The Diffusive Conductivity of the Stomata of Wheat Leaves

A leaf chamber (described in detail) was used alternately witha resistance porometer to measure resistance to viscous flowof air through the leaf, and with a diffusion porometer to measurethe differential diffusive flow of hydrogen and air (V_H–V_A)through the leaf and the component of hydrogen flow (V'_H) movingstraight across the leaf. The resistance of the mesophyll isneeded for interpretation: estimates by three different methodsfor viscous flow did not agree very well, but two differentmethods for diffusive flow gave good agreement. For wheat leaves,only very large errors are important. Formal analysis is in three appendixes: I. Interpretation ofviscous and diffusive flow in small pores involves some problemsin molecular physics, complicated by the particular geometryof the wheat stoma. With some uncertainty, formal expressionsare derived for the viscous resistance of a single stoma, rv,and for the resistances to diffusion of hydrogen and air, andof water vapour and carbon dioxide, all expressed as r_s persquare centimetre of leaf surface. The analysis for hydrogen/airis the most uncertain; that for water vapour and carbon dioxideis more reliable. II. An indication is given of the flow characteristicsof the leaf-chamber system, from which rv can be derived, andof the basis for estimating mesophyll resistance. III. The methodof converting estimates of r_s into estimates of V_H–V_Aand V'_H is given. The results presented are expressed as nearly as possible interms of the quantities which were measured. For five leavesthe dependence of V_H–V_A on V'_H agrees well with theoreticalpredictions; the dependence of V_H–V_A (and V'_H) on rv,on average, agrees well with prediction, but involves the assumptionthat the stomata get shorter as they close. The agreement isgood enough to suggest that the formal expressions for r_s interms of stomatal dimensions and molecular gas constants arereliable enough to be carried forward into future transpirationand assimilation studies. The minimum value of ra for watervapour (c. 3 sec cm⁺¹) is close to values found elsewhere bydifferent techniques. At very small stomatal openings there was a large deviationfrom predicted behaviour, such as would occur if the imposedexcess air pressure further closed the stomata during viscousflow experiments.     

An Examination of the Factors affecting Variability in the Growth of the Mesocotyl and Coleoptile of Etiolated Avena Seedlings

Experiments were carried out on the effect of rate of air-flowand of humidity on the growth of Avena seedlings. The experimentalmethods used are described in some detail. The effect of air-flow on mesocoryl growth was considerablewhen unsaturated air was used, but with saturated air growthwas independent of air-flow. The effect must therefore be dueto variation in transpiration rate. A 10 per cent, variationin relative humidity, at a constant rate of flow, caused a 30per cent, variation in mesocotyl length. The coleoptiles showedless pronounced effects, but even in saturated air variabilitywas not eliminated. Under the conditions used a difference of 2·3 mm. inmesocotyl length (per 50 plants), i.e. 8 per cent., was significantat P = 0·05; for the coleoptiles a difference of 1 mm.(8 per cent.) was significant at this level.     

Leaf Temperatures in a Gas Exchange Chamber and in the Open Air

Leaf temperatures in a Koch fully climatized gas-exchange chamberas designed by Siemens and in a similarly equipped open-airreference were measured with horizontally and vertically insertedthermocouples on Nerium oleander L. On a sunny day with onlylittle air movement and an average air temperature of 20.4 °C,leaf over-temperatures in the gas-exchange chamber were loweron average by 2.2 K. The extent of reduction of over-temperaturein the chamber is determined by the reduced global radiationin the chamber and the differences of wind velocities in chamberand reference. Differences in the ventilation intensity in thechamber have no demonstrable influence on the leaf over-temperatures.The over-temperatures of the reference leaves, on the otherhand, depend to a large degree on air velocity. The changedradiation and air flow conditions in the chamber as comparedwith open-air conditions have consequences for the physiologicalreactions of the enclosed plant and must be taken into accountwhen comparing results from gas-exchange measurements with open-airconditions. For further improvements of gas-exchange measurementequipment, air flow conditions and radiation quantity and qualitymight be starting points     

Localization of Thermo-Osmotically Active Partitions in Young Leaves of Nuphar lutea

The submerged roots and rhizomes of the aquatic vascular macrophyteNuphar lutea (L.) Sm. are aerated, at least in part, by pressurizedventilation. Depending on temperature differences of up to 5K between the inside of young, just-emerged leaves and the surroundingair, pressure differences of 79 to 100 Pa higher than atmosphericare detectable inside the lacunuous spongy parenchyma of theleaf blades. The pressurization is a consequence of structuralfeatures of leaf tissues separating the air filled spaces ofthe spongy parenchyma from the atmosphere. These tissues areacting as thermo-osmotic partitions. Whereas the dimensionsof the stomatal openings (about 5·6 x 2·4 µm)and of the intercellular spaces of the palisade parenchyma (diametersabout 15 µm) are too large, those of the monolayers ofcells separating the palisade and the spongy parenchyma (diameters:0·7–1·2 µm) are small enough to impedefree gaseous diffusion. This inner non-homogeneous partitioninggives rise to the so-called Knudsen diffusion, a physical phenomenonleading to pressurization of the warmer air inside the spongyparenchyma. The rising pressure difference is strong enoughto establish an air flow through the aerenchyma of the wholeplant and out of the most porous older leaves in which a temperatureinduced pressurization is never detectable. These thermo-osmoticallyactive leaves enhance the influx of air to the rhizome and thediffusion path for oxygen to the roots is shortened to the distancebetween rhizome and root tips. Therefore, pressurized ventilationin Nuphar is seen to be of considerable ecological importancefor plant life in anaerobic environments. Key words: Aeration, leaf anatomy, thermo-osmosis of gases, Nuphar lutea     

Relationships between Acetylene Reduction Activity, Hydrogen Evolution and Nitrogen Fixation in Nodules of Acacia spp.: Experimental Background to Assaying Fixation by Acetylene Reduction under Field Conditions

Hansen, A. P., Pate, J. S. and Atkins, C. A. 1987. Relationshipsbetween acetylene reduction activity, hydrogen evolution andnitrogen fixation in nodules of Acacia spp.: Experimental backgroundto assaying fixation by acetylene reduction under field conditions.—J.exp. Bot. 38: 1–12 Glasshouse grown, symbiotically-dependent seedlings of Acaciaalata R.Br., .A. extensa Lindl., and A. pulchella R.Br. wereexamined for acetylene reduction in closed assay systems usingundisturbed potted plants, excavated whole plants, nodulatedroots or detached nodules. Nitrogenase activity declined sharplyover the first hour after exposure of detached nodules to acetylene(10% v/v in air), less steeply or not at all over a 3 h periodin assays involving attached nodules. Using detached nodules,rates of acetylene reduction, nitrogen (¹⁵N₂) fixation, andhydrogen evolution in air (¹⁵N₂) and acetylene-containing atmosphereswere measured in comparable 30 min assays. Total electron flowthrough nitrogenase in air was determined from rates of nitrogen(¹⁵N₂) fixation ( ? 3) plus hydrogen evolution, that in thepresence of acetylene from rates of acetylene reduction andhydrogen evolution in air: acetylene. Values for the ratio ofelectron flow in air: acetylene to that in air ranged from 0?43to 0?83 in A. pulcheila, from 0?44 to 0?66 in A. alala and from0?37 to 0?70 in A. extensa, indicating substantial inhibitionof electron flow through nitrogenase of detached nodules byacetylene. Relative efficiencies of nitrogenase functioningbased on hydrogen evolution and acetylene reduction were from0?15 to 0?79, those based on nitrogen (¹⁵N₂) fixation and hydrogenevolution from 0?53 to 0?87. Molar ratios of acetylene reducedto nitrogen (¹⁵N₂) fixed were 2?82 ? 0?24, 201 ? 0?15, and 1?91? 0?11 (?s.e.; n = 7) for A. pulcheila,A. extensa and A. alata respectively A standard 5–10 min acetylene reduction assay, conductedon freshly detached unwashed nodules in daytime (12.00–14.00h), was calibrated for field use by comparing total N accumulationof seedlings with estimated cumulative acetylene reduction overa 7-week period of glasshouse culture. Molar ratios for acetylenereduced: nitrogen fixed using this arbitrary method were 3?58for A. alata, 4?82 for A. extensa and 1?60 for A. pulchella.The significance of the data is discussed. Key words: Acacia spp, nitrogenase functioning     

Rectifier-like Activities of Roots of Two Desert Succulents

Axial and radial water flows for roots in response to appliedhydrostatic pressure drops, water loss from roots after variousperiods of drying, and development of new roots after rewettingdroughted plants were examined for two sympatric desert succulents.Agave deserti Engelm. and Ferocactus acanthodes (Lemaire) Brittonand Rose. For a 40 kPa hydrostatic pressure drop applied to20 mm long root pieces, radial water flows from the epidermisto the root xylem were 2- to 5-fold greater at the tip thanat midlength and were much less than axial flows along the xylem.Upon drying detached roots in air at 20 °C and a water vapoursaturation deficit of 1.2 kPa (50% relative humidity), radialwater flow decreased more than 10-fold in 3–6 h, and couldrecover to the original level 6 h after rewetting. The rateof water loss from attached roots of plants dried in air at20 °C and a 1.2 kPa saturation deficit decreased about 200-foldin 72 h, which would greatly limit water loss from the plantto a drying soil. At 96 h after rewetting roots of A. desertithat had been exposed to air at 20 °C and a 1.2 kPa saturationdeficit for 120 h, rehydration of existing roots and developmentof new roots contributed about equally to water uptake by thewhole plant. In summary, roots of these desert succulents canreadily take up water from a wet soil but do not lose much waterto a dry soil, thus effectively acting like rectifiers withrespect to plant-soil water movement. Key words: Agave, Cactus, Drought, Root, Water flow, Xylem     

Influence of localized auxiliary heating on hand comfort during cold exposure

There is a needfor a hand-heating system that will keep the hands warm during coldexposure without hampering finger dexterity. The purpose of this studywas to examine the effects of torso heating on the vasodilativeresponses and comfort levels of cooled extremities during a 3-hexposure to 15°C air. Subjects were insulated, but theirupper extremities were left exposed to the cold ambient air. The effectof heating the torso [torso-heating test (THT)] on handcomfort was compared with a control condition in which no torso heatingwas applied, but Arctic mitts were worn [control test(CT)]. The results indicate that mean finger temperature, meanfinger blood flow, mean toe temperature, mean body skin temperature, body thermal comfort, mean finger thermal comfort, and rate of bodyheat storage were all significantly (P < 0.05) higher on average (n = 6)during THT. Mean body heat flow was significantly (P < 0.05) lower during THT. Therewere no significant differences (P  0.05) in rectal temperature between CT and THT. Mean unheated body skintemperature and mean unheated body heat flow (both of which did notinclude the torso area in the calculation of mean body skin temperatureand mean body heat flow) were also calculated. There were nosignificant differences (P  0.05) inmean unheated body skin temperature and mean unheated body heat flowbetween CT and THT. It is concluded that the application of heat to the torso can maintain finger and toe comfort for an extended period oftime during cold exposure.

     

Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

The paper describes the effect of soil moisture content andair humidity on CO₂ exchange (P_N), CO₂ diffusion resistance(Cr) and transpiration (E) in four varieties of japonica rice(Oryza sativa L.). A decrease in soil moisture content reducedthe rate of photosynthesis to a varying degree in the varieties.Reduction in photosynthesis was attributed to increase in Cr.The effect of low soil moisture on photosynthesis and CO₂ diffusionwas further intensified by decrease in air humidity. By maintaininga high humidity in the air around the leaves however, the effectof soil moisture deficiency was reduced considerably, exceptin Rikuto Norin 21 which was very sensitive to soil-moisturedeficiency alone. Dryness of the air enhanced the transpirationrate, although the increase was relatively less in the plantsfacing a simultaneous water crisis at the root surface. In plantsgrowing under flooded conditions, a decrease in air humiditycaused a slight depression in P_N despite the simultaneous decreasein Cr. Oryza sativa L., rice, photosynthesis, transpiration, diffusion resistance, soil moisture, air humidity     

Studies on the Development of the Air Pores and Air Chambers of Marchantia paleacea: 1. Light Microscopy

The ontogeny of the air pores and air chambers of Marchantiapaleacea begins with the schizogenous development of protodermalintercellular spaces of the initial apertures, and is completedwith the formation of the air pores and giant sub-epidermalair chambers bearing numerous photosynthetic filaments. Intercellularspace formation commences from the thallus surface and proceedsinwards to the first internal layer of cells. The cells amongwhich spaces develop do not originate from one mother cell.Spaces are formed only in the regions of the intersection ofthe anticlinal walls of three, four, or sometimes more successivederivatives of S₁, S₃ and S₄ segments of the apical cell, oneor two of which have been divided periclinally and the restanticlinally. Protodermal intercellular spaces appear in mostor all the corners of these cells, the anticlinal walls of whichexhibit an opposite disposition. The S₁, S₂, S₃ and S₄ segmentsare produced by definite divisions of a five-sided apical celland by a series of divisions give rise to initial cells of theinternal layers of the thallus and initial cells of the protodermaland sub-protodermal layers. The concept of a quiescent apicalcell cannot be accepted, since dividing apical cells have beenobserved, and the pattern of wall disposition of the thallusapex cannot be explained without the active participation ofthe apical cell. The air chambers are apparently of exogenous origin. They resultfrom the broadening of the bottom of the initial apertures bythe coordination of the rate of anticlinal divisions and growthof the protodermal and sub-protodermal cells surrounding theintercellular spaces of the initial apertures. The ontogenyof the pore rings starts at an advanced stage of air chamberformation not from a mother cell but from the cells which surroundthe closed entrance of the air chamber, by a shift of the planeof division from anticlinal to periclinal. Before the periclinaldivisions a new axis of growth perpendicular to the thallussurface is established in the mother cells of the pore. By a polarized growth into the air chamber followed by periclinaldivisions, the cells of the floor form initial cells of thephotosynthetic filaments. The latter divide again to form singleor branched photosynthetic filaments. Marchantia paleacea, air pore, air chamber     

Microvascular Regulation of Cutaneous Gas Exchange in Amphibians

SYNOPSIS. Gas exchange across amphibian skin is regulated bythe cutaneous microcirculation. Parameters involved in regulatinggas exchange are capillary density, radius and blood flow. Changesin capillary density and radius should affect gas exchange byaltering the cutaneous diffusing capacity (D₂) while changesin capillary blood flow affect the perfusive conductance ofthe skin. A simple model predicts that the effect of capillary densitychanges on D₂ will become more pronounced as capillary densityand epidermal thickness decrease. Changes in capillary radiusshould have only a minor effect on D₂ Previous analyses havesuggested that cutaneous gas exchange is not significantly affectedby the perfusive conductance of the skin. Consequently, it hasbeen thought that changes in total capillary blood flow havelittle impact on cutaneous gas exchange. Earlier analyses, however,may have underestimated the importance of perfusive conductancein amphibian skin, primarily because functional heterogeneitiesin the microcirculation were not considered. The density of perfused capillaries is regulated in the footweb of Rana esculenta by environmental Po₂ and PCO₂, and alsoby lung ventilation. In Rana catesbeiana, capillary densityin the web decreases during air exposure. Chronic exposure toenvironmental hypoxia increases total capillary density in bullfrogtadpole skin. In Rana pipiens, regulation of cutaneous gas exchangeby environmental and pulmonary O₂ probably involves changesin total capillary blood flow.     

Take-off of Mould Spores in Relation to Wind Speed and Humidity

Using horizontal tube-cultures of various moulds belonging tothe genera Thamnidmmt, Phymatotrichum, Trichotheciwm, Ptptocephalis,Trichoderma, Mucor and Mycogone, the take-off of dispersal units(usually spores) under the influence of air currents of variousspeeds and of different humidities has been studied. It is foundthat in all the dry-spore forms the number of spores set freeincreases as the speed of the air stream rises. Further, atany given air-stream rate, the numbers of spores set free aregreatest in the first interval of time and rapidly fall offin subsequent intervals. In all species, spores are more readilyset free in air streams of relatively low as compared with thoseof relatively high humidity. Although Trichoderma viride hasbeen regarded as a slime-spore fungus, its conidia can readilybe blown from the conidiophores. No spores could be inducedto take off from Mucor ramarmianus even at the highest air speedsused.     

ECOPHYSIOLOGICAL RESPONSES OF CERASTODERMA EDULE (L.) AND C. GLAUCUM(BRUGUIERE) TO DIFFERENT SALINITY REGIMES AND EXPOSURE TO AIR

The estuarine bivalve Cerastoderma edule and the lagoonal C.glaucum were exposed in the laboratory to different salinityregimes and the effects in the osmotic concentration of themantle cavity liquid, extrapallial fluid and haemolymph determined.The behavioural responses of the two cockles to changing salinityand exposure to air were investigated by monitoring valve movements. Both C. edule and C. glaucum are euryhaline osmo-conformerswhen exposed to different environmental salinities, but differencesare seen in their behavioural responses to sudden exposure tolow salinity and cyclic changes in salinity. C. glaucum postponedthe effect of sudden exposure to low salinity by complete valveclosure whilst C. edule partially closed its valves and intermittentlygaped during the same period. During exposure to a sinusoidalfluctuating salinity regime, C. edule responded first to thefalling salinity by retracting siphons and partially closingvalves. In contrast, C. glaucum responded more slowly to fallingsalinity than did C. edule. C. glaucum closed valves faster,accompanied by erratic adductions. During an acclimation period in a continuous automatic tidalsystem, C. edule and C. glaucum were entrained to the tidalrhythm of immersion and exposure to air and demonstrated differentresponses of valve gaping and adductions. This rhythm was lostupon continuous submergence indicating the rhythm is exogenouslyinduced. The two cockles gaped during exposure to air at lowtide, suggesting that both can respire in air, contrary to previousreports. The different physiological and behavioural responses of C.edule and C. glaucum to changing salinity and exposure to airwere found to be a reflection of their respective environments.C. edule is adapted to daily changes and stresses in its estuarinehabitat whilst C. glaucum is subjected to seasonal changes. (Received 19 September 1985;     

The Boundary Layer over a Populus Leaf

Air flow over a Populus leaf was investigated using a hot-wireanemometer. When the air flow in the wind tunnel was laminar,the boundary layer was often turbulent at a wind speed of only1.5 m s^–1, particularly when encouraged by uneven topographyand roughness of the surface, as on the lower side of the leaf.The smoother upper surface behaved in a similar way to a flatplate when at low wind speeds, and the profiles of wind speedcould be shown to be equivalent to those expected from laminarboundary layer theory. Nevertheless, the boundary layer becameturbulent at Reynolds numbers much lower than those requiredto cause the transition to turbulence in a flat plate. Turbulentair flow in the wind tunnel greatly increased boundary layerturbulence but had only a small effect on evaporation from amodel of the leaf. The evaporation rates observed were 2.5 timeshigher than expected from theory, irrespective of the turbulenceregime.     

Ultrastructural and Cytochemical Studies of 'Air Blisters' in Pilea cadierei Gagnep. and Guillaumin

Cells from the sub-epidermal layer of Pilea cadierei preparedfor electron microscopy using standard fixation and embeddingprocedures appear extremely osmiophilic, with the organellesstanding out in negative relief. However, when tissues werefixed in glutaraldehyde supplemented with either procaine orcaffeine (substances known to complex with phenols) the osmiophilicmaterial was generally limited to the vacuole. After procaineor caffeine fixation the surrounding cytoplasm appeared as inadjacent, nonphenolic cells. Some small aggregates of phenolicmaterial appear in the cisternae of the endoplasmic reticular,indicating these organelles may be involved in either the synthesisor transport of phenolics in Pilea. Since one of the major functionsof phenolics is in light-screening, air blisters may serve toscreen out damaging radiation from the underlying tissue. Thepresence of typical shade-type plastids in Pilea air blistersis a further indication of this light-screening role. Pilea cadierei, aluminium plant, air blister, cytochemistry, ultrastructure, light screening, phenolics     

Energetics of Plant Growth Under Anoxia: Metabolic Adaptations of Oryza sativa and Echinochloa phyllopogon

Unlike most plant species, Oryza sativa L. cv. S-201 and Echinochloaphyllopogon (Stev.) Koss germinate and grow under anaerobicconditions. In both species, the radicle or shoot emerged byday 3 when the seeds were germinated in air or N₂. Under eithercondition, shoot and/or root dry weight (d. wt) increased linearlyfrom day 3 to day 7, with a corresponding decrease in seed d.wt. In anaerobically grown O. sativa, d. wt accumulation wasreduced to 7% of that in air whereas d. wt lost from the seedwas reduced to only 37%. No root growth occurred during anaerobicgermination and shoot d. wt accumulation accounted for 10% ofthe d. wt lost from the seed. In E. phyllopogon, d. wt accumulationduring anoxia was 25% of that in air, but loss of d. wt fromthe seed was 44% of the aerobic rate. In air, 48% of the d.wt lost from the seed was converted to shoot or root d. wt.Like O. sativa, E. phyllopogon does not produce a root underN₂, but shoot growth accounted for 27% of the d. wt lost fromthe seed. Thus, either in air or N₂, E. phyllopogon was moreefficient at converting seed reserves to shoot/root structuraldry matter than O. sativa . Based on changes in metabolite pools,O. sativa appeared to shift exclusively to fermentation duringanaerobic growth. In E. phyllopogon, however, fermentation alonecannot satisfy the energy requirement for growth without O₂.Rather, fermentation, coupled with limited tricarboxylic acid(TCA) cycle operation could supply sufficient ATP for growthunder anaerobic conditions. An active oxidative pentose phosphatepathway and lipid synthesis were discussed as important mechanismsfor converting NADH to NAD, a necessary cofactor for fermentationand TCA cycle activity.Copyright 1994, 1999 Academic Press Anaerobiosis, Echinochloa phyllopogon, energetics model, fermentation, mitochondrial activity, Oryza sativa, rice, tricarboxylic acid cycle, watergrass     

春季麻栎树干边材木质部液流垂直变化及其滞后效应

利用热扩散式边材液流茎流探针(TDP)和微型自动气象站组成的测定系统,对泰山林科院林场麻栎(Quercus acutissima)人工林树干不同高度边材液流及其相关环境因子进行了连续观测,对影响边材液流的主要环境因子进行了相关性和滞后效应分析。结果表明:同一立木,树干上位边材液流流速上升快,高峰期持续时间短,但高峰流速较高,最大流速在0.002 cm·s^-1以上;树干下位边材液流流速上升、下降慢,液流高峰期持续时间较长,最大流速不超过0.001 cm·s^-1。太阳净辐射是麻栎边材液流最主要的影响因子,且成正相关,空气温度、空气相对湿度对边材液流的影响较小,空气温度与麻栎边材液流的影响成正相关,相对湿度与边材液流速率成负相关。边材液流与主要环境因子日周期波动在时间上存在延迟效应,延迟效应因树干高度和环境因子而变。树干上、中和下部边材液流与太阳净辐射变化的滞后时间分为80、20和30 min,与空气温度的滞后时间分别为60、130和110 min,与空气相对湿度的滞后时间分别为170、160和90 min。     

Responses to Saturation Deficit in a Stand of Groundnut (Arachis hypogaea L.) 1. Water Use

Stands of groundnut were grown in computer-controlled glasshouseson water stored in an undisturbed soil profile. The maximumsaturation vapour pressure deficit (D) of the air was either1.0, 2.0, 2.5, or 3.0 kPa, and the mean air temperature was27 °C. Transpiration (E), determined from the soil water balance, wasstrongly dependent on D, because D influenced both the fractionof incident solar radiation intercepted by foliage (f) and thetranspiration rate per unit f (E/f). When D exceeded 2 kPa,canopy expansion was restricted and f reduced during early growth,but differences in f diminished as the canopies closed. E/fincreased with D, implying that any restriction of transpirationthrough stomatal closure at large D was outweighted by a steeperhumidity gradient from leaf to air. In all treatments E/f decreased as the soil profile dried. Saturationdeficit per se had little influence on the proportional reductionin E/f with time, even though soil water deficit was considerablygreater at large D. This lack of response occurred because plantscompensated for the greater evaporative demand by extractinglarger amounts of water from deep in the profile. Groundnut, Arachis hypogaea L., humidity, rooting depth, transpiration     

Water Permeability of the Wood of Grand Fir (Abies grandis (Doug.) Lindl.) in Relation to Infestation by the Balsam Woolly Aphid, Adelges piceae (Ratz.)

The water permeability of sapwood and heartwood of Abies grandis(Doug.) Lindl. was found for normal trees and those infestedby balsam woolly aphid Adelges Piceae (Ratz.). It was determinedas the rate of flow of water through plugs of the wood of standarddimensions and under constant suction. The permeability of normaltrees was less in the inner than the outer sapwood and thisdifference was correlated with a greater void space (gas-filledtracheids) in the inner sapwood. The permeability of the heartwoodwas less than 5 per cent that of the sapwood. Aphid infestationreduced the permeability of the outer sapwood to about the samelevel as normal heartwood. The infested wood had a high percentageof void space and again permeability was negatively correlatedwith void space. But for a given level of void space the infestedwood had a much lower permeability than normal wood. This suggeststhat there was factor additional to the air in the tracheids,which contributed to the low permeability of infested wood.The possible nature of this factor is briefly discussed.     

Cytochromes of Mitochondria from Rice Seedlings Germinated under Water and Their Changes during Air Adaptation

Rice seeds were germinated for up to 5 days under water (submerged)and some for another day in air (air-adapted). Control seedswere germinated for 6 days throughout in air. Low-temperaturedifference spectra of shoot mitochondria were compared amongthese three types of seedlings. All cytochromes found in theaerobic seedlings were present in the submerged seedlings. However,there were some differences in the cytochromes b₅₅₃ and c ofthese two types of seedlings. The cytochrome aa₃ peak heightand cytochrome oxidase activity per mitochondrial protein increased1.6- and 2.8-fold, respectively, during air adaptation. Slightlyhigher concentrations of the b-type cytochromes than found inair-adapted mitochondria were already present in submerged mitochondria.The computed difference between the dithionite-reduced differencespectra of mitochondria from submerged seedlings before andafter air adaptation, showed that cytochromes aa₃ and c hadincreased more than cytochrome b₅₅₇ during air adaptation. (Received November 16, 1987; Accepted March 16, 1988)     

Activity of the Pentose Phosphate and Glycolytic Pathways During Anaerobic Germination of Echinochloa crus-galli (barnyard grass) Seeds

Changes in the activity of key enzymes in glycolysis and theoxidative pentose phosphate pathway were studied in Echinochloacrus-galli (L.) Beauv. var. oryzicola seeds during germinationin air or nitrogen. In addition, the metabolism of specificallylabelled [^I4C]glucose was followed to evaluate the activityof both pathways during anaerobic germination. During the 7 d time period studied there was no difference betweenair and nitrogen in phosphofructokinase activity. Under anaerobicconditions, fructose-1, 6-bisphosphate aldolase increased morethan two-fold in 7 d; whereas in air, it decreased. The activityof the pentose phosphate pathway enzyme, glucose-6-phosphatedehydrogenase, increased under N₂ until day three, when it levelledoff, whilst it continued to increase up to day seven in air. Incubation of Echinochloa seedlings with specifically labelledglucose also resulted in differences between anaerobic- andair-grown seedlings. Labelling of phosphorylated sugars andlipids predominated under N₂; whereas in air, malate and fumaratewere the most heavily labelled compounds. In both air and N₂,there was a greater percentage of label in CO2 from [l-¹⁴C]glucose,while [6-14C] resulted in a greater percentage label in ethanol.These differences were more pronounced under N2, especiallyduring the first 24 h of imbibition, suggesting increased activityof the pentose phosphate pathway. Key words: Echinochloa, Anaerobic metabolism, Oxidative pentose phosphate pathway