A Humidity-induced Convective Throughflow Ventilation System Benefits Annona squamosa L. Explants and Coconut Calloid

A simple apparatus is described for generating pressurized throughflowventilation in plant tissue culture vessels. No pumps or gas-cylindersare required and the flow is driven by humidity-induced diffusionacross microporous membranes. In the experiments described,pressurized flows of sterile humidified air were supplied atrates of up to 1 ml min^-1and these had beneficial effects onleaf survival and production inAnnona cuttings and on calloidform in coconut. Ethylene (ethene) was removed more quicklyfrom the pressure-flow ventilated culture vessels (t ₅₀, 0.4–0.7h) than from those aerated by diffusion through conventionalpolypropylene membranes (t ₅₀, 1.6–2.4 h). InAnnona cuttings leaf production was greatly increased andethylene-induced leaf fall considerably delayed when culturedwith the forced as opposed to diffusion-based ventilation ofthe vessels. With throughflow ventilation, coconut calloid was more convolutedthan under wholly diffusive aeration and had a smooth distinctepidermal surface and clearly defined sub-epidermal meristematicnodules. It resembled freshly initiated calloid from which regenerationof plantlets via somatic embryogenesis can be obtained. Underwholly diffusive aeration, calloid developed a rough, relativelyundifferentiated surface, more haustorial (i.e. cotyledonary)in appearance, and characteristic of cultures where regenerationpotential has been lost. It is suggested that other benefits of the pressurized throughflowventilation may be the removal of volatiles such as ethanoland acetaldehyde, the removal of excess carbon dioxide at nightand its improved supply during the day, and sustained oxygenconcentrations at levels close to atmospheric both night andday. Abscission; callus; ethylene; explants; tissue-culture; growth; ventilation     

Mechanical and anatomical adaptations in terrestrial and aquatic buttercups to their respective environments

The mechanical adaptations of the stems of four species of Ranunculusto their respective environments were studied by combining tensile,bending and flow-tunnel tests, with anatomical observation. Stems of the two terrestrial species, R. acris and R. repens,had high values for rigidity, EI, because they were stiffenedby large quantities of peripherally placed lignified material.This trend is less evident in R. repens, which had a lower rigidity,though it with stood a higher breaking strain than R. acris.This may adapt R. repens to its creeping habit and help it withstandtrampling. The aquatic R. peltatus and R. fluitans, which live in stilland fast-flowing water, respectively, are both more flexibleand have higher breaking strains, of 0.1–0.15, than terrestrialplants, which may allow them to withstand sudden tugs due toflow. R. peltatus maintains the central lumen, places structuralelements away from the centre, and has a higher rigidity thanR. fluitans, which may allow it to avoid self-shading, and supportitself when the water level falls. The stem of R. fluitans shows adaptations for withstanding dragfrom fast-flowing water. The stem has a low rigidity which allowsit to minimize inertial drag forces by aligning itself parallelto the direction of the local flow. However, the rigidity (andthe second moment of area, I) does not appear to be minimized.This may allow the plant to avoid drag due to flag-like fluttering.A weak region of the stem near the base may act as a ‘mechanicalfuse’ which protects the root system by allowing seasonalgrowth to be lost. Key words: Ranunculus, mechanics, flow, anatomy     

Inhibition of Ion Transport in Excised Barley Roots by Abscisic Acid; Relation to Water Permeability of the Roots

Previous papers have shown that abscisic acid can inhibit transportof ions across the root to the xylem vessels, resulting in reducedexudation from excised roots or inhibiting guttation from intactplants. However, it has not been established whether the inhibitionwas due to a reduction in salt transport (J_s) or in permeabilityof the roots to water (L_p). This paper investigates the effectof ABA on L_p and J_s separately. It is shown that L_p increasedin ABA and then fell, but was about the same as in control rootswhen transport was inhibited. The effect of ABA on exudationtherefore appeared to be mainly due to reduction in J_s. Inhibitionof J_s was also present in intact, transpiring plants and sowas not due to reduced water flow. The inhibition of ion releaseto the xylem affected Na⁺, Mg²⁺, Ca²⁺, and phosphate as wellas the major ion in the exudate, K⁺. It is concluded that ABAinhibits salt transport to the shoot by acting on ion transportinto the xylem, and not by reducing water flow coupled withsalt transport.     

Simulating Growth and Root-shoot Partitioning in Prairie Grasses Under Elevated Atmospheric CO2and Water Stress

We constructed a model simulating growth, shoot-root partitioning,plant nitrogen (N) concentration and total non-structural carbohydratesin perennial grasses. Carbon (C) allocation was based on theconcept of a functional balance between root and shoot growth,which responded to variable plant C and N supplies. Interactionsbetween the plant and environment were made explicit by wayof variables for soil water and soil inorganic N. The modelwas fitted to data on the growth of two species of perennialgrass subjected to elevated atmospheric CO₂and water stresstreatments. The model exhibited complex feedbacks between plantand environment, and the indirect effects of CO₂and water treatmentson soil water and soil inorganic N supplies were important ininterpreting observed plant responses. Growth was surprisinglyinsensitive to shoot-root partitioning in the model, apparentlybecause of the limited soil N supply, which weakened the expectedpositive relationship between root growth and total N uptake.Alternative models for the regulation of allocation betweenshoots and roots were objectively compared by using optimizationto find the least squares fit of each model to the data. Regulationby various combinations of C and N uptake rates, C and N substrateconcentrations, and shoot and root biomass gave nearly equivalentfits to the data, apparently because these variables were correlatedwith each other. A partitioning function that maximized growthpredicted too high a root to shoot ratio, suggesting that partitioningdid not serve to maximize growth under the conditions of theexperiment.Copyright 1998 Annals of Botany Company plant growth model, optimization, nitrogen, non-structural carbohydrates, carbon partitioning, elevated CO₂, water stress,Pascopyrum smithii,Bouteloua gracilis, photosynthetic pathway, maximal growth     

Cell Membrane Stability and Leaf Water Relations as Affected by Potassium Nutrition of Water-Stressed Maize

A field experiment was conducted to investigate the effect ofK nutrition under water stress conditions on cell membrane stabilitymeasured by the polyethylene glycol test, plant growth, internalplant water relations and solute and mineral concentrationsin maize (Zea mays L.). Water-stressed plants showed greateradaptation to water deficits at higher K levels. Cell membranestability increased, leaf water potential and osmotic potentialdecreased, turgor potential increased and stomatal resistancedecreased with increasing K nutrition. Osmotic adjustment wasevident and it may have been influenced by increased K⁺ concentrationsin leaf tissues with increasing K nutrition. Higher leaf thicknessand higher leaf water content were observed at higher K levels.Results suggested that higher supplies of K nutrition may increaseplant production during periods of water stress. Key words: Zea mays L., cell membrane stability, leaf water potential, osmotic adjustment, osmotic potential, potassium nutrition, water stress     

Wheat Cultivars Respond Differently to a Drying Top Soil and a Possible Non-Hydraulic Root Signal

Research has shown that when plant roots are exposed to a dryingsoil a non-hydraulic (chemical) signal is produced in the rootand transported to the shoot, causing stomatal closure and growthretardation. This study was designed to reveal genetic diversityin wheat response to soil conditions which elicit a root signal,as the first step in the investigation of the genetic controlof the production of and the response to the root signal. Five spring wheat (Triticum aestivum L.) cultivars were establishedin the growth chamber in soil-filled polyvinyl chloride tubes,120 cm long and of an internal diameter of 10·2 cm. Soilwas well fertilized and wet to field capacity at emergence whentwo treatments were imposed: (1) tubes were watered from thetop as needed to eliminate stress (control); and (2) tubes hada constant water table at a soil depth of 100 to 120 cm, withno applied water. Measurements were performed on five dateson leaf water status and stomatal diffusive resistance. Above-groundbiomass and grain yield per plant were determined at maturity. The water table treatment resulted in dry and hard top soilconditions which were previously indicated to elicit a possibleroot signal. Under these experimental conditions, cultivarsdiffered in their leaf water status, stomatal diffusive resistance(R_s) and plant production. In the control treatment, R_s of cultivarsincreased with reductions in their relative water content (RWC)and leaf water potential (LWP), indicating the expected controlof R_s by leaf water status. Under conditions of a drying topsoil, relative water content (RWC) and leaf water potential(LWP) increased in cultivars that had a higher R_s, indicatingthat stomatal activity was controlling leaf water status. Itwas therefore suggested that the drying top soil elicited aroot signal which caused stomatal closure and reduced plantproduction. Under such conditions, two cultivars (Bethlehemand V748) consistently maintained relatively low R_s and highplant production, despite their relatively lower RWC and LWP,as compared with cvs C97, V747 and V652. Limited observationssuggest that in these two cultivars relatively fewer roots mayhave been exposed to the drying top soil, as compared with theother three cultivars. Key words: Triticum aestivum, cultivars, soil moistrue, drought stress, root, root signal, stomata, relative water content, leaf water potential, biomass, yield     

Dry Weight Production and Partitioning inMedicago minimaandErodium cicutariumUnder Water Stress

Medicago minimaandErodium cicutariumare two naturalized annualspecies in extensive semi-arid, temperate rangelands of centralArgentina. A field study was conducted during 1989 and 1990to evaluate the effects of different levels of soil water availabilityon above- and below-ground dry weight production and partitioningin these species. Dry weight production byM. minimawas moresensitive to water stress than that byE. cicutarium. Althoughthe response was more marked inM. minima, both species allocateda larger proportion of total plant dry weight to fruits underwater stress than under irrigated conditions during early spring.Percentage allocation of total plant dry weight into reproductiveorgans in both species, and stems and peduncles inE. cicutarium,was correlated with total dry weight of these organs; this mightindicate a correlation between sink size and strength. Persistenceof both species in the local flora appears to be associatedwith their capacity to colonize open, degraded areas and growin association with native perennial grasses, as well as totolerate severe drought periods.Copyright 1998 Annals of BotanyCompany Medicago minima(L.) Grufb. var.minima,Erodium cicutarium(L.) L'Herit, water stress, dry matter production and partitioning.     

Flow Cytometric Determination of Nuclear Replication Stage in Seed Tissues

Flow cytometric determination of DNA levels in embryos of fullymatured seeds of various plant species revealed large amountsof 2C DNA signals, indicating that most cells had arrested thecell cycle at the presynthetic G₁ phase of nuclear division.The accumulation of cells at G₁ was found both in orthodox andin recalcitrant (i.e. Castanea sativa) seed species. As recalcitrantseeds are characterized by the absence of maturation drying,the arrest of the cell cycle in the presynthetic phase may notbe linked to the seed water status. Apart from the 2C signal, 4C values were found in the embryoof some seed species (e.g. Raphanus sativus) indicating thatcells were arrested in G₂ Cells arrested in G₂ were primarilylocated in the root-tip region of the embryo. In addition, combinationsof higher C values (i.e. 8C, 12C, 16C and 64C) were observedin the endosperm of Solanum melongena and Lycopersicon esculentum,and in the root-tip cells of Phaseolus vulgaris and Spinaciaoleracea. These mixtures of polyploid nuclei (also called 'polysomaty')may arise from a developmentally controlled cellular endoreduplicationand indicates that in each cell type of the seed the amountof DNA is regulated both spatially and temporally.Copyright1993, 1999 Academic Press Endive, Cichorium endiva, lettuce, Lactuca sativa, egg-plant, Solanum melongena, pepper, Capsicum annuum, tomato, Lycopersicon esculentum, radish, Raphanus sativus, bean Phaseolus vulgaris, spinach, Spinacia oleracea, chestnut, Castanea sativa, beech, Fagus sylvatica, pine, Pinus nigra, DNA content, flow cytometry, seed, nuclear replication stage, C levels, storage     

Interaction between L-Pipecolic Acid and Water Extracts of Various Plant Species in Floral Induction of Lemna paucicostata

The flower-inducing activity of L-pipecolic acid was synergisticallyenhanced by simultaneous application of the water extracts ofLemna paucicostata and Pharbitis nil, but suppressed by thewater extracts of all other plants we examined. Simultaneousapplication of the water extract of Lemna enhanced the flower-inducingactivity of all plant water extracts. (Received June 6, 1990; Accepted July 7, 1990)     

Water channels in Chara corallina

Water relations parameters ofChara corallina inter-nodes weremeasured using the single cell pressure probe. The effect ofmercurials, which are recognized as non-specific water channelinhibitors, was examined. HgCl₂ concentrations greater than5 mmol m^–3 were found to inhibit hydraulic conductivity{Lp) close to 90%, whereas pCMPS was found to have no effecton Lp. The activation energy of water flow was increased significantlyfrom 21.0 kJ mol^–1 to 45.6 kJ mol^–1, following theapplication of HgCl₂. These results are in accordance with evidencefor Hg²⁺sensitive water channels in the plasma membrane of charophytes(Henzler and Steudle, 1995; Tazawa et al., 1996). The metaboliceffects must, however, be considered in view of the rapid inhibitionof respiration and the depolarization of the membrane potentialwith HgCl₂ concentrations lower than those found to affect Lp.It was possible to measure simultaneously water relations andmembrane PD, in order to examine the contribution of potassiumchannels to Lp. Cells were induced into a K⁺ permeable state.The K⁺ channels, assumed to be open, were subsequently blockedby various blockers. No significant difference in Lp was foundfor any of these treatments. Finally, the permeability of C.corallina membranes to ethanol was examined. HgCl₂ was foundto cause a decrease in reflection coefficient, coinciding witha decrease in Lp, but there was no change in the ethanol permeabilitycoefficient. This has been interpreted in terms of both thefrictional model and composite model of non-electrolyte membranetransport. Key words: Water channels, Chara, hydraulic, conductivity, membrane transport models, reflection coefficient     

Growth of Individuals in Plant Populations

Relationships between individual plant weight and net photosynthesisper day (G(t, x) function of plant weight) in plant populationsof various stand structures were simulated based on a canopyphotosynthesis model. The G(t, x) functions of plant weightare determined mainly by LAI (leaf area index), the relationshipbetween individual plant weight and leaf area, canopy structureand extinction coefficient. The concave relationship betweenindividual plant weight and leaf area at small LAI (<2),at small extinction coefficient (< 0.5), or at the canopystructure having the maximum leaf area density at the bottomproduces a concave G(t, x) function, which generates negativeskewness of plant weight. The linear relationship between individualplant weight and leaf area at large LAI (> 2) produces aconvex G(t, x) function, which generates positive skewness ofplant weight. These simulation results coincide with G(t, x)functions obtained experimentally and with the well-known phenomenonof stand dynamics in which skewness of plant weight becomesnegative in the early growth stage and then increases to a positivevalue as a stand grows and becomes crowded. Helianthus annuus L., individual plant size, mean growth rate, canopy photosynthesis model, skewness, stand structure     

The Effect of Drying Rate on the Survival of Three Desiccation-tolerant Angiosperm Species

The effect of drying rate on the survival of three angiospermresurrection plants, Craterostigma wilmsii (homoiochlorophyllous),Xerophyta humilis (poikilochlorophyllous) and Myrothamnus flabellifolius(homoiochlorophyllous) was examined. All species survived slowdrying, but only C. wilmsii was able to survive rapid drying.C. wilmsii was rapidly able to induce protection mechanismssuch as folding of cell walls to prevent mechanical stress andcurling of leaves to minimize light stress, and thus survivedfast drying. Rapid drying of X. humilis andM. flabellifoliusappeared to allow insufficient time for complete induction ofprotection mechanisms. In X. humilis, there was incomplete replacementof water in vacuoles, the photosynthetic apparatus was not dismantled,plasma membrane disruption occurred and quantum efficiency ofphotosystem II (F_V/F_M) did not recover on rehydration. Rapidlydried leaves of M. flabellifolius did not fold tightly againstthe stem and F_V/F_Mdid not recover. Ultrastructural studies showedthat subcellular damage incurred during drying was exacerbatedon rehydration. The three species co-occur in environments inwhich they experience high desiccation pressures. C. wilmsiihas few features to retard water loss and thus the ability forrapid induction of subcellular protection is vital to survival.X. humilis and M. flabellifolius are able to retard water lossand protection is acquired relatively slowly. Copyright 1999Annals of Botany Company Chlorophyll fluorescence, Craterostigma wilmsii, drying rate, Myrothamnus flabellifolius, resurrection plant, ultrastructure, Xerophyta humilis.     

Control of crops leaf growth by chemical and hydraulic influences

Three species of forage grasses (Festuca arundinacea, Eragrostiscurvula, Sporobolus stapfianus) commonly grown in the Mediterraneanregion were subjected to a soil drying treatment. Leaf growthrate in F. arundinacea was highly sensitive to soil drying andlow growth rates were associated with high laminar turgors.The production of ABA was stimulated by soil drying and therewas a clear relation between increasing ABA accumulation andreduction in leaf growth. Leaf growth of E. cutvula, a C⁴ warmseason grass, was relatively insensitive to soil drying whichwas not accompanied by a substantial increase in leaf ABA content.S. stapfianus, a resurrection plant, was highly sensitive todecreasing soil water availability. In these two latter species,leaf growth was substantially restricted before ABA accumulationoccurred. It is suggested that reductions in laminar turgorof E. curvula and S. stapfianus may be limiting leaf growthas soil dries. The results indicated a different mechanism ofsensing and responding to reduction in soil water availabilityfor the three species studied. The relative importance of thechemical and hydraulic control of leaf growth is discussed. Key words: Leaf growth, water relations, abscisic acid, Festuca arundinacea, Eragrostis curvula, Sporobolus stapfianus     

Uptake of DOM by Nemertean Worms: Association of Worms with Arthrodial Membranes

SYNOPSIS. Carcinonemertes errans is a nemertean worm, the juvenilesof which are found as epibionts on the Dungeness crab, Cancermagister, in close association with the arthrodial membranesof the crabs. The juvenile nemerteans appear to have no meansof taking in particulate food but survive for many months onthe surface of the host. We show that the juvenile C. erransare capable of removing amino acids from dilute solution insea water, that the water near the arthrodial membranes wherethe worms are found contains high concentrations of primaryamines, and that there is a low resistance pathway for low molecularweight amino acids across the arthrodial membrane examined invitro.     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

The Partitioning of Hydraulic Conductances within Mature Orange Trees

Sap flow (F) and leaf water potential (LWP) were followed diurnallyin mature Valencia and Shamouti orange trees in an orchard.The hydraulic conductance of these trees was computed from thediurnal relationship between the LWP and F. The driving forcefor water movement was estimated from a weighted average ofsunlit and shaded LWP, assuming that leaves in the shade transpireto some extent. LWP of covered, non-transpiring leaves was alsomeasured hourly. It was assumed to represent the xylem waterpotential within the axial conduit of the trunk. Relating coveredLWP to F on an hourly basis enables the computation of the hydraulicconductance of the root system, including axial conductances.The hydraulic conductance of the transpiring crown was computed.Its magnitude was comparable to the root system hydraulic conductance. Key words: Orange trees, hydraulic conductance, sap flow, leaf water potential     

Escherichia coli as an expression system for K(+) transport systems from plants

The value of theEscherichia coli expression system has long been establishedbecause of its effectiveness in characterizing the structure andfunction of exogenously expressed proteins. When eukaryotic membraneproteins are functionally expressed in E. coli, thisorganism can serve as an alternative to eukaryotic host cells. A fewexamples have been reported of functional expression of animal andplant membrane proteins in E. coli. This mini-review describes the following findings: 1) homologousK⁺ transporters exist in prokaryotic cells and ineukaryotic cells; 2) plant K⁺ transporters canfunctionally complement mutant K⁺ transporter genes inE. coli; and 3) membrane structures of plant K⁺ transporters can be elucidated in an E. colisystem. These experimental findings suggest the possibility ofutilizing the E. coli bacterium as an expression system forother eukaryotic membrane transport proteins.

     

Influence du d?bit d'eau de mer dans un dispositif de culture ? fibres creuses dialysantes sur la croissance phytoplanctonique et 1'extraction des nitrates du milieu

It is demonstrated that the productive capacity of mass dialysisculture of phytoplankton is intimately related to the rate offlow of nutrient medium along the membrane. Comparison of culturesof Phaeodactylum tricornutum, subject to different medium flowrates (92 versus 250 ml.min^–1) during a 17-day growthperiod, reveals increased productivity (in terms of cell numbers,chlorophyll a, dry weight, cell nitrogen, cell carbon, ATP)at the higher flow rate. Differences are most pronounced inthe latter stages of growth (i.e., linear and stationary) attainingratios between 2 and 3 for cell nitrogen, cell carbon and ATP.Lower C/N ratios for the greater yielding culture translatesas enhanced osmotic diffusion as well as cellular assimilationof nitrates. The positive effects of increasing medium flowrate on phytoplankton growth result from improved dialyzer performancewith respect to low molecular weight solutes. This is evidencedin the proportionately greater values obtained for mass transferof nitrate-nitrogen. Accordingly, measures of nitrate clearanceindicate a progression from 29 to 85 ml.min^–1 in responseto augmenting sea water flow from 32 to 292 ml.min ^–1.The culture apparatus recently developed consists of a separatedialysis unit (a hollow-fiber cartridge used in hemodialysis)coupled to a temperature-controlled growth chamber. Culturesreceive a continuous flow of natural sea water and are grownin the batch dialysis mode. The main advantages of this methodrelate to its potential for large-scale, axenic algal culturebased on the abundant source of cheap nutrients that constitutesnatural sea water.     

空心莲子草叶甲室内大量繁殖研究

为了大量繁殖供环境释放的空心莲子草叶甲Agasicles hygrophila以实现空心莲子草区域减灾, 我们探索出室内大量饲养与繁殖空心莲子草叶甲的方法与流程, 包括用叶片法或苗水培法孵化卵粒、用盒养法饲养各龄幼虫与成虫并供成虫产卵、用栽培活苗笼养法化蛹羽化。在室内成虫终日均能取食、交配、产卵, 产卵前期约4～5 d, 产卵高峰期在羽化后第7～24 天, 每雌平均产卵21.08块, 约570粒。盒养法叶片平均可着卵4.28块, 叶背与叶面着卵量相近; 笼养法叶片平均着卵为1.46块, 卵主要产于叶背。盒养法与笼养法得到的卵孵化率分别为94.02%与92.50%。空心莲子草叶甲除化蛹需在栽培活苗上完成外, 各龄幼虫与成虫均可用离体新鲜苗盒养法密集饲养。初孵1龄幼虫转株（叶）期、3龄老熟幼虫转化蛹苗期是室内大量饲养与繁殖空心莲子草叶甲的关键时期, 高密度成功饲养与繁殖空心莲子草叶甲的最适化蛹接虫量是每株8头, 产卵期雌虫的最适密度是每株5头。