conductance, althoughinternal conductance may also be involved. The effects of NO₂exposure of barley on carbon dioxide exchange rates, transpirationand water vapour conductance were also influenced by the N statusof the plant. Key words: Hordeum vulgare, ¹⁵N-labelled NO₂, carbon dioxide exchange, transpiration     

Vacuolar Na/K Exchange, its Occurrence in Root Cells of Hordeum, Atriplex and Zea and its Significance for K/Na Discrimination in Roots

Using excised low-salt roots of barley and Atriplex hortenslsthe transport of endogenous potassium through the xylem vesselswas studied It was enhanced by nitrate and additionally by sodiumions which apparently replaced vacuolar potassium which wasthen available in the symplasm of root cells for transport tothe shoot Vacuolar Na/K exchange also has been investigatedby measurements of longitudinal ion profiles in single rootsof both species. In Atriplex roots a change in the externalsolution from K⁺ to Na⁺ induced an exchange of vacuolar K⁺ forNa⁺, in particular in the subapical root tissues and led toincreased K⁺ transport and loss of K⁺ from the cortex. In inverseexperiments a change from Na⁺ to K⁺ did not induce an exchangeof vacuolar Na⁺; merely in meristematic tissues Na⁺—apparentlyfrom the cytoplasm—was extruded in exchange for K⁺. Inroots of barley seedlings without caryopsis, as in excised roots,a massive exchange of K⁺ for Na⁺ was observed in the continuouspresence of external 1.0 mM Na and 0.2 mM K. This exchange alsowas attributed to the vacuole and was most pronounced in theyoung subapical tissues. It did not occur, however, in the correspondingtissues in roots of fully intact barley seedlings. In these,the young tissues retained a relatively high K/Na ratio alsoin their vacuoles. Similarly, contrasting results were obtainedwith intact and excised roots of Zea mays L. Based on theseresults a scheme of the events that lead to selective cationuptake in intact barley roots is proposed. In this scheme acrucial factor of selectivity is sufficient phloem recirculationof K⁺ by the aid of which K⁺ rich cortical cells are formednear the root tip. When matured these cells are suggested tomaintain a high cytoplasmic K/Na ratio due to K⁺ dependent sodiumextrusion at the plasmalemma and due to recovery of vacuolarK⁺ by Na/K exchange across the tonoplast. Key words: Potassium/Sodium selectivity, Vacuolar exchange, Xylem transport, Hordeum, Zea, Atriplex     

Proton-Chloride Symport in Barley Roots

An increase in the acidity of the incubation medium from pH6 5 to pH 4.0 increased Cl- flux into ATP-depleted Hordeum vulgareL roots more than three times This pH-dependent Cl^– fluxwas inhibited by p-chloromercuriphenyl sulphonic acid. The effectof pH on Cl- influx was eliminated when the pH gradient wasdissipated by addition of salts of permeable weak acids, andin K-loaded roots in the presence of a protonophore togetherwith valinomycin The results support the assumption that a H⁺-Cl^–symportsystem is present in barley root cells Hordeum vulgare L., barley, excised roots, ion transport, proton-chloride symport     

Environmental Factors Affecting the Loss of Carbon from the Roots of Wheat and Barley Seedlings

The amounts of carbon released into soil from roots of wheatand barley seedlings grown under three environmental conditionsfor 3 weeks with shoots in constant specific activity ¹⁴CO₂are reported. This carbon loss was measured as respired ¹⁴CO₂from both the root and the accompanying microbial populationand as root derived ¹⁴C-labelled organic C compounds in thesoil. With a 16 h photoperiod, growth at 15 ?C constant or 18?C day/14 ?C night gave a loss of 33–40% of the totalnet fixed carbon (defined as ¹⁴C retained in the plant plus¹⁴C lost from the root). The proportion of ¹⁴C translocatedto the roots that was released into the soil did not changewith temperature, so carbon distribution within the plant musthave changed. With a 12 h photoperiod and a temperature regimeof 18 ?C/14 ?C carbon loss from the roots was decreased to 17–25%of the total fixed carbon. Key words: Cereals, Roots, Carbon loss     

Root-Tiller Interrelationships in Spring Barley (Hordeum distichum (L.) Lam.)

Root-tiller relations were investigated in spring barley grownin soil in deep pots. The total dry wt of the root system reachedits maximum 6 weeks from sowing, when the shoot weight was only50 per cent of its value at maturity. Seminal and nodal rootscomprised 40 and 60 per cent, respectively, of the total rootdry wt at maturity; the majority of the nodal root weight wasassociated with the main shoot. The main shoot had approximatelytwice as many nodal roots as either of the first two primarytillers (T1 and T2), and the primary and secondary tillers appearinglater were very poorly rooted. Some tillers, especially secondarytillers that died prematurely, produced no nodal roots. Theweight of the seminal roots and nodal roots attached to themain shoot continued to increase up to maturity but the drywt of nodal roots on tillers declined with time. This patternof growth was closely related to the pattern of ¹⁴C assimilateddistribution within the root system. A very small proportionof ¹⁴C assimilated by the main shoot and T1 and T2 was exported.The majority of the exported assimilate went to the seminalroot system and to nodal roots attached to the main shoot. Individualnodal and seminal roots seemed to have different roles in supplyingnutrients to the shoot system, with the former mainly providing³²P-phosphate to its tiller of origin and the latter generallysupplying the main shoot and primary tillers. Hordeum distichum. (L.) Lam., barley, root growth, nodal roots, seminal roots, tillering, assimilate distribution, ³²P-distribution     

Extrusion of Sodium Ions by Barley Roots I. Characteristics of the Extrusion Mechanism

Evidence is presented for an outwardly directed sodium ion pumpin excised barley roots. The efflux has a Q₁₀ of about 2 andis inhibited by ouabain at concentrations of the inhibitor downto 10^–5 M. A threefold stimulation of the sodium losswas observed both with ATP and inorganic phosphate at concentrationsof 10^–3 M. A stimulatory effect of different concentrationsof DNP on the extrusion of sodium has been observed and is attributedto permeability changes resulting from the use of this inhibitor.It is suggested that the sodium extrusion mechanism reportedhere for excised barley roots is similar to the sodium pumpsfound in animal tissues and certain algal cells.     

Uptake and Movement of 14C-Chlormequat Chloride Applied to Leaves of Barley and Wheat

Chlormequat chloride labelled with ¹⁴C was applied to the thirdleaf of Proctor barley and Maris Dove wheat; after 1 d lessthan a fifth could be washed off with water. More ¹⁴C-labelledmaterial moved from treated areas of wheat than of barley toaccumulate in tips of treated leaves, younger main-stem leaves,main stems, and ears. Relatively small amounts of radioactivematerial accumulated in roots, but less in wheat than barley.About 80% of the radioactivity was recovered from plants upto 1 week after application, but the amounts recovered in aqueouswashings and extracts decreased faster from wheat than frombarley.     

L-Tyrosine carboxy-lyase of barley roots

_L-Tyrosine carboxy-lyase (E.C. 4. 1. 1. 25) was isolated fromroots of germinating barley (Hordeum vulgare). The enzyme requirespyridoxal phosphate for maximum activity. The optimum pH foractivity is about 7.0. The enzyme is inhibited by p-chloromercuribenzoateand hydroxylamine at 10^–3 M. Enzyme activity is foundin extracts from young roots, especially from those in earlystages of development, but not in extracts from shoots of thesame plant. Localization and changes in the amounts of _L-tyrosinecarboxy-lyase and aromatic amines in developing barley seedlingswere measured. Participation of carboxy-lyase in the formationof aromatic amines in barley roots is suggested. (Received July 17, 1970; )     

In vivo Treatments That Modulate PPi-Dependent H+ Transport Activity of Tonoplast-Enriched Membrane Vesicles from Barley Roots

The PP_i-dependent H⁺ transport activity of tonoplast-enrichedmembrane vesicles prepared from barley roots was greatly reducedwhen the plants were grown for 4 or 5 days with an additional3 raM KC1 in growth medium that contained only 0.1 mM CaCl₂in water. To characterize the mechanism of this reduction inactivity, we attempted to treat barley roots with K⁺ ions, Cl^-ions(or acetate), and A23187 [GenBank] (with or without Ca²⁺ ions), whichmight be expected to cause alkalization, acidification and mobilizationof Ca²⁺ ions in the cytoplasm, respectively. One-day treatmentof barley roots with K⁺ ions significantly decreased PP_i--dependentH⁺ transport activity of prepared tonoplast-enriched membranevesicles, while treatment with Cl^- ions or acetate significantlyincreased the activity. A similar increase in the activity alsooccurred by treatment with Ca²⁺ ions alone or in combinationwith A23187 [GenBank] . Determination of the PP_i-hydrolyzing activity ofmembrane vesicles showed that changes in this activity by thevarious treatments were similar to those in the PP_i-dependentH⁺ transport activity. The changes in ATP-dependent H⁺ transportactivity of membrane vesicles caused by these treatments weresmall. These results indicate that the in vivo treatments hadsignificant effects on the H⁺ transport activity of H⁺-PP_i-ase,one of the two active vacuolar H⁺-pumps (H⁺-PP_iase and H⁺-ATPase).In addition, these results suggest the possibility that changesin levels of cytoplasmic H⁺ or Ca²⁺ ions may be involved inmodulation of the H⁺ transport activity of the vacuolar H⁺-PP_iaseduring plant growth. (Received September 14, 1992; Accepted March 1, 1993)     

Increase in Proton-Transport Activity of Tonoplast Vesicles as an Adaptive Response of Barley Roots to NaCl Stress

H⁺-Transport activity of the vesicles prepared from barley rootswas studied at the early phase after application of NaCl stress.The activity reached maximal level at 3 days after the treatmentwith 200 mM NaCl which moderately reduced the growth. This activityincrease could be suppressed in the presence of cycloheximideand actinomycin D. The properties of the membrane vesicles associated with H⁺-transportactivity prepared from both control and NaCl-stressed rootssuggested that it was of tonoplast origin based on the followingfindings: optimal pH at 7.5, strong inhibition by nitrate butnot by vanadate, and stimulation by chloride. The density gradient centrifugation of vesicles with DextranT70 did not show any detectable difference in the distributionpatterns of H⁺-transport activities between control and NaClstressedroots. Furthermore, K_m values for ATP of the H⁺-transport activityof vesicles prepared from control and NaCl-stressed roots werethe same. Therefore, H⁺-transport activity with properties similarto those of the control roots was increased by NaCl stress.The results are discussed in terms of an adaptive mechanismof barley against salt stress. ¹Permanent address: Department of Horticulture, College of Agriculture,Chonnam National University, Chonnam 500, Korea. (Received April 18, 1988; Accepted July 20, 1988)     

The absorption of potassium and several organic compounds by barley roots: Effect of siduron

Absorption of ⁴²K by excised roots of barley (Hordeum vulgareL.) grown in 0 or 5 ppm siduron (l-(2-methylcyclohexyl)-3-phenylurea)was a linear function of time for at least 60 minutes with transportbeing unidirectional. Absorption of siduron was a function ofthe external concentration to the limits of its solubility (0.09mM). However, the siduron- ¹⁴C absorbed by roots grown in either0 or 5 ppm siduron was in a readily exchangeable form and desorptionfor 4 hr exchanged 80 % of the label. Glucose-¹⁴C, adenine-8¹⁴Cand leucine¹⁴C were actively absorbed with 70 to 85 % of thelabel being absorbed in 24 hr. Although roots grown in iduronabsorbed less ⁴²K, glucose-¹⁴C, adenine-¹⁴C and siduron-¹⁴C,and more leucine-¹⁴C than similar roots grown in water culture,it is probable that these differences were not large enoughto account for the noted reduction (60%) in root growth. (Received January 9, 1968; )     

Volatile Compound-Mediated Interactions between Barley and Pathogenic Fungi in the Soil

Plants are able to interact with their environment by emitting volatile organic compounds. We investigated the volatile interactions that take place below ground between barley roots and two pathogenic fungi, Cochliobolus sativus and Fusarium culmorum. The volatile molecules emitted by each fungus, by non-infected barley roots and by barley roots infected with one of the fungi or the two of them were extracted by head-space solid phase micro extraction and analyzed by gas chromatography mass spectrometry. The effect of fungal volatiles on barley growth and the effect of barley root volatiles on fungal growth were assessed by cultivating both organisms in a shared atmosphere without any physical contact. The results show that volatile organic compounds, especially terpenes, are newly emitted during the interaction between fungi and barley roots. The volatile molecules released by non-infected barley roots did not significantly affect fungal growth, whereas the volatile molecules released by pathogenic fungi decreased the length of barley roots by 19 to 21.5% and the surface of aerial parts by 15%. The spectrum of the volatiles released by infected barley roots had no significant effect on F. culmorum growth, but decreased C. sativus growth by 13 to 17%. This paper identifies the volatile organic compounds emitted by two pathogenic fungi and shows that pathogenic fungi can modify volatile emission by infected plants. Our results open promising perspectives concerning the biological control of edaphic diseases.     

Interaction of Salinity and Anaerobiosis in Barley and Rice

Barley and rice at the early tillering stage were exposed simultaneouslyto anaerobiosis and high [NaCl]. Barley was grown at 0.5, 70,and 125 mol m^–3 NaCl, and rice at 2, 20, 40, and 80 molm^–3 NaCl. Surprisingly, anaerobiosis only slightly aggravatedthe adverse effects of high [NaCl] on root and shoot growthof both species. For rice and barley grown under aerobic conditions, high [NaCl]increased [Na⁺] and [Cl^–] and decreased [K+] in both rootsand shoots. However, the changes in ion concentrations in theshoots were smaller for rice than for barley. For roots of barley, anaerobiosis decreased [Na⁺], [Cl^–],and [K⁺] at both low and high [NaCl], possibly as a result ofinhibition of active ion accumulation. For barley shoots, anaerobiosisincreased [Na⁺] and [Cl^–], but only at high salinity;in contrast, [K⁺] was reduced by anaerobiosis at both low andhigh [NaCl]. These results indicate that anaerobiosis slightlyincreased the permeability of the barley root system to Na+and Cl^–. For rice, the most important interaction between salinity andanaerobiosis occurred in the shoots, where anaerobiosis increased[Na⁺] and decreased [K⁺], particularly at 40 and 80 mol m^–3NaCl, while there was no interaction between anaerobiosis andsalinity for Cl^– uptake. It is therefore suggested thatanaerobic treatment of rice decreased the selectivity for K⁺over Na⁺ of cation transport to the shoots, at least for plantsgrown at high salinities.     

Assimilation of Nitrogen in Mutants Lacking Enzymes of the Glutamate Synthase Cycle

¹⁵N labelling was used to investigate the pathway of nitrogenassimilation in photorespiratory mutants of barley (Hordeumvulgare cv. Maris Mink), in which the leaves have low levelsof glutamine synthetase (GS) or glutamate synthase, key enzymesof ammonia assimilation. These plants grew normally when maintainedin high CO₂, but the deletions were lethal when photorespirationwas initiated by transfer to air. Enzyme levels in roots weremuch less affected, compared to leaves, and assimilation oflabelled nitrate into amino acids of the root showed very littledifference between wild type and mutants. Organic nitrogen wasexported from roots in the xylem sap mainly as glutamine, levelsof which were somewhat reduced in the GS-deficient mutant andenhanced in the glutamate synthase deficient mutant. In theleaf, the major effect was seen in the glutamatesynthase mutant,which had an extremely limited capacity to utilize the importedglutamine and amino acid synthesis was greatlyrestricted. Thiswas confirmed by the supply of [¹⁵N]-glutamine directly to leaves.Leaves of the GS-deficient mutant assimilatedammonia at about75% the rate found for the wild type, and this was almost completelyeliminated by addition of the inhibitormethionine sulphoximine.Root enzymes, together with residual levels of the deleted enzymesin the leaves, have sufficient capacityfor ammonia assimilation,through the glutamate synthase cycle, to provide adequate inputof nitrogen for normal growth of themutants, if photorespiratoryammonia production is suppressed. Key words: Hordeum vulgare, ¹⁵N, glutamine synthetase, glutamate synthase, ammonia assimilation     

Possible Involvement of Abscisic Acid in Increases in Activities of Two Vacuolar H+-Pumps in Barley Roots under Aluminum Stress

Levels of abscisic acid (ABA) in barley roots increased upontreatment with AlCl₃. Treatment with AlCl₃ or ABA increasedboth ATP-dependent and PP_i-dependent H⁺-pumping activities intonoplast-enriched membrane vesicles. Increase in the H⁺-pumpingactivities caused by aluminum stress could result from increasedlevels of ABA. ¹Present address: Department of Botany, Faculty of Science,Hirosaki University, Hirosaki, Aomori, 036 Japan     

Extrusion of Sodium Ions by Barley Roots: II. Localization of the Extrusion Mechanism and its Relation to Long-distance Sodium Ion Transport

An active sodium effux hasbeen demonstrated in excised barleyroots. Isolated cortical and stelar tissues from the same materialdo not show any evidence of such an efflux mechanism. When intactbarley plantswere allowed to absorb ²²Na active sodium extrusionwas not observed, although the percentage of ²²Na transportedto the shoot was stimulated 20 to 40 percent by ouabain at 5x 10^–4 M. Absorption and long-distance transport of phosphatewas unaffected by ouabain at this concentration. Interpretationof these data lead to the conclusion.that the sodium-effluxpump in barley roots is located at or near the endodermis externalto the Casparian band. This pump thus provides a mechanism wherebysodium can be partially excluded from the shoots of barley plants.     

Growth and Phosphate Transport in Barley and Tomato Plants During the Development of, and Recovery from, Phosphate-stress

Barley and tomato plants were cultured in nutrient solutionsincluding 0.15 mol m^–3 H²PO^–₄. The phosphate supplywas discontinued and the subsequent effects on growth, internalphosphorus concentrations, phosphate absorption and translocationwere measured at frequent intervals. Growth rates were at firstunchanged and the internal phosphorus concentration decreased.During this phase the rate of phosphate transport by the rootssometimes increased significantly. Growth slowed more in shootsthan in roots during a second phase of stress development andvisual symptoms of deficiency appeared in tomato but not inbarley. During this phase, enhancement of phosphate uptake capacityreached a maximum in both species. The subsequent decline inuptake capacity was associated with visible symptoms of deficiencydeveloping in barley and intensifying in tomato. When stressedplants were returned to a solution containing 0.15 mol m^–3H₂PO^–₄ rapid absorption continued for several days afterthe internal phosphorus concentration had returned to the levelof the controls. Phosphate toxicity may have been the causeof leaf lesions and necrosis during the ‘recovery’phase. Stomatal conductance in tomato was decreased at an early stageof stress development. Foliar-applied phosphate was absorbedmore rapidly by P-stressed barley leaves than by their controlsand much larger amounts were translocated from the leaves tothe roots.     

Synthesis and 15N-labelling of glutamine and glutamate in maize roots during early stages of 15N-ammonium assimilation

The concentrations of glutamine and glutamate, and the abundanceof ¹⁵N in these compounds, were measured in roots of intact,nitrate-grown maize plants fed with ¹⁵N-nitrate or ¹⁵N-ammoniumfor periods of 3–80 min. On supplying ¹⁵N-ammonium therewas a rapid and almost linear accumulation of glutamine, itsconcentration in the roots rising 3-fold over 1 h. Supplying¹⁵N-nitrate instead of ¹⁵N-ammonium did not increase root glutamine,and the concentration of glutamate was not affected by eithertreatment. The time-course of amide ¹⁵N-labelling seen in glutamine extractedfrom roots which had been supplied with ¹⁵N-ammonium could bestbe explained by a model in which (a) the ‘additional’glutamine which accumulates rapidly during ¹⁵N-ammonium feedingis heavily amide-labelled from the outset, and (b) of the glutaminealready present in the roots, only a small proportion (c. 10–15%)incorporates ¹⁵N during the initial 60–80 min of ¹⁵N-ammoniumfeeding, the remainder (c. 85–90%) remaining essentiallyunlabelled over this period. The latter is assumed to be locatedin the vacuoles. Even though prior N-starvation stimulated ammonium net uptakemarkedly, the data were not of sufficient quality to show whetherthe relative sizes of the extra-vacuolar and vacuolar glutaminefractions were altered by this treatment. For that reason itwas not possible to determine whether cytosolic glutamine hasa role in regulating N-absorption. Key words: Subcellular compartmentation, regulation, N-absorption