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Acute ozone injury to bean (an ozone-sensitive species) is reduced more than 50% by pretreatment with a low level of ozone (0.02 μl/liter), as compared with pretreatment in ozone-free air. In contrast, mint (an ozone-tolerant species) demonstrates a synergism of low and injurious doses. The reduction in susceptibility of bean is accompanied by a long-term effect of low ozone levels on stomatal conductance.

Transpiration and absorption of water by the roots of Piper betle L. have been measured simultaneously with intact single-leaf plants. The degree of stomatal opening has been calculated from leaf temperature, air humidity and wind speed. The roots were aerated at intervals.In an atmosphere of unchanged composition, the stomata of Piper betle L. remain closed or only slightly open at a leaf temperature of 36-38° C in the dark and at night. However, if the temperature is raised above 40° C, they open rapidly after a short time lag to a degree normally met only under daylight conditions.Opening occurs independently of the length of the preceding dark period and hour of the night. The high degree of opening in the dark does not change considerably for many hours, and is more pronounced at high air humidity. At temperatures above 40° C the degree of opening is little influenced by the change from light to dark or from dark to light.The results give evidence that heat resistance could be strongly affected by stomatal reactions at high temperatures. The maximum temperature during the experiments did not exceed 45° C. To ensure that Piper betle L. had not been damaged by the high temperature the experiments were repeated with the same plants on several consecutive days, and the same results were obtained.Close agreement was found between the highest possible stomatal conductance derived from transpiration and that calculated from scanning electron microscopic analysis.

Summary Two methods for studying the role of stomata in controlling leaf water status are compared, using data for field grown spring wheat (Triticum aestivum L.). The first is based on comparisons of leaf water potential and stomatal conductance and their responses to different soil water treatments as obtained by irrigation or by placing plastic rainwater gutters between rows to remove a proportion of the incident rainfall. The second method exploits the varying potential evaporation and the consequent changing leaf water potential and stomatal conductance during the course of a day. Good stomatal control is indicated by large values of the ratio of the amount of variation in stomatal conductance to that of leaf water potential. A particular advantage of the latter method is that it does not require a range of soil water treatments, and it can therefore be more readily used to compare the degree of stomatal control in a range of genotypes. There was generally good agreement between the methods, with the second method showing greater sensitivity. Stomatal conductances were measured with a continuous flow diffusion porometer which had a thermostatically controlled leaf chamber. This feature had the advantage that conductances could be obtained directly from the output of the humidity sensor without the necessity for routine measurement of, and correction for, leaf temperature.

Xanthium pennsylvanicum plants received four treatments in the factorial experiment (a) debudded v. not debudded, and (b) long days v. photoinductive short days. Rates of net photosynthesis, carbon dioxide compensation points (jT), and stomatal conductances were assessed after 8 days and before leaf growth or stomatal size were appreciably affected. Leaf size, stomatal frequencies, and lengths of guard cells were estimated at this time and again 22 days after treatment. Debudding alone slightly increased stomatal conductance ; induction alone had a similar but larger effect. Debudding and induction together caused a more than additive increase in net photosynthesis at 8 days, with marked decreases in P. At 22 days this combination caused more than additive increases in leaf size and guard-cell lengths while stomatal frequencies had decreased. Induction alone directly increased stomatal conductance and this may be responsible for the increase in photosynthesis ; but debudding alone may directly affect photosynthesis by increas ing the supply of cytokinins to the leaves. The positive interaction of these factors in photo synthesis could not be explained in terms of stomatal conductance and a synergism between cytokinins and a photoperiodically induced hormone is suggested. In Phaseolus vulgaris plants, 4 days after partial defoliation, stomatal conductances and rates of net photosynthesis increased greatly in the remaining leaflets.

Plants of Solidago virgaurea L. from exposed and shaded habitats differ with respect to the response of the photosynthetic apparatus to the level of irradiance during growth. An analysis was carried out on leaf characteristies which might be responsible for the differences established in the rates of Hght-saturated CO2 uptake. The clones were grown in controlled environment chambers at high and low levels of irradiance. Light-saturated rates of photosynthesis and transpiration were measured at natural and lower ambient CO2 concentrations. A low temperature dependence of light-saturated CO2 uptake at natural CO2 concentrations, and a strong response to changes in stomatal width, suggested that the rate of CO2 transfer from ambient air towards reaetion sites in chloroplasts was mainly limiting the pholosynthetic rate. Resistances to transfer of CO2 for different parts of the pathway were calculated. There was a weak but significant correlation between stomatal conductance and the product stomatal frequency ± pore length. Mesopbyll conductance and dry weight per unit area were highly correlated in leaves not damaged by high irradiance. This suggests that mesophyll conductance increases with increasing cross sectional area (per unit leaf area) of the pathways of CO2 transfer in the mesophyll from cell surfaces to reaction sites. The higher light-saturated photosynthesis in clones from exposed habitats when grown at high irradiance than when grown at low irradiance was attributable mainly to a lower mesophyll resistance. In shade clones the effect upon CO2 uptake of the increase in leaf thickness when grown at high irradiance was counteracted by the associated inactivation of the photosynthetic apparatus. The difference in CO2 uptake present between clones from exposed and shaded habitats when preconditioned to high irradiance resulted from differences in both mesophyll and stomatal resistances. A few hybrid clones of an F1-population from a cross between a clone from an exposed habitat and a clone from a shaded habitat reacted, on the whole, in the same way as the exposed habitat parent. When grown at high irradiance, the hybrid clones showed higher photosynthetic rates than either parent; this was largely attributable to the unusually low stomatal resistance of the hybrid leaves.

Effects and possible interaction of elevated CO 2 and water stress on the stomatal morphology and the pattern of gas exchange in leaves of eggplants ( Solanum melongena L. cv. Senryo No. 2) were investigated. Sedlings were grown to maturity in controlled growth chamber using ambient CO 2 (365~370 ppm) and elevated CO 2 (700 ppm) and at frequent watering as control and watering after every 21 days for simulating periodic water stress and recovery from stress. A complementary acclimatisation of photosynthesis in water stressed eggplants grown under elevated CO 2 was evident. Despite decreased stomatal conductance and transpiration rate under elevated CO 2 conditions, increased net leaf photosynthesis rate was observed. Stomatal length and width decreased under water stress and increased CO 2 . Key words: Water stress; Adaptation; Eggplant; Gas exchange; Stomatal density; Transpiration rate DOI: http://dx.doi.org/10.3329/bjb.v40i1.7985 Bangladesh J. Bot. 40 (1): 1-8, 2011 (June)

The air pollution stress around the thermal power plant lead to the significant reduction in size and biomass of root and shoot, photosynthetic rate, stomatal conductance, intercellular CO 2 concentration, photosynthetic pigments and photosynthetic area of Croton bonplandianum . The resulting stresses of air pollution and reduced foliage further affected the over all morphology and physiology of the plant. Root biomass and chlorophyll a showed maximum reduction than any other selected parameters studied in the stressed area. Chlorophyll a was found to be four and half times more sensitive to air pollutants than carotenoids. Key words: Air pollution; Thermal power plant; Morphology and physiology; C. bonplandianum DOI: 10.3126/eco.v17i0.4103 Ecoprint An International Journal of Ecology Vol. 17, 2010 Page: 35-41 Uploaded date : 29 December, 2010

Unlike other leaves investigated, maize leaves were found to be able to exhaust atmospheric C02-content to zero concentration. This occurred at 20o C. with a light intensity of 100 f.c. and at 30o C. with a light intensity of 500 f.c. The influences of temperature, light intensity, and waterstrain on this property of maize leaves were investigated systematically and a permanent after effect of waterstrain on the leaves was found. Stomatal conductance measurements showed that maize stomata are sensitive to CO2-concentrations between zero and 100 p.p.m., a circumstance not yet reported for other leaves.

Royal Sovereign strawberries, grown in sand culture with pure inorganic nutrients and controlled levels of iron supply, have shown that restriction of the iron supply can cause marked reduction in growth and crop yield before the onset of characteristic symptoms of iron deficiency. At the levels where visual symptoms first occur, fruit yield was reduced some 40% below that of plants adequately supplied with iron.Visible deficiency symptoms were associated with an iron content of 50 p.p.m. Fe in the dry leaf at harvest. Leaves with a higher iron content did not show symptoms. Increasing the supply caused an increase in growth and crop yield, and the iron content in the leaf dry matter rose to 70 p.p.m. Fe. A still higher level of supply raised the leaf content of iron to 80 p.p.m. but did not increase growth or crop yield above that obtained with a leaf content of 70 p.p.m.Eight other nutrient elements were determined by leaf analysis. Five of these (zinc, manganese, copper, magnesium, potassium) showed a ...

SUMMARY A method is described of following the behaviour of stomata by utilizing a diffusion phenomenon, the Dufour effect. Hydrogen at laboratory temperature is blown on to one side of the leaf. As it diffuses through the leaf and out the other side it is accompanied by a rapid temperature wave of considerable magnitude. This is picked up by a fine thermocouple near the leaf and passed to a quick period galvanometer. The 'flick' of this measures the stomatal conductance. An experiment is described in which the behaviour of a wheat leaf was followed. The results agree well in broad outline with those obtained by other methods. Advantages claimed are that an approximation, at least, is obtained to the value of the important diffusive conductance of the stomata ; that the leaf does not have to be enclosed in any way, and that the instrument can easily be made automatic and recording. Ambient temperature changes are not troublesome. The purpose of this paper is to describe a new method for investigating the stomatal behaviour of leaves. The principle is, so far as is known, quite new and it has the advantage of depending on a diffusion phenomenon. To some extent therefore it gives information directly applicable to an analysis of the way in which stomata actually control the processes of carbon-dioxide supply and water loss. Before describing the method itself it will be helpful to make a few remarks on the physical principles underlying it. The Dufour effect. It is a phenomenon found very widely in the physical world in which two agencies of quite distinct nature often interfere with each other to produce additive results in the spheres of each. About 1872, Dufour discovered that when two gases at the same temperature are allowed to diffuse

Triadimefon, a triazole compound increased survival per cent of micropropagated Gladiolus ( Gladiolus grandiflorus L.) plantlets. Applica-tion of triadimefon caused a retarding effect on height of the plant (14.86 cm) compared to the untreated plants one month after planting to ex vitro conditions. Triazole application increased root number of the plants. Plants treated with triazole showed delayed leaf production interval of 10.45 and 14.48 days for first and second leaves, respectively. Triazole treated plants exhibited a lower stomatal conductance which indicated the reduced water loss from the leaves. Leaf area index was high for untreated plants(1.08) compared to treated plants. Key words: Gladiolus, Triazole, Micropropagation,Triadimefon, Acclimatization D.O.I. 10.3329/ptcb.v20i2.6896 Plant Tissue Cult. & Biotech. 20 (2): 171-178, 2010 (December)

Measurements of transpiration, leaf water content, and flux of water in a cotton plant exhibiting sustained oscillations, in stomatal conductance are presented, and a model of the mechanism causing this behaviour is developed. The dynamic elements, of the model are capacitors-representing the change of water content with water potential in mesophyll, subsidiary and guard cells-interconnected by resistances representing flow paths in the plant. Increase of water potential in guard cells causes an increase in stomatal conductance. Increase of water potential in the subsidiary cells has the opposite effect and provides the positive feed-back which can cause stomatal conductance to oscillate. The oscillations are shown to have many of the characteristics of free-running oscillations in real plants. The behaviour of the model has been examined, using an analogue computer, with constraints and perturbations representing some of those which could be applied to real plants in physiological experiments. Aspects of behaviour which have been simulated are (a) opening and closing of stomata under the influence of changes in illumination, (b) transient responses due to step changes in potential transpiration, root permeability and potential of water surrounding the roots, (c) the influence of these factors on the occurrence and shape of spontaneous oscillations, and (d) modulation of sustained oscillations due to a circadian rhythm in the permeability of roots.

SUMMARY Twelve-week-old Ricinus communis plants were transplanted to boxes of sand or soil in which the water table was maintained at various levels below the root system. The boxes were placed in a climatological wind tunnel and transpiration varied by altering the humidity of the air stream. Responses in the water potential depression (= suction force or D.P.D.) of the leaves (AW1) and stomatal conductance were followed. With a fine sand it was found that when the water table was high (I5 cm below the roots) AW1 was 6 atm. irrespective of the rate of transpiration and behaved therefore as if the roots were surrounded by free water as previously shown. When the water table was 25 cm below the roots, AW1 was also 6 atm. provided the transpiration rate was low (0.4 g/dm2 leaf/hour) but when the transpiration rate was raised threefold, A W1 rose steeply to a value of I2 atm., a steady state value being approached in about 8 hours (see Fig. 3). On reducing the transpiration rate, AW1 returned to 6 atm. This rise in AW1 is interpreted as due to a rise in the AW of the water in the sand at the root surface, this in turn resulting from the low water conductivity of the sand at this height above the water table. Varying the humidity continuously between saturation and about 4000 relative humidity through a 24-hour cycle produced a regular 24-hour cycle of transpiration (see Figs. 4, 5 and 6). Responses in AW1 in plants rooted in fine sand, clay soil and moorland soil were explicable in terms of the above hypothesis of the development of perirhizal zones of soil water tension. These results suggest that much of the ecologically significant water stress in plants is a manifestation of the dynamic gradients of water potential developing in the perirhizal zones and that these can be considerable even when the water stress in the bulk of the soil is virtually zero.

It is supposed that oscillations in stomatal conductance are associated with the dynamic properties of the loop in which rate of evaporation affects, through physiological processes, the aperture of stomata and stomatal aperture in turn affects rate of evaporation. It is therefore predicted that their occurrence must be influenced by the magnitude of what is termed environmental gain: the sensitivity of rate of evaporation to change in leaf conductance to vapor transfer. Two methods of manipulating gain, and their effects on stomatal behavior in cotton (Gossypium hirsutum L. cv. Deltapine Smooth Leaf), are described. In the first, gain was increased by decreasing ambient humidity; in the second, it was made zero by regulating ambient humidity to keep rate of evaporation constant despite changes in conductance. The results are in accord with the supposition.

Greenhouse-grown plants of Xanthium strumarium L. were exposed in a growth cabinet to 10 C during days and 5 C during nights for periods of up to 120 hours. Subsequently, CO(2) exchange, transpiration, and leaf temperature were measured on attached leaves and in leaf sections at 25 or 30 C, 19 C dew point of the air, 61 milliwatts per square centimeter irradiance, and CO(2) concentrations between 0 and 1000 microliters per liter ambient air. Net photosynthesis and stomatal conductance decreased and dark respiration increased with increasing duration of prechilling. The reduction in net photosynthesis was not a consequence of decreased stomatal conductance because the intercellular CO(2) concentration in prechilled leaves was equal to or greater than that in greenhouse-grown controls. The intercellular CO(2) concentration at which one-half maximum net photosynthesis occurred remained the same in prechilled leaves and controls (175 to 190 microliters per liter). Stomata of the control plants responded to changes in the CO(2) concentration of the air only slightly. Prechilling for 24 hours or more sensitized stomata to CO(2); they responded to changes in CO(2) concentration in the range from 100 to 1000 microliters per liter.

Stomatal resistance was measured daily with a stomatal diffusion porometer during a 4-week period in leaves of bean (Phaseolus vulgaris L., var. Bush Blue Lake) and barley (Hordeum vulgare L., var. Liberty) plants having roots equally split between two differentially salinized nutrient solutions. The stomatal conductance (reciprocal of stomatal resistance) of plants with half their roots in saline solutions was intermediate between the stomatal conductances of plants grown in nonsaline solutions and those grown in saline solutions.

CO2 exchange and air flow through the stomata were measured in leaf sections of Zea mays at temperatures between 7 and 52° and under optimal water supply. The results were summarized in polynomials fitted to the data. In leaf samples brought from 16° and darkness into different experimental temperatures and light, CO2 assimilation has a maximum near 30°. Above 37° (in other experiments above 41°), net CO2 uptake stops abruptly and is replaced by CO2 evolution in light. If a 1-hr treatment with 25° and light is inserted between darkness and the experimental temperatures, the threshold above which the assimilatory system collapses shifts 3 degrees upwards, to 40° (or 44°); the decline of CO2 assimilation with high temperatures is less steep than without pretreatment; and the upper compensation point moves upscale by as much as 5 degrees. Stomatal conductance for CO2 does not, in general, follow an optimum curve with temperature. Between 15 and 35° it is approximately proportional to net CO2 assimilation, indicating control by CO2; but above 35°, stomatal aperture increases further with temperature (and so does stomatal variability): the stomata escape the control by CO2 and above 40° may be wide open even if CO2 is being evolved. Stomatal conductance for CO2 below 15° may also be larger than would be proportional to CO2 assimilation. Net CO2 assimilation and stomatal conductance at 25° were reduced if the leaf samples were pretreated with temperatures below approximately 20° and above 30°. Stomata were more sensitive to past temperatures than was CO2 assimilation.