Effect of glucose level on the batch production of β-1,3-glucanase by Trichoderma harzianum and cell growth

The effect of initial glucose concentration on g-1, 3-glucanase production by Trichoderma harzianum NCIM 1185 and cell growth was studied in a batch stirred tank bioreactor. The initial glucose level was varied between 5 g/dm³ and 100 g/dm³. A maximum g-1,3-glucanase production of 0.820 U was obtained using the fully optimized medium which had an initial glucose level of 8.63 g/dm³ and thereafter there was a steady decrease in g-1,3-glucanase production. No g-1,3-glucanase production was observed beyond initial glucose concentrations of 40 g/dm³ which suggests a possible catabolic repression on the enzyme synthesis. The inhibitory effect of increased initial glucose concentrations on cell growth has been studied and the Luong and the Han-Levenspiel models were used to explain the mechanism of inhibition.     

Isolation, Culture, and Plant Regeneration of Protoplasts of Two Shrubby Oxalis Species from South America

Protoplasts were successfully isolated from internodal callustissues of both Oxalis glaucifolia and O. rhombeo-ovata whenthey were digested in a solution containing 0.1% (w/v) MacerozymeR-10, 0.5% (w/v) cellulase Onozuka R-10 and 0.3 mmol m^–3sucrose. Protoplasts proliferated to give cell colonies on Gamborget al.'s B5 medium supplemented with 0.3 mmol m^–3 mannitol,0.5 mg dm^–32, 4-D, and 2.0 mg dm^–3 kinetin. Calluswas produced upon transfer of cell colonies to Murashige andSkoog medium containing 2.0 mg dm^–3 l-naphthaleneaceticacid (NAA) and 0.1 mg dm^–3 kinetin for O. glaucifolia,or with 5.0 mg dm^–3 NAA and 0.5 mg dm^–3 6-benzylaminopurine,for O. rhombeo-ovata. Plants were regenerated from O. glaucifoliaprotoplasts on a medium containing 0.1 mg dm–3 NAA, 1.0mg dm^–3 kinetin and 1.0 mg dm^–3 gibberellic acid,but only vascular nodules were differentiated by O. rhombeo-ovataprotoplast-derived calli. Key words: Tissue culture, protoplasts, plant regeneration, Oxalis spp     

Direct Organogenesis from Petiole and Thin Cell Layer Explants in Sugar Beet Cultured In Vitro

Detrez, C., Tetu, T., Sangwan, R. S. and Sangwan-Norreel, B.S., 1988. Direct organogenesis from petiole and thin cell layerexplants in sugar beet cultured in vitro.—J. exp. Bot.39: 917–926. Plant regeneration was obtained by direct bud formation frompetiole as well as from thin cell layer explants taken fromsugar beet (Beta vulgaris L.) plants grown in vitro. The budswere mainly induced in the blade-petiole transition zone ofthe explants. High frequency bud regeneration was observed inpetiole and thin layer explants of 10 different breeding linesof sugar beet tested. Organogenesis resulted when petiole explantsexcised from 8-d-old seedlings grown on half-strength Murashigeand Skoog medium (MS) containing 3.0 mg dm^–3 naphthaleneacetic acid (NAA), 3.0 mg dm^–3 6-benzylaminopurine (BAP)and 1.0 mg dm^–3 2, 3, 5, triiodobenzoic acid (TIBA) werecultured on MS with 3.0 mg dm^–3 NAA and 3.0 mg dm^–3BAP. Thin cell layer strips isolated from shoot apices culturedon MS medium supplemented with 0–9 mg dm^–3 BAP or1.0 mg dm^–3 indolebutyric acid (IBA) formed adventitiousbuds on MS medium containing 0–5 mg dm^–3 NAA + 5.0mg dm^–3 BAP. Histological studies confirmed the sub-epidermalorigin of shoots. Key words: Beta vulgaris, direct organogenesis, in vitro culture, petiole, regeneration, thin cell layer     

Scanning Electron Microscope Studies of Multiple Shoot Production by Meristem Tip Cultures of Solarium x curtilobum

A meristem tip culture isolated from Solatium x curtilobum cv.Mallku produced a limited amount of callus at the cut surfaceof the explant when cultured on Murashige and Skoog medium containing1 mg dm³ 6--{dimethylallylamino)purine and O.01 mg dm³ naphthaleneacetic acid. A single sheet of cuticle-like material develops on localizedregions of the callus surface and the cells beneath it decreasein mean cell size. These meristematic centres develop into fullyorganized shoot meristems, and each will grow out into a leafyshoot when the culture is transferred to growth medium containingo.1 mg dm³ gibberellic acid (GA₃) as the only growth hormone.This system has considerable value in the rapid clonal propogationof Solanum species, since as many as fifty shoots can be producedfrom a single meristem tip culture.     

Effects of Colchicine, Vinblastine, Cytochalasin B and Phalloidin on the Seismonastic Movement of Mimosa pudica Leaf and on Motor Cell Ultrastructure

Fleurat-Lessard, P., Roblin, G., Bonmort, J. and Besse, C. 1988.Effects of colchicine, vinblastine, cytochalasin B and phalloidinon the seismonastic movement of Mimosa pudica leaf and on motorcell ultrastructure.—J. exp. Bot. 39: 209–221. Colchicine at 1 x 10^–3 mol dm^–3 does not affectthe seismonastic movement of Mimosa pudica leaves but disruptsmicrotubules in motor cells. Vinblastine at 5 x 10^–3 moldm^–3 does not affect this movement and partly disruptsmicrotubules. Vinblastine at 1 x 10^–4 mol dm^–3 alwaysdisrupts microtubules, even after a 12 h reversibility whenthe movement is restored. These drugs, applied at the same respectiveconcentrations, do not alter cytoplasmic and vacuolar fibrils.Cytochalasin B and phalloidin alter the seismonastic movementof Mimosa leaves when applied at concentrations of 1.25 x 10^–3and 2.4 x 10^–4 mol dm^–3 respectively. These drugs,used at the same respective concentrations, also affect themotor cell structure and, in particular, modify the arrangementand the structure of the fibrils but they do not destroy themicrotubules. These data suggest that microtubules are not directly involvedin the seismonastic reaction whereas fibrils, formed by thin(3.0 nm wide) filaments, may be implicated in this reaction. Key words: Colchicine, cytochalasin B, phalloidin, Mimosa pudica, motor cells, vinblastine     

The Interaction of Genotype, Explant and Media on the Regeneration of Shoots from Complex Explants of Brassica napus L.

The relative importance of explant type, genotype and growthregulator regime in the determination of shoot regenerationfrequencies from complex explants of Brassica napus L. has beenevaluated. Cotyledon, hypocotyl and stem sections taken fromone spring (Westar) and three winter (Ariana, Cobra, Libravo)varieties of B. napus were cultured on three different growthregulator regimes, 0.5 mg dm^–3 NAA + 2.0mg dm^–3BAP, 0.5 mg dm^–3 NAA + 4.0mg dm^–3 BAP and 1.0mgdm^–3 NAA + 4.0mg dm^–3 BAP. The most significanteffects on shoot regeneration were due to explant type and variety.The regeneration from stem segments was not only two to threetimes higher than from hypocotyls or cotyledons, in all varieties,but the response was also more uniform across the varieties.The explant effect accounted for 44–95% of the regenerationresponse. In contrast, the contribution of growth regulatorregime was negligible. Although the growth regulator regimeas an independent effect was unimportant, regeneration fromboth Ariana and Libravo was significantly affected by the interactionof genotype with growth regulator regime. The importance ofboth the high shoot regeneration frequency from stem segmentsand the relative uniformity of response across the four testedgenotypes is discussed with respect to the potential benefitsof using this explant source in Agrobacterium-based transformationexperiments. Key words: Brassica napus, regeneration, genotype, tissue culture, complex explant     

Combined Effect of Some Growth Regulators on Growth and Gametangial Formation in the Liverwort Riccia gangetica Ahmad

The present work deals with the effect of IAA-kinetin, IAA-GA³and GA³-ABA interactions on growth and gametangial formationin Riccia gangetica in vitro. Inhibitory effect of high concentrationof IAA on vegetative growth is overcome by the co-addition ofkinetin. The best response in terms of fresh and dry weightyields of thalli is obtained by a combination of 10^–5mol dm^–3 kinetin+ 10^–7 mol dm^–3 IAA. Interactionof IAA and kinetin has an additive effect on archegonial formation.Co-addition of IAA and GA³ decreases production of archegoniaand antheridia as compared to those produced in response toIAA and GA³ alone, respectively. Combination of GA³ and ABAreduces vegetative growth, as well as the number of anthendiaand archegonia. Key words: Riccia gangetica, growth, growth regulators, gametangial formation     

Production of Potato Spindle Tuber Viroid (PSTV) by Large Scale Fermentation of PSTY-Infected Potato Cell Suspension Cultures

Berlin, J., Wray, V., Forche, E., Reng, H.–G , Schler,H, Luckinger, R. and Mhlbach, H.–P. 1985. Production ofpotato spindle tuber viroid (PSTV) by large scale fermentationof PSTV–infected potato cell suspension cultures.—J.exp. Bot 36: 1985–1995. Cell suspension cultures of Solatiumdemissum, infected with the potato spindle tuber viroid (PSTV),were scaled up to volumes of up to 800 dm³ to provide sufficientand uniform plant material for subsequent studies on viroidbiosynthesis. Here we describe the technological aspects ofproducing the required amounts of biomass and viroid. The cells,which had been maintained on a medium containing expensive coconutmilk, were first adapted to rapid growth on the less expensiveB5–medium. The physiological state of the cells was monitoredby in vivo ³¹P–NMR spectroscopy Under the chosen conditionsthe scale–up from 10 dm³ inoculum from shake flasks tothe harvest of the 800 dm³ stirred fermenter lasted 38 d andprovided 112 kg biomass. Growth characteristics and viroid productionin shake flasks and large bioreactors were rather similar. Gelelectrophoretic analysis of isolated nucleic acids using silverstaining and Northern blot hybridization revealed a PSTV–contentof approximately 700 µg PSTV per kg fresh mass of culturedcells. Key words: Solanum demissum, plant cell cultures, potato spindle tuber viroid, biomass production, fermentation, in vivo ³¹P-NMR     

Cyclic Nucleotides and In Vitro Plant Cultures: I. INDUCTION OF ORGANOGENESIS IN TOBACCO (NICOTIANA TABACUM CALLUS CULTURES

Mangat, B. S. and Janjua, S. 1987. Cyclic nucleotides and invitro plant cultures. I. Induction of organogenesis in tobacco(Nicotiana tabacum) callus cultures.—J. exp. Bot. 38:2059–2067. The possibility that cyclic nucleotides have a mediatory rolesimilar to cytokinins in plant tissue cultures was examined.Calli obtained from tobacco pith tissue were incubated on growthmedia supplemented with either cyclic AMP, cyclic GMP, adenosineor guanosine, in concentrations ranging from (mg dm^–3)0 to 2·0 together with 2·0 mg dm^–3 of IAA.Results were compared with identical calli grown on media containingcomparable amounts of kinetin and IAA. Increase in callus growthwas observed on all media containing cyclic AMP, cyclic GMP,adenosine, guanosine or kinetin. Adenosine or guanosine didnot promote organogenesis. Low concentrations (0·02 and0·05 mg dm^–3) of kinetin stimulated extensive rootdevelopment. Some root formation was also elicited with higheramounts of cyclic AMP (0·1 and 0·2 mg dm^–3)or cyclic GMP (0·2 and 0·5 mg dm^–3). Bothkinetin and cyclic GMP promoted shoot differentiation. However,in contrast to kinetin, cyclic GMP induced organogenesis atlower concentrations (0·02 and 0·1 mg dm^–3).The addition of 2·0 mg dm ^–3 of cyclic AM P toIAA-free growth media elicited shoot differentiation. This wasalso the case with a similar concentration of kinetin or cyclicGMP. Results suggest cytokinin activity for the two cyclic nucleotides. Key words: Tobacco, Nicotiana tabacum, tissue culture, cyclic nucleotides, cyclic AMP, cyclic GMP organogenesis     

Response to Waterlogging and Differing Sensitivity to Divalent Iron and Manganese in Clones of Dactylis glomerata L. derived from Well-drained and Poorly-drained Soils

Clonally propagated plants of Dactylis glomerata derived froma well-drained, heavily grazed cliff habitat (clone L) and froman undergrazed poorly-drained soil (clone A) were tested forwaterlogging tolerance in soil-culture. Water-logging did notaffect the two clones differentially, a result, which contrastedstrongly with that of a previous experiment in which simulatedgrazing (clipping to 20 cm) unexpectedly caused clone A to beless tolerant of waterlogging than clone L. Maximum leaf andleaf sheath length was reduced more by water-logging in cloneL than in clone A (P < 0.05). In solution-culture when providedwith factorial combinations of 0.5, 5 and 50 mg dm^–2 ofFe²⁺ and Mn²⁺ the shoot dry weight yield of the dry-soil clonewas reduced more than that of the wet-soil clone by 50 mg Fedm^–3 irrespective of Mn²⁺ concentration (P < 0.01)but the reduction of growth was less at higher Mn²⁺ concentrations.Fifty milligrams of Mn²⁺ dm^–3 reduced the growth of thedry soil clone but increased the growth of the wet soil clonewith Fe²⁺ at 5 mg dm^–2 (P < 0.05). Iron at 0.5 mg dm^–2was suboptimal for shoot growth of both clones at any levelof Mn²⁺ and caused more severe leaf chlorosis in the wet soilclone. Leaf tissue of clone L contained more iron than thatof clone A after waterlogging (P < 0.01) but in solutionculture, though increasing iron from 0.5 to 50 mg dm^–3almost doubled leaf iron content (P < 0.001), the interactionClones x Mn x Fe just failed to reach significance at P <0.05. The manganese content of leaf tissue from the two clonesvaried differently in response to solution manganese (Clonesx Mn P < 0.01), clone A showing a slightly greater increaseof manganese content at high solution concentration. Iron at50 mg dm^–3 suppressed Mn uptake (Mn x Fe, P < 0.001)in both clones. The two clones thus show marked environmentaladaptation to the chemistry of wet and dry soils. Dactylis glomerata, Cocksfoot grass, Orchard grass, waterlogging, iron, manganese, toxicity, deficiency, ecotypes     

Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature

Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO₂ concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO₂ concentrationduring growth was increased from 160 to 990 mm³ dm^–3.Photosynthetic rates of canopies grown at 330 and 660 mm³ CO₂dm^–3 were similar when measured at the same CO₂ concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO₂ concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm³ CO₂ dm^–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm³ CO₂ dm^–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO₂ concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO₂ aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO₂ limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO₂ concentration, soybean, canopy photosynthesis     

Effects of CO2 and Photosynthetic Photon Flux on Yield, Gas Exchange and Growth Rate of Lactuca Sativa L. 'Waldmann's Green'

Knight, S. L. and Mitchell, C. A. 1988. Effects of CO₂ and photosyntheticphoton flux on yield, gas exchange and growth rate of Lactucasativa L. ‘Waldmann’s Green'.—J. exp. Bot.39: 317–328. Enrichment of CO₂ to 46 mmol m^–3 (1 000 mm³ dm^–3)at a moderate photosynthetic photon flux (PPF) of 450 µmolm^–2 s^–1 stimulated fresh and dry weight gain oflettuce leaves 39% to 75% relative to plants at 16 mmol m^–3CO₂ (350 mm³ dm^–3). Relative growth rate (RGR) was stimulatedonly during the first several days of exponential growth. ElevatingCO₂ above 46 mmol m^–3 at moderate PPF had no further benefit.However, high PPF of 880–900 µmol m^–2 s^–1gave further, substantial increases in growth, RGR, net assimilationrate (NAR) and photosynthetic rate (Pn), but a decrease in leafarea ratio (LAR), at 46 or 69 mmol m^–3 (1000 or 1500 mm³dm^–3) CO², the differences being greater at the higherCO₂ level. Enrichment of CO₂ to a supraoptimal level of 92 mmolm^–3 (2000 mm³ dm^–3) at high PPF increased leaf areaand LAR, decreased specific leaf weight, NAR and Pn and hadno effect on leaf, stem and root dry weight or RGR relativeto plants grown at 69 mmol m^–3 CO₂ after 8 d of treatment.The results of the study indicate that leaf lettuce growth ismost responsive to a combination of high PPF and CO₂ enrichmentto 69 mmol m^–3 for several days at the onset of exponentialgrowth, after which optimizing resources might be conserved. Key words: Photosynthesis, relative growth rate, CO₂ enrichment     

The Relationship Between the Rates of Carbon Transport and of Photosynthesis in Tomato Leaves

The rate of carbon transport based on the carbon balance overa 6-h period from a mature tomato leaf was measured overa rangeof net photosynthetic rates from 0.1 to 4.9 mg C dm^–2h^–1 under light flux densities from 4 to 140 W m^–2.A proportional relationship was demonstrated between the rateof carbon transport and carbon fixation when the carbon fixationrate was higher than 2 mg C dm^–2 h^–1.Below a carbonfixation rate of 1 mg C dm^–2 h^–1, the rate of carbonexport was maintained at 1 mg C dm^–2 h^–1 at theexpense of the breakdown of starch. A highly significant correlationwas observed between sucrose concentration and the rate of carbontransport. The sucrose concentration in the leaf appears tobe the factor controlling carbon export.     

The Effects of 2,4-Dichlorophenoxyacetic Acid on Ion Uptake by Maize Roots

The effects of the synthetic auxin and herbicide 2,4-dichlorophenoxyaceticacid (2,4-D) on K^$ and Cl^– uptake and H^$ release by youngexcised maize roots has been studied. Brief exposure to 2,4-D(0.01 mmol dm^–3) at pH 3.5 causes a large depolarizationof the electrical potential across the root plasma membranesand converts K^$ uptake to K^$ leakage into the bathing solution.These results can be explained by the increased H^$ permeabilityof the membranes induced by the weak acid 2,4-D. The depolarizationresults in a less favourable electrochemical potential gradientfor K^$ uptake across these membranes. These effects are notrelated to the auxin properties of 2,4-D as the nonauxin 3,5-dichlorophenoxyaceticacid (3,5-D) gives rise to similar effects. The relative depolarizationsinduced by a range of weak acids appear to be unrelated to theiroil/water partition coefficients. In contrast, on bathing the roots for longer periods in solutions(pH > 5) containing 2,4-D (0.01 mmol dm^–3) K^$ and Cl^–uptake and H^$ release are inhibited. These effects are not shownwith 3,5-D suggesting an auxin-linked action for 2,4-D. Alsothe electrical potential across the plasma membranes is onlyslightly depolarized so that a change in the electrochemicalpotential gradient cannot be invoked to explain the loweredion fluxes. The evidence is consistent with the removal of anenergy supply to a metabolically linked K^–/H^– exchangemechanism in the plasma membranes. It is likely that both modes of action would operate to lowerion uptake under soil-grown conditions, the former becomingmore manifest in acidic soils.     

Induction of Cell Division in Leaf Cells of Coconut Palm by Alteration of pH and its Correlation with Glyoxalase-I Activity

Cell division in suspension cultures obtained from leaf cellsof coconut was influenced by pH of the culture media. A 3-foldincrease in cell number was obtained at pH 7.0 compared to suspensionsgrowing at pH 5.0. The pH of both cells and media changed after48 h of growth. Internal cell pH showed a significant increasewhen cultures were grown at pH 7.0 and 8.0 and increased onlyslightly at pH 5.0 and 6.0. Glyoxalase-I activity of cells insuspension culture was found to be pH-depcndent, showing maximumactivity at pH 7.0. Glutathione, a co-enzyme for the substratemethylglyoxaJ for glyoxalase-I, produced a 2-fold increase incell number at a concentration of 5 x 10^–3 mol dm ^–3.The polyamine, spermidine, promoted cell division maximallyat a concentration of 10^–6 mol dm^–3. Methylglyoxal-bis(guanylhydrazone), an inhibitor of spermidine biosynthesis,strongly inhibited cell division giving maximum inhibition ata concentration of 3 x 10^–6 mol dm ^–3. These resultsindicate a positive correlation between cell division and glyoxalase-Iactivity. Key words: Cocos nucifera, glyoxalase-I, pH, spermidine     

Phytotoxicity of Phthalate Plasticisers: 2. SITE AND MODE OF ACTION

The effects of phthalate esters on chlorophyll a₂ fluorescencein radish plants (Raphanus sativus L. cv. Cherry Belle) wereexamined Fluorescence yield was increased in those plants exposedto an aerial concentration of 120 ng dm^–3 dibutyl phthaiatc(DBP) at a rate of 3.0 dm³ min^–1 for 13 d. Comparisonof fluorescence enhancement ratios and F_red/F_ox, suggests thatDBP inhibits photosynthesis in radish plants at a site afterQ_A. Both DBP and diisobutyl phthalate (DIBP) strongly inhibiteduncoupled (PS2+PS1) electron transport rates in thylakoids isolatedfrom spinach. At a chlorophyll concentration of 10 µgcm^–3 the concentrations of DBP and DIBP exhibiting 50%inhibition were 44 mmol m^–3 and 42 mmol m^–3 respectively.Basal electron transport rates were also inhibited, with 87mmol m^–3 of DBP or DIBP producing 50% inhibition. Measurementof photosystcm 1 activity suggested that the main site of actionof these phthalates was localized at a site near the reducingside of photosystem 2. Key words: Phthalate, plasticiser, chlorophyll, fluorescence, photosynthesis, inhibition     

The Role of Benzyladenine in the Differentiation of Tracheary Elements in Jerusalem Artichoke Tuber Explants Cultured in vitro

The role of benzyladenine (BA) in the differentiation of trachearyelements in Jerusalem artichoke (Helianthus tuberosus L.) tuberexplants was studied. For maximum differentiation of trachearyelements (25–30% of the cell population), treatment withoptimal concentrations of benzyladenine (5.0 mg dm^–3)in the presence of -naphthaleneacetic acid |NAA| (1.0 mg dm^–3)for the first 6 d was as effective as its continued presenceduring the entire 14 d period of study. A majority of the differentiatedtracheary element appeared between the 10th and 14th days ofculture. It was further observed that concentrations of activecytokinins in the tissue were considerably reduced within 2d after transfer from the BA-containing medium to a BA-freemedium. This was shown in three different ways: (1) monitoringthe amount of ethanol-soluble radioactivity at various timesafter transfer from |14C|-BA containing medium to BA-free medium;(2) bioassay of various cytokinin fractions from tissue extractseparated by thin layer chromatography; (3) indirect assay oftissue cytokinin activity through its interaction with abscisicacid for the promotion of auxin-induced cell division in thistissue. Both gibberellic acid (5.0 mg dm^–3) and abscisic acid(2–0 mg dm^–3) effectively inhibited the differentiationof tracheary elements even if provided after 6 d of pre-incubationin a high tracheid inducing medium. However, the appearanceof differentiated cells for the first 2 d after transfer wasnot significantly affected. A hypothetical scheme for the role of benzyladenine in the differentiationof tracheary elements in this tissue is discussed. It is suggestedthat during one or more critical cell divisions in the presenceof optimal levels of benzyladenine, a proportion of cells areinduced or committed for later differentiation into trachearyelements. The high concentrations of benzyladenine requiredduring induction are not needed during the intervening celldivisions, nor for the actual differentiation of the trachearyelements. Key words: Tracheary element differentiation, Jerusalem artichoke (Heliantlus tuberosus), Benzyladenine, Gibberellic acid, Abscisic acid     

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     

H+ Efflux and Trans-Root Potential Measured while Increasing the Temperature of Solutions Bathing Excised Roots of Zea mays

Kennedy, C. D. and Gonsalves, F. A. N. 1988. H⁺ efflux and trans-rootpotential measured while increasing the temperature of solutionsbathing excised roots of Zea mays.—J. exp. Bot. 39: 37–49. Novel temperature-ramp procedures have been used to measureH⁺ efflux and trans-root potential of excised roots of Zea mays(var. Fronica). Two types of experiment were performed: (1),increasing temperature from 17°C, and (2), pre-cooling theroots to 1°C before starting the temperature ramp. The ratesof increase of temperature for H⁺ efflux and trans-root potentialexperiments were 0·5 and 2·1°C min^–1respectively The H⁺ scans revealed strong sharp maxima at 30°C and 32°C,for non-pre-cooled and pre-cooled roots respectively, the latterbeing significantly smaller. The trans-root potential scansfor the pre-cooled roots showed a corresponding maximum at 30°C,which was inhibited by KCN (1-0 mmol dm^–3) with or withoutSHAM (10 mmol dm^–3), or Hg²⁺ (1, 10, 100 µmol dm^–3)in the bathing solutions. Some of the evidence suggests thatthese maxima are associated with electrogenic H⁺ pumping, mediatedby a plasma membrane-bound ATPase. However, no correspondingmaximum was observed in the trans-root potential scans for non-pre-cooledroots, the potential remaining at about — 75 m V from20°C to 35°C. As there is a 7-fold increase in H⁺ effluxbetween 20°C and 30°C, the relationship between netH+ efflux and electrogenic proton pumping in these roots isby no means clear. Some possibilities are considered here. Pre-cooled and non-pre-cooled roots show clear maxima in thetrans-root potential scans at about 46°C, at which temperaturethere is a slight net H⁺ influx. This, and other less prominentfeatures observed, are briefly discussed. Key words: H⁺ efflux, trans-root potential, temperature-ramp procedure, Zea mays, roots     

Export, Mobilization, and Respiration of Assimilates in Uniculm Barley during Light and Darkness

The respiratory losses and the pattern of carbon supply froma leaf of unicuim barley were examined during a complete diurnalperiod using a steady state ¹⁴C-labelling technique. After a delay of c. 1 h a portion of the ¹⁴C exported from acontinuously assimilating leaf was lost in respiration in thelight. This respiratory loss amounted to c. 20% of the total¹⁴C fixed. A further 28% of the total ¹⁴C fixed was respiredduring the dark period. In the light, carbon was fixed at a rate of c. 8·9 mgC dm^{–2 h–1} and exported from the leaf at ^c. 5·3mg C dm^{–2 h–1}. Dark export averaged ^c. 31% of theday-time rate. Carbohydrate was stored in the leaf during the day and was almostcompletely remobilized during the dark. Sucrose, the major reservecarbohydrate, was exported first whilst the starch level remainedconstant. After some 9 h of darkness, sucrose declined to alow level and starch remobilization began.