Experimental Studies of the Factors Controlling Transpiration: II. THE RELATION BETWEEN TRANSPIRATION RATE AND LEAF WATER CONTENT

Data are presented which show, when stomatal control is eliminated,that wheat leaves may lose 5–6 per cent. and Pelargoniumleaves 10–12 per cent. of their water without any reductionin the transpiration rate. Experiments in which Pelargonium and wheat leaves, with stomatalcontrol present, were submitted to cycles of changing watercontent also failed to establish any direct relation betweentranspiration rate and leaf water content. It is concluded that leaf water content over the range of 70–100per cent. of that present in the turgid state has no significanteffect in determining the rate of water loss from leaves. A repetition of Knight's experiment showed that stomata openedin still air and closed in moving air. This was not recordedby Knight, who used a porometer cup permanently attached tothe leaf. It is concluded that the higher transpiration raterecorded by Knight after a period of still air was due to widerstomatal aperture and not to the higher leaf water content assuggested by him.     

Studies in Stomatal Behaviour: VI. AN INVESTIGATION OF THE LIGHT RESPONSES OF WHEAT STOMATA WITH THE ATTEMPTED ELIMINATION OF CONTROL BY THE MESOPHYLL

An apparatus is described enabling light responses of wheatstomata to be followed by periodical porometer readings, betweenwhich the substomatal cavities can be swept with carbon dioxide-freeair forced in through the stomata. This is held to eliminatethe influence of changes in the carbon dioxide content of theintercellular space atmosphere brought about by photosynthesisand respiration in the mesophyll. Using this apparatus in anexperiment of ‘Latin square’ design with 6-foldreplication of three light treatments, a statistically significantresponse to light was found in a leaf area subjected to varyinglight intensities from 90 to 800 f.c. This response was reflectedin a similar significant effect, though of smaller magnitude,occurring in a similarly swept ‘control’ area 2cm. distant and maintained at a constant light intensity of270 f.c, the intervening portion of leaf being illuminated with800 f.c. throughout. It is argued that this transmission ofa light effect from one area to another does not occur via theintercellular spaces, nor by means of carbon dioxide gradientsfrom cell to cell. It is concluded from the data that thereis an indirect effect of light and perhaps also a direct effectupon the guard cells themselves; it is probable that neitherof the two effects concerned operates by reduction of the internalcarbon dioxide content in the guard cells.     

Studies in Stomatal Behaviour: VI. AN INVESTIGATION OF THE LIGHT RESPONSES OF WHEAT STOMATA WITH THE ATTEMPTED ELIMINATION OF CONTROL BY THE MESOPHYLL

As in the previous investigation (Part I), stomatal responsesin wheat were followed by means of porometer readings; betweenthese, air was forced through the stomata to sweep out the substomatalcavities. Instead of forcing the whole of a relatively slowair-flow in through the stomata, however, a fast flow was sweptacross the leaf surface and a portion of this passed into theintercellular space system. This helped to maintain the desiredcarbon dioxide content close to the stomatal openings and thestomata could thus be treated with different carbon dioxideconcentrations. A factorial experiment was carried out in which6 carbon dioxide concentrations from zero to 0084 per cent,were combined with 3 light intensities from 90 to 800 f.c, the18 treatments being replicated 6 times in three ‘66 latinsquares’. A supplementary experiment in which the same6 carbon dioxide treatments were given in darkness was carriedout in duplicate. The results confirmed previous findings inthat the stomata showed no appreciable response to variationof external carbon dioxide supply between zero and 001 percent, concentration and that a large and highly significantlight response was found at each of these two carbon dioxidelevels. This is held to indicate the existence of a light effect(direct or indirect) not operating by reduction of the internalcarbon dioxide content of the guard cells. On the assumptionthat the rates of air flow through the stomata were adequate,the combined results of the two experiments are interpretedmainly in terms of two direct effects of light upon the stomata,one depending on photosynthetic reduction of carbon dioxidein the guard cells and the other, mentioned above, not so operating.To these must be added the indirect effect responsible for the‘transmission’ described in Part 1, which mightpossibly account for the whole of the second direct effect postulated.Finally, if the rates of flow were in fact grossly inadequate,the trends attributed to the first direct effect mentioned abovemight have been due to indirect control by the mesophyll viathe intercellular space atmosphere. Such control must accountfor part of the light responses which occur under natural conditions.The natural light response is thus made up of at least two andmore probably four components—two direct and two indirect,in each case one operating by the internal carbon dioxide andthe other not. A highly significant diurnal rhythm of stomatalmovement under constant illumination and temperature is shownto occur in wheat. The measure of stomatal resistance used (logresistance per 10,000 stomata) is discussed, and it is concludedthat although it is empirical a much more satisfactory measureis not at present available.     

Experimental Studies of the Factors Controlling Transpiration: I. APPARATUS AND EXPERIMENTAL TECHNIQUE

Apparatus and experimental techniques are discussed for usein the investigation of transpiration rate of leaves as controlledby stomatal aperture and leaf water content. The leaf chambers used and the methods adopted for the estimationof the water transpired are described. The designs of the porometer cups used for the different typesof leaves (Pelargonium and wheat) employed in the work are described.To obviate the difficulty that stomata within the cup behaveabnormally, the design employed makes possible a removal ofthe cup from the leaf except during the short periods requiredto estimate stomatal resistance to air flow at intervals duringthe course of an experiment. In these experiments the water content of the leaf is changedat will by interrupting the water-supply and re-establishingit to permit recovery from wilting. The methods used to carryout this cycle of operations are fully dealt with. Determinationsof the transpiration and absorption rates during the experimentand of the final leaf water content make it possible to followchanges in leaf water content throughout the experiment. An account is given of the methods used for varying the speedof flow, the humidity, and the CO₂ concentration of the airstreams.     

Studies in Stomatal Behaviour: The Effects of Moving, Normal and Carbon Dioxide-Free Air on the Stomata of Some Plants

A series of experiments were conducted to investigate the effects of moving, normal and carbon dioxide-free air on the stomata within porometer cups attached to the illuminated leaves of Datura stramonium, Pelargonium zonale, Duranta plumieri and Clerodendron inerme. A marked opening stomatal response was obtained in Datura and Pelargonium on changing to carbon dioxide-free air. In general no such response was established in Duranta and Clerodendron. Indications of even an opposite closing effect were shown in the case of Duranta. The present results seem to disprove the reduction of carbon dioxide by photosynthesis as the major factor controlling the wide stomatal opening within a porometer cup. The possibility of a humidity effect is also suggested.     

The Influence of Water Strain on the Minimum Intercellular Space Carbon dioxide Concentration {lambda} and Stomatal Movement in Wheat Leaves

Eight detached wheat leaves were each subjected to varying degreesof controlled water strain, in a specially constructed leafchamber (which is described in detail) connected to a closedsystem incorporating an infra-red gas analyser. The water strainwas varied by applying successively to their leaf sheaths twoconcentrations of mannitol solution (0·2 M. and 0·4M.) each preceded and followed by water. Conditions were maintainedconstant for light (900 f.c.), leaf temperature (25° C.)and humidity (50 per cent. RH) of the circulating air as itentered the leaf chamber. Steady-state values (gamma) of thecarbon dioxide concentration in the closed system were recordedboth for the water and mannitol treatments and the data analysedstatistically. The two mannitol treatments were found to increasegamma from 80 p.p.m. with water to 94 and 116 p.p.m. respectively,all differences being highly significant. Concomitant measurementswere made of stomata1 resistance with a porometer and of transpirationby means of wet and dry thermocouples; the stomata showed markedclosure in response to mannitol treatment (complete closurewith the higher concentration) and partial reopening with theleaf sheath in water once more, transpiration also falling andrising inversely with water strain. It is concluded that part of the closing response of wheat stomatato water strain under natural conditions must be operated byincrease in the intercellular-space carbon dioxide concentration,but a comparison with previous experimental results suggeststhat this can only be a small part unless sensitivity to carbondioxide is greatly increased by water loss. The initial response to mannitol treatment was a preliminaryopening of the stomata and a fall of about 10 per cent. in carbondioxide concentration. These results imply that under naturalconditions the preliminary opening of wheat stomata with wiltingmay be partly passive and partly active with a carbon dioxide-operatedmechanism. A subsidiary experiment with water strain varied by removingand restoring the water supply to the leaf sheath gave increasesand decreases in carbon dioxide similar to those in the mainexperiment; the results of the latter need not, therefore, beattributed to metabolism of the mannitol. It is suggested that values of gamma give a good measure ofthe efficiency of the mesophyll for net carbon dioxide absorption,with the stomatal factor eliminated, under the given conditionsand with carbon dioxide ‘limiting’ in the senseused by Maskell (1928).     

Studies in Stomatal Behaviour: VII. EFFECTS OF ANAEROBIC CONDITIONS UPON STOMATAL MOVEMENT--A TEST OF WILLIAMS'S HYPOTHESIS OF STOMATAL MECHANISM

An experiment was carried out to investigate stomatal responsesin wheat to four ‘closing treatments’, viz. highcarbon dioxide concentration, darkness, dry air and nil, eachgiven under both aerobic and anaerobic conditions. Thus theeffect of lack of oxygen on the closing (or opening) tendencywas estimated. Changes in calculated from resistance porometer readings were used as data and reasonsare given for thinking this is the best available measure forinvestigating stomatal dynamics in wheat. Williams's hypothesisdemands that lack of oxygen should cause stomatal opening orprevent closure; the present experiment shows that anaerobicconditions significantly increase the closing tendency when‘closing treatments’ are first applied. There isalso some suggestion that oxygen-lack itself tends to causeclosure in the absence of any other ‘closing treatment’.Williams's hypothesis in its original form is thus disproved(for wheat) but the present results would be consistent withan ‘active’ uptake of water by the guard cells contributingto stomatal opening. A nearly significant interaction betweencarbon dioxide and oxygen suggests that under anaerobic conditionsa ‘closing substance’ may perhaps be formed, forexample, by the union of some intermediate in glycolysis withcarbon dioxide.     

Experimental Studies of the Factors Controlling Transpiration: III. THE INTERRELATIONS BETWEEN TRANSPIRATION RATE, STOMATAL MOVEMENT, AND LEAF-WATER CONTENT

Transpiration rates of single leaves of Pelargonium and wheatwere measured under constant conditions of light, temperature,and air flow. Concurrently, stomatal movement was followed withthe resistance porometer during cycles of changing water contentof the leaf and changes induced by light and darkness. Stomatalmovement was found to exert a large controlling influence onthe transpiration rate, whereas water content had an extremelysmall or negligible effect. An approximately inverse linearrelation between transpiration rate and logarithm of resistanceto viscous flow through the leaf is believed to be the resultantof an inverse curvilinear relationship between the diffusiveconductance of the stomata and log. leaf resistance and thedecreasing difference of vapour pressure arising from the highertranspiration rates with increasing stomatal conductances. Nevertheless,the relation demonstrates that the transpiration rate is influencedby the degree of stomatal opening throughout its entire range. There was some evidence of lower transpiration rates duringand after recovery from wilting than before wilting. This isattributed to a decrease in a cell-wall conductance, the evaporatingsurface being located within the cell wall. During wilting partiallyirreversible contraction of the cell wall occurs. There wasalso evidence of slow changes in cell volume at full turgidityattributable to plastic flow. These occurred when the leaf wastransferred from environments of a high to low potential forevaporation. Extensive movement of the stomata followed changes in leaf water,passive opening resulting from decrease and closure from increaseof leaf water. It is suggested that the direction and extentof stomatal changes induced by water deficits is a consequenceof the rate of change of leaf water content and not of the absolutevalues. The stomata also showed an enhanced tendency to closein dry moving air following a period of wilting even after theleaf had regained turgidity.     

Studies in Stomatal Behaviour: V. THE ROLE OF CARBON DIOXIDE IN THE LIGHT RESPONSE OF STOMATA

Experiments are described in which the responses of wheat stomatato carbon dioxide concentration (0·00, 0·01, 0·02,0·03 per cent.), light intensity (275, 625, 975 f.c.),and rate of air flow (2, 5, 12·5 l./hr.) were studied. Reduction of carbon dioxide concentration from 0·03 to0·01 per cent. resulted in marked stomatal opening; furtherreduction to 0·00 per cent, was accompanied by a slightbut not significant closure. These effects were found at alllight intensities and rates of flow, except at 975 f.c. with2 l./hr. air flow, where no effect of carbon dioxide concentrationwas detected. This last is attributed to excessive depletionof the carbon dioxide supply by assimilation. The apparent lowerlimit of 0·01 per cent, carbon dioxide causing maximalstomatal opening is discussed in relation to recent assimilationexperiments. Increase of light intensity caused considerable stomatal opening,this effect being as great with air of 0·00 and 0·01per cent. as with higher concentrations of carbon dioxide. Thissuggests an effect of light on stomatal movement other thanthat exerted indirectly through photosynthesis by the mesophylcells. Increased rate of flow of dry air caused closure of the stomata;this was shown to be a drying effect and was absent when moistair was used.     

Carbon Assimilation at Low Carbon Dioxide Levels: II. THE PROCESSES OF APPARENT ASSIMILATION

The relation of the net uptake or output of carbon dioxide bydetached leaves of Pelargonium zonale or wheat to ambient carbondioxide concentration was investigated at two or three lightintensities. The statistics of fitted curves were used as datain analysis of variance. For Pelargonium the results were consistentwith a hypothesis of a ‘straight balance’ betweena rate of photosynthetic uptake proportional to concentrationand a constant rate of respiratory production. For wheat, however,the curve was steeper near than at lower carbon dioxide levels;this disproved the ‘straight balance’ hypothesisand was consistent with an increase in carbon dioxide fixationor a reduction in output over a limited concentration rangeon either side of . The characteristics of light respiration, possibly carbon dioxidedependent, were investigated further in an experiment on theeffect of oxygen concentrationupon r values for two species(P. zonale and Hydrangea sp.) at two light intensities; theywere also studied by measuring the ‘burst’ of carbondioxide output when leaves were darkened after illuminationat four different light intensities and at two temperatures. was linearly related to oxygen tension up to 610 mm partialpressure of mercury and a fivefold increase in light intensityhad only a very small effect indicating that photoxidation wasnot important. The carbon dioxide burst on darkening showedrelations to temperature and previous light intensity quitedifferent from those of which should be proportional to lightrespiration. These results, therefore, do not support the viewthat the burst represents the persistence of an enhanced lightrespiration.     

The Measurement of Stomatal Responses to Stimuli in Leaves and Leaf Discs

A comparison has been made of stomatal responses in intact leaves,leaf discs supplied with water via their cut edges and leafdiscs floating on water. Xanthium pennsylvanicum leaf discswatered via their cut edges appeared to be more turgid thanintact leaves; this considerably slowed down the rate of stomatalopening but it slightly increased the final steady-state stomatalopening. When the water potential of such leaf discs was loweredby pre-treatment with mannitol solutions rates of stomatal openingincreased whereas maximum steady-state openings decreased. In tobacco leaf discs floating on water the stomata in contactwith water were wider open than those in contact with normalair and they did not respond to treatment with carbon dioxide-freeair. The rate of photosynthesis was severely reduced in tobaccoleaf discs floating with the lower epidermis on water, mostprobably owing to the slow rate of diffusion of carbon dioxidein water. By floating such discs on osmotica the degree of stomatalopening was increased, however, a response to treatment withcarbon dioxide-free air was still not measurable. It is postulatedthat, on account of the relative unavailability of carbon dioxidefrom the water, the carbon dioxide concentration in the substomatalcavities of the lower surface is abnormally low, irrespectiveof whether ordinary air or carbon dioxide-free air is availableto the upper surface. A comparison between porometer readings and measurements ofsiliconerubber impressions of stomatal pores taken from insidethe porometer cup confirmed that the silicone-rubber impressionmethod of assessing stomatal responses to stimuli has severelimitations, especially at small stomatal apertures.     

Response of Stomata to Subnormal Carbon Dioxide Concentrations

In a preliminary note in Nature (vol. 161, p. 179, 1948) andin two recent papers in this Journal (vol. 1, pp. 29 and 227,1950) I described work leading to the finding that stomata ofPelargonium and of wheat respond markedly to small changes inthe carbon dioxide content of the air below the normal 0?03per cent.; I have now for the first time seen a paper by Freudenberger(Protoplastna, 25, 15, 1940) in which a similar discovery (inqualitative terms) is announced for Canna and some other genera.I much regret that owing to the war the volume of Protoplasmain question has not been available and I was thus unable torefer to this interesting paper. This work of Freudenberger'swill be discussed in relation to my own in due course.     

The Hydraulic Pathways in Nicotiana glauca (Grah.) and Tradescantia virginiana (L.) Leaves, and Water Potentials in Leaf Epidermes

The hydraulic conductances of leaves of a species which exhibitsstomatal responses to humidity (Nicotiana glauca) are significantlylower than the conductances in a species which does not exhibitsuch responses (Tradescantia virginiana). This difference couldat least partly account for their difference in stomatal responseto humidity. In both species, the hydraulic conductance betweenthe leaf bulk and its epidermis is much lower than the conductancein any other part of the pathway. The apparently conflictingresults, reported in recent literature, on the hydraulic conductancesand water pathways in leaves are reinterpreted, and shown tobe due to misinterpretation of results. The recently publishedcriticisms of a technique used to measure hydraulic conductivityare commented on and refuted. An examination of the factors that influence the water potentialat the sites of evaporation from the inner walls of the epidermisnear stomatal pores showed that the water potential at thesesites is lower than the bulk epidermal water potential. Thewater potential at these sites changes in a complex way as stomatalaperture changes. As it is reduced the ratio of: ‘waterpotential at sites of evaporation on the inner walls of theepidermis near stomatal pores/bulk leaf water potential‘increases. The positive feedback effect of this phenomenon,which tends to keep stomatal water potential constant as thestomata close and therefore enhances closure, and two other‘passive’ positive feedback effects on the waterpotential at sites of evaporation near stomata that have beenreported in the literature are briefly discussed. Nicotiana glauca (Grah.), Tradescantia virginiana (L.), sub-stomatal cavities, peristomatal evaporation, stomata, humidity response, leaf hydraulic conductance, water potential     

Studies in Stomatal Behaviour: II THE ROLE OF STARCH IN THE LIGHT RESPONSE OF STOMATA PART 4. VARIATION UNDER CONSTANT CONDITIONS

A quantitative study has been made of the extent and natureof the variation in starch-content and aperture of the stomataof Pelargonium. It is shown that distribution over the surfaceof a single leaf is substantially normal in form; that underexperimental conditions in common use there is a highly significantdifference between groups of stomata on the lower epidermisof a single leaf; that the variation between different leaveson the same plant, or between similar leaves on different plants,does not differ significantly from that between strips fromthe same leaf; that not less than 20 stomata should be measuredon each strip; and that pore-width is a satisfactory measureof the area of the stomatal aperture.     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

Studies on the Growth in Culture of Plant Cells: XI. THE INFLUENCE OF SHAKING RATE ON THE GROWTH OF SUSPENSION CULTUEES

The influence of shaking rates (expressed as revolutions permin) on orbital shaking platforms (1 in (2.54 cm) diam. rotarymotion) on the growth of cell suspension cultures of Acer pseudoplatanusL. and Atropa belladonna cultivar lutea Döll are described.By following cell growth and respiration and the levels of oxygenand carbon dioxide in the media during the progress of incubationit is concluded that the reduction of growth at sub-optimalshaking rates is not due to oxygen deficiency or toxic accumulationof carbon dioxide. The growth of the Atropa cell suspensionin ‘closed systems’ has been studied by the developmentof modified culture vessels and evidence obtained that the reducedgrowth in the systems is due to the formation by the culturesof an unidentified volatile growth inhibitor and not to eitheroxygen depletion or toxic accumulation of either carbon dioxideor ethylene. It is suggested that the reduced growth in ‘opensystems’ cultures at sub-optimal shaking speeds is eitherdue to retention of this volatile inhibitor or to restrictionof nutrient uptake by the existence of a stationary liquid-phaseboundary to the cells.     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 1. Grown as Simulated Swards During a Regrowth Period

Simulated swards of each of two selection lines of Lolium perennecv. S23 with ‘fast’ and ‘slow’ ratesof ‘mature tissue’ respiration were establishedin growth rooms at 20/15 °C day/night temperatures and studiedover four successive regrowth periods of 46, 30, 26 and 53 daysduration. The ‘slow’ line outyielded the ‘fast’,both in harvestable shoot (above a 5 cm cut) and in root andstubble. Its advantage increased over successive regrowth periodsto 23 per cent (total biomass). Gas analysis measurements onthe entire communities (including roots), during the final regrowthperiod, showed that the ‘slow’ line had a 22–34per cent lower rate of dark respiration per unit dry weight.This enabled it to maintain its greater mass of tissue for thesame cost in terms of CO₂ efflux per unit ground area. Halfthe extra dry weight produced by the ‘slow’ line,relative to the ‘fast’, could be attributed to itsmore economic use of carbon. The rest could be traced to a 25per cent greater tiller number which enabled the ‘slow’line to expand leaf area faster (though not at a greater rateper tiller), intercept more light and fix more carbon, earlyin the regrowth period. Lolium perenne L., ryegrass, respiration, maintenance respiration, tiller production, simulated swards, canopy photosynthesis, carbon economy     

Leaf Abscission and Stem Lesions (Intumescences) on Poplar Clones after SO2 and O3 Fumigation: A Link with Ethylene Release?

Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO₂ (90–100 nl l^–1)and O₃ (70–80 nl l^–1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. ‘italicd’ L., and the hybridsP. nigra cv. ‘italica’ xP. deltoides (He-X/3) andP. nigra cv.‘italica’ x P. nigra cv. ‘Serres’(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO₂ (100 nl l^–1), O₃ (75 nll^–1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. ‘italica’ production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 1–2,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO₂ and/or O₃ entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions     

Studies in Stomatal Behaviour: II. THE ROLE OF STARCH IN THE LIGHT RESPONSE OF STOMATA

The relationship between starch-content and aperture in thestomata of Pelargonium has been investigated by a quantitativetechnique. Heath's suggestion of an inherent diurnal rhythmin starch-content is confirmed, and the light effect which hasbeen the subject of previous contradictory reports is foundto be dependent on external humidity. When humidity is high,light (which in these experiments is confounded with reducedC0₂-content) causes a striking reduction in stomatal starch;when humidity is low, light has no effect on starch, but itseffect on aperture is unchanged. No evidence for any dependenceof aperture on carbohydrate status was obtained, and it is suggestedthat the function of carbohydrate changes in stomata is, asearlier suggested by Kisselew, the amplifying and stabilizingof changes primarily controlled by other factors.     

Stomatal Responses of Bean (Phaseolus Vulgaris L.) Leaves to Changing Irradiance,Air Humidity,and Water Potential of Root Medium

Stomatal responses of attached bean (Phaseolus vulgaris L.) leaves to changing spectral composition ("white" - WL., blue - BL, or red - RL radiation), air humidity (100 % or about 4 % RH), and water potential of the root medium (close to 0 or −1.2 MPa) were determined by air flow porometer. Opening of stomata always increased under BL and decreased under RL. In response to decline in air humidity, leaf conductance showed transient increase before it reached lowered steady state. BL enhanced and RL diminished this response. This revised version was published online in June 2006 with corrections to the Cover Date.