Zur Methodik kontinuierlicher Wassergehalt-Bestimmungen an Blättern mittels β-strahlenabsorption

Summary A brief introduction to the beta-ray gauging technique is given with its application in determining the water content of leaves.Some aspects for the choice of the radioactive isotope, the detector and the recording system are discussed in respect to their utilization and precision. A short review of the instrumentation used until now is given. The construction of a new beta-ray gauge is described.Krypton-85 (E _max=0.67 mev) with an activity of 0.35 mc served as the radiation source (active diameter=1 mm). This point-shaped and relatively energyrich beta-ray source permits a working distance between source and detector of several centimeters and allows within certain limits a choice of test surface area. A halogen-quenched Geiger-Müller-counter with a window of 2 cm diameter and 1.5–2.0 mg/cm² was used. In the construction of the measuring set-up special attention was paid to the reproducibility of the geometry between source, sample and detector. The impulses which reach the detector were recorded by an electronic scaler-timer-system.Count rate measurements were taken at various distances between emitter, absorber and detector. Furthermore the dependence of beta-ray absorption on the nature of the sample was examined. Comparative measurements were made with homogeneous materials (aluminium foils, plastic sheets and filter paper) and heterogeneous materials (leaves with varying anatomical structure). Large differences were found between the amounts of beta-radiation absorbed by the same weights per unit area of these materials. These differences are discussed.A calibration method is described which allows an accurate determination of the dependence of count rate on water content of the tested leaf area after the experiment. A difference in weight per unit surface area of 0.1 mg/cm² can be exactly determined.Leaves of the same species were examined under natural conditions in the habitat of the plants. With these continuous measurements of beta-radiation absorption great daily fluctuations in leaf water content were found according to the special weather conditions.     

Influence of Water Deficits on Gas-Exchange and the Leaf Area Development of Cassava Cultivars

Measurements of gas-exchange, leaf water potential and the leafdiffusive conductance of the abaxial leaf surface of six cassavacultivars, M Mex 59, M Ven 218, M Col 1684, M Col 72, M Col22, and M Col 638, were made at 48 h intervals and between 1200–1500h, on potted plants, grown outdoors during a 58 d period ofwithdrawal of irrigation. Rates of net-photosynthesis of about28 mg CO₂ dm^–2 h ^–1 were reduced to zero withinthe first 5 d of the drying cycle, despite the small differencesin leaf water potential of 0.15 MPa. Water shortage also causeda reduction in mean conductance to < 1.0 mm s^–1 atwhich level the control of transpiration maintained leaf waterpotential at > —1.6 MPa. Cultivar differences in theresponse of net-photosynthesis and leaf diffusive conductanceto water shortage were seen within 2 d of the dry cycle andthe leaf water potential was commonly 0.15 MPa lower than inthe wet controls. The most vigorous cultivars (M Mex 59, M Ven218 and M Col 1684) reduced their rates of net-photosynthesisto zero by day 5 of the dry cycle when the soil water contentwas depleted by 65%. Less vigorous cultivars (M Col 72, M Col22 and M Col 638) reduced their rates of net-photosynthesisto zero by day 30, when the soil water content was depletedby 75%. Measurements are also reported of the leaf productionper apex and leaf extension for leaves produced during the dryingcycle. Key words: Cassava (Manihot esculenta Crantz), Gas-exchange, Leaf diffusive conductance, Water deficits     

北京山区干旱胁迫下侧柏叶片水分吸收策略

干旱与半干旱地区,水分是限制树木生长的重要影响因子。由于降水稀缺且分配不均,叶片吸收水分是此地区树木吸收和利用小量级降水和凝结水的主要方式。北京山区处于易旱少雨的生态脆弱地带,森林植被经常遭受干旱胁迫,所以对该地区的森林系统而言,叶片直接吸收利用截留的降雨是干旱时期树木获得水分的重要途径。基于野外对比控制试验和室内盆栽模拟试验,选取北京山区的主要造林树种侧柏为研究对象,进行利用天然降雨与模拟降雨试验,研究降雨前后侧柏叶片吸水特征,探究侧柏在干旱环境下如何通过叶片吸水缓解干旱胁迫。结果表明：当侧柏长期处于干旱胁迫状态时,叶片可以利用降雨,从中获益用来缓解树木的干旱胁迫状态;叶片的吸水能力与降雨强度呈正相关关系,与土壤含水率呈负相关关系;重度干旱下侧柏植株在降雨强度为15 mm/h时叶片吸水现象最明显,叶水势变化最大为(1.18±0.17) MPa,叶片含水率变化最大为(8.47±1.00)mg/cm~2;当土壤水率高于20.8%时,基本不发生叶片吸水现象。试验结果说明在干旱地区叶片吸水是树木除根系吸水外的重要水分来源方式,并且对干旱地区有效利用短缺水资源,减轻植物水分亏缺具有重要意义。     

Characteristics of Starch Grains Isolated from Mature Pepper Leaves Grown under Different Irradiances and Daylengths

The size, shape and number of starch grains have been determinedin mature pepper leaves taken from plants grown under definedconditions of daylength and irradiance. Starch grains were 0.2–7.0 µm diameter and 02–1.5µm in thickness. Grain diameter was positively relatedto daylength and the number of grains per unit leaf area inverselyrelated to daylength. Mean grain diameter was also positivelyrelated to leaf area. Analysis of starch grains from leaves having a wide range ofstarch contents showed that grain diameter was linearly relatedto leaf starch content. However, mean diameter only doubledwith a 10-fold increase in starch content. The number of grainsincreased from approximately 5 ? 10¹⁰ m^–2 of leaf to over200 ? 10¹⁰ m^–2 with increasing starch content. The totalsurface area of grains increased from less than 1.0 m² m^–2leaf to over 20 m² m^–2 leaf. Leaf starch grain shape and size are compatible with both efficientstorage as disc-shaped chloroplasts and the maintenance of hightotal grain surface area by increasing grain number more thandiameter. Possible mechanisms for the control of grain initiation,growth and degradation are suggested. Key words: Starch grains, size, shape, pepper leaves     

An Analysis of the Effects of Tobacco Mosaic Virus on Growth and the Changes in the Free Amino Compounds in Young Tomato Plants

Tomato plants at the four-leaf stage were inoculated on thefirst leaf with TMV in a growth room and the effects studiedin systemically-mfected leaves with reference to growth, virusmultiplication and changes in water, nitrogen, nitrate and chlorophyllcontents. Parallel changes in the free amino compounds werealso studied in the growth room (incident radiation 152 mwhcm^-2 day^-1) and in two experiments in a glasshouse (352 and226 mwh cm^-2 day^-1) Dry matter accumulation and leaf expansion in leaves 3, 4 and5 were checked by TMV 5–7 days after inoculation but notin leaf 2. In the period 7–25 days after inoculation therelative growth rates of whole plant and leaves 3 and 6 andnet assimilation rate were not affected by TMV. Stem heightand dry weight were not affected by TMV but ‘root’dry weight was reduced from days 5–15. Virus was presentin the stem and in leaves 2 and 6 by days 3, 5 and 15 respectivelyso that infection per se did not always check growth. Chlorophyllcontent of systemically-infected leaves was reduced 10 daysafter inoculation. Total N and ammonia contents were not affectedby TMV but infected leaves contained less nitrate. At the two lower levels of incident radiation the initial effectof TMV was to reduce the content of total free protein aminoacids and amides, which were minimal 5–7 days after inoculation.In the glasshouse experiment a reduction could be measured only1 day after inoculation or before virus was present in the youngerleaves. With high incident radiation there was no initial reductionbut an increase at day 13 when mottling symptoms were visible.Total non-protein amino acids, of which amino butyric acidwas the major constituent, were increased by TMV in all threeexperiments for up to 13 days after inoculation. It is suggested that inoculation of a leaf with TMV temporarilyinterferes with export of photosynthates and import of root-synthesisedamino acids and that the results reported above can be interpretedin this context. Evidence in support of this is adduced froman experiment in which 13 foliar sprays of gibberellic acid(2·5 ppm) were combined with TMV inoculation and thechanges in free amino compounds followed. It is concluded that analyses of the changes in individual freeamino compounds are unlikely to provide useful information concerningthe sources of virus coat protein.     

Differences in Iron Nutrition Strategies of Two Calcifuges,Carex piluliferaL. andVeronica officinalisL.

Veronica officinalisandCarex pilulifera, widespread calcifugeplants in Europe, were cultivated in acid and calcareous soilsto study differences in Fe aquisition strategies indicated inprevious studies. The experiments were performed in a computer-controlledglasshouse at a soil solution moisture content of 50–60%water holding capacity; additional light was supplied at 70W m^-2if ambient light was <100 W m^-2between 0600 and 1800h.Both species developed chlorosis when grown in the calcareoussoil.C. piluliferaproved unable to translocate sufficient amountsof Fe to the leaves when cultivated in calcareous soil, butmuch Fe accumulated in, and especially as a precipitate on thesurface of roots. In contrast,V. officinalistended to increaseFe taken up into the leaves of plants grown on calcareous soil,but a much greater proportion of the leaf tissue Fe was accumulatedas less active forms not extracted by Fe complexing agents,e.g. 1,10-phenanthroline, than was the case in acid-soil grownplants. Considerably less Fe was accumulated in the root biomassofV. officinaliscompared toC. pilulifera.It is concluded thatchlorosis inC. piluliferais related to insufficient Fe uptakein the leaves, whereas leaf immobilization of Fe in physiologicallyless active forms is the problem inV. officinalis. Iron; chlorosis; calcifuge; iron immobilization; leaf tissue; fractionation; Carex pilulifera; Veronica officinalis     

Varietal differences in sodium uptake in barley cultivars exposed to soil salinity or salt spray

Barley varieties are known to differ in the extent of Na⁺ andCl^– accumulation in leaves when grown in saline soil orhydroponic culture. In particular, the cv. Chevron accumulatesmore Na⁺ than the more salt-tolerant cv. CM67, and has lowerleaf K⁺ concentrations. When salt was applied as a spray tothe leaves, CM67 accumulated more Na+ than Chevron, and theselection Sinis 27 (from a landrace collected on the Sinis Peninsulaof Sardinia) accumulated more Na⁺ than Sinis 28. In some casesleaf K⁺ concentrations decreased in response to high concentrationsof salt sprayed on to the leaves. Accumulation of Na⁺ was greaterin the 4th leaf than in the flag leaf. Added CaCI₂ had oppositeeffects when added to the salt applied to the soil or to thesaline spray. In the soil, CaCI₂ reduced Na⁺ uptake; appliedto the leaf it increased Na⁺ uptake. Pre-wetting the leavesbefore the salt spray, or washing the leaves with non-salinewater 1 h after the salt spray, reduced the uptake of Na⁺ andCl^–. It is clear that tolerance to salt applied as saltspray or in the soil are different characteristics. Key words: Barley, salt, foliar uptake, calcium     

Effect of soil compaction on barley (Hordeum vulgare L.) growth: I. Possible role for ABA as a root-sourced chemical signal

Wild-type (Steptoe) and abscisic acid (ABA)-deficient mutant(Az34) genotypes of barley were grown in compacted soil to examinethe potential role of ABA as a root-to-shoot signal. Root andshoot growth and leaf conductance were all reduced when plantswere grown in compacted soil with a bulk density of 1.7g cm^–3,relative to uncompacted control plants (1.1 g cm^–3. Theseeffects occurred in the absence of detectable changes in leafwater status or foliar abscisic acid (ABA) content. Analysisof Steptoe and Az34 xylem sap showed that the ABA concentrationwas greatly increased at 6 d after emergence (6 DAE) when seedlingswere grown in compacted soil (1.7 g cm^–3); however, ABAconcentrations were never as high in the mutant as in the wildtype. The increase in xylem sap ABA concentration observed athigh bulk density was closely correlated with reductions inleaf conductance, but not leaf area. These increases were transitory,and xylem sap ABA concentrations subsequently decreased towardsthe control level by 18 DAE in both genotypes. The ABA-deficient mutant, Az34, produced a much lower leaf areathan Steptoe at a bulk density of 1.6 g cm^–3. Examinationof epidermal characteristics indicates that this effect resultedmainly from reductions in cell expansion rather than cell division,suggesting that the higher ABA concentrations detected in xylemsap from the wild-type Steptoe may have exerted a positive rolein maintaining leaf expansion in this treatment. The possibleinvolvement of ABA as a root-to-shoot signal mediating the effectsof compaction stress is discussed. Key words: Soil compaction, bulk density, ABA, ABA-deficient mutant, leaf growth     

模拟喀斯特不同土壤生境下黑麦草对水分胁迫的生长和光合生理响应

以多年生草本黑麦草为对象,模拟喀斯特生境土壤特征设置浅而宽(Shallow and wide, SW:30×30×5 cm³)和深而窄(Deep and narrow, DN:10×10×45 cm³)两种土壤容器,以正常降水量为对照供水(W100%),设减水50%(W50%)和减水70%(W30%)共3种水分处理进行盆栽实验,探究了两种不同土壤生境中土壤水分变化对黑麦草生长及光合生理的影响,以进一步理解喀斯特地区植物的适应对策。结果显示:(1)SW生境对水分变化敏感,随供水减少土壤含水量显著下降。轻度减水下植物叶面积增大,光合速率提高,地上部分生长得到促进,但水分严重减少对其生长和光合生理有抑制作用,但地上质量分数和水分利用效率却显著升高;(2)DN生境保水能力较好,随供水减少土壤水分含量下降较为平缓。叶片相对含水量、气孔导度和比叶面积在各水分处理之间差异不显著,但严重减水条件下总生物量、地上质量分数和水分利用效率均有回升。研究表明:浅而宽生境中植物倾向于通过提高地上部分的生长,保持较高的光合速率,并向地上部分分配较多生物量来应对水分胁迫;...     

Regulation of Assimilate Translocation Between Leaves and Fruits in the Tomato

Simultaneous measurement of export from leaves and import tofruits were made on tomato plants reduced to one fully expandedleaf and one fruit. Experimental leaves were exposed to sixlight flux densities (0.5–100 W m^–2) for 24 h whilerapidly growing fruits were kept in the dark at 22 °C. The rates of export of assimilate from these leaves varied from70 to 120 mg C leaf^–1 day^–1 corresponding with ratesof carbon fixation from 3 to 290 mg C leaf^–1 day^–1.Export from leaves with the lowest carbon fixation rates weremaintained by a loss of up to one-sixth of their initial carbon.In contrast, leaves with the highest carbon fixation rates exportedonly half the newly fixed carbon. The rates of import of assimilate to similar-sized fruits (c.16 cm³) were between 80 and 110 mg C fr^–1 day^–1but differed from the export rates of the source leaves. Thespecific growth rates and the specific respiration rates ofthe fruits were related to their initial carbon content at thebeginning of the experiment. Thus, over 24 h, the rate of importwas predetermined by the developmental stage of the fruit unalteredby the rate of current carbon fixation in the source leaf. Translocationof assimilate was regulated by sink demand under both source-and sink-limiting conditions in this short-term situation. The dynamic relationship between assimilate production in leavesand its utilization in fruits is discussed together with therole of sucrose concentration in these organs in regulatingtransport. Lycopersicon esculentumL, tomato assimilate translocation, source-sink relationships     

The Effects of Partially Drying Part of the Root System of Helianthus annuus on the Abscisic Acid Content of the Roots, Xylem Sap and Leaves

Plants of Helianthus annuus were grown in soil in pots suchthat approximately 30% of the root system protruded throughthe base of the pot. After 7 d further growth in aerated nutrientsolution, the attached, protruding roots were air-dried for10–15 min and thereafter surrounded with moist still air,in the dark, for 49 h, whilst the soil was kept at field capacity.The roots of the control plants remained in the nutrient solutionthroughout the experiment. This treatment rapidly reduced the water content of protrudingroots from 20.5 to 17.8 g g^–1 dry mass (DM), which remainedless than that of the control roots for the rest of the experiment.This treatment also reduced root turgor and water potential.The abscisic acid (ABA) concentrations in the protruding roots,xylem sap and leaves of the treated plants increased significantly,compared to values recorded for control plants. In treated roots, the ABA concentration was significantly increased4 h after treatment, with a maximum of 4.4+0.1 nmol g^–1(DM) after 25 h. The ABA concentration in the xylem sap of thetreated plants was significantly greater than in the controls25 h, 30 h, and 49 h after the partial drying of the roots,with a maximum concentration of approximately 970 pmol ABA cm-3at 49 h. Initially, the ABA concentration in the leaves was0.45 nmol g^–1 (DM) which increased significantly to 1.1±0.1 nmol g^–1 at 25 h, to 1.7±0.3 nmol g^–1at 49 h. Leaf conductance was significantly less in plants with air-driedroots than in the controls 8 h after the start of the treatmentand thereafter. The water relations of the leaves of the treatedplants did not differ from those of the control plants. These results confirm previous reports that ABA is rapidly generatedin partially-dried and attached root systems and demonstratesa concomitant large increase in the ABA content of the xylemsap. It is suggested that partial dehydration of some of theroots of Helianthus annuus, increases ABA concentration in thetranspiration stream and decreases leaf conductance in the absenceof changes in leaf water status. As these responses were initiatedin free-growing roots the stimulus is independent of any increasesin soil shear strength that are associated with soil drying. Key words: Soil drying, roots, ABA, leaf conductance, water relations     

Leaf movement of bush bean: a biometeorological perspective

 Leaf movements of bush bean plants were studied at the relatively low photon flux density of 0.2 mmol/m² per s, and air temperatures of 25° and 35° C in a growth chamber. A beta-ray gauge system was used to monitor continuously pulvinus water status and bending. Leaf angles were below the horizontal and were linearly related to the soil water content (R≥−0.91 at 25° C and R≥−0.93 at 35° C). The beta-ray transmission maxima coincided with the stem temperature minima in darkness and vice versa when brightness prevailed as the growth chamber temperature varied with the photoperiod. Leaf angle increased linearly with increased beta-ray transmission. The Q₁₀ temperature coefficient, a measure of the metabolic energy requirement for leaf movement between 25° and 35° C was estimated at 1.8, and the corresponding mean Arrhenius constant at 423 kJ/mol for bush bean. Received: 19 July 1996 / Accepted: 9 September 1996     

Leaf traits variation during leaf expansion in <Emphasis Type="Italic">Quercus ilex</Emphasis> L.

The morphological, anatomical and physiological variations of leaf traits were analysed during Quercus ilex L. leaf expansion. The leaf water content (LWC), leaf area relative growth rate (RGR_l) and leaf dry mass relative growth rate (RGR_m) were the highest (76±2 %, 0.413 cm² cm⁻² d⁻¹, 0.709 mg mg⁻¹ d⁻¹, respectively) at the beginning of the leaf expansion process (7 days after bud break). Leaf expansion lasted 84±2 days when air temperature ranged from 13.3±0.8 to 27.6±0.9 °C. The net photosynthetic rate (P _N), stomatal conductance (g _s), and chlorophyll content per fresh mass (Chl) increased during leaf expansion, having the highest values [12.62±1.64 μmol (CO₂) m⁻² s⁻¹, 0.090 mol (H₂O) m⁻² s⁻¹, and 1.03±0.08 mg g⁻¹, respectively] 56 days after bud break. Chl was directly correlated with leaf dry mass (DM) and P _N. The thickness of palisade parenchyma contributed to the total leaf thickness (263.1±1.5 μm) by 47 %, spongy layer thickness 38 %, adaxial epidermis and cuticle thickness 9 %, and abaxial epidermis and cuticle thickness 6 %. Variation in leaf size during leaf expansion might be attributed to a combination of cells density and length, and it is confirmed by the significant (p<0.001) correlations among these traits. Q. ilex leaves reached 90 % of their definitive structure before the most severe drought period (beginning of June — end of August). The high leaf mass area (LMA, 15.1±0.6 mg cm⁻²) at full leaf expansion was indicative of compact leaves (2028±100 cells mm⁻²). Air temperature increasing might shorten the favourable period for leaf expansion, thus changing the final amount of biomass per unit leaf area of Q. ilex.     

Changes of Anatomical Features, Photosynthesis and Ribulose Bisphosphate Carboxylase-Oxygenase Content of Mango Leaves

Changes in anatomical and physiological features, includingchanges in amount per unit area of anthocyanin and chlorophyll,in leaves of seedling mango (Mangifera indica L. cv. Irwin)trees were determined to understand what controls the rate ofphotosynthesis (Pn) at various stages of development. The youngleaves of seedling trees contained high concentrations of anthocyanin.During enlargement of leaves, the disappearance of anthocyaninand the accumulation of chlorophyll occurred concomitantly;the anthocyanin content began to decrease markedly once theleaf area had reached a maximum. During the early period ofleaf development, the thickness of mesophyll tissue decreasedtemporarily, but when the length of the leaf reached half thatof a mature leaf, the mesophyll began to thicken again. Smallstarch grains appeared in the chloroplasts of the young leavesand chloroplast nucleoids (ct-nuclei) were distributed throughoutthe chloroplasts. When leaves matured, ct-nuclei were displacedto the periphery of chloroplasts because of the accumulationof large starch grains. Compared with young leaves, green andmature leaves contained greater concentrations of ribulose bisphosphatecarboxylase-oxygenase (RuBisCO) protein. The results of immunocytochemicalexamination of RuBisCO under the light microscope reflectedthe results of electrophoresis measurements of RuBisCO. Pn waslow during the chocolate-coloured stage of early leaf development.In green and mature leaves Pn was higher; the average Pn was7·6 mg CO₂ dm^-2 h^-1 under light at intensities above500 µmol m^-2 s^-1.Copyright 1995, 1999 Academic Press Mangifera indica L., mango leaf, chloroplast nucleoids, chloroplast ultrastructure, starch accumulation, anthocyanin, chlorophyll, DAPI staining, SDS-PAGE, immunocytochemical technique     

Effect of growth irradiance on the maximum photosynthetic capacity of water hyacinth [Eichhornia crassipes (Mart.) Solms]

We grew water hyacinth [Eichhornia crassipes (Mart.) Solms]for 60 days in a greenhouse under natural light and in a controlledenvironment room at 31/25?C day/night temperatures and 90, 320and 750/µEm^–2sec^–1. We then determined maximumphotosynthetic rates in 21% and 1% oxygen, stomatal diffusionresistances, contents of chlorophyll and soluble protein, andthe size and density of the photosynthetic units (PSU) in representativeleaves from the four treatments. In air containing 21% oxygen,maximum photosynthetic rates were 14, 27 and 29 mg CO₂ dm^–2hr^–1for plants grown in artificial light at 90, 320 and 750µEm^–2sec^–1,respectively. Plants grown in natural light (maximum of 2000µEm^–2sec^–1) had maximum photosynthetic ratesof 34 mg CO₂ dm^–2hr^–1. In all treatments, photosyntheticrates in 1% oxygen were about 50% greater than rates in normalair, indicating the presence of photorespiration in water hyacinth.There was no apparent relationship between maximum photosyntheticrate per unit leaf area and stomatal conductance, chlorophyllcontent per unit area, or PSU density per unit area. However,the higher maximum photosynthetic rates were associated withgreater mesophyll conductances, specific leaf weights and proteincontents per unit area. When plants grown at 90µEm^–2sec^–1for 120 days were transferred to 750µEm^–2sec^–1for 5 days, only young leaves that were just beginning to expandat the time of transfer exhibited adaptation to the higher irradiance.The 40% increase in light-saturated photosynthetic rate in theseyoung leaves was associated with increases in mesophyll conductance,soluble protein content per unit area, and specific leaf weight. ¹ Mississippi Agricultural and Forestry Experiment Station cooperating. (Received July 19, 1978; )     

Leaf-like Structure in the Photosynthetic, Succulent Stems of Cacti

This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are ‘leafless’, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm^–2in the lower epidermis, 38.1 mm^–2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm ₂, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm^–2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm₂ cm^–2 which is higher than in Pereskia stemcortex (0.0150 cm₂ cm^–3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm₂ cm^–3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution     

An Improved Method of Soil Moisture Control with Observations on Tomato Growth and Water Uptake

The control of soil moisture depended on the arrangement ofnumerous auto-irrigation cells radially around the plant, allowingrelatively unrestricted spread of the root system, the cellsbeing so placed that no point in the soil was more than about1 in from a water-supplying surface. Water for the cells wassupplied from barostat reservoirs fixed at the levels requiredto give the target hydrostatic pressures of –27, –84,–149, –266 mb at the centre of the cells. The degree of soil moisture control achieved was assessed bysoil moisture tensiometers. Three months after sowing mean matricpotentials were reduced below target levels to minimum valuesof only –33, –104, –178, and –329 mb.At this time some of the tomato plants had leaf areas in excessof 2000 cm² per plant and water uptakes of 200 ml per day perplant in the –27 mb and of 150 ml in the –266 mbtreatment. Leaf area per plant decreased with decrease in matric potential;leaf dry weight decreased with matric potentials less than –84mb; root growth, observed in glass panels, was depressed atboth the largest and smallest matric potentials. The reductionin water uptake with decreasing matric potential was more thancould be accounted for by a smaller leaf area alone.     

Internal water balance of barley under soil moisture stress

Leaf water potential, leaf relative water content, and relative transpiration of barley were determined daily under greenhouse conditions at 3 growth stages: tillering to boot, boot to heading, and heading to maturity. The leaf moisture characteristic curve (relative water content versus leaf water potential) was the same for leaves of the same age growing in the same environment for the first 2 stages of growth, but shifted at the heading to maturity stage to higher leaf relative water content for a given leaf water potential. Growth chamber experiments showed that the leaf moisture characteristic curve was not the same for plants growing in different environments.

Relative transpiration data indicated that barley stomates closed at a water potential of about −22 bars at the 3 stages studied.

The water potential was measured for all the leaves on barley to determine the variation of water potential with leaf position. Leaf water potential increased basipetally with plant leaf position. In soil with a moisture content near field capacity a difference of about 16.5 bars was observed between the top and bottom leaves on the same plant, while in soil with a moisture content near the permanent wilting point the difference was only 5.6 bars between the same leaf positions.

     

Suppression of Stomatal Opening in Leaves Treated with Abscisic Acid

Small doses of abscisic acid (approximately 0.02 µg cm^-2of leaf) applied to the leaf surface as a 10^-4 M solution causedmarked stomatal closure in Xanthium pennsylvanicum, and theeffect persisted for up to 9 days after application. Similareffects were found when 10^-4 M abscisic acid was supplied todetached tobacco leaves via their petioles. CO²-free air didnot cause a reversal of the closure, and it was therefore concludedthat the effect was not due simply to an increase in the intercellularCO²concentration; a more direct effect on the stomatal apparatusis suggested. It is considered that abscisic acid could playan endogenous role in the control of stomatal aperture, andthat this, and/or related substances, might be more useful as‘anti-transpirants’ than the phytotoxic substancescurrently employed for this purpose.     

The Effects of Foliar Applications of (2-Chloroethyl)-trimethylammonium Chloride on Leaf Area and Dry Matter Production by the Brussels Sprout Plant

When CCC was applied as a spray to the leaves of Brassica oleraceaL. (Brussels sprout) grown in pots, plant height and mean internodelength were reduced. The effects appeared more slowly and wereless pronounced than those previously observed when CCC hadbeen applied to the soil; other differences were that root growthwas not inhibited, stem weight was only significantly reducedat the highest rate of application (2 per cent), and stomatalnumber per unit area of lower leaf epidermis was not affected.In common with soil applications, leaf thickness, stem diameter,and the percentage moisture contents of the leaves were allincreased by foliar applications.In a further experiment theprogress of wilting was observed in untreated plants and inplants treated with CCC applied either to the leaves or to thesoil. The rates of water loss and the moisture contents of theleaf laminae of the treated plants, after a period of wilting,were not significantly different from the controls. The treatedplants, however, looked less ‘wilted‘ for the changein angle of the leaf lamina to the stem was less and their leaveswere therefore held more upright.