Solute Regulation in the Euryhaline Marine Alga Enteromorpha prolifera (O. F. Mull) J. Ag.

Young, A. J., Collins, J. C. and Russell, G. 1987. Solute regulationin the euryhaline marine alga Enteromorpha prolifera (O. F.Mll) J. Ag.—J. exp. Bot. 38: 1298–1308. The physiological basis for salt tolerance has been studiedin the euryhaline alga Enteromorpha prolifera. Levels of inorganicions and organic (compatible) solutes have been measured. K⁺makes the major contribution towards the internal osmotic potentialof the cell, while Cl^– and, in particular, Na⁺ contentsare low. Levels of the organic solute ß-dimethylsulphonio-propionate(DMSP) are high but are fairly insensitive to changes in theexternal salinity. Levels of amino-acids, calcium, phosphateand sulphate contribute relatively little towards the internalosmotic potential of the alga. As salinity is altered there are marked changes in the tissuewater content and volume. These changes directly affect theconcentration of the osmotic solutes within the cell. In diluteseawaters there is an increase in turgor as there is littlechange in the internal solute content of the cell compared tovalues in normal sea water. Inorganic ions, in particular K⁺,and organic solutes are accumulated in concentrated seawaters,although concentrations greater than 2·00 x seawaterresult in a reduction in the internal osmotic potential of thecell, mainly through loss of K⁺. Key words: Enteromorpha, salinity, osmoregulation     

麻栎茎段体胚发生和组织学观察初报

分别于2010年4月和6月采集同一麻栎母株的成熟茎段,在培养基MS+6-BA 1 mg·L^-1+IBA 1 mg·L^-1+谷氨酰胺1 000 mg·L^-1+脯氨酸500 mg·L^-1上诱导体胚发生,选出较好的外植体采集时间。通过组织学和扫描电镜观察,研究麻栎体胚的起源和愈伤组织结构特征。结果表明,外植体较好的采集时间为4月。组织切片表明,麻栎体胚具有三种不同的起源方式,起源于愈伤组织内部、表皮或者初生胚性复合体表面;胚性愈伤组织的细胞较小,细胞质浓厚,染色较深,和非胚性组织细胞明显不同。扫描电镜(SEM)观察表明,胚性愈伤组织细胞呈球形,大小均一,多以细胞团形式存在;非胚性愈伤组织细胞无规则形状,细胞间隙较多,大多分散存在,这些可以作为区分两类愈伤组织的典型特征。     

Translocation in Plants Possessing Supernumerary Phloem: T. 14C-ASSIMILATES AND AUXIN IN THE INTERNAL PHLOEM OF TO BACCO (NICOTIANA TABACUML.)

Tobacco plants were exposed to ¹⁴CO₂ or treated with [¹⁴C]IAAin order to study the transport capacity of the internal phloem.It is shown that the translocation of assimilates in both theinternal as well as the external phloem is controlled by a source-sinkrelationship. The internal phloem is of a lesser conductiveimportance in the intact plant whereas in the girdled stemsit is of main importance as conductor. Auxin and other materialscontrolling apical dominance can also be translocated downwardsin the internal phloem in a sufficient amount in order to keepaxillary buds suppressed. Exogenous auxin applied to decapitatedstem can also be transported via the internal phloem and bypassgirdles, thus maintaining apical dominance.     

The Role of the Mesocotyl in Sodium Exclusion from the Shoot of Zea mays L. (cv. Pioneer 3906)

Drew, M. C. and Lauchli, A. 1986. The role of the mesocotylin sodium exclusion from the shoot of Zea mays L. (cv. Pioneer3906).—J. exp. Bot. 38: 409–418. The mesocotyl, located between the root and shoot, can stronglyaccumulate Na⁺ from the ascending transpiration stream, therebypotentially acting as a sink to protect the shoot from excessNa⁺. To determine the quantitative importance of the mesocotylas a Na⁺ sink, we grew plants with either short (9·0mm) or long(21 mm) mesocotyls, the latter resembling the sizefound in field-grown plants. At 13 d, plants were transferredfrom Na ⁺ -free nutrient solution to a ²²Na⁺ labelled solutionin which the concentration of NaCl was (mol m^–3) 1·0,10 or 100. The concentration of Na⁺ accumulated in the mesocotylin 24 h (g^–1 fr. wt.) exceeded that in the roots thatwere directly exposed to the nutrient solution. The amountsof ²²Na⁺ retained in the long mesocotyl were about double thatin the short ones and increased with time of exposure and NaClconcentration. At 1·0 and 10 mol m^–3 NaCl, theamounts of ²²Na⁺ retained in the mesocotyl were 6–19%of those reaching the shoot in 24 h, but with 100 mol m^–3NaCl, a damaging concentration for maize, this declined to 3–8%.The mesocotyl, even as a fully elongated structure is, therefore,unlikely to provide an appreciable alternative sink for Na⁺when NaCl reaches injurious concentrations. Key words: Ion transport, potassium, roots, salinity     

The Effects of Salinity upon Ion Content and Ion Transport of the Marine RedAlga Porphyra purpurea(Roth) C.Ag.

Ion contents and concentrations (K⁺, Na⁺, Cl^–, Ca²⁺, Mg²⁺,SO^2–₄, NO^–₃, HPOJ^2–₄, amino and organic acids)of P. purpurea have been studied in relation to salinity variation.Cells were shown to accumulate large amounts of K⁺ and Cl^–against their respective gradients of electrochemical potentialin all dilute and concentrated seawater media. Active influxof SOJ^2–₄, NO^–₃, and HPOJ^2–₄ is also suggested,while Na⁺ is actively excluded from cells under hyposaline andhypersaline conditions. The relative proportions of individualcomponents of the internal osmotic potential were found to changeaccording to the external salt concentration. KCL forms themajor fraction of _j} in concentrated seawater media while K⁺-aminoacids form the major fraction in dilute seawaters. Other intracellularsolutes comprise less than 15% oft_j, in all media. Unidirectional fluxes of K⁺ and Cl^– were studied by radioisotopicmeans. Fluxes of K⁺ and Cl^– are reduced in hyposalinemedia, as is absolute KCL content per cell. Intracelhilar KCLcontent was also found to be markedly dependent upon externalK⁺ concentration, rather than water potential. Changes in KC1levels induced by salinity variation occur over a 6 h period.     

Effects of vertical-horizontal coupling on the horizontal distribution of chlorophyll a

The distributions of chlorophyll a and salinity were sampledon successive days along horizontal transects in central LongIsland Sound. Changes in the variance spectra over a periodof three days following a wind event suggest that there wasan input of variance at wave numbers of the order 6 ? 10^–3radians per meter. There was an associated increase in coherencysquared between chlorophyll and salinity. During this periodvertical structure in both chlorophyll and salinity was reestablished.It appears that horizontal structure was generated by the interactionof this vertical structure with a vertical shear in horizontalcurrents at semidiurnal and lower frequencies and possibly byshort period internal waves with frequencies near the V?is?l?frequency.     

The Effect of 2,4-Dichlorophenoxyacetic Acid and Related Compounds on the Fine Structure of the Primary Leaves of Phaseolus vulgaris

The epidermal cuticle of the abaxial surface of the primaryleaves of Phaseolus vulgaris used for these experiments is notmore than 0.15 µm thick except on the walls of basal cellsof epidermal hairs. The cuticle apparently has no internal structure;neither channels or canals can be seen passing through it. An examination of the fine structure of leaf tissue 24 h afterthe application of 1.6 x 10^–3 M solutions of 2-chlorophenoxyaceticacid (2-CPA), 4-chlorophenoxyacetic acid (4-CPA), 2,6-dichlorophenoxyaceticacid (2,6-D), and 2,4-dichlorophenoxyacetic acid (2,4-D) hasshown that 2,4-D alone, and then only in the light, induceschanges in the morphology and internal structure of the chloroplast.As early as 4 h after application, there is an apparent breakdownin the structure of the membrane systems of the cells of theepidermis, palisade, and mesophyll. After 8 h the chloroplastsare distorted and contain electron-dense granules, and the cellsappear to be plasmolysed. Subsequently these changes becomemore pronounced. It is possible that the specific disturbancesbrought about by 2,4-D reflect its phytotoxic properties.     

Effect of linolenate on photosynthesis by intact spinach chloroplasts II. Influence of preillumination of leaves on the inhibition of photosynthesis by linolenate

The inhibitory effect of linolenate on intact spinach chloroplastsdepends on the level of the internal pool of metabolites. Chloroplastsfrom preilluminated leaves or chloroplasts artificially loadedwith 3-phosphoglyceric acid required higher concentrations oforthophosphate for maximal rates of CO₂ dependent O₂ evolutionthan untreated chloroplasts. The loaded chloroplasts were moresensitive to linolenate, and in the presence of linolenate theoptimal phosphate concentration was shifted toward lower values.We propose that the inhibition of photosynthesis by linolenateis due to inhibition of the "phosphate translocator". ¹ Part of this work has been published in the Book of Abstracts,4th International Congress on Photosynthesis, Reading, U.K.,1977, p. 265–266. ² This work is part of a doctoral programme carried out by L.Mv6 Akamba in this laboratory. ³ To whom reprint requests should be adressed. (Received October 14, 1978; )     

Dependency of H+ efflux on ATP in cells of Chara australis

The internodal cell of Chara australis was made tonoplast-freeby internal perfusion with a medium containing a Ca²⁺-chelatorEGTA and the net H⁺ efflux across the plasma membrane was estimatedeither by titration of the external medium or by measuring thechange in pH in the external medium. The amount of H⁺ effluxwas high in the presence of internal ATP and low in its absence.The ATP-dependent net H⁺ efflux was about 40 nmoles/m²/sec.This amount is smaller than that estimated for the pump currenton the basis of electrical data obtained earlier (3). This discrepancyis discussed. (Received June 18, 1980; )     

Transport and Fixation of Inorganic Carbon during Photosynthesis in Cells of Anabaena Grown under Ordinary Air: III. Some Characteristics of the HCO3--Transport System in Cells Grown under Ordinary Air

In cells of cyanobacterium Anabaena variabilis grown under ordinaryair (low-CO₂ cells), the transport of both CO₂ and HCO₃^–was significantly enhanced by Na⁺. This effect was pronouncedas the external pH increased. When low-CO₂ cells were treatedwith an inhibitor of carbonic anhydrase (CA), only CO₂ transportbut not HCO₃^– transport, was inhibited. The initial rateof photosynthetic carbon fixation as a function of the concentrationof internal inorganic carbon (IC) was practically the same irrespectiveof whether CO₂ or HCO₃^– was externally supplied. Theseresults suggest that IC is actively transported through theplasma membrane in a form of HCO₃^– probably by some transporterand that the transmembrane Na⁺ gradient is involved in thisIC transport system. Free CO₂ may be hydrated by CA to HCO₃^–and then transported to the cells by this transporter. On the other hand, CO₂ is actively taken up by cells grown withair containing 5% CO₂ (high-CO₂ cells) though the enhancingeffect of Na⁺ was much smaller in high- CO₂ cells than in low-CO₂cells. The initial rate of fixation as a function of internal IC concentrationindicated that the rate of the carboxylation reaction of accumulatedIC is higher in I0W-CO₂ cells than in high-CO₂ cells. The studieswith ethoxyzolamide indicated that even in low-CO₂ cells, CAdoes not function inside Anabaena cells. These results suggestthat inside the low-CO₂ cells of Anabaena, some mediator(s)facilitates the transport of IC to RuBPCase. (Received January 23, 1987; Accepted April 24, 1987)     

The importance of benthic recruitment to the population development of Aphanizomenon flos-aquae and internal loading in a shallow lake

The recruitment of Aphanizomenon flos-aquae out of the sedimentswas measured in the shallow, hypereutrophic Agency Lake, Oregon.There were two main episodes of recruitment, the latter of whichaccounted for 8.2% of the water column population increase duringits main growth phase. Phosphorus (P) content was higher innewly recruited cells than in water column cells. Recruitmentduring one weekly episode constituted an internal P load rateof 3.56 mg P m^–2 day^–1, accounting for 27% of thecorresponding increase in water column total phosphorus (TP).However, the majority of internal loading in the lake did notcoincide with, and therefore could not be explained by, biotranslocationdue to benthic recruitment of A.flos-aquae. ¹Present address: WES-ES-P, USAE Waterways Experiment Station,3909 Halls Ferry Road, Vicksburg, MS 39180, USA     

Regulation of Sulphate Transport in a Tropical Legume, Macroptilium atropurpureum, cv. Siratro

When young plants of Macroptilium atropurpureum, cv. Siratrowere deprived of external sulphate (-S plants) growth of shootsand roots continued at rates comparable to those in plants wellsupplied with sulphate (control) for 3 d and 5 d respectively.Dilution of internal sulphur therefore took place and redistributionof sulphur occurred between inorganic and organic forms andbetween roots and younger leaves. Even when S-deficiency limitedgrowth, plants contained 16% of their total sulphur as sulphate,but most of this was retained in old leaves and redistributedslowly to growing zones. The capacity for sulphate uptake increased in roots of –Splants very soon after they were deprived of external sulphate;within 24 h the absorption from 0.25 mol m^–3 SO₄^2–was more than five times that of control roots. Maximum increasedcapacity was reached after 2–3 d stress when the V_maxof system 1 was 1948 nmol h^–1g^–1root fr. wt. in–S plants and 337 nmol h^–1g^–1root fr. wt.in controls. The K^mfor system 1 did not change significantlywith S-stress being between 5–8 µM in both setsof plants. Absorption of L-cysteine was not stimulated by S-stress. There was a close, positive relationship between plant growthrate and the rate at which sulphate uptake capacity was enhancedby withholding sulphate from culture solutions. When –S plants were replaced in sulphate-containing solutiontheir capacity for SO₄^2– declined to the control levelwithin 24 h. Very marked repression of capacity was also foundwhen –S plants were treated with L-cysteine, but therewas no immediate effect with methionine. Roots of this species appear to have a very active system fordegrading L-cysteine to sulphate, 30% of the label in ³⁵S-cysteineabsorbed by roots was recovered in ³⁵SO₄^2– after 20 minor 2 h incubation. By contrast, roots had a very weak abilityto reduce sulphate. When part of the root system was in solution lacking sulphatethere was enhanced uptake of sulphate by other parts which themselveswere amply supplied with sulphate. This is seen as an exampleof compensatory absorption. The response to S-stress is specific and there were no positiveinteractions between S-stress and the absorption of phosphate,or P-stress and the uptake of sulphate. The results are discussed in relation to the close control ofsulphate uptake by internal sulphate concentration, redistributionof forms of sulphur during stress and mobility of sulphate inthe phloem. Key words: Kinetics, Amino-S, Sulpholipid, Repression;, Deficiency     

Hormonal responses to partial drying of the root system of Helianthus annuus

Plants of Helianthus annuus were pot-grown in soil, with approximately30% of the root system protruding through the base. After 7d, the upper part of the root system of half of the plants wasexposed to drought (internal roots) while the lower part waskept in aerated nutrient solution (protruding root). The treatmentrapidly reduced the internal roots' water content from 26.1to 21.9 g g^–1 dry weight (DW), while in protruding rootsof stressed plants it slowly and continuously decreased from31.9 to 25.2 g g^–1 DW. Leaf water content rapidly decreasedin treated plants from 7.4 to 6.4 g g^–1 DW in the first2d and then reached a plateau. In stressed plants leaf stomatalresistance was significantly higher in the first 3 d while leafwater potential was lower only on the last day. Abscisic acid (ABA) concentration in treated plants increasedsignificantly compared to the controls. In treated internalroots, ABA rose from the first day, reaching a maximum of 1.48±0.49nmol g^–1 DW after 3 d. In treated protruding roots a maximumof 0.99±0.09 nmol g^–1 DW was reached after 1 d.ABA concentration in the xylem sap increased 2 d and 3 d afterthe start of soil drying, with a maximum of 113±12nmoll^–1 during the third day. The ABA rise in the leaves oftreated plants was less significant. Indol-3yl-acetic acid (IAA) concentration in internal rootsof treated plants reached a maximum of 22.54±3.34 nmolg^–1 DW on the third day, then decreased dramatically.The protruding root system of control plants showed a maximumvalue of 16.05±1.77 nmol g^–1 DW on the sixth day. Little difference in cytokinin content of xylem sap was notedbetween control and treated plants. Hormonal variations in different parts of the plant are discussedin relation to drought stress. Key words: Soil drying, roots, ABA, IAA, cytokinins     

P2 purinoceptor of the globular substance in the otoconial membrane of the guinea pig inner ear

The biological characteristics of the globular substance, aprecursor of otoconia, are unclear. In the present study, the ATP-induced internal free Ca²⁺ concentration([Ca²⁺]_i) changes of the globular substanceand the ATP distribution in the vestibular organ were investigatedusing a Ca²⁺ indicator, fluo 3, and an adeninenucleotide-specific fluorochrome, quinacrine, by means of confocallaser scanning microscopy. [Ca²⁺]_i showed arapid and dose-dependent increase in response to ATP with a 50%effective concentration (EC₅₀) of 16.7 µM. Thisreaction was independent of external Ca²⁺, indicating thepresence of an internal Ca²⁺ reservoir. Neither adenosine,,-methylene-ATP, 3'-O-(4-benzoylbenzoyl)-ATP, ADP, norUTP evoked this reaction, whereas 2-methylthio-ATP induced an increaseof [Ca²⁺]_i with an EC₅₀ of 14.4 µM. Moreover, P2 antagonists, reactive blue 2 and suramin, and aphospholipase C inhibitor, U-73122, inhibited the ATP-induced[Ca²⁺]_i increase. These findings indicate thepresence of a P2Y purinoceptor on the globular substance. In addition,granular fluorescence was observed in the quinacrine-stained macularsensory epithelium, indicating the presence of ATP-containing granulesin this tissue. These results suggest that a paracrine mechanisminvolving ATP may exist in the macula and that this mechanism regulatesthe biological behavior of the globular substance.

     

The Long-Term Effects of Nitrate on the Growth and Nodule Structure of the Caesalpinioid Herbaceous Legume Chamaecrista fasciculata Michaux.

Various nitrate concentrations (0, 1, 2, 4, 8, 20, 50 mol m^–3)were applied at weekly intervals for 10 weeks to the caesalpinioidlegume Chamaecrista fasciculata. Microscopic techniques andgeneral growth studies showed that nitrate affected both theplant and its rhizobial symbiosis. As the nitrate concentrationwas increased, nodule structure became increasingly disruptedeven though nitrate remained limiting to plant growth until8 mol m^–3. Poly-ß-hydroxybutyrate (PHB) was observedusing transmission electron microscopy; as nitrate increasedfrom 0 to 2 mol m^–3, the PHB stores were utilized Key words: Chamaecrista fasciculata, poly-ß-hydroxybutyrate, nitrogen fixation     

A Model for C3 Leaves Describing the Dependence of Net Photosynthesis on Irradiance: II. APPLICATION TO THE ANALYSIS OF FLAG LEAF PHOTOSYNTHESIS

Measurements of the photosynthesis-light response of flag leavesin a winter wheat crop were made during the period from maximumelongation until complete senescence. Immediately followingleaf elongation, the maximum rates of photosynthesis and thevalues of efficiency at low light were in the range 2.8–3.6g CO₂ m^–2 h^–1 and 8–11 µg CO₂ J^–1respectively. The shape of the photosynthesis-light responseremained constant throughout and was close to a ‘Blackman’type response rather than a rectangular hyperbola. The resultswere analysed, therefore, using a more recent model which isa non-rectangular hyperbola. Stomatal and internal resistanceswere equally important in limiting the maximum rate of photosynthesis.     

The Chemical and Mechanical State of the Cell Wall of Pea Root Tips: II. THE EFFECTS OF SOME METABOLIC CHANGES

The area covered by a tissue-squash prepared by a standard procedurefollowing an acid treatment was taken as a quantitative inversemeasure of the intercellular cohesion. The effect on this acid-resistantcohesion of prior incubations in buffered (5x10^-5M. to 5x10^-13M.)ß-indolylacetic acid, sucrose (2.3 per cent w/v),and thioglycollate (10^-1 M. to 10^-4 M.) was studies, and alsothe effect of performing these incubations under nitrogen. Theauxin and sucrose treatments resulated in a weakening of theacid-resistant cohesion, and the thioglycollate incubation impededthe increase in acid-resistant cohesion induced by anaerobiosis. The results are discussed in terms of chemical changes thatmust occur in the structure of the middle lamella.     

Electrophysiological Measurements on the Root of Atriplex hastata

The ion contents and membrane potentials of the cells of young,hydroponically cultured seedlings of Atriplex hastata L. var.salina, Wallr. have been measured at several different NaClconcentrations. The total tissue concentrations of Na⁺ and Cl^–increase as external NaCl increases, but there is always a markedexcess of internal Na⁺ over Cl^–; this is balanced by endogenousorganic anion formation with a concomitant extrusion of H⁺ tothe bathing solution. Membrane potentials of the root cells remain essentially invariantwith changes in external NaCl at approx. –130 mV; thereis no evidence of a radial gradient of potential across theroot. The potential seems to contain a cyanide-sensitive electrogeniccomponent, also invariant with NaCl concentration, of about–70 mV, and a diffusion component. The electrogenic componentseems likely to be a H⁺ efflux, probably through a H⁺ uniportATPase.     

The Role of Potassium in the Control of Turgor Pressure in a Gas-Vacuolate Blue-Green Alga

The contribution of K⁺ accumulation to cell turgor pressurewas investigated in the gas-vacuolate blue-green alga Anabaenaflos-aquae. The cell turgor pressure, measured by the gas vesiclemethod, drops in cells suspended in culture medium depletedof K⁺ but rapidly rises again, by 100 kPa or more, when K⁺ isresupplied. A similar though rather slower rise in turgor pressureis supported by an equivalent concentration of Rb⁺. The internalK⁺ concentration rose from 66 to 91 mM when K⁺ was suppliedat an external concentration of 0.4 mM. This rise was light-dependent.Greater increases in internal K⁺ concentration and turgor pressureoccurred when K⁺ was supplied at a higher concentration, 3.6mM. In both cases over 60% of the observed turgor pressure risecould be accounted for by accumulation of K⁺. The turgor pressurerise supported by light-stimulated K⁺ uptake can cause collapseof enough of the alga's gas vesicles to destroy its buoyancy.The effect of K⁺ availability on buoyancy regulation by planktonicblue-green algae is discussed.     

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.