11 Direct Observations of Stomatal Movements
L. Kappen, G. Schultz, and R. Vanselow
11.1 Introduction
Stomata, the main channels for CO2 and water vapor exchange, are well
known as systems responding to internal factors mediated by the leaf tissues,
and to external factors resulting from ambient conditions acting directly or
indirectly. This was well documented by Raschke (1979) and has been
discussed and reviewed in more recent times (e.g., Schulze and Hall 1982;
Zeiger et al. 1987; and others).
The ecophysiological parameters for stomatal movements are depicted in
Fig. 11.1. The relationships between these parameters and the stomatal
responses are shown as far as they are relevant for the present study. For
further understanding of stomatal functions and plant water relations, the
reader is referred to Losch and Schulze (Chap. 9, this Vol.). Our considerations are based on the following concept.
Light is known to be one of the principal parameters causing opening of
the stomatal apparatus. Light acts directly (Sharkey and Ogawa 1987;
Poffenroth et al. 1992) and indirectly as it controls photosynthetic CO 2
assimilation and therefore induces a CO2 gradient between ambient and
substomatal CO2 concentration (Morison 1987). The CO2 gradient dependence is obviously quite strong as it causes closing of the stomata of
CAM plants in light (Ting 1987). Nevertheless, stomata of various C 3 plant
species are not always totally closed in darkness (Meidner and Mansfield
1968). Several findings demonstrate that opening of stomata is caused by
COTfree air or nitrogen (Louguet 1972) in darkness.
Because CO2 uptake and water loss occur concomitantly, a conflict may
arise between water stress and carbon assimilation. An optimalization of the
relation between CO2 gain and water loss was, for instance, modeled by
Cowan and Milthorpe (1968).
Evidence is given (Stalfelt 1962) that ambient heat influences stomatal
aperture not only indirectly by changing evaporative conditions and CO 2
metabolism but also directly by the fact that stomata are wide open at
superoptimal temperatures even in darkness (Brunner and Eller 1974).
Water stress resulting from reduced soil water supply to the roots is
transmitted to the stomatal apparatus by a decrease of the xylem water
L. Kappen, G. Schultz, and R. Vanselow
11.1 Introduction
Stomata, the main channels for CO2 and water vapor exchange, are well
known as systems responding to internal factors mediated by the leaf tissues,
and to external factors resulting from ambient conditions acting directly or
indirectly. This was well documented by Raschke (1979) and has been
discussed and reviewed in more recent times (e.g., Schulze and Hall 1982;
Zeiger et al. 1987; and others).
The ecophysiological parameters for stomatal movements are depicted in
Fig. 11.1. The relationships between these parameters and the stomatal
responses are shown as far as they are relevant for the present study. For
further understanding of stomatal functions and plant water relations, the
reader is referred to Losch and Schulze (Chap. 9, this Vol.). Our considerations are based on the following concept.
Light is known to be one of the principal parameters causing opening of
the stomatal apparatus. Light acts directly (Sharkey and Ogawa 1987;
Poffenroth et al. 1992) and indirectly as it controls photosynthetic CO 2
assimilation and therefore induces a CO2 gradient between ambient and
substomatal CO2 concentration (Morison 1987). The CO2 gradient dependence is obviously quite strong as it causes closing of the stomata of
CAM plants in light (Ting 1987). Nevertheless, stomata of various C 3 plant
species are not always totally closed in darkness (Meidner and Mansfield
1968). Several findings demonstrate that opening of stomata is caused by
COTfree air or nitrogen (Louguet 1972) in darkness.
Because CO2 uptake and water loss occur concomitantly, a conflict may
arise between water stress and carbon assimilation. An optimalization of the
relation between CO2 gain and water loss was, for instance, modeled by
Cowan and Milthorpe (1968).
Evidence is given (Stalfelt 1962) that ambient heat influences stomatal
aperture not only indirectly by changing evaporative conditions and CO 2
metabolism but also directly by the fact that stomata are wide open at
superoptimal temperatures even in darkness (Brunner and Eller 1974).
Water stress resulting from reduced soil water supply to the roots is
transmitted to the stomatal apparatus by a decrease of the xylem water