Diurnal Changes in Citrus Leaf Thickness, Leaf Water Potential and Leaf to Air Temperature Difference

Diurnal changes in leaf water potential and leaf thickness ofwell-watered citrus trees were found to be highly correlated.Midday decreases in leaf thickness of about 30–35 µm reflected midday decreases in leaf water potential of about1.1–1.3 MPa from predawn values. Leaf water potentialwas also correlated with changes in leaf-to-air temperaturedifference and ambient vapour pressure deficit. Leaf thicknessas well as leaf to air temperature difference could possiblybe used to monitor leaf water status continuously as an indicatorof citrus tree water stress.     

Leaf Thickness and Water Deficit in Plants: A Tool for Field Studies

B?rquez, A. 1987. Leaf thickness and water deficit in plants:a tool for field studies.—J. exp. Bot. 38: 109–114. A technique for estimating plant water deficits using a relativelyinexpensive micrometer to measure leaf thickness was developed.A strong correlation was found between leaf thickness and relativewater content (RWC) in Brassica napus, Mirabilis jalapa, Phaseolusvulgaris and Impatiens parviflora. Although leaf thickness ata given RWC varied between plants, it increased linearly withleaf RWC, the rate of change being similar in leaves of plantsof the same age and species. Due to this relationship, the constructionof a pressure-volume curve makes possible the estimation ofleaf water potential. In this case a calibration curve is neededfor each population studied or, for the highest accuracy, foreach individual. The technique is particularly useful in fieldconditions where other techniques are not reliable because ofdifficulties in controlling temperature and where non-destructivemeasurements are required. Key words: Leaf thickness, relative water content, water potential     

An Ecophysiological Comparison of Measurements of the Diurnal Rhythm of the Leaf Elongation and Changes of the Leaf Thickness of Salt-resistant Dicotyledonae and Monocotyledonae

Rozema, J., Arp, W., van Diggelen, J., Kok, E. and Letschert,J. 1987. An ecophysiological comparison of measurements of thediurnal rhythm of the leaf elongation and changes of the leafthickness of salt-resistant Dicotyledonae and Monocotyledonae.—J.exp. Bot. 38: 442–453. The continuous measurement of leaf elongation and leaf thicknesswith the use of a rotation potentiometer set up revealed a rapidand sensitive reaction of halophytic plants to conditions affectingthe plant's water relations. At increased salinity (450 molm^–3 NaCl) the rate of leaf elongation decreased both inAster tripolium and in Sparlina anghca. Increased shrinkageduring the day and a long period for recovery swelling at nightin leaves of Aster iripolium at increased salinity illustratesthat water shortage is part of the cause of salinity-inducedgrowth reduction. All dicotyledonous species analysed (Aster tripolium, A triplexhastata, A. littoralis, Suaeda maritima and Beta vulgaris) showeda day/night ratio of the leaf elongation rate lower than 1,while this ratio was higher than or equal to 1 in Monocotyledons(Spartina anglica, Juncus gerardii, J. maritimus, Festuca rubrassp. litoralis, Elymus pycnanthus). With the exception of Triglochinmaritima none of the monocotyledonous halophytes tested (Sparlinaanglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis,Elymus pycnanthus) exhibited a diurnal rhythm of leaf thicknesschanges, such as was observed for all dicotyledonous speciesstudied (Aster tripolium, Atriplex hastata, A. littoralis, Salicorniabrachyslachya, Suaeda maritima, Glaux maritima, Odontites vernassp. serotina). The diurnal pattern of the leaf elongation rateand the leaf thickness changes can be explained by variationof photosynthetic rate and transpiration water losses by stomatalclosure in the dark and opening in the light such as shown forthe dicotyledon species Glaux maritima. This difference betweendicot and monocot species in diurnal variation of the leaf elongationrate and leaf thickness may partly be explained in terms ofthe different position of the growth zone and possibly by adifference in elasticity of the tissue of halophytic monocotyledonsand dicotyledons. The consequences of these differences arediscussed. Key words: Leaf elongation rate, leaf thickness, water relations, salt resistance, Dicotyledonae, Monocotyledonae     

An Infra-red Psychrometer for Detecting Changes in the Humidity of Leaf Boundary Layers

An apparatus is described which uses the principle of the absorptionof infra-red light by water vapour, for the measurement of water-vapourconcentrations in the atmosphere or in the boundary layers ofleaves.     

An Instrument for Non-Destructive Measurement of the Pressure Potential (Turgor) of Leaf Cells

An instrument is described which permits the non-destructivemeasurement of the mean pressure potential (turgor)of leaf laminacells. Calibration shows that the instrument gives a voltageoutput which is linearly related to mean pressure potentialof living leaf cells as determined with a pressure chamber.Measurements may be made very quickly in the field or controlledenvironment with a resolution of at least 50 k Pa.     

Psychrometric Field Measurement of Water Potential Changes following Leaf Excision

In situ measurement of sudden leaf water potential changes has not been performed under field conditions. A laboratory investigation involving the measurement of leaf water potential prior to and 2 to 200 minutes after excision of citrus leaves (Citrus jambhiri) showed good linear correlation (r = 0.99) between in situ leaf psychrometer and Scholander pressure chamber measurements. Following this, a field investigation was conducted which involved psychrometric measurement prior to petiole excision and 1 minute after excision. Simultaneous pressure chamber measurements were performed on neighboring leaves prior to the time of excision and then on the psychrometer leaf about 2 minutes after excision. These data indicate that within the first 2 minutes after excision, psychrometer and pressure chamber measurements were linearly correlated (r = 0.97). Under high evaporative demand conditions, the rate of water potential decrease was between 250 and 700 kilopascals in the first minute after excision. These results show that the thermocouple psychrometer can be used as a dynamic and nondestructive field technique for monitoring leaf water potential.     

An Instrument for Continuous Viewing of Roll Tube Cultures under a Stereoscopic Microscope

An instrument which fits on the stage of a CTS M6100 stereoscopic microscope and provides a continuous field of view for roll tube cultures is described. It has been used to facilitate the rapid counting of colonies on soil extract agar.     

Senescence-Related Changes in the Leaf Apoplast

The extracellular space of leaves is a highly dynamic compartment harboring a number of activities involved in signal recognition, import/export of organic and inorganic compounds, and defense against pathogens. Although this has not been extensively studied, there is evidence for the involvement of the extracellular space in signal perception and nutrient remobilization during senescence. Integration of the apoplast into the larger picture of cellular activities during senescence may help understand key events in the terminal phase of leaf development. Important events associated with senescence occur in the apoplast, and these events may offer targets for genetic manipulation to modulate senescence. In this paper we look into changes in the extracellular space of leaves accompanying senescence, with a special focus on apoplastic proteins and plasma membrane proteins related to signaling and export of amino acids. Other not less relevant senescence-related metabolic changes such as NH₄ accumulation and the oxidative burst are beyond the scope of this review.     

A Vapour-pressure Instrument for the Measurement of Leaf and Soil Water Potential

A previously described vapour-pressure osmometer has been adaptedfor the measurement of depression of water potential (DPD) insamples of leaf tissue and soil. A pile of about 30 leaf annuliare contained in an air-tight metal capsule through the lidof which passes a pipette. A drop of water hangs from the tipof the pipette into the central cavity of the pile of leaf annuli.The drop is drawn bath into the pipette from time to time andthe rate of evaporation from it measured directly. The water-potentialdepression is linearly related to the rate of evaporation. Theinstrument is calibrated empincally. A period of a hours isnecessary to attain vapour equilibnum before readings are takenThe readings then occupy less than 30 minutes. For the calibration data, using filter paper moistened withNaCl solution, the 5 percent inverse tolerance limits for singlereadings of water-potential depression were ±0.26 atm.With leaf material the errors appear to be about the same, althoughrelease of cell sap at the cut edges of the disks may causean overestimation by as much as 0.5 atm. with turgid leaf material.Lining the capsule with leaf strips gave erroneous results.Using a suitably modified capsule the instrument can be usedfor soil-water potential measurement. Equilibration takes only30 minutes so that a reading can be completed within an hour.     

A Mobile Apparatus for Measuring Leaf Photosynthesis in the Field

An apparatus is described that has been designed to measurethe gas exchange of individual cereal leaves in the field, usinginfrared gas analysis. Measurements on leaves of winter wheatshowed that there was true saturation of net photosynthesisat high irradiances but as irradiance decreased there was aproportional decrease in net photosynthesis. Measurements madeon wheat plants grown in a controlled environment, for comparison,showed the photosynthesis–light response curve to be betterfitted by a rectangular hyperbola. This dissimilar responseof photosynthesis to irradiancc for plants grown in controlledenvironments indicates the possible problems of extrapolationfrom the laboratory to the field.     

Water Stress and Leaf Growth of Field Beans (Vicia faba L.) in the Field: Leaf Number and Total Leaf Area

The leaf area growth of field beans grown under covers in thefield was measured non-destructively on plants subjected tothree different degrees of soil water stress by means of dryingcycles of different lengths in 1974 and 1975. After a periodof 46 days the total leaf area of the well-watered plants wasabout double that of the non-watered ones. The total leaf areaat the final-sampling and the mean plant water potential duringthe observation period were linearly related with highly significantcorrelation coefficients (0·96 in 1974 and 0·86in 1975). The differences between treatments in total leaf areawere mainly produced by the mechanisms determining leaf sizerather than those associated with leaf production and maintenance,namely leaf production, unfolding and death. In neither yearwas leaf production or unfolding sensitive to water stress beforeflowering. Plant water potential () exerted a cumulative longterm effect on these two mechanisms. The threshold values of for reducing the rates of leaf production and unfolding weremore negative in the drier year (1975). Leaf death was affectedby drought earlier than leaf production and unfolding. Vicia faba, field bean, water stress, leaf area     

Leaf Determination in the Fern Osmunda cinnamomea--A Reinvestigation

Earlier studies of leaf determination in the fern Osmunda cinnamomeaL., using the technique of excision and sterile culture, indicatedthat the apices of incompletely determined leaf primordia areconverted into shoot apices after isolation. Subsequently otherworkers questioned this interpretation, suggesting that a primordiumis determined as a leaf shortly after its inception and thatany shoot which arises from it is an adaxial adventitious bud.Because of the importance of this distinction in the interpretationof determination, the phenomenon has been reinvestigated byscanning electron microscopy and histological methods. Sincefixation for electron microscopy was inconsistence, the workwas performed on the primordia using resin models formed indental plastic moulds. Our data, on explanted P3, P4, and P5leaf primodia, provide strong confirmation for the interpretationthat the leaf apex is indeed converted to a shoot apex in incompletelydetermined primodia after explantation. This new evidence formsthe basis for interpreting leaf determination in this experimentalsystem.Copyright 1993, 1999 Academic Press Leaf determination, in vitro, surface replica, scanning electron microscopy, Osmunda cinnamomea L., cinnamon fern     

Translocation from the Flag Leaf of Winter Wheat in the Field

Translocation of assimilate from the flag leaf of winter wheat(Triticum aestivum cv. Maris Huntsman) was studied in the fieldby monitoring the export of photo-assimilated [^l4C]carbon dioxidewith a Geiger-Miiller counter placed under the fed area of leaf.The resulting export curve was analysed as a sum of two exponentialterms, and interpreted as a two-pool compartmental system. Therate constant for export from the leaf increased slightly frommaximum elongation to anthesis, then declined to almost halfits peak value just before the leaf lost all visible chlorophyll.The inter-pool transfer rate constants did not change significantlyover the same period, but all rate constants varied with timeof day. Short-term changes in the environment of the flag leaf had nodiscernible influence on translocation in the field. The timeconstants of the two pools of assimilate agreed with those forother species reported in the literature. These results areconsistent with the suggestion that sucrose is stored in thevacuole of mesophyll cells. The variations in rate constants with time of day, and deviationsof the export data from the two-pool model, suggest that exportand inter-pool transport have saturation kinetics. A model withMichaelis-Menten kinetics was formulated, and simulations ofthis model showed similar deviations from a simple two-poolsystem to those seen in our data.     

淹水对玉米叶片细胞超微结构的影响

对淹水过程中玉米（Ｚｅａ ｍａｙｓ Ｌ．）叶片细胞超微结构的变化进行连续观察。淹水２ｈ后,液泡膜发生明显内陷。淹水６ｈ后,液泡膜内陷加剧,呈极度松弛状态;叶发体被膜局部向外突出一个由单层膜包裹的泡状结构。淹水１２ｈ后,液泡膜局部破裂;叶绿体被膜破坏加剧,成为一松弛的单膜结构,同时,基质类囊体出现空泡化。淹水１８ｈ后,叶绿体的破坏进一步加剧：被膜完全消失,基质类囊体开始消化;同时,线粒体膜和核膜也开     

An Instrument for Biofeedback Applied to Vision

One hundred and ten patients (179 eyes) with reduced visual acuity caused by different ocular disorders underwent visual rehabilitation with an instrument for biofeedback: improved biofeedback integrated system (Ibis). One hundred and fourteen eyes had age-related macular degeneration, 39 eyes had myopic macular degeneration, and 26 eyes were affected by different ocular disorders. A placebo training was developed on 34 patients (47 eyes). Thirty-three eyes had age-related macular degeneration and 15 eyes had myopic macular degeneration. Visual acuity was found to be improved in 130/179 eyes (72.62%). Mean visual acuity was 0.24 before training and 0.36 at the last follow-up. A review of the literature and possible mechanisms are discussed.     

Leaf Discs or Press Saps? A Comparison of Techniques for the Determination of Osmotic Potentials in Freeze-Thawed Leaf Material

Two standard methods for the determination of osmotic potentialsin plant organs, thermocouple hygrometry of press saps and offreeze-thawed leaf discs, were compared on leaves of ten species.Strictly parallel samples invariably showed lower (more negative)osmotic potentials for the leaf discs. Evidence is presentedthat osmotically-active solutes are not completely extractedduring the preparation of press saps and that the discs contain,on average, a smaller amount of apoplastic water than the saps.Hydrolysis of macromolecules in the discs was not responsiblefor the differences. The presence of the cutinized epidermisresults in a comparatively long equilibration time for leafdiscs, which may be reduced by appropriate measures. Key words: Thermocouple psychrometry, vapour pressure equilibration, leaf discs, press saps, solute extraction     

An Automatic Device for Measuring Leaf Area

The design and construction of a digital device, which measuresthe area of leaves by scanning with a rapidly moving spot oflight, is described.     

Metabolic Regulation in the Senescing Tobacco Leaf: II. Changes in Glycolytic Metabolite Levels in the Detached Leaf

Yellowing of detached mature tobacco leaves standing in water in the dark was accompanied by a strong “climacteric rise” in respiration rate. During this period the ATP level and energy charge of the adenylate system also rose. The levels of glycolytic intermediates between glucose 1-phosphate and triose phosphates rose, those between 3-phosphoglycerate and phosphoenolpyruvate fell, and pyruvate rose. On the assumption of a drop in NAD/NADH ratio, as found by other workers in wheat leaves, the reverse crossover between triose phosphates and 3-phospholglycerate was attributed to inhibition of glyceraldehyde 3-phosphate dehydrogenase. The forward crossover between phosphoenolpyruvate and pyruvate was taken to indicate activation of pyruvate kinase, possibly by fructose diphosphate. Secondary large rises in pyruvate and fructose diphosphate occurred well after the climacteric peak had been passed. No evidence was found for participation of phosphofructokinase in metabolic control in the yellowing leaf. Possible limitations to the use of the crossover theorem in the present situation, such as changes in compartmentation and in flux through branch points, are emphasized.