Stomatal Mechanism Research Articles

Stomatal mechanism as the basis of the evolution of CAM and C4 photosynthesis

Stomatal mechanism as the basis of the evolution of CAM and C4 photosynthesis

Dark Stomatal Movement in Sunflowers in Response to Illumination under Nitrogen

Experiments were performed on intact sunflowers (Helianthus annuus) placed in a specially designed experimental chamber which allows instantaneous modifications of the atmospheric composition without changing any other conditions. After one night in normal conditions, the plant was illuminated under pure nitrogen atmosphere; the opening stomatal movement, measured as a transpiration rate variation, was inhibited. After an anoxia time period not exceeding one hour, the light was turned off and normal air restored. The stomatal movement was no longer inhibited, and a transient increase in the transpiration rate, referred to here as the postillumination transpiration peak (PITP), was observed.The quantity of transpired water during the PITP can be related to the total incident light energy supplied during the light-nitrogen period. Furthermore, the addition of a dark-nitrogen period between the light-nitrogen and dark-air periods caused the PITP to decrease. The PITP is almost suppressed after a 20-minute dark-nitrogen period.It is shown that the PITP does not result from a hydropassive mechanism but is metabolically controlled. Moreover, it seems that the PITP is not due to a CO(2)-suppression effect during the light-nitrogen period.The results are interpreted in terms of stomatal mechanism. The metabolites leading to PITP originate from the reducing equivalents created during the light-nitrogen period. They could be synthesized at the beginning of the PITP period (darkness under normal air) or during the dark-nitrogen plus CO(2) period between the light-nitrogen and PITP periods. The results obtained are related to the first steps of classical photoactive stomatal opening.

The evolutionary relationship between stomatal mechanism, crassulacean acid metabolism and C4 photosynthesis

Abstract. All of the features of crassulacean acid metabolism (CAM) and most characteristics of C4 photosynthesis are exhibited by stomatal guard cells. It is proposed that CAM and possibly also C4 photosynthesis result from the expression in photosynthetic cells of genetic information which is expressed only in guard cells of C3 plants.

The evolutionary relationship between stomatal mechanism, crassulacean acid metabolism and C4 photosynthesis

The evolutionary relationship between stomatal mechanism, crassulacean acid metabolism and C4 photosynthesis

Cell wall architecture: normal development and environmental modification of guard cells of the Cyperaceae and related species*

Abstract. The development and cell wall architecture of guard cells in the Cyperaceae were studied with light and electron microscopy. Development occurs along parallel files and results in a stomatal complex that consists of two guard cells each flanked by a subsidiary cell. The developmental pattern and general morphology are thus similar to that in the Gramineae. Several key differences, however, were observed. Wall synthesis in the Cyperaceae, as observed in the polarization and fluorescence microscope, occurs suddenly, within three to four complexes along a file, but is more gradual in the Gramineae. Mature cell walls in the Cyperaceae predominantly contain microfibrils oriented radially relative to the pore, while those in the Gramineae contain axial microfibrils. This difference was demonstrated in numerous species using freshly‐collected as well as preserved material. In Cyperus esculentus, however, the alignment of microfibrils appears to be subject to environmental modification. Plants grown in the greenhouse contain guard cells with axial microfibrils, compared to the radial arrangement found in those grown in the field. In the former, wall is deposited gradually, as in the Gramineae. On return to more stressful conditions, radially micellated guard cells again develop. In each case, the cortical cytoplasm adjacent to areas where the wall is to thicken contains microtubules oriented parallel to the microfibril alignment characteristic of that treatment. These results are discussed in terms of the role of varied wall architecture in stomatal mechanics, the regulation of cell wall biosynthesis, and the evolutionary relationship of the Cyperaceae, Gramineae, and other taxa.

Stomatal response to environment and a possible interrelation between stomatal effects on transpiration and CO2 assimilation

Abstract It had been hypothesized that if daily CO2 assimilation is to be maximized at a given level of daily transpiration, stomatal apertures should change during the day so that the gain ratio (∂A/∂g)/(∂E/∂g) remains constant. These partial differentials describe the sensitivity of assimilation rate (A) and transpiration rate (E) to changes in stomatal conductance (g). Experiments were conducted to determine whether stomata respond to environment in a manner which results in constant gain ratios.Gas–exchange measurements were made of the stomatal and photosynthetic responses of Vigna unguiculata L. Walp. in controlled environments. Leaf conductance to water vapour responded to step changes in temperature and humidity so that for different steady‐state conditions the gain ratio remained constant on all but one day. Depletion of water in the root zone resulted in day‐to‐day increases in gain ratio which were correlated with decreases in maximum leaf conductance to water vapour. The significance of the results for plant adaptation and stomatal mechanisms, and methods for measuring the gain ratio, are discussed.

Stomatal mechanics II*: material properties of guard cell walls

Abstract In this revised formulation of guard cell mechanics, the material properties of the walls are re‐examined. The observed elastic anisotropy of guard cell walls can be explained by non‐random orientation of the cellulose micellae in the unstrained state. This micellar network is assumed to be loosely embedded in the wall matrix causing a two phase elongation process. In the first phase, the micellar network is ‘loose’ resulting in the walls behaving as an isotropic polymer when stretched. As the volume of the cell expands beyond some threshold, the network becomes ‘tightened’ and a second phase of elongation is initiated. During this anisotropic phase of cell expansion, wall elasticity reflectes changes in the orientation of the network to reduce its load.Using the above theoretical analysis, a turgor‐pressure versus lumen volume relationship is simulated for Vicia faba. The relationship between aperture and water potential for this species is also established. The simulated results agree with the experimental evidence reported for Vicia faba. The estimated shear modulus of elasticity for guard cell walls is 2 MPa (20 bars) which is well within the limits of reported values for other biological tissues.

Vesicles in guard-cell walls and their possible roles in the stomatal mechanism.

A variety of vesicular inclusions have been observed in guard-cell walls. They have been seen in a number of species and are mostly membrane-bound. They appear confined to the upper and ventral walls of the guard cell. A number of possible origins and functions are discussed. They may be involved in wall deposition or cuticle formation possibly in a role similar to ectodesmata. They also may serve to increase the wall-plasmalemma interface to enhance the movement of ions during the stomatal mechanism.

Stomatal Mechanisms Determining Genetic Resistance to Ozone in Phaseolus vulgaris L.1

Abstract The ozone-sensitive bean cultivars ‘Spurt’ and ‘Blue Lake Stringless’ and the ozone-resistant cultivars ‘Black Turtle Soup’ and ‘French’s Horticultural’ were grown from seed in a growth chamber. The resistant cultivars had 25% fewer stomata per mm2 leaf area than the sensitive cultivars and exhibited partial stomatal closure following exposure to 134 pphm ozone for 1 hr, while the sensitive cultivars did not. Stomatal closure was determined to be more important than reduced stomatal frequency in providing resistance to ozone. On the basis of previously established ozone dose-response data for P. vulgaris, the stomatal mechanisms appeared to account for the difference in ozone sensitivity between the sensitive and resistant cultivars. Neither leaf area nor leaf expansion rate were correlated with genetic resistance to ozone in these cultivars.

Direct Measurements of Turgor Pressure Potentials

Measurements were made of turgor pressures in epidermal, subsidiary, and guard cells at different degrees of stomatal opening. The results are correlated with estimates of solute potentials of the different cell saps and with a postulated matric potential of cell walls. The results contribute to an understanding of the role of the subsidiary cells in the stomatal mechanism especially in the Graminaceous type and the role of ‘tissue tension’ as a pressure involved in turgor phenomena in epidermal tissue. The results make it possible to explain the abnormally large stomatal openings found after floating illuminated leaf tissue on water or keeping it in humid CO2-free air.

Stomatal mechanics: volume changes during opening

Abstract. The determination of guard cell lumen volume in relation to its geometric characteristic dimensions is presented. Stomatal movements can be divided into two stages: Spannungsphase and motorphase, with a transition point between them. During the Spannungsphase movement, the lumen volume increases as a result of the change in its geometric shape. At transition, the lumen volume is approximated by a portion of a circular tube with a rounded cross‐section. The volume increase during the motorphase comes from three different sources: expansion by wall stretching, increasing inner cross‐section of a guard cell by wall thinning, and polar expansion. The relationship between the aperture and the lumen volume is also established. The results set forth in this geometric model are essential to studies of the pressure interaction between a guard cell and its surrounding epidermal cells.

Effect of abscisic acid on solute transport in epidermal tissue

AN important aspect of the stomatal mechanism in green plants is the transport of solutes into and out of guard cells in response to stimuli such as illumination1. The effect of abscisic acid (ABA) in causing stomata to close has been ascribed to ABA-promoted solute leakage from guard cells2. The experiments reported here show that leakage alone is insufficient to explain stomatal closure caused by ABA. The involvement of live epidermal cells, acting as recipients of solutes from guard cells, is necessary, as Penny and Bowling have suggested, especially when considering intact leaves3.

STUDIES OF MALATE FORMATION IN ‘ISOLATED’ GUARD CELLS

SUMMARYAfter they had been ‘isolated’ by a low pH treatment which destroyed all the other cells of the epidermis, stomatal guard cells retained the capacity to produce malate when presented with fusicoccin as a stimulus to opening. For a given level of stomatal opening, the amount of malate in epidermis with isolated stomata was practically the same as in intact epidermis. It is concluded that malate transport to and from the subsidiary cells is not an essential part of the stomatal mechanism. Changes in CO2 concentration over the range 0–100 ppm affected neither stomatal aperture nor malate levels in epidermis of Commelina communis. This suggests that carboxylation of phosphenolpyruvate plays no major part in the formation of malate in guard cells.

Low K+ in Paphiopedilum leeanum leaf epidermis: implications for stomatal functioning

Abaxial epidermal strips from leaves of Paphiopedilum leeanum were analyzed via sodium cobaltinitrite staining and atomic absorption spectrophotometry for the presence and location of potassium. On a dry weight basis K content of the abaxial epidermis was found to be 103 times less than has been reported in other species, and unlike other species no localization of K+ in guard cells of open stomata could be detected via the sodium cobaltinitrite stain for potassium.Flame photometric analysis of the mesophyll indicated that it contained normal amounts of K+ (about 1.87% on a dry weight basis). Analysis showed that the K+ content of the abaxial epidermis (0.032%) was considerably less than that of the mesophyll, a situation unlike previous reports for other species in which the epidermal concentration was found to be greater than the mesophyll. A process for exclusion of K+ from the abaxial epidermis is suggested, as is the lack of involvement of K+ as the major osmoticum in the stomatal mechanism of this species.

Malate-switch hypothesis to explain the action of stomata

DURING the past ten years major advances have been made in our understanding of the mechanics of stomata. A most important discovery has been that potassium enters the guard cells in sufficient quantities to account for the decreases in osmotic potential which occur on stomatal opening1. Association of potassium with stomatal movements has now been reported for at least 22 species2. There is doubt, however, about the nature of the anions which accompany K+. Chloride has been found to balance about 40% of the K+ in Zea mays3 and considerably less in Commelina communis4. Malate could be the balancing anion as it has been found to accumulate in the guard cells on stomatal opening5 although it is not clear whether it is synthesised in the guard cells or is transported there from the surrounding cells. Clearly an understanding of the mechanism of the ion transport in and out of the guard cells is necessary as a first step to the unravelling of the stomatal mechanism. An hypothesis is proposed here which attempts to explain the transport aspect of stomatal function. It is based mainly on data obtained from studies with the monocotyledon C. communis but should be applicable to other species.

Der Einfluß von Aluminiumionen auf den Stärkemetabolismus von Vicia faba-Epidermen

In order to analyze effect of aluminium in closing stomata, its influence on starch metabolism was tested which plays an important role in stomatal mechanism. Starch hydrolyzing (β-amylase and phosphorylase with addition of phosphate) and starch synthesizing enzymes (phosphorylase with addition of glucose-1-phosphate and ADPG-transglucosylase) were tested under conditions of increasing Al3+-concentrations. While effect of aluminium in starch hydrolyzing was minimal, starch synthesis was amplified even by little Al3+-concentrations: 100 μM Al3+ caused an increase of 40 %, 1000 μM Al3+ of 80 % against the control. These experiments make probable that the closing effect of Al3+ on the stomata is caused by an influence on the starch metabolism.

A Finite Element Shell Analysis of Guard Cell Deformations

ABSTRACT IN this paper the width of the stomatal aperture, as postulated by von Mohl in 1856, is shown to be a function of the hydrostatic (turgor) pressure in the guard cells, Pg, and the pressure, Ps, of the immediately surrounding epidermal cells, which will be referred to as the subsidiary cells in this paper. The aperture does not depend solely upon the pressure difference (Pg-Ps) as believed by Ursprung and Blum (1924) and StSlfelt (1966). Instead, aperture width is shown to be a simple multi-linear relationship (i.e., a linear com-bination) of Pg and Ps. The recent re-search by Glinka (1971) and Edwards, Meidner and Sheriff (1976), showing the relative contributions of the oppos-ing pressures Pg and Ps, is, thus, given a simple and lucid interpreta-tion. The analysis of a guard cell as an elliptical torus shows that a stomate could function without either of the two conditions classically believed to be essential (Meyer et al. 1960, p. 84, Meidner and Mansfield 1968, pp. 14-17, Bidwell 1974, p. 298). The thick-ened wall (ventral wall) of the guard cell facing the aperture need not neces-sarily be stiffer than the dorsal wall common to the adjacent epidermal cell for the proper functioning of a stomate. The radially oriented cellu-lose microfibrils in the guard cell wall are not vital but are important for quite different reasons than claimed by Aylor et al. (1973). Consideration of the radial stiffening by means of the in-troduction of a mechanically equiva-lent orthogonally anisotropic (i.e., or-thotropic) material causes the aperture width to be more sensitive to a unit increment in Ps than to a unit incre-ment in Pg (for parameters of physi-cal interest3). The guard cell volume, however, is smaller than the adja-cent cell volume and Pg is believed to be larger than Ps, in general. We conjecture that this increased sensi-tivity for the subsidiary cell (i.e., clos-ing) pressure is important for the functioning of the feedback control loops regulating the aperture width. We define an antagonism ratio to characterize this property. The pore length in the model is shown to be surprisingly constant during opening, as is reported for many species (Meidner and Mansfield 1968, p. 12). The guard cell is generally believed to bulge into the neighboring epider-mal cell upon opening (Meidner and Mansfield 1968, p. 15). However, the shell model suggests that the outer-most portion of the guard cell at the widest point (and not visible in an in vivo situation) actually moves away from the neighboring cell. The ap-proximate point at which the exposed surface of the epidermal cell joins the guard cell exhibits only limited mo-tion. Note that there are especially thin regions here in the epidermal cell thought to behave as hinges (Hautgelenke). Even when the ex-treme, unphysiological case of a fixed aperture length is imposed, the outermost perimeter moves away from the adjacent cell. If the epidermis is opaque, the view from outside the leaf suggests that the guard cell bulges into the neighboring cell, as claimed in the classical hypothesis, provided the stiffening effect of the micellae is sufficiently prominent and provided the guard cell pressure is significantly larger than the epidermal cell pres-sure. The opposing influence of the turgor pressure in the guard cells and in the adjacent epidermal cells is shown to be an inherent part of the stomatal mechanism (von Mohl 1856). Pressure influence coefficients for the guard cell are defined and related to parameter changes, e. g., material and thickness. The multilinear relationship of aperture width to the opposing turgor pressures was found and revealed that pore width does not depend solely on the pressure difference between the guard cell and the adjacent epidermal cell. Finally, the theory developed is shown to embrace and to clarify the experimental results of Glinka's plas-molytic study (1971) and the direct method of Edwards et al. (1976).

Effect of the Soil and Plant Water Potentials on the Dry Matter Production of Snap Beans1

AbstractThe need for greater plant yields and more efficient use of water makes it essential that the relations between soil‐water content, soil‐water potential, transpiration rate, and plant response be made ever more quantitative.The dry matter production rate of snap beans (Phaseolus vulgaris L., var. Bush Blue Lake) growing under field conditions on a sandy soil is analyzed during a drying period.Measurements of plant‐ and soil‐water potentials, dry matter accumulation, and stomatal resistance were made as soil‐water was depleted, while the transpiration rates were obtained by a model for a loosely structured canopy.The transpiration and dry matter production rates decreased curvilinearly with soil‐water potential. When the soil‐water potential decreased from −0.28 to −0.40 bar, there was 47% reduction in the dry matter production rate. This is related to the turgor pressure‐operated stomatal mechanism. The adaxial stomatal resistances increased at leaf‐water potentials lower than −8 bars, which coincided with a rapid decrease in the dry matter production rate. It was found that stomatal closure due to water stress resulted in a greater reduction of growth rate than in transpiration.

Ecology of Indian Desert: V. On the Water Relations of Salvadora Species

Investigations have been carried out on the ecophysiological adaptations for survival of the two important desert trees: Salvadora persica Linn, and S. oleoides Decne., in arid regions of Indian desert. The water loss and stomatal mechanism, water content of leaves, their absorption capacity and water deficit were examined during different hours of the day with reference to the effect of long dry summer. These species have been shown to loose very much water as their stomata remain open at the time of excessive heat thus enabling the plants to have leaf temperatures fairly close to ambient levels. Features like vertical position of leaves and deep roots are additional ecophysiological adaptations. Such studies on the importance of various ecophysiological adaptations in arid zone are useful for foresters as well who may be concerned with the water and photosynthetic relations of different types of trees in relation to reafforestation.

Effects of abscisic acid on potassium uptake and starch content of stomatal guard cells

Abscisic acid (ABA) at a concentration of 100 μm reduced the mean stomatal aperture on isolated epidermis of Commelina communis from 9.5 to 3.1 μm. This closure resulted from a fall in osmotic pressure of the guard cells from 14.1 to 9.8 bars; the osmotic pressure of the subsidiary cells did not change significantly. Histochemical tests showed that the potassium concentration in guard cells was reduced by ABA-treatment, while the starch content of the chloroplasts increased. ABA was found to exert a significant effect on Rb(86) uptake into leaf discs, but this was relatively small in magnitude. It is concluded that ABA has a greater effect on ion uptake into guard cells than into the leaf tissues as a whole.Recent hypotheses of the stomatal mechanism are discussed in relation to these new observations, and the rejection by some writers of any major role for starch hydrolysis is challenged. Evidence from several sources suggests that starch disappearance occurs simultaneously with K(+) entry into guard cells. Breakdown of starch may lead to formation of organic anions, with which K(+) uptake may be associated. In this case starch breakdown would contribute as much to the increased osmotic pressure as does K(+) uptake.