Die abhängigkeit der spaltöffnungsreaktionen von der wasserbilanz

Stålfelt, M. G.

doi:10.1007/bf01916623

Cited by 117 publications

(33 citation statements)

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“…Subsequently, the stomata closed and reduced the rate of evaporation. These "hydropassive" movements of the stomata have been well documented previously (5,11,13,14). They may be explained in terms of the differing effects of turgor changes in guard cells and neighboring epidermal cells on the aperture of the stomata and difference in the speeds with which the water contents of these cells are affected by a perturbation in the rate of water transport through the plant as a whole.…”

Section: Methodssupporting

confidence: 72%

Oscillations in Stomatal Conductance

Farquhar

Cowan²

1974

Plant Physiol.

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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, Self-sustained oscillations, having a period of about 40 min, in stomatal aperture, and plant functioning associated with stomatal aperture, are known to occur in many plant species (1,3). Several models of the mechanism responsible for these oscillations have been described (3, 7-9, 1 1). They have in common one basic assumption: that the oscillations are due to the 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. The models differ in the way they describe the physiological processes. The model described by Cowan (3) suggests itself: can we manipulate the total gain of the loop in an unambiguous way and show that the stability of the stomatal mechanism is affected in the manner expected? Any attempt to alter the characteristics of the physiological component of the loop would fall short of what is required because it would presume a detailed understanding of the processes involved. On the other hand, the environmental component of loop gain, which is the sensitivity of rate of evaporation to change in stomatal aperture, can be readily manipulated in a way which is unequivocal because the physical process involved is well understood. We report here on two experiments in which environmental gain has been altered and the effects on the stability of the stomatal mechanism have been observed. MATERIALS AND METHODSThe plants used were cotton (Gossypiumn hirsutum L. cv.Deltapine Smooth Leaf), 1 month old, having five or six leaves with a total area of 0.05 to 0.06 M2. The apparatus is described in detail elsewhere (6). In brief, it consists of a small closedcircuit wind tunnel. The working section, which contains the upper parts of the plant, is of Plexiglas and is illuminated from above by a xenon arc lamp. The flux of radiation is 80 w m-2 in the wavelength range 370 to 820 nm. Wind speed is about 1 m s-'. The stem of the plant is sealed in the floor of the working section, the roots below being immersed in aerated Hoagland solution.Ambient temperature is regulated, through the combination of a water-cooled heat exchanger and an electrical heater in the air stream approaching the plant, in such a way as to maintain the temperature of the leaves, rather than that of the air stream, as constant as possible. Thermojunctions (44 s.w.g. copper-constantan) are inserted into the main veins of three of the leaves, with the reference junctions in ice. The signals are continuously recorded on strip-chart; one is amplified and used to provide the error signal for proportional control of the electrical heating of the air stream. The bandwidth varies with thermal load, but is always less than 1 C. The humidity of the air stream is sensed by a dew-point hygrometer and is proportionally controlled by regulating the f...

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Section: Methodssupporting

confidence: 72%

Oscillations in Stomatal Conductance

Farquhar

Cowan²

1974

Plant Physiol.

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“…St'alfelt's hypothesis of "hydroactive" responses in the stomata (36,37) would imply that the water potential in the leaf controls the osmotic pressures in all epidermal cells, including the guard cells. The experimental results reported in this paper, however, do not indicate the functioning of such a "hydroactive" mechanism in maize under the conditions described.…”

Section: Discussionmentioning

confidence: 99%

“…The second effect is indirect and is due to pressure changes in the epidermis and possibly also the mesophyll (36). It leads to transient stomatal responses in a direction opposite to the direct effect; i.e., a decrease in water potential in the supply system of a leaf produces a temporary opening, and an increase in water supply causes a temporary closure.…”

mentioning

confidence: 99%

“…A reduction of the water potential in the xylem will, therefore, also cause a reduction of the turgor in the epidermal cells and thereby ease the pressure exerted by the epidermis on the guard cells of the stomata. Stailfelt called this effect the "hydropassive" response of the stomata (36,37), and von Mohl recognized as early as 1856 that an "antagonism" exists between the guard cells and the epidermal cells (27).…”

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confidence: 99%

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Stomatal Responses to Pressure Changes and Interruptions in the Water Supply of Detached Leaves of Zea mays L.

Raschke¹

1970

Plant Physiol.

151

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Stomata of Zea mays L. respond to changes in hydrostatic pressure in the water supply of the leaves almost instantaneously and in all leaf parts simultaneously. Therefore, the leaf is a hydraulic unit. The stomata are part of it and their aperture is controlled by the water potential in the water-conducting system. Stomatal aperture is not uniquely related to the relative water content of a leaf. The relation depends also on the humidity in the air and is different for the upper and the lower epidermis.Stomata respond to changes in the chemical potential of water in the water supply system of a leaf, and one component of this potential is the tension produced by transpiration in the water conduits of the plant. This was concluded from experiments with isolated leaf sections of maize which were exposed to C02-free air and subjected to changes in atmospheric humidity and water supply (33). Changes of the water potential in the supply system of a leaf produce two opposing effects on the stomata.One of these effects is direct. It makes the water potential in the guard cells follow the potential changes in the water conduits and causes the stomata to close upon a reduction of the water potential. The second effect is indirect and is due to pressure changes in the epidermis and possibly also the mesophyll (36). It leads to transient stomatal responses in a direction opposite to the direct effect; i.e., a decrease in water potential in the supply system of a leaf produces a temporary opening, and an increase in water supply causes a temporary closure. This indirect effect is caused by the fact that all leaf tissues, including the epidermis, respond to changes in water supply to the leaf. A reduction of the water potential in the xylem will, therefore, also cause a reduction of the turgor in the epidermal cells and thereby ease the pressure exerted by the epidermis on the guard cells of the stomata. Stailfelt called this effect the "hydropassive" response of the stomata (36, 37), and von Mohl recognized as early as 1856 that an "antagonism" exists between the guard cells and the epidermal cells (27).If stomatal aperture is controlled by the water potential in the xylem, it should be possible to cause two-phased stomatal responses not only by the addition of osmotica to the water supply of the leaves but also by a sudden variation of the hydrostatic pressure in the liquid. Changes in hydrostatic pressure can easily be produced by directly applying pressure to the water into which detached leaves are dipping. Since the interest is in stomatal regulation of water loss, this pressure will have to be negative. Pressure changes can also be produced indirectly by allowing the transpiration stream to develop a potential drop along the flow resistances in the leaf. Still larger negative pressure will occur in the xylem if the water supply to the leaf is completely interrupted and tension is determined by the radii of the capillaries into which the air-water interfaces retreat.Stomatal activity follows a pronounced gradie...

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“…In addition to the hypotheses described above for processes within the leaf, stomatal biologists also have long been interested in the evaporating sites because of the perception that the c of epidermal and guard cells will be more negative if they support a large fraction of evaporation (a corollary of hypothesis 3 above), thus influencing stomatal function (Meidner, 1976;Cowan, 1977;Tyree and Yianoulis, 1980;Sheriff, 1984; (Darwin, 1898;Stalfelt, 1929;Meidner, 1986;Buckley, 2005. Similarly, preferential evaporation from guard cells in dry air could explain the stomatal response to humidity by causing a larger turgor decline in guard cells than in epidermal cells, overcoming the epidermal mechanical advantage (Maier-Maercker, 1983;Sheriff, 1984;Dewar, 1995Dewar, , 2002.…”

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confidence: 99%

The Sites of Evaporation within Leaves

et al. 2017

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The sites of evaporation within leaves are unknown, but they have drawn attention for decades due to their perceived implications for many factors, including patterns of leaf isotopic enrichment, the maintenance of mesophyll water status, stomatal regulation, and the interpretation of measured stomatal and leaf hydraulic conductances. We used a spatially explicit model of coupled water and heat transport outside the xylem, MOFLO 2.0, to map the distribution of net evaporation across leaf tissues in relation to anatomy and environmental parameters. Our results corroborate earlier predictions that most evaporation occurs from the epidermis at low light and moderate humidity but that the mesophyll contributes substantially when the leaf center is warmed by light absorption, and more so under high humidity. We also found that the bundle sheath provides a significant minority of evaporation (15% in darkness and 18% in high light), that the vertical center of amphistomatous leaves supports net condensation, and that vertical temperature gradients caused by light absorption vary over 10-fold across species, reaching 0.3°C. We show that several hypotheses that depend on the evaporating sites require revision in light of our findings, including that experimental measurements of stomatal and hydraulic conductances should be affected directly by changes in the location of the evaporating sites. We propose a new conceptual model that accounts for mixed-phase water transport outside the xylem. These conclusions have far-reaching implications for inferences in leaf hydraulics, gas exchange, water use, and isotope physiology.The pathways for water transport through a plant are often perceived to end at the sites of evaporation outside the xylem within leaves (Holmgren et al

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Die abhängigkeit der spaltöffnungsreaktionen von der wasserbilanz

Cited by 117 publications

References 14 publications

Oscillations in Stomatal Conductance

Oscillations in Stomatal Conductance

Stomatal Responses to Pressure Changes and Interruptions in the Water Supply of Detached Leaves of Zea mays L.

The Sites of Evaporation within Leaves

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