Factors Affecting Polyamine Accumulation in Barley (Hordeum vulgare L.) Leaf Sections during Osmotic Stress

Turner, L. B. and Stewart, G. R. 1988. Factors affecting polyamineaccumulation in barley (Hordeum vulgare L.) leaf sections duringosmotic stress.-J. exp. Bot. 39: 311–316. Polyamine concentrations in peeled leaf sections of Hordeumvulgare were unaffected by decreases in leaf water potentialif osmotic adjustment took place and leaf turgor was maintained.Putrescine accumulation occurred concomitantly with a decreasein leaf turgor. Increases in the order of 3-to 4-fold were observed.An apparently greater putrescine accumulation (7-fold) occurredwhen leaf sections were osmotically stressed in the presenceof exogenous phosphate ions. This was the result of water lossfrom the tissue and the large decline which occurred in theputrescine levels of control tissue sections incubated withphosphate ions. Putrescine accumulation was at its maximum after4 h osmotic stress. In contrast, proline accumulation took placebetween 4 h and 24 h after the imposition of osmotic stress. Key words: Hordeum vulgare, osmotic stress, polyamine     

Polyamine Content in Relation to Embryo Growth and Dedifferentiation in Barley (Hordeum vulgare L.)

Putrescine, spermidine, and spermine content were analysed inzygotic embryos of barley (Hordeum vulgare L.). Changes in polyaminecontent were observed during zygotic embryo growth. In two cultivars,‘Bomi’ and ‘Golden Promise’, the totalpolyamine content in the embryos was 2.6–2.9 nmol mg^–1fresh weight 10 d after anthesis, the highest content observed.It dropped to 1.3 nmol mg^–1 fresh weight 14 d after anthesis.This drop was caused by decreases in all three polyamine concentrations.From 14 to 35 d after anthesis the putrescine content continuedto decrease while the spermidine and spermine content increased,thus the total polyamine content remained constant until 35d after anthesis. The mutant ‘Ris? 1508’ showeda constant polyamine content around 1.3 nmol mg^–1 freshweight from 14 to 35 d after anthesis. The polyamine patternwas conserved in all three lines throughout the period of investigationshowing a spermidine content higher than putrescine contentwhich was, in turn, higher or equal to the spermine content.The polyamine content measured as nmol µg^–1 proteindecreased from 14 to 21 d post anthesis in all three lines,because the protein content (µg mg^–1 fresh weight)increased during the period. In dedifferentiating zygotic embryoscultured in vitro the putrescine content (nmol mg^–1 freshweight) rose by a factor of nine and the spermidine contentdoubled within the first week of cultivation, whereas sperminecontent did not change. For embryoderived calli a repeated patternof change in polyamine content was observed throughout the subculturingperiod. Key words: Polyamines, Hordeum vulgare L., embryo development     

Response of Cultured Embryos of Phaseolus vulgaris and Hordeum vulgare to Farnesol

Excised embryos of Phaseolus vulgaris incubated in a mediumcontaining 10 mg dm^–3 farnesol showed enhanced root growthwhereas the leaves remained rudimentary At lower concentrationsof exogenous farnesol normal leaf development occurred and rootgrowth was comparable to untreated cultures. Enhanced root growthalso occurred when excised embryos of Hordeum vulgare were treatedwith farnesol but only at 10 mg dm^–3 and this treatmentdid not prevent leaf growth X-ray micro-probe analysis of leavesrevealed an increased phosphorus content in P vulgaris and adecreased sulphur content in H vulgare in comparison to untreatedplants. Hordeum vulgare L., barley, Phaseolus vulgaris, bean, embryo culture, farnesol, X-ray microprobe analysis, root growth     

Stomata and Mesophyll Characteristics of Barley Leaf as Affected by Light: Stereological Analysis

The anatomical structure of the second leaf blade of barley{Hordeum vulgare L. cv. Koral) was studied in plants exposedto a photosynthetic photon flux density (PPFD) of 200 µmolm^–2 s^–1 compared with those grown under 25µmolm^–2–11. Design-based stereological methods wereused for the estimation of various leaf anatomical characteristicssuch as mesophyll volume, proportion of intercellular spaces,number of mesophyll cells, mean mesophyll cell volume, and internalleaf surface area. The structure of the mesophyll was more affectedby different levels of PPFD than were the stomatal characteristics.Increased PPFD produced thicker leaves with a larger mesophyllvolume having a higher number of less elongated mesophyll cellsand a larger internal leaf surface area. Key words: Hordeum vulgare, light effect, mesophyll, stereology, stomata     

Regulation of Storage Protein Synthesis by Sulphur and Nitrogen Nutrition in Cultured Immature Caryopses of Barley

Techniques are described for the culture of developing barley(Hordeum vulgare L.) caryopses. Over a 7 d period in culturethe dry weights and the amounts of starch and protein increasedby at least twofold. Growth was sustained for at least 20 d.The effects of glutamine and cysteine on the amount and compositionof the hordein storage proteins were also studied. Glutaminestimulated total hordein accumulation but caused a disproportionateincrease in the amount of the S-poor ‘C’ hordeinswhen supplied at 100 mol m^–3. Addition of cysteine at1·0 mol m^–3 did not increase the amount of Srich‘B’ hordeins. The results suggest that althoughisolated caryopses are able to take up sucrose and glutamineand convert them to starch and protein there is some limitationin their ability to convert externally supplied cysteine intoproteins. Key words: Hordeum vulgare L., Caryopses, Glutamine, Cysteine, Storage proteins     

Accumulation of Pigments during the Greening of Etiolated Seedlings of Hordeum vulgare L.

The pigment changes that occur during transformation of etioplaststo fully developed chloroplasts have been studied in seedlingsof barley (Hordeum vulgare L.) by greening with white lightof low (15–25 µmol m^–2 s^–1) and medium(150 µmol m^–2 s^–1) intensity. At least 24h longer was required in the low light regime for the same concentrationof pigment to be accumulated in the seedlings. The increasein pigment content was mainly due to the synthesis of chlorophyllsa and b. Of the carotenoids present, the increases in the levelsof neoxanthin and, especially, ß-carotene were muchgreater than those observed for the other carotenoids. Levelsof lutein also increased but this change was small by comparisonto those observed for neoxanthin and ß-carotene. Inthe long-term the concentration of violaxanthin remained unalteredalthough significant transient changes were recorded. The levelsof antheraxanthin and zeaxanthin were markedly reduced duringgreening. The rate of pigment synthesis decreased with increasingcell age, i.e. from the base to the tip of the primary leaf.Overall, carotenoid levels increased by approximately 100% atthe base of the seedling but hardly at all at the tip. Key words: Hordeum vulgare, carotenoids, violaxanthin-cycle, etiolation     

Drought Influences the Activity of Enzymes of the Chloroplast Hydrogen Peroxide Scavenging System

Smirnoff, N. and Colomb?, S. V. 1988. Drought influences theactivity of enzymes of the chloroplast hydrogen peroxide scavengingsystem.—J. exp. Bot. 39: 1097–1108. The effect of drought on the activity of ascorbate peroxidase(AP), glutathione reductase (GR) and monodehydroascorbate reductase(MDAR) in leaves of barley (Hordeum vulgare) and tef {Eragrostistef) was studied. These enzymes are components of the chloroplasthydrogen peroxide scavenging system. Severe leaf water deficit(<–30 M Pa) resulted in increased activity (leaf dryweight basis) of GR and MDAR in barley and of AP and MDAR intef. The specific activity of all the scavenging enzymes wasgreater in droughted plants. The activities (dry weight basis)of two ‘control’ enzymes, malate dehydrogenase (barley)and phosphoenolpyruvate carboxylase (tef), not directly involvedin the scavenging system, were not affected by drought. These data suggest that drought may cause an increase in thecapacity of the hydrogen peroxide scavenging system and thatit may, therefore, increase the rate of hydrogen peroxide formationin chloroplasts. Key words: Water stress, hydrogen peroxide, enzyme activity     

Osmotic Adjustment and Stomatal Response to Water Deficits in Maize

A pot experiment was carried out using five maize {Zea maysL.) cultivars under three soil moisture levels (MPa 0 to –0.05,–0.3 to –0.9 and –1.2 to –1.5) to investigatethe effects of water deficits on osmotic adjustment and stomatalconductance. The degree of leaf rolling and the sugar and nutrientconcentrations in leaf cell sap were measured. Leaf water potential and osmotic potential decreased and stomatalconductance decreased with increasing water deficits. Stomatalconductance correlated positively with leaf water potentialand osmotic potential. Degree of leaf rolling was lower in cultivarswhich maintained higher turgor. Osmotic adjustment of 0.08 to0.43 MPa was found under the lowest soil moisture level in fivecultivars used. Sugar and K were the major osmotic substancesin the maize plant. Sugar, K and Mg concentrations increasedunder water deficit, and correlated negatively with a decreasein osmotic potential. Key words: Zea mays L., leaf water relations, leaf rolling, osmotic adjustment, stomatal conductance, water deficit     

In vivo Nitrate Reductase Activity in Barley (Hordeum vulgare L.) during Ear Development

Experiments were conducted during the 1974–75 and 1975–76winter season with the barley (Hordeum vulgare L.) cultivarJyoti. From amongst the various plant parts, the flag leaf bladehad higher in vivo nitrate reductase (NR) activity than thelower two leaf blades, glumes, and grains. However, the potentialof a plant part to reduce NO₃^– is a function of its freshweight and the NR per unit fresh weight. On this basis, thesecond and third leaf blades could reduce more NO₃^– thanthe flag leaf blade. N fertilizer application resulted in enhancementof the activity of the leaf blades alone. N fertilizer appliedduring the reproductive phase was taken up and assimilated bythe various plant parts. The studies suggest that, even whenthe fertilizer is applied at optimum levels for obtaining maximumyields, the upper leaf blades have sub-optimal NR activity andthat there is a likelihood of either a preferential flow ofNO₃^– to the leaf blades or transnational barriers to NO₃^–movement to the ear.     

Localization of ATPase Activity on the Plasmalemma of Scutellar Epithelial Cells of Germinating Barley (Hordeum vulgare L.)

Chaffey, N. J. and Harris, N. 1985. Localization of ATPase activityon the plasmalemma of scutellar epithelial cells of germinatingbarley (Hordeum vulgare L.).—J. exp. Bot 36: 1612–1619. ATPase activity has been localized at an ultrastructural levelin the absorptive region of the scutella of germinating barley(Hordeum vulgare L.). The enzyme is localized on the plasmalemmaof the epithelial cells. Using the Gomori reaction the depositionof reaction product on the plasmalemma, which is dependent uponthe presence of supplied ATP, was precluded or reduced by theinhibitors orthovanadate, mercuric chloride and DCCD, whilstß-glycerophosphate would not act as an alternativesubstrate. The mitochondria demonstrated phosphatase activitywith both ATP and ß-glycerophosphate as substrate.The results are discussed in relation to the active uptake ofmetabolites by the scutellum during germination and the structuralmodification of the plasmalemma of the epithelial cells to formplasmatubules. Key words: ATPase, Hordeum vulgare L., localization (ultrastructural)     

Temperature-stress Pretreatment in Barley Anther Culture

Methods of pretreating anthers at different temperatures priorto culture have been tested, with respect to pollen-callus productionand plant regeneration, in Hordeum vulgare cv. Sabarlis. For callus production, pretreatment of excised spikes (in sealedPetri dishes) was more effective than pretreatment of excisedtillers (in water or in polythene) at both 4 and 25 °C.Pretreatment of individual anthers at these temperatures wasdeleterious. Greater callus yields resulted from pretreatmentat 4 than at 25 °C, both for spikes and tillers, 3–5weeks being required for maximal yields at 4 °C and 3–5days at 25 °C. At 4 °C, a shorter pretreatment was requiredfor spikes than for tillers. Pretreatment of spikes was alsomore effective at 4 than at 7, 14 or 20 °C. Pretreatmentof individual spikelets at 4 °C was as effective as thatof whole spikes. For plant regeneration, calluses derived from pretreatment ofspikes were more effective than those derived from pretreatmentof tillers. More plants resulted from pretreatment at 4 thanat 25 °C, both for spikes and tillers. Maximal pretreatmenttimes for plant regeneration generally exceeded those for callusproduction. Following spike pretreatment at 4 °C the maximumfor plant regeneration exceeded that for callus production byabout 2 weeks. With this optimal pretreatment approximately60 per cent of the calluses gave rise to plantlets. Among this60 per cent, for every three calluses giving albinos, two gavegreen plantlets, equivalent to five green plantlets on averagefor every 100 anthers (= two spikes) cultured. The ratio ofgreen to albino plantlets was lower for all other pretreatments. Hordeum vulgare L., barley, anther culture, pollen callus, pollen plant-production, temperature stress     

A Comparative Study of Early Seed Development in Genotypes of Barley and Rye

Early seed development was studied in 17 genotypes of barley,Hordeum vulgare L., and 11 genotypes of rye, Secale cerealeL. The numbers of cells and nuclei in the embryos and endospermsof developing seeds were scored daily for 5 days after selfpollination. For embryos, the mean cell doubling times variedfrom 9.2–12.9 h for barley and 15.7–22.7 h for rye.Endosperm mitotic cycle times of both species were shortestover the first 24 h after pollination but then became longer.A non-linear correlation was found between the number of embryocells and the number of endosperm nuclei in barely and rye andis similar to that for other members of the Triticeae. Hordeum vulgare L., Secale cereale L., barley, rye, embryo, endosperm, mean cell doubling time     

Water uptake resumption following soil drought: a comparison among four barley genotypes

Soil water resulting from episodic growing season rainfall evaporatesrapidly in semi-arid regions. Plants may mnot benefit from suchwater additions if near-surface roots are unable to resume wateruptake rapidly following periods of soil water deficit. Ourobjectives were to develop a means of quantifying root uptakeresponses in the upper soil layer following rewetting aftersoil water deficit, and to evaluate the existence of genotypicdifferences among four diverse barley (Hordeum vulgare L.) genotypesin this regard. Plants were grown in replicate soil columnshaving hydraulically isolated surface and subsoil layers, andinstrumented with time-domain reflectometry (TDR) waveguides.The upper 0.05 m soil layer was allowed to dry to —1.8to —3.0 MPa for 10-14 d, during which time subsoil wetnesswas maintained at about —0.6 to —0.7 MPa. The time-courseof soil water uptake was monitored at 0.5 h intervals followingrewetting of the surface layer. Substantial water uptake began1 d after rewetting following 10 d, and 2-3 d after rewettingfollowing 14 d of water deficit. Rate of water uptake was morerapid in response to a second rewetting 5-7 d later. Consistentgenotypic responses in terms of cumulative water uptake on awhole plant and leaf area-specific basis were observed duringeach trial. These results have application to evaluating droughthardiness and interspecific competitive ability under semi-aridconditions, and to investigations of root physiological andmorphological changes that contribute to recovery from waterdeficit Key words: Hordeum vulgare, root water uptake, soil water deficit, time-domain reflectometry     

Inhibition of Sugar and Salt Elimination by Glands with the Amino Acid Analog p-Fluorophenylalanine

The amino acid analog p-fluorophenylalanine (FPA) inhibitedsugar and K⁺ secretion by nectary glands. FPA specifically reducedthe net excretion of Na⁺ and Cl^– by the salt glands ofthe halophyte Limonium vulgare and ³⁶Cl^–excretion by theglands of the pitcher walls of the carnivorous plant Nepenthes.Net uptake and net accumulation of Na⁺ and Cl^– by Limoniumleaf tissue and ³⁶Cl^– accumulation in Nepenthes pitchertissue were much less inhibited than excretion. The resultsare discussed in relation to literature reporting similar specificeffects of FPA on transport of ions from the symplast of barleyroots into the dead xylem elements. Limonium vulgare, Nepenthes hookeriana, salt-glands, excretion, p-fluorophenylalanine     

Zinc stress induces changes in apoplasmic protein content and polypeptide composition of barley primary leaves

Excessive zinc in the rooting medium, and consequently increasingzinc content in the shoot of barley (Hordeum vulgare) seedlings,strongly affected the protein content and the polypeptide compositionof the leaf apoplasm. In contrast, only small changes In polypeptide composition (in the IEF range of pH 4–8 and between14 and 80 kDa) were detected In mesophyll and epidermis protoplasts.The zinc stress-induced changes In apoplasmic protein contentwere analysed in detail. The apoplasmic protein content Increasedby more than 3-fold when the zinc concentration in the mediumwas increased from 0.02 to about 200 µmol l^–1; athigher zinc concentrations no further changes occurred. Theincrease in apoplasmic protein content was due both to a generalincrease in abundance of the most dominant apoplasmic polypeptidesand to a pronounced increase in the abundance of specific polypeptidesas monitored in electrophoretic separations or by measuringthe activity of apoplasmic enzymes. The largest induction wasseen for four apoplasmic polypeptides of molecular masses 16,23, 27, and 28 kDa with as yet unknown function. Key words: Apoplasm, barley, leaf, peroxidases, potypeptide, zinc stress     

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     

Water Relations of Chromium VI Treated Bush Bean Plants (Phaseolus vulgaris L. cv. Contender) under both Normal and Water Stress Conditions

The effect of Chromium VI on leaf water potential (^w), solutepotential (^a), turgor potential (^p) and relative water content(RWC) of primary and first trifoliatc leaves of Phaseolus vulgarisL. was studied under normal growth conditions and during anartificially induced water stress period in order to establishthe possible influence of this heavy metal on the water stressresistance of plants. Plants were grown on perlite with nutrientsolution containing 0, 1•0, 2•5, 5•0 or 10•0µg cm^–3 Cr as Na₂Cr₂O₇.2H₂O. The effect of Cr onwater relations was highly concentration dependent, and primaryand first trifoliate leaves were affected differently. The growthreducing concentrations of Cr (2•5, 5•0 and 10•0µg cm^–3) generally decreased _s and _w and increased_p in primary leaves. The 1•0 µg cm^–3 Cr treatmentdid not affect growth, but altered water relations substantially:in primary leaves _w and _p were increased and _s decreased, whilein trifoliate leaves the effect was the opposite. All Cr treatedplants resisted water stress for longer than control plants.The higher water stress resistance may be due to the lower _sand to the increased cell wall elasticity observed in Cr VItreated plants. Key words: Phaseolus vulgaris, Chromium VI, water stress, Richter plot     

Nitrate Accumulation and its Relation to Leaf Elongation in Spinach Leaves

The leaf elongation rate (LER) of spinach leaves during theday was twice that during the night when grown at a photon fluxdensity of 145 µmol m^–2 s^–1. All leaves showedthe same LER-pattern over 24 h. Due to low turgor, LER was lowin the afternoon and in the first hours of the night until wateruptake restored full turgor. Osmotic potential remained constantdue to increased nitrate uptake and starch degradation in thisperiod. LER increased to high rates in the second part of thenight and in the morning. The lower rate in the dark comparedto the light was not caused by the lower night temperatures,as increased photon flux density during growth resulted in equalrates in the light and the dark. Increased relative humiditydecreased LER and afternoon rates were most sensitive to waterstress. A ‘low light’ night period did not changeLER-pattern during the night or on the following day. We concludethat nitrate is not an obligatory osmoticum during the nightand can be exchanged for organic osmotica without decreasingLER. During the night the turgor is first restored by increasingwater uptake, nitrate uptake and starch degradation. This resultedin increased leaf fresh weight in this period. Thereafter, elongationincreased by simultaneous uptake of nitrate and water. Nitrateconcentration was, therefore, constant in the older leaves.In the younger leaves nitrate concentration increased to replacesoluble carbohydrates. The vacuoles of the old leaves were filledwith nitrate before those of the young leaves. Key words: Spinacia oleracea L., nitrate accumulation, osmotic potential, organic acids     

The In Vitro Culture of Immature Barley Embryos on Different Culture Media

Immature barley embryos (Hordeum distichum var. Julia) of between0•20 and 0•80 mm in length, were isolated from thedeveloping grain and cultured in vitro on various culture media.The subsequent development of the embryos was followed overa period of weeks, and where germination ensued the growth rateof shoot and root meristems was compared with in vivo germinationrates. Various growth media were assessed for their abilityto support normal development of immature embryos. A numberof published media failed to support satisfactory developmentof young embryos. The addition of 1–15 per cent coconutmilk to Norstog's Medium I (mineral + vitamin solns) enhancedembryo development and lowered the threshold of viability fromembryos of 0•50 mm in length to 0•35 mm. Althoughin many cases germination ensued, embryo development was largelyabnormal. A slightly greater enhancement of growth was achievedwith 0•05–0•30 per cent casein hydrolysate asthe growth medium supplement, although abnormal developmentwas not eliminated. A further lowering of the viability thresholdto include embryos of 0•25 mm in length was obtained bycombining 2•7 mM glutamine with the casein hydrolysatesupplement. Normal development and germination of embryos assmall as O25 mm was however obtained on Norstog's Medium JJand the results were reproduced in four additional if . distichumvarieties. In each case the critical threshold of viabilitywas found to lie in embryos of 0•20–0•30 mmin length.     

Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare

Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m^–3‘control’ and 100 mol m^–3) in the presenceof 6.5 mol m^–3 K ⁺. Between 16 and 31 d after germination,before stem elongation started, xylem sap was collected by useof a pressure chamber. Collections were made at three differentsites on leaves 1 and 3: at the base of the sheath, at the baseof the blade, i.e. above the ligule, and at the tip of the blade.Phloem sap was collected from leaf 3 at similar sites throughaphid stylets. The concentrations of K ⁺, Na⁺, Mg2⁺ and Ca²⁺were measured. Ion concentrations in xylem sap collected at the base of leaves1 and 3 were identical, indicating there was no preferentialdelivery of specific ions to older leaves. All ion concentrationsin the xylem decreased from the base of the leaf towards thetip; these gradients were remarkably steep for young leaves,indicating high rates of ion uptake from the xylem. The gradientsdecreased with leaf age, but did not disappear completely. In phloem sap, concentrations of K⁺ and total osmolality declinedslightly from the tip to the base of leaves of both controland salt-treated plants. By contrast, Na⁺ concentrations inphloem sap collected from salt-treated plants decreased drasticallyfrom 21 mol m^–3 at the tip to 7.5 mol m^–3 at thebase. Data of K/Na ratios in xylem and phloem sap were used to constructan empirical model of Na⁺ and K⁺ flows within xylem and phloemduring the life cycle of a leaf, indicating recirculation ofNa⁺ within the leaf. Key words: Hordeum vulgare, xylem transport, phloem transport, NaCl-stress