112
H. Pfanz
Table 5.4. Proton concentrations of various cellular compartments as determined in intact
tissues and isolated cell organelles
Cellular compartment
Apoplast
Vacuole
Chloroplast stroma
Thylakoid
Cytosol
Mitochondria
Reference a
1-4
5-14
15-18
18, 19
10,20,21
22,23
pH
5.25-6.40
0.67-6.5
Light: 8; dark 7.2-7.4
5.0-6.5
7.2-7.6
aI, Pfanz and Dietz (1987); 2, Grignon and Sentenac (1991) and references therein;
3, Hartung et al. (1988); 4, Hoffmann et al. (1992); 5, Meeuse (1956); 6, McClintock
et al. (1982); 7, Kurkdjian and Guern (1989a); 8, Kurkdjian and Guem (1989b); 9, Smith
and Raven (1979); 10, Martin et al. (1982); 11, Strack et al. (1987); 12, Steigner et al.
(1988); 13, Kaiser and Hartung (1981); 14, Matile (1978); 15, Heber and Heldt (1981);
16, Heldt et al. (1973); 17, Oja et al. (1986); 18, Werdan et al. (1975); 19, Falkner et al.
(1976); 20, Mathieu et al. (1986); 21, Guern et al. (1986); 22, Addanki et al. (1968);
23, Roos and Boron (1981).
It is known that the pH of the illuminated chloroplast stroma in vivo is
approximately pH 8 (Heldt et al. 1973; Enser and Heber 1980; Espie and
Colman 1981; Oja et al. 1986). In darkened leaves, stromal pH is around
pH 7.4 and thus near the proton concentration of the cytosol embedding the
chloroplasts (see Table 5.4). The acidification of the chloroplast stroma
during the light/dark transition greatly influences the activity of several
Calvin cycle enzymes. The pH optimum of the Calvin cycle enzyme fructosebisphosphatase (FBPase) is near 8. Below pH 7.5, activity is hardly measurable (Leegood et al. 1982; Woodrow et al. 1984). Alkalization from pH 5.5
to 8.5 shifts the sedoheptulose-bisphosphatase dimer (which is inactive) to
the monomeric "active" form of the enzyme (Buchanan et al. 1976).
5.3.2.2 Extracellular pH Changes and Photosynthesis
Within a normal life cycle, a protoplast is very often confronted with situations of varying pH. PH changes occur in the apoplast during cell extension
and leaf growth, (Taiz 1984); but also during uptake of potentially acidic
or alkaline air pollutants transient pH perturbations cannot be excluded
(Mansfield and Freer-Smith 1981; Pfanz and Heber 1989; Yin et al. 1991).
The pH of an external solution optimal for protoplast or cell photosynthesis
is around pH 7. Figure 5.2 gives an impression of the photosynthetic behaviour of leaves and leaf cells measured under various "external" proton
conditions. The experiments were performed with isolated protoplasts of
mono- and dicotyledonous plant species (Hordeum and Ficaria), free-living
green algae (Euglena), and with leaf tissues of conifers (Tsuga), deciduous
H. Pfanz
Table 5.4. Proton concentrations of various cellular compartments as determined in intact
tissues and isolated cell organelles
Cellular compartment
Apoplast
Vacuole
Chloroplast stroma
Thylakoid
Cytosol
Mitochondria
Reference a
1-4
5-14
15-18
18, 19
10,20,21
22,23
pH
5.25-6.40
0.67-6.5
Light: 8; dark 7.2-7.4
5.0-6.5
7.2-7.6
aI, Pfanz and Dietz (1987); 2, Grignon and Sentenac (1991) and references therein;
3, Hartung et al. (1988); 4, Hoffmann et al. (1992); 5, Meeuse (1956); 6, McClintock
et al. (1982); 7, Kurkdjian and Guern (1989a); 8, Kurkdjian and Guem (1989b); 9, Smith
and Raven (1979); 10, Martin et al. (1982); 11, Strack et al. (1987); 12, Steigner et al.
(1988); 13, Kaiser and Hartung (1981); 14, Matile (1978); 15, Heber and Heldt (1981);
16, Heldt et al. (1973); 17, Oja et al. (1986); 18, Werdan et al. (1975); 19, Falkner et al.
(1976); 20, Mathieu et al. (1986); 21, Guern et al. (1986); 22, Addanki et al. (1968);
23, Roos and Boron (1981).
It is known that the pH of the illuminated chloroplast stroma in vivo is
approximately pH 8 (Heldt et al. 1973; Enser and Heber 1980; Espie and
Colman 1981; Oja et al. 1986). In darkened leaves, stromal pH is around
pH 7.4 and thus near the proton concentration of the cytosol embedding the
chloroplasts (see Table 5.4). The acidification of the chloroplast stroma
during the light/dark transition greatly influences the activity of several
Calvin cycle enzymes. The pH optimum of the Calvin cycle enzyme fructosebisphosphatase (FBPase) is near 8. Below pH 7.5, activity is hardly measurable (Leegood et al. 1982; Woodrow et al. 1984). Alkalization from pH 5.5
to 8.5 shifts the sedoheptulose-bisphosphatase dimer (which is inactive) to
the monomeric "active" form of the enzyme (Buchanan et al. 1976).
5.3.2.2 Extracellular pH Changes and Photosynthesis
Within a normal life cycle, a protoplast is very often confronted with situations of varying pH. PH changes occur in the apoplast during cell extension
and leaf growth, (Taiz 1984); but also during uptake of potentially acidic
or alkaline air pollutants transient pH perturbations cannot be excluded
(Mansfield and Freer-Smith 1981; Pfanz and Heber 1989; Yin et al. 1991).
The pH of an external solution optimal for protoplast or cell photosynthesis
is around pH 7. Figure 5.2 gives an impression of the photosynthetic behaviour of leaves and leaf cells measured under various "external" proton
conditions. The experiments were performed with isolated protoplasts of
mono- and dicotyledonous plant species (Hordeum and Ficaria), free-living
green algae (Euglena), and with leaf tissues of conifers (Tsuga), deciduous