Soya Bean Seed Growth and Maturation by In Vitro Pod Culture

Immature Glycine max (L.) Merr. seeds initially at 50–70mg fresh weight were successfully grown and matured in vitroin detached pods. Surface sterilized pods were floated in aliquid medium containing 5 per cent sucrose, minerals, and glutaminein 125 ml Erlenmeyer flasks and incubated at 25 °C under350–400 µE m^–1 s^–1 white light. Seedswhich were matured in vitro increased tenfold in dry weight,were visually similar to commercial seeds of the same size,were tolerant to desiccation and germinated with normal seedlinggrowth. Excised pods transported dye from the pedicel to thegrowing seed within 120 min. Soya bean pod culture is a usefultechnique to study the influence of single or combinations ofchemical or environmental parameters on regulation of seed growth,seed maturation, and subsequent germination events without theconfounding interactions with the mother plant. Glycine max (L.) Merr., soya bean, pod culture, seed culture, seed growth, seed maturation, germination     

Modulation of Sucrose Content by Fructose 2,6-bisphosphate during Photosynthesis in Rice Leaves Growing at Different Light Intensities

Reddy, A. R. and Das, V. S. R. 1987. Modulation of sucrose contentby fructose 2,6-bisphosphate during photosynthesis in rice leavesgrowing at different light intensities.—J. exp. Bot. 38:828–833. The relationship between the rate of CO₂ fixation and sucroseconcentration in the leaves of rice (Oryza sativa L.) grownat different light intensities was investigated. Maximum sucrosecontent coincided with maximum rates of CO₂ fixation, achievedat a photon flux density of 1600 µmol m^–2 s^–1.The levels of sucrose and fructose 2,6-bisphosphate were alsocompared in the leaves under different light intensities. Fructose2,6-Msphosphate accumulated during growth at low light. Theactivity of fructose-6-phosphate 2-kinase was high in the leavesgrown at low light while that of fructose-2,6-bisphosphatasewas low. The activities of phosphoglucose isomerase and phospho-glucomutasewere slightly increased by growth at low light The activitiesof UDP glucose pyrophosphorylase were adversely affected invitro with increased concentrations of fructose 2,6-bisphosphatewhile those of sucrose phosphate synthase were moderately affected.Phosphoglucose isomerase and phosphoglucomutase were activatedby fructose 2,6-bisphosphate (8-0 mmol m^–3) by 12-15%.The results suggested that low light intensities during growthresult in an accumulation of fructose 2,6-bisphosphate whichmodulates the key enzymes of sucrose biosynthesis thus regulatingcarbon flow under conditions of limited photosynthesis. Key words: Oryza sativa, photosynthesis, sucrose synthesis, fructose 2,6-bisphosphate, light     

The Relationship between Sucrose and Starch during 'Dark' Export from Leaves of Uniculm Barley

Uniculm barley plants were grown in 8 h photoperiods at a quantumflux density of 655 µE m^–2 s^–1. Groups ofplants were transferred to four different light environmentsfor one 8 h photoperiod (106, 270, 665, and 975 µE m^–2s^–1) and harvested at intervals throughout the succeedingdark period for subsequent carbohydrate analysis of the youngestmature leaf. Sucrose was the predominant carbohydrate in the leaves (attaininga level of c. 100 mg dm^–2 after 8 h at 975 µE m^–2s^–1) but starch was also of significance (20 mg dm^–2after 8 h at 975 µE m^–2 s^–1). During the dark period, following a photoperiod at the threehighest light levels (270, 665, and 975 µE m^–2 s^–1),sucrose was exported first while the starch level remained fairlyconstant. When the-sucrose level fell to 15–20 mg dm^–2starch degradation began. This critical sucrose level was reachedearlier in those plants subjected to lower quantum flux densitiesduring the preceding photoperiod. The delay in the remobilizationof starch suggests an important regulatory mechanism which maybe dependent upon the sucrose level. At 106 µE m^–2s^–1 the sucrose level rose to only 10 mg dm^–2. Herethere was no discernible delay in the depletion of sucrose orstarch.     

Some comparisons among the calming and pain-relieving effects of sucrose, glucose, fructose and lactose in infant rats

Ultrasonic vocalizations were recorded from 10-day-old albinorats while they were isolated from their dam and siblings. Eachrat received a 1.0% BW intra-oral infusion of sucrose, fructose,glucose or lactose at a concentration range of 0.22–0.66M for 3 min and their vocalizations were determined during theinfusion and for an additional 7 min. Sucrose, fructose andglucose all significantly reduced vocalizations to about 50%of baseline levels, whereas lactose, the milk sugar, was ineffective.Moreover, the dose–response function was flat for thethree effective sugars. In a second experiment, the effectsof these sugars on heat escape latency were measured. Sucrose,fructose and glucose each elevated the latency with which infantrats removed a paw from a 48°C surface; lactose did not.These findings of lactose ineffectiveness and the flat dose-responsefunction for the other three sugars exactly parallel those obtainedfor human newborns. Their implications are discussed.     

The Effect of Shade During Leaf Expansion on Photosynthesis by White Clover Leaves

In three experiments measurements of photosynthesis were madeon single leaves of white clover (Trifolium repens L.) on threecultivars grown in a controlled environment. Plants which had grown under an irradiance of 30 J m^–2s^–1, or in shade within a simulated mixed sward, producedleaves with photosynthetic capacities some 30 per cent lowerthan did plants grown at 120 J m^–2 s^–1 without shade.There were no differences between treatments either in photosynthesismeasured at 30 J m^–2 s^–1, or in respiration ratesper unit leaf dry weight. Respiration per unit leaf area washigher in the plants grown at 120 J m^–2 s^–1, reflectingthe lower specific leaf area of these leaves. There were nodifferences between the three cultivars examined. Leaves which were removed from the shade of a simulated swardshortly after becoming half expanded achieved photosyntheticcapacities as high as those which were in full light throughouttheir development. It is suggested that it is this characteristicwhich enables clover plants growing in an increasingly densemixed sward to produce a succession of leaves of high photosyntheticcapacity, even though each lamina only reaches the top of thesward at a relatively late stage in its development. Trifolium repens L., white clover, photosynthesis, leaf expansion, shade, specific leaf area, stomatal conductance     

Field Measurements of the Gas Exchange of Woody Plant Species in Simulated Sunflecks

The photosynthetic responses of eight tree and shrub speciesto simulated sunflecks was measured in the field. The net carbonexchange (NCE) of Corylus avellana and Ulmus glabra increasedwith irradiance up to the maximum irradiance of 230 µmolm^–2 s^–1. The NCE of Fraxinux excelsior, Hedera helixand the sun and shade forms of Rhododendron ponticum saturatedat about 120 µmol m^–2 s^–1 whereas the NCEof Ilex aquifolium, Daphne laureola and Fagus sylvatica hadeffectively saturated at 27 µmol m^–2 s^–1. In all cases the quantum efficiency of NCE could be predictedfrom measurements of chlorophyll fluorescence and the maximumvalue for NCE from measurements of stomatal conductance. Therelationships were combined into a model for predicting NCE/irradiancecharacteristics. Corylus avellana L., Daphne laureola L., Fagus sylvatica L., Fraxinus excelsior L., Hedera helix L., Ilex aquifolium L., Prunus laurocerasus L., Rhododendron ponticum L., Ulmus glabra Huds., gas exchange, stomatal resistance, water use efficiency, chlorophyll fluorescence, quantum efficiency     

Bulbing in Long-day Onion (Allium cepa L.) Cultured In Vitro: Comparison Between Sugar Feeding and Light Induction

Bulbs were obtained on onion plants cultured in vitro. No bulbinghappened under long days with fluorescent light and 30–40g l^–1 sucrose. Bulb formation was mainly dependent eitheron sucrose concentration in the culture medium, or on lightspectral composition. Raising the sucrose concentration from40 to 120 g l^–1 increased plant basal swelling and stoppedfurther vegetative development. These plants were not dormant.When fluorescent light was enriched in incandescence duringa long day period, bulbs were obtained in two months and underwenta consecutive dormancy. Bulb, dormancy, light spectral quality, photoperiod, R: FR ratio, sugar, tissue culture     

The Response of the C3-CAM Tree, Clusia rosea, to Light and Water Stress: I. GAS EXCHANGE CHARACTERISTICS

Gas exchange measurements were undertaken on 2-year-old plantsof Clusia rosea. The plants were shown to have the ability toswitch from C₃-photosynthesis to CAM and vice versa regardlessof leaf age and, under some conditions, CO₂ was taken up continuously,throughout the day and night. The light response was saturatedby 120 µmol m^–2 s^–1 typical of a shade plant. Gas exchange patterns in response to light, water and VPD wereexamined. All combinations of daytime and night-time CO₂ uptakewere observed, with rates of CO₂ uptake ranging from 2 to 11µmol m^–2 s^–1 depending upon water status andlight. Categorization of this plant asC₃, CAM or an intermediateis impossible. Differing VPD affected the magnitude of changesfrom CAM to C₃-photosynthesis (0 to 0.5 and 0 to 6.0 µmolm^–2 s^–1 CO₂, respectively) when plants were watered.Under well-watered conditions, but not under water stress, highPPFD elicited changes from CAM to C₃ gas exchange. This is unusualnot only for a shade plant but also for a plant with CAM. Itis of ecological importance for C. rosea, which may spend theearly years of its life as an epiphyte or in the forest understorey,to be able to maximize photosynthesis with minimal water loss. Key words: Clusia rosea, CAM, C₃, stress     

The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

The Relationship between Sucrose Supply, Sucrose-cleaving Enzymes and Flower Abortion in Pepper

Abortion of pepper flowers depends on the light intensity perceivedby the plant and on the amounts of sucrose taken up by the flower(Aloni B, Karni L, Zaidman Z, Schaffer AA. 1996.Annals of Botany78: 163–168). We hypothesize that changes in the activityof sucrose-cleaving enzymes within the flower ovary might beresponsible for the changes in flower abortion under differentlight conditions. In the present study we report that the activityof sucrose synthase, but not of cytosolic acid invertase, increasesin flowers of pepper plants which were exposed, for 2 d, toincreasing photosynthetically active radiation (PAR) in therange of 85–400 µmol m^-2s^-1at midday. Sucrose synthaseactivity increased in parallel with the increasing concentrationsof starch in the flower ovary. Feeding flower explants, preparedfrom 3-d-predarkened plants, with 100 mM sucrose for 24 h, causeda 23% increase in reducing sugars and a 2.5-fold increase instarch concentration, compared with explants fed with buffer.Likewise, feeding explants of pepper flowers with sucrose, glucose,fructose and also mannitol increased the sucrose synthase activityin the ovaries. Concomitantly, sucrose, glucose and fructose,but not mannitol, reduced the abortion of flower explants. Itis suggested that sucrose entry into the flower increases theflower sink activity by inhibiting abscission and inducing metabolicchanges, thus enhancing flower set. Pepper; Capsicum annuum L.; abscission; light; pepper flowers; sucrose; glucose; fructose; starch; acid invertase; sucrose synthase     

Biochemical Limitations to Carbon Assimilation in C3 Plants--A Retrospective Analysis of the A/Ci Curves from 109 Species

Species-specific differences in the assimilation of atmosphericCO₂ depends upon differences in the capacities for the biochemicalreactions that regulate the gas-exchange process. Quantifyingthese differences for more than a few species, however, hasproven difficult. Therefore, to understand better how speciesdiffer in their capacity for CO₂ assimilation, a widely usedmodel, capable of partitioning limitations to the activity ofribulose-1,5-bisphosphate carboxylase-oxygenase, to the rateof ribulose 1,5-bisphosphate regeneration via electron transport,and to the rate of triose phosphate utilization was used toanalyse 164 previously published A/C_i, curves for 109 C₃ plantspecies. Based on this analysis, the maximum rate of carboxylation,Vc_max, ranged from 6µmol m^–2 s^–1 for the coniferousspecies Picea abies to 194µmol m^–2 s^–1 forthe agricultural species Beta vulgaris, and averaged 64µmolm^–2 s^–1 across all species. The maximum rate ofelectron transport, J_max, ranged from 17µmol m^–2s^–1 again for Picea abies to 372µmol m^–2 s^–1for the desert annual Malvastrum rotundifolium, and averaged134µmol m^–2 s^–1 across all species. A strongpositive correlation between Vc_max and J_max indicated that theassimilation of CO₂ was regulated in a co-ordinated manner bythese two component processes. Of the A/C_i curves analysed,23 showed either an insensitivity or reversed-sensitivity toincreasing CO₂ concentration, indicating that CO₂ assimilationwas limited by the utilization of triose phosphates. The rateof triose phosphate utilization ranged from 4·9 µmolm^–2 s^–1 for the tropical perennial Tabebuia roseato 20·1 µmol m^–2 s^–1 for the weedyannual Xanthium strumarium, and averaged 10·1 µmolm^–2 s^–1 across all species. Despite what at first glance would appear to be a wide rangeof estimates for the biochemical capacities that regulate CO₂assimilation, separating these species-specific results intothose of broad plant categories revealed that Vc_max and J_maxwere in general higher for herbaceous annuals than they werefor woody perennials. For annuals, Vc_max and J_max averaged 75and 154 µmol m^–2 s^–1, while for perennialsthese same two parameters averaged only 44 and 97 µmolm^–2 s^–1, respectively. Although these differencesbetween groups may be coincidental, such an observation pointsto differences between annuals and perennials in either theavailability or allocation of resources to the gas-exchangeprocess. Key words: A/C_i curve, CO₂ assimilation, internal CO₂ partial pressure, photosynthesis     

Development of sucrose preference in rabbit pups

Taste preference behavior in developing rabbit pups was examinedat 2–4 days, 6–8 days and 14–16 days postnatally.0.3 M sucrose and distilled water were presented alternatelyat 2 min. intervals, and volumes ingested were recorded. Sweetpreferences were not expressed until late in the second postnatalweek. Since it is known that rabbit pups exhibit distinctivefacial displays to different taste stimuli at birth (Ganchrowet al., 1979) the delay in the expression of sweet preferencewas postulated to be related to the postnatal maturation ofneural processes central to peripheral and brainstem gustatorycoordinating mechanisms.     

Changes in Steady-State Photosynthetic 14C-Incorporation into cellular Metabolites of Chlorellax pyrenoidosa during Transitions from High to Low Irradiance

Changes in the levels of ¹⁴C-labelled metabolites were monitoredin Chlorella pyrenoidosa cells during a transition from highto low irradiance, i.e., from 700 to 430 µmol quanta (400–700nm) m^–2 s^–1. Chlorella cells assimilated ¹⁴CO₂ photosynthetically(steady-state ¹⁴C-labelling) for 12 min at the high irradianceand then 10 min at the low irradiance. With the transition tolow light, the level of ¹⁴C-labelled ribulose 1,5- bisphosphate(RuBP) did not decrease, even though the rate of total ¹⁴C-incorporationdecreased by 80%. The data suggest that RuBP carboxylase deactivatesrapidly (within 1 or 2 min) on exposure to low light, causingRuBP pool sizes to be maintained (or even increased) in spiteof a decreased rate of RuBP regeneration. There was also evidenceof light modulation of other enzymes, including some enzymesinvolved in sucrose synthesis. The rate of sucrose synthesisdecreased with decrease in light intensity while the level ofuridine diphosphoglucose increased, but within a few minutes,both returned to their former levels. ¹Present address: Chemical Biodynamics, Lawrence Berkeley Laboratory,Building 3, 1 Cyclotron Road, Berkeley, CA 94720, U.S.A. (Received March 8, 1986; Accepted June 25, 1986)     

Effects of Sucrose Concentration on the Photosynthetic Ability of Rose Shoots In Vitro

Reducing the concentration of sucrose in the culture mediumover successive subcultures has been tested as a method forincreasing the ability of rose shoots grown in vitro (Rosa cvsIceberg and Peace) to take up CO₂. Shoots maintained on ‘constant’10, 20 and 40 g I^–1 sucrose showed decreased levels ofCO² uptake at higher sucrose concentrations, although cv. Peacegrew least at 10 g l^–1 and showed correspondingly lowamounts of CO₂ uptake compared with 20 and 40 g l^–1. Bothcultivars died when sucrose was omitted from the medium. Assucrose concentration was reduced in the medium, so CO₂ uptakeof shoots initially cultured on 20 and 40 g l^–1 sucrosewas found to increase, although a concentration of 10 gl ^–1sucrose seemed to be limiting, below which the growth and chlorophylllevels of shoots declined. Rosa hybrid, rose, shoot culture in vitro, photosynthetic ability, sucrose, infra-red gas analysis     

Photosynthesis and Degree of Polymerization of Fructan during Reproductive Growth of Meadow Fescue at two Temperatures and two Photon Flux Densities

Accumulation of dry weight was measured in plant parts of meadowfescue (Festuca pratensis Huds.) that was grown at 16/11 °Cor 26/21 °C and with 20 or 60 nE cm^–2 s^–1 photosyntheticallyactive radiation. Plants reached anthesis about 3 weeks laterat 16/11 °C than at 26/21 °C and had then a higher proportionof dry weight in inflorescences and less in leaf blades. Growthtemperature had little effect on CO₂ exchange rate (CER) butplants grown at 60 nE cm^–2 s^–1 had higher CER thanthose grown at 20 nE cm^–2 s^–1. The concentration of water-soluble carbohydrates (WSC) at similargrowth stages was usually higher at 16/11°C than at 26/21°C.High radiation also led to higher WSC in stem and leaf tissue.Root tissue changed least and WSC did not exceed 10% of dryweight during the experiment. In all tissues, when WSC was high,the fructans were distributed into a group with a high degreeof polymerization (DP) and another with a low DP. The low DPgroup included sucrose, reducing sugars and fructans up to about20 units long. An apparent threshold concentration of WSC wasnecessary for synthesis of the high DP fructans. This concentrationwas near 12% for leaf tissue, about 6% for stem base tissue,and 2.5% for root tissue. The average apparent DP of the highDP fructan group was 43 to 50 for leaf tissue, 31 to 93 forstem base tissue, and 27 to 31 for roots. These characteristicsappeared to be mostly tissue dependent with less effect fromtemperature and radiation. Key words: Fructans, Meadow fescue, Environmental effects, Dry weight distribution     

The Composition of Phloem Exudate and Xylem Sap from Tree Tobacco (Nicotiana glauca Grah.)

The composition of xylem sap and exudate from stem incisionsof Nicotiana glauca Grah. was compared in detail. Exudationfrom stem incisions occurred over a 5 min period in certainplants, enabling collection of 5–30 µl of sap. Therate of exudation showed an exponential decline. Exudate hada high dry matter content (170–196 mg ml^–1) andhigh sugar (sucrose) levels. Xylem sap had a low pH (5.8) andexudate a pH of 7.9. Glutamine dominated the amino compoundsin xylem sap and exudate, and K⁺ was the major cation. Totalamino compounds in stem exudate reached 10.8 mg ml^–1 whereasxylem sap contained much lower levels (0.28 mg ml^–1).All mineral elements and amino compounds with the exceptionof calcium were more concentrated in stem exudate than in xylemsap. Sucrose was labelled heavily in stem exudate following pulsingof an adjacent leaf with ¹⁴CO₂. A concentration gradient ofsugar (2.1 bar m^–1) was recorded for stems. Levels ofsucrose, amino compounds and K⁺ ions in stem exudate showeda diurnal periodicity. Each commodity reached maximum concentrationat or near noon and minimum concentration about dawn. The evidencesuggests that exudate from stem incisions of N. glauca is arepresentative sample of solutes translocated in the phloem. Nicotiana glauca Grah., phloem sap, xylem sap, sucrose, amino compounds, mineral ions     

Effects of algal concentration, bacterial size and water chemistry on the ingestion of natural bacteria by cladocerans

Journal of Plankton Research, 11, 1273–1295, 1989. The values of P/U⁰ (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 1289–1290) and severalequations (footnote b of Table I; p. 1290, lines 3–4)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studied^aGnathobaseof trunklimb number. ^bP = 8µU₀/(b(1 – 21nt + 1/6(t²) - 1/144(t⁴))), whereP = pressure drop in dyn cm^–2, =3.1416, U₀ = fluid velocityin cm s^–1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s^–1cm^–2. Formula from Jørgensen (1983). The text (p. 1289, line 19 to p. 1290, line 10) should read: organism. Using a similar argument, a 0.5 mm Ceriodaphnia witha filter area of 0.025 mm² (Ganf and Shiel, 1985) and pressuredrop P = 2757 dyn cm^–2 (with fluid velocity of 0.07 cms^–1) allocates only 2171 ergs h^–1 to filtrationof a total energy expenditure of 10⁴ ergs h^–1 [filtrationenergy (ergs h^–1) = area (cm²) x pressure drop (dyn cm^–2)x 3600 (s h^–1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h^–1) = respiration(0.05 µl O₂ ind^–1 h^–1 consumed; Gophen, 1976)x conversion factor (2 x 10⁵ ergs µl^–1 O₂). Withan estimated 0.034 mm² in filter area, fluid velocity of 0.041cm s^–1 and respiration of 1.8 x 10⁴ ergs h^–1 (calculatedfrom Porter and McDonough, 1984), a 0.5 mm Bosmina uses <4%of its metabolism to overcome filter resistance. The velocities used in the original examples (0.4 cm s^–1for Ceriodaphnia, 0.2 cm s^–1 for Bosmina) were derivedfrom literature values of appendage beat rate and estimatesof the distance travelled by the appendages during each beatcycle. This approach unnecessarily assumes that all water movedpasses through the filter. In the new calculations, the flowacross the filter needed for food to be collected by sieving(0.07 cm s^–1 for Ceriodaphnia and 0.041 cm s^–1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection.     

Sucrose metabolism and cell elongation in developing sunflower hypocotyls

The relationships between cell elongation and changes in specificactivities of enzymes of sucrose metabolism were investigatedin the growing region of hypocotyls of sunflower seedlings {Helianthusannuus L.) that were grown either in darkness or irradiatedwith continuous white light (WL). After transfer of dark–grownseedlings into WL an inhibition of cell elongation was observed.In etiolated stems, changes in enzymes of sucrose breakdown(acid invertase, sucrose synthase) were closely correlated withthe rate of cell elongation. Irradiation with WL induced a largedrop in acid invertase and a significant decrease in sucrosesynthase. The changes in concentration of sucrose were inverselycorrelated with the activities of the sucrose breakdown enzymes.A short–term experiment revealed that the effect of WLon growth was more rapid than the inhibitory effect on invertaseactivity. In dark–grown stems the activities of enzymesof sucrose biosynthesis (sucrose–phosphate synthase, ribulose1,5 bisphosphate carboxylase/oxygenase) were very low. AfterWL irradiation significant enhancements were measured. However,activities of enzymes of sucrose breakdown were still much largerthan those of sucrose biosynthesis, indicating that the green(de–etiolated) stem remains a sink for sucrose. We suggestthat the relative maintenance of cell osmotic pressure and turgorduring rapid cell elongation in darkness is due to enhancedhydrolysis of imported sucrose, which is cleaved by two enzymes(invertase, sucrose synthase). This process is regulated bylight and hence is under environmental control. Key words: Cell elongation, organ growth, Helianthus annuu, sucrose metabolism, source-sink relationship     

Effects of photon flux density on carbon partitioning and rhizosphere carbon flow of Lolium perenne

The distribution and partitioning of dry matter and photoassimilateof Lolium perenne was investigated under two light regimes providingphotosynthetically active radiation of 350 µmol m^–2s^–1 (low light treatment) or 1000 µmol m^–2s^–1 (high light treatment). Plants were grown at specificgrowth conditions in either soil or sand microcosm units tofollow the subsequent release of carbon into the rhizosphereand its consequent incorporation into the microbial biomass(soil system) or recovery as exudates (sand system). The distributionof recent assimilate between the plant and root released carbonpools was determined using ¹⁴CO₂ pulse-chase methodology atboth light treatments and for both sand- and soil-grown seedlings.A significant (P     

Some Experimental and Theoretical Observations Concerning Mass Flow in the Vascular Bundles of Heracleum

The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, L_EE = 5 ? 10–⁴ mho cm^–1,L_pE = 9 ? 10^–6 cm³ s^–1 cm^–2 volt^–1 cm,and L_PP = 0.16 cm³ s^–1 cm^–2 (J cm^–3)^–1cm. In uncut phloem strands L_EE is about 1 ? 10^–3 mhocm^–1. In xylem in 2 x 10^–3 N KCI, L_pp = 50 to 225,L_PE = 2 ? 10^–4, and L^EE = 4 ? 10^–3. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga ‘long distance’ current pathway can be the majormotive ‘force’ for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm^–1endogenous in the phloem.