Effect of Salinity on Germination and Seedling Growth of twoAtriplexspecies (Chenopodiaceae)

Salinity is one of the environmental factors that has a criticalinfluence on the germination of halophyte seeds and plant establishment.Salinity affects imbibition, germination and root elongation.However, the way in which NaCl exerts its influence on thesevital processes, whether it is through an osmotic effect ora specific ion toxicity, is still not resolved. Dimorphic seedsof the halophytesAtriplex prostrataandA. patulawere treatedwith various iso-osmotic solutions of NaCl and polyethyleneglycol (PEG). For each treatment, imbibition, germination rate,percent germination, germination recovery and nuclear area ofroot tip cells were compared. Higher concentrations of NaCl(-1.0 MPa) were more inhibitory to imbibition, germination andseedling root elongation than iso-osmotic PEG solutions. Allseeds recovered from a pre-treatment with -2.0 MPa NaCl andPEG solutions, except large seeds ofA. prostratawhich failedto germinate following transfer from -2.0 MPa NaCl. NaCl causeda greater increase in nuclear volume than iso-osmotic PEG solutions.These data suggest that the influence of NaCl is a combinationof an osmotic effect and a specific ion effect.Copyright 1998Annals of Botany Company Atriplex patula,Atriplex prostrata,cytophotometry, osmotic potential, salinity, seed germination.     

Comparison of Growth Responses of Barnyard Grass (Echinochloa oryzoides) and Rice (Oryza sativa) to Submergence, Ethylene, Carbon Dioxide and Oxygen Shortage

Unlike germination of wheat (Triticum aestivum), millet (Eleucinecoracana), and sorghum (Sorghum caudatum), that of Echinochloaoryzoides (barnyard grass) and Oryza satwa (rice) was not inhibitedby poorly aerated solutions with 11 k Pa oxygen (equilibriumpartial pressure) or less In the dark, seedling shoots of riceincluded a coleoptile, and in Echinochloa, a mesocotyl alsoGrowth in fresh and dry weight of shoots was strongly depressedby poorly aerated solutions in both rice and Echinochloa butthe effects on extension differed in the two species in rice,coleoptile extension was promoted by solutions partly depletedof oxygen, and also by the absence of oxygen The stimulationin partly de-oxygenated solutions resulted from the combinedpromoting effects of small oxygen partial pressures, carbondioxide, ethylene and buoyant tension in contrast, these treatmentsneither promoted nor inhibited elongation by the Echinochloacoleoptile while severely inhibiting extension of the mesocotyl Overall, poorly aerated solutions lengthened the shoot of riceand shortened it in Echinochloa when compared with those submergedin well-aerated solutions These opposite effects were broughtabout by the same gaseous changes, i e oxygen shortage, elevatedethylene and carbon dioxide The effect on Echinochloa was almostentirely restricted to the mesocotyl, coleoptile extension beingremarkably insensitive to large increases in ethylene and carbondioxide, or to extreme oxygen shortage Seedlings of the twospecies thus have contrasting strategies for survival Stress, submergence, ethylene, oxygen shortage, carbon dioxide, adaptation, anaerobiosis, rice (Oryza sativa L), barnyard grass [Echinochloa oryzoides (Ard) Fritseh]     

Aluminium and the Hydraulic Conductivity of Quercus rubra L. Root Systems

Two hydroponic experiments were conducted to determine the effectsof brief and prolonged AI³⁺ exposures on the hydraulic conductivity(Lp) of northern red oak (Quercus rubra L.) root systems. RootLp was determined using the pressure chamber method of Fiscus(1977). In the first experiment, 28- to 40-d-old seedlings weretreated for 4 d with complete nutrient solutions containingone of three Al concentrations (0.04, 1.85 or 3.71 mol m^–3)and either 0 or 50 mmol m^–3 P. Neither Lp nor daily transpirationwas affected by treatment. In Experiment II, seedlings were grown for 48–63 d incomplete solutions containing one of three Al concentrations(0, 0.75 or 2.00 mol m^–3) and either 10 or 250 mmol m^–3Ca. Lp and leaf area to root length ratio (LA/RL) were reducedwhen (AI³⁺/ Ca²⁺), the solution activity ratio, was 2.9 andhigher. Lp and LA/RL were also negatively correlated with Alconcentration and Al/Ca concentration ratio in the roots. Lpwas positively correlated with LA/RL in both experiments. Itis unclear whether Lp in the second experiment was reduced directlyby solution and root chemistry or whether Lp changed in responseto altered leaf/root balance. Key words: Al phytotoxicity, Al x Ca interaction, Quercus rubra, root hydraulic conductivity     

Dependence of Na+-K+ pump current-voltage relationship on intracellular Na+, K+, and Cs+ in rabbit cardiac myocytes

To examine effects of cytosolicNa⁺, K⁺, and Cs⁺ on the voltagedependence of the Na⁺-K⁺ pump, we measuredNa⁺-K⁺ pump current (I_p)of ventricular myocytes voltage-clamped at potentials(V_m) from 100 to +60 mV. Superfusates weredesigned to eliminate voltage dependence at extracellular pump sites.The cytosolic compartment of myocytes was perfused with patch pipette solutions with a Na⁺ concentration ([Na]_pip)of 80 mM and a K⁺ concentration from 0 to 80 mM or withsolutions containing Na⁺ in concentrations from 0.1 to 100 mM and K⁺ in a concentration of either 0 or 80 mM. When[Na]_pip was 80 mM, K⁺ in pipette solutionshad a voltage-dependent inhibitory effect on I_pand induced a negative slope of theI_p-V_m relationship. Cs⁺ in pipette solutions had an effect onI_p qualitatively similar to that ofK⁺. Increases in I_p with increasesin [Na]_pip were voltage dependent. The dielectriccoefficient derived from[Na]_pip-I_p relationships at thedifferent test potentials was 0.15 when pipette solutions included 80 mM K⁺ and 0.06 when pipette solutions were K⁺ free.

     

Soil Solution Chemistry Controlling the Field Distribution of Melica ciliata L.

Germination, establishment and growth of Melica ciliata L.,an 'acidifuge' species of rocky habitats in Europe, were studiedexperimentally and related to chemical properties of the soilsolution, including pH, base cation composition, Al concentrationand speciation, and Mn concentration. M. ciliata failed to establishin acid leptite soil. However, it was able to grow in solutionat pH 3·6 and exhibited vigorous growth at pH 3·9,a typical soil solution pH of leptite sites, which Melica isunable to colonize. Higher concentrations of Mn than those measuredin any leptite soil solutions did not influence growth. Exposureto 0·037 mmol l^-1 (1 mg l^-1) of Al³⁺, a concentrationusually exceeded in the soil solution of leptite sites, severelyretarded root growth. Speciation technique applied to Al insoil solutions obtained by centrifugation demonstrated a closerelationship between H⁺ and Al concentrations and, in particular,between H⁺ and free ionic (quickly reacting) Al species. Soilsolution concentrations of free ionic Al proved to be < 0·002mmol l^-1 in sites lacking Melica , but often > 0·10mmol l^-1 in site lacking Metalica . It is concluded that theinability of M. ciliata to establish in acid soils is not primarilydue to the high H⁺ concentration but to the high soil solutionconcentrations of Al, especially free Al ionic species at lowsoil pH.Copyright 1993, 1999 Academic Press Melica ciliata, distribution, soil solution, pH, aluminium speciation, manganese, base cations, iron     

Thermal and Water Relations of Roots of Desert Succulents

Two succulent perennials from the Sonoran Desert, Agave desertiEngelm. and Ferocactus acanthodes (Lem.) Britton and Rose, loselittle water through their roots during drought, yet respondrapidly to light rainfall. Their roots tend to be shallow, althoughabsent from the upper 20 mm or so of the soil. During 12–15d after a rainfall, new root production increased total rootlength by 47 per cent to 740 m for A. deserti and by 27 percent to 230 m for F. acanthodes; root dry weight then averagedonly 15 per cent of shoot dry weight. The annual carbon allocatedto dry weight of new roots required 11 per cent of shoot carbondioxide uptake for A. deserti and 19 per cent for F. acanthodes.Elongation of new roots was greatest near a soil temperatureof 30°C, and lethal temperature extremes (causing a 50 percent decrease in root parenchyma cells taking up stain) were56°C and -7°C. Soil temperatures annually exceeded themeasured tolerance to high temperature at depths less than 20mm, probably explaining the lack of roots in this zone. Attached roots immersed in solutions with osmotic potentialsabove -2·6 MPa could produce new lateral roots, with50 per cent of maximum elongation occurring near -1·4MPa for both species. Non-droughted roots lost water when immersedin solutions with osmotic potentials below -0·8 MPa,and root hydraulic conductance decreased markedly below about-1·2 MPa. Pressure-volume curves indicated that, fora given change in water potential, non-droughted roots lostthree to five times more water than droughted roots, non-droughtedleaves, or non-droughted stems. Hence, such roots, which couldbe produced in response to a rainfall, will lose the most tissuewater with the onset of drought, the resulting shrinkage beingaccompanied by reduced root hydraulic conductance, less contactwith drying soil, and less water loss from the plant to thesoil. Agave deserti, Ferocactus acanthodes, roots, soil, temperature, water stress, drought, Crassulacean acid metabolism, succulents     

Relationship between Coleoptile Elongation and Alcoholic Fermentation in Rice Exposed to Anoxia. I. Importance of Treatment Conditions and Different Tissues

The relationship between coleoptile elongation and alcoholicfermentation of rice under anoxia is examined using seeds either:(a) N₂ flushed during submergence, (b) incubated in stagnantdeoxygenated agar at 0·1% w/v to simulate the stagnantconditions of waterlogged soil, or (c) incubated in waterloggedsoil. Coleoptile elongation growth was greater for N₂ flushing> stagnant agar > soil; seed survival was also greatestin this order over 1-5 d. Ethanol concentrations in coleoptiles and intact seeds (cv.IR42) were approximately 300 and 100 mol m^-3 respectively whenseeds were grown 3 d in stagnant agar, however 92% of the ethanolin seeds diffused into the external medium when solutions weremixed for 5-10 s. Coleoptile growth under anoxia was relatedto rates of ethanol synthesis (R_E) in different treatments;there was greater coleoptile growth and R_E for seeds in N₂ flushedsolutions than in stagnant deoxygenated agar. Coleoptile growthof individual seeds was also related to the R_E of each seedat 2-3 d after anoxia (r² = 0·46). Analysis of different tissues was important in evaluating growthand metabolism of coleoptiles. Although the coleoptile onlyaccounted for 0·7% of seed dry weight at 3 d after anoxia,it contained 21% of the ethanol produced by rice seeds. Therewere also three-fold higher rates of R_E on a fresh weight basisin expanding tissues in the base of the coleoptile relativeto the elongated tissues at the apex. Results are discussedin terms of the importance of environmental conditions usedto impose anoxia, quantification of R_E in specific tissues andthe possibility that under stagnant conditions high ethanolconcentrations in tissues may limit R_E and coleoptile growth.Copyright1994, 1999 Academic Press Anoxia, ethanol, alcoholic fermentation, Oryza sativa L., rice, submergence     

Some Factors Concerning the Centripetal Disposition of Bundle Sheath Chloroplasts during the Leaf Development of Eleusine coracana

Factors concerning the chloroplast disposition in bundle sheathcells were investigated in finger millet (Eleusine coracanaGaertn.), and NAD malic enzyme type C₄ plant with the centripetalarrangement of bundle sheath chloroplasts. Segments were cutfrom immature regions of emerging leaves in which the centripetalarrangement of bundle sheath chloroplasts had not yet been established.The leaf segments were floated on solutions with or withoutreagents. Sections were made of the segments at time intervalsand the distribution of bundle sheath chloroplasts was observedby light microscopy. The bundle sheath chloroplasts migratedto the vascular bundle and established a centripetal arrangementby 12-16 h in control solutions. Auxins, cycloheximide and cytochalasinB inhibited the disposition of bundle sheath chloroplasts whilechloramphenicol and colchicine had no effect. The inhibitoryeffect of auxins appeared only at early stages of chloroplastmigration while cycloheximide and cytochalasin B were effectiveeven at later stages. Cessation of elongation growth, cytoplasmicprotein synthesis and microfilaments seemed to be associatedwith the centripetal disposition of bundle sheath chloroplasts.Copyright1993, 1999 Academic Press Bundle sheath chloroplast, C₄ plant, chloroplast orientation, Eleusine coracana, finger millet     

Development and Evaluation of an In Vitro System to Study Strawberry Fruit Development

Growth and ripening of strawberry (Fragariaananassa Duch.)fruit harvested at immature stages of development was accomplishedby placing the peduncles of individual fruit in solutions composedof hydroxyquinoline hemisulphate (HQS) and sucrose. Fruit cultivarand developmental stage at harvest were the major determinantsof in vitro performance. ‘Pajaro’ fruit harvestedat 50 to 60% maturity exhibited the greatest and most uniformweight gain when placed in solutions containing 200 mol m^–3HQS and 88 mol m^–3 sucrose. Although the final fruit weightof in vitro-ripened fruit was less than that of field-ripenedfruit, colour development in vitro occurred at the same rateand to the same extent as field-grown fruit. Key words: Ripening, non-climacteric fruit     

Non-linear dynamics of a pelagic ecosystem model with multiple predator and prey types

Using numerical techniques, we explored the dynamics of a one-dimensional,six-component nutrient–phytoplankton–zooplankton(NPZ) model in which zooplankton grazed on a mixed prey field.Five alternative functional forms were implemented to describezooplankton grazing, and the form for predation on mesozooplanktonwas prescribed by a product of a specific predation rate (h)and the mesozooplankton concentration raised to a power (q),which we varied between one and two. With all five grazing functions,Hopf bifurcations, where the form of the solution transitionedbetween steady equilibrium and periodic limit cycles, persistedacross the q–h parameter space. Regardless of the valuesof h and q, with some forms of the grazing function, we wereunable to find steady equilibrium solutions that simultaneouslycomprised non-zero concentrations for all six model components.Extensions of Michaelis–Menten-based single resource grazingformulations to multiple resources resulted in periodic solutionsfor a large portion of the q–h space. Conversely, extensionsof the sigmoidal grazing formulation to multiple resources resultedin steady solutions for a large portion of q–h parameterspace. Our results demonstrate the consequences of the functionalform of biological processes on the form of the model solutions.Both the steady or oscillatory nature of state variable concentrationsand the likelihood of their elimination are important considerationsfor ecosystem-modelling studies, particularly when attemptingto model an ecosystem in which multiple phytoplankton and zooplanktoncomponents are thought to persist simultaneously for at leasta portion of the seasonal cycle.     

Calcium and Rhizodermal Differentiation in Primary Maize Roots

Rhizodermal differentiation of maize (Zea mays L. cv. LG 11)roots cultured in humid air was influenced by a pretreatmentfor 2 h in CaCl₂ or CaSO₄ solutions. This increased the numberof hair-producing roots and the density of hairs. Ethylene glycol-bis-(ß-aminoethylether)N,N'-tetraacetic acid (EGTA) was inhibitory. Root hairsemerged in the part of the cell nearer to the tip. Trichoblastswere shorter and elongated more slowly than atrichoblasts. Theelongation of the lower part of the trichoblast was less thanthat of the upper part. Key words: Cell length, cell number, hair position     

Permeability Changes in Tissues and Other Effects of Cell-separating Solutions from Soft Rots Caused by Corticium praticola and Erwinia atroseptica

Cell-free extracts from soft rots of potato tubers caused byErwinia atroseptica and Corticium praticola readily caused cellseparation and loss of electrolytes in discs of potato tubers.Both were most rapid at pH and Ca⁺⁺ ion concentration optimalfor the activity of a pectate trans-climinase in the E. atrosepticaextract and a pectate polygalacturonase in the C. praticolarot extract. Permeability changes and killing of protoplastsbut not cell separation were delayed when solutes at plasmolysingconcentrations were added to the solutions of the cell-separatingenzymes. The role of these enzymes in the permeability changesand killing of protoplasts is discussed.     

The Biological Activity of Organoboron Compounds in the Promotion of Root Growth

The growth of the bean (Vicia faba var. minor) radicle in nutrientsolution requires the presence of borate. Optimum extensiongrowth, over 41 h, was obtained in the presence of 0.5 µMboric acid. This requirement of borate for root growth couldalso be satisfied by PhB(OH)₂, 2-OCH₃PhB(OH)₂, and 4-OCH₃PhB(OH)₂.These three compounds also complex in vitro with catechol-3,5-disulphonic acid. NaPh₄B and 2, 6-OCH₃)₂PhB(OH)₂ did not formsuch complexes in vitro, but were biologically active as sourcesof boron for radicle growth. This activity of NaPh₄B was absentif roots were grown in solutions which were changed every 8h. The activity of both NaPh₄B and 2,6-(OCH₃)₂PhB(OH)₂ was increasedby using stock aqueous solutions which were not freshly prepared.Theresults are considered to provide support for the hypothesisthat the activity of borate, as an essential plant nutrient,depends upon its ability to form a biologically active complexwith an in vivo cis-diol compound.     

Angiotensin regulates the selectivity of the Na+-K+ pump for intracellular Na+

Treatment of rabbits with angiotensin-converting enzyme (ACE)inhibitors increases the apparent affinity of theNa⁺-K⁺pump for Na⁺. To explore themechanism, we voltage clamped myocytes from control rabbits and rabbitstreated with captopril with patch pipettes containing 10 mMNa⁺. When pipette solutions wereK⁺ free, pump current(I_p) formyocytes from captopril-treated rabbits was nearly identical to thatfor myocytes from controls. However, treatment caused a significantincrease in I_pmeasured with pipettes containingK⁺. A similar difference wasobserved when myocytes from rabbits treated with the ANG II receptorantagonist losartan and myocytes from controls were compared.Treatment-induced differences in I_p wereeliminated by in vitro exposure to ANG II or phorbol 12-myristate 13-acetate or inclusion of the protein kinase C fragment composed ofamino acids 530-558 in pipette solutions. Treatmentwith captopril had no effect on the voltage dependence ofI_p. We concludethat ANG II regulates the pump's selectivity for intracellularNa⁺ at sites near the cytoplasmicsurface. Protein kinase C is implicated in the messenger cascade.

     

Genetic Sensitivity to 6-n-Propylthiouracil (PROP) and Hedonic Responses to Bitter and Sweet Tastes

Genetically mediated sensitivity to the bitter taste of 6-n-propylthiouracil(PROP) has been associated with greater acuity for bitter andfor some sweet tastes. Thus far, few studies have explored therelationship between PROP taste sensitivity and hedonic responsesto bitter and sweet. In this study, 87 normal-weight young womenwere divided into PROP non-tasters (n = 18), regular tasters(n = 49), and supertasters (n = 20), based on their PROP detectionthresholds and the scaling of five suprathreshold solutionsof PROP and NaCl. Non-tasters had thresholds >1.8 x 10^–4mol/l PROP. Supertasters had thresholds <3.2 x 10^–5mol/l PROP and PROP/NaCl ratios >1.70. As expected, dislikeof the bitter taste of PROP was determined by its perceivedintensity, which was greater among supertasters than among regulartasters or non-tasters. Significant correlations were observedbetween PROP taste thresholds and the sum of intensity ratings(r = –0.61) and between summed intensity and summed hedonicratings (r = –0.80). PROP taste sensitivity was weaklylinked to enhanced perception of sweet taste, but did not predicthedonic responses to sucrose or to saccharin solutions. Giventhat the dislike of PROP solutions is determined by their perceivedintensity, hedonic responses to PROP solutions may provide arapid way of screening for PROP taster status. Chem. Senses22: 27–37, 1997.     

羟基香茅醛缩醛类化合物的合成及对蚊虫的驱避活性

为了寻找新的萜类驱避剂, 以羟基香茅醛为原料, 合成羟基香茅醛二甲缩醛、 羟基香茅醛乙二醇缩醛、 羟基香茅醛1, 3-丙二醇缩醛和羟基香茅醛1, 2-丙二醇缩醛, 用红外光谱IR、 质谱MS分析其结构, 对羟基香茅醛1, 2-丙二醇缩醛还进行了¹H NMR及¹³C NMR分析。按国标GB/T 13917.9-2009测定了它们对白纹伊蚊Aedes albopictus、 中华按蚊Anopheles sinensis及淡色库蚊Culex pipiens的驱避活性。结果表明: 10%（质量分数）羟基香茅醛二甲缩醛和羟基香茅醛1, 2-丙二醇缩醛对中华按蚊的驱避时间均达到国标B级; 羟基香茅醛1, 2-丙二醇缩醛还对其他的蚊虫具有驱避作用, 20%（质量分数）羟基香茅醛1, 2-丙二醇缩醛对白纹伊蚊的驱避时间超过国标B级; 10%（质量分数）羟基香茅醛1, 2-丙二醇缩醛对淡色库蚊的驱避时间超过国标A级。这些结果说明它们对不同蚊种驱避活性的差别, 为不同场合的驱蚊需要提供了理论基础。     

赤松毛虫性信息素次要组分的鉴定——组分、电生理和田间效果

用带有极性和非极性毛细柱的气相色谱(GC)分析赤松毛虫Dendrolimus spectabilis性信息素腺体提取物,发现腺体中除含有已鉴定的性信息素(顺,反)-5,7-十二碳二烯醇(Z5,E7-12∶OH)外,还有微量的(顺,反)-5,7-十二碳二烯醛(Z5,E7-12∶Ald)和(顺,反)-5,7-十二碳二烯乙酸酯(Z5,E7-12∶Oac),三种成分以100∶5-6±5-4∶3-2±1-8的比例存在。使用气相色谱-质谱选择性离子检测法（GC-MS-SIM）分析赤松毛虫腺体提取物,发现腺体中确实含有微量的Z5,E7-12∶Oac和痕量的Z5,E7-12∶Opr。赤松毛虫腺体提取物的气相色谱和触角电位检测联用（GC-EAD）分析发现只有Z5,E7-12∶OH能激起EAD反应,然而使用较高剂量的标准化合物进行GC-EAD分析发现Z5,E7-12∶OH、Z5,E7 12∶Oac和(顺,反)-5,7-十二碳二烯丙酸酯(Z5,E7-12∶Opr)均能刺激起EAD反应,而Z5,E7-12∶Ald则不能。触角电位（EAG）剂量-反应关系研究表明,当剂量变化范围在0.01～1 μg时,雄虫触角对Z5,E7-12∶OH最敏感,对Z5,E7-12∶Oac和Z5,E7-12∶Opr次之。田间试验表明,由Z5,E7-12∶OH, Z5,E7-12∶Oac和Z5,E7-12∶Opr配制的三组分诱芯,其诱蛾量显著高于由Z5,E7-12∶OH组成的单组分或是它与其乙酸酯或丙酸酯组成的两组分诱芯,当Z5,E7-12∶OH,Z5,E7-12∶Oac和Z5,E7-12∶Opr的比例为100∶3∶25时,诱蛾效果最佳。在上述三组分混合物中加入一定量的Z5,E7-12∶Ald,则对诱蛾有明显的抑制作用。上述事实表明,Z5,E7-12∶Oac和Z5,E7-12∶Opr是赤松毛虫性信息素的两种次要组分,而Z5,E7-12∶Ald则是信息素的抑制剂。     

Characterization of new strains of nonphotosynthetic mutants of Chlamydomonas reinhardtii II. Quinones and cytochromes b-559, b-563 and c-553 in twelve mutants having impaired Photosystem II function

Twelve new strains of nonphotosynthetic mutants of Chlamydomonasreinhardtii having impaired functioning of Photosystem II werestudied with respect to their quinone and chloroplastic cytochromecontents and to various photooxidation reactions of cytochromesb-559 and c-553. The quinones were analyzed by chromatography,cytochromes b-563 and c-553 were measured spectrophotometricallyafter solubilization by Triton X-100, and cytochrome b-559 wasstudied by means of low-temperature difference spectra. Noneof these mutants showed a great deficiency of plastoquinoneA, ubiquinone Q9, cytochrome b-563 or cytochrome c-553. Butall lacked an ascorbate-reducible pool of cytochrome b-559 photooxidizableat 77?K. In spite of this deficiency, five mutants (Fl 18, Fl29, Fl 47, Fl 50, Fl 59) showed an appreciable photooxidationof cytochrome b-559 in the presence of FCCP at room temperature.The other strains performed only weak cytochrome b-559 photooxidationin the presence of FCCP, DCMU and DBMIB or p-benzoquinone (Fl39, Fl 42, Fl 52, Fl 54, Fl 57, Fl 60); in the mutant Fl 33,no cytochrome photooxidation was observed. These results pointed out that the pool of ascorbate-reduciblecytochrome b-559 photooxidizable at 77?K is different from thepool photooxidizable in the presence of FCCP at room temperature. (Received February 8, 1979; )     

Contents of Cytochromes, Quinones and Reaction Centers of Photosystems I and II in a Cyanobacterium Synechococcus sp.

The contents of photosystem I and photosystem II reaction centers,cytochrome c-553, cytochrome c-550, cytochrome f, cytochromeb-559, cytochrome b-563, plastoquinone and vitamin K₁ in thecyanobacterium Synechococcus sp. were determined. About threephotosystem I reaction centers were present for each photosystemII reaction center. The amounts of cytochromes functioning betweenthe two photosystems were approximately half those of the photosystemI reaction center. Plastocyanin was not detected, while plastoquinoneand vitamin K₁ were present in excess of other electron carriersand reaction centers. The results indicate the importance ofplastoquinone and cytochrome c-553 for cooperation of the tworeaction centers through electron transport. ¹Present address: Toray Basic Research Laboratory, 1111 Tebiro,Kamakura, Kanagawa 248, Japan. (Received June 17, 1982; Accepted January 17, 1983)     

Effect of Water Potential and Temperature on the Germination of Four Species of African Savanna Trees

The germination responses of seeds from the African tree speciesColophospermum mopane, Combretum apiculatum, Acacia tortilisand Acacia karroo under varying regimes of temperature and waterstress (induced by incubation in PEG 8000) are reported Withthe exception of Combretum (at –0.14 and –0.29 MPa)and Colophospermum (at –0.29 MPa), incubation in PEG decreasedthe maximum achieved germination percentage (90–100% forall species), but did not extend the germination lag (exceptin Combretum) or affect the time required to reach maximum germinationCombretum and Colophospermum were found to germinate under thewidest range of temperatures and water potentials, for example,as strongly negative as –1.0 MPa at 20 and 30 °C,respectively These seeds also showed greater or equivalent hypocotylelongation in PEG solutions creating potentials of –0.14,–0.29 or –0.51 MPa when compared with seeds germinatedin water, indicating an additional stress adaptation Acaciaspecies showed progressive reduction in germination rates andradicle elongation in response to decreasing water potentialExperiments giving pre-imbibition treatments in water priorto transfer to PEG solutions showed that both Acacia speciesgerminated at approximately 90% if given such pre-treatmentand less than 10% if transferred directly to PEG It is concludedthat the most stress-adapted species studied are Colophospermummopane and Combretum apiculatum, a finding generally correlatedwith the growth habit of these trees Colophospermum mopane, Combretum apiculatum, Acacia tortilis, Acacia karroo, germination, water stress, Zimbabwe