Apoplastic & Symplastic Proton Concentrations & Their Significance for Metabolism 107
NMR spectrometry. This technique allows simultaneous pH measurements
of at least the vacuole and the chloroplast compartment (for review see
Roberts 1984). Through NMR, a vast amount of literature has accumulated
on symplastic pH values (Guern et aI. 1986; Kurkdjian and Guern 1989a,b).
5.3 Cellular pH
5.3.1 The Apoplastic pH
5.3.1.1 The Apoplast - What It Is
One can consider a whole plant cormus as consisting of two main "compartments"; one being the continuum of the protoplasts of all organs
of a plant body linked with each other via the plasmodesmata, called
the symplast, the other, the counterpart, in form of a continuous "watercontaining cellulose skeleton" being the apoplast. The apoplast consists of
two main fractions. These fractions are: (1) the gaseous intercellular air
space and (2) the aqueous cell wall phase. The intercellular air space (lAS)
borders the external air space at the substomatal cavity. The labyrinthlike lAS penetrates through leaves, petioles, stems, and roots, forming an
infinite air-filled continuum. The concentration of carbon dioxide in the
intercellular air space is of vital importance for a working photosynthesis
and for the calculation of photosynthetic rates (Beyschlag et aI., this VoL).
In aquatic plants, a special aerenchyma has evolved to guide oxygen to the
roots or rhizomes, thus avoiding anaerobiosis (Schroder et aI. 1986).
The cell wall phase again consists of two fractions, one being the aqueous
phase and the other being a fibrillar cellulose skeleton (the proper cell
wall; see below). The cell wall is thus a "continuous, more or less tough
integument ... , formed mainly by a fibrillar framework within which the
interstices are filled with an amorphous material" (Colvin 1981) and an
aqueous medium.
The cell wall was long considered to be a dead compartment of minor
importance and its only significance was seen in the stabilization of the plant
cells. Yet it has been recognized and it is now generally accepted that the
plant cell wall is a "living" reaction room with vital functions (Varshney and
Varshney 1985; Pfanz and Oppmann 1991; Grignon and Sentenac 1991;
Pfanz et aI. 1992). The different functions are: (1) The cell wall is a rigid
cytoskeleton that allows plant growth up to heights of 100m and more. All
the "naked" protoplasts are embedded in, and surrounded by the cell wall,
and there is tight contact between the plasmalemma and the apoplastic
solution. The cell wall protects the pro top lasts from mechanical injuries like
abrasion, desiccation, ultraviolet radiation or excessive light, etc. (Colvin
1981). (2) The apoplast of roots and leaves is the very first target for
NMR spectrometry. This technique allows simultaneous pH measurements
of at least the vacuole and the chloroplast compartment (for review see
Roberts 1984). Through NMR, a vast amount of literature has accumulated
on symplastic pH values (Guern et aI. 1986; Kurkdjian and Guern 1989a,b).
5.3 Cellular pH
5.3.1 The Apoplastic pH
5.3.1.1 The Apoplast - What It Is
One can consider a whole plant cormus as consisting of two main "compartments"; one being the continuum of the protoplasts of all organs
of a plant body linked with each other via the plasmodesmata, called
the symplast, the other, the counterpart, in form of a continuous "watercontaining cellulose skeleton" being the apoplast. The apoplast consists of
two main fractions. These fractions are: (1) the gaseous intercellular air
space and (2) the aqueous cell wall phase. The intercellular air space (lAS)
borders the external air space at the substomatal cavity. The labyrinthlike lAS penetrates through leaves, petioles, stems, and roots, forming an
infinite air-filled continuum. The concentration of carbon dioxide in the
intercellular air space is of vital importance for a working photosynthesis
and for the calculation of photosynthetic rates (Beyschlag et aI., this VoL).
In aquatic plants, a special aerenchyma has evolved to guide oxygen to the
roots or rhizomes, thus avoiding anaerobiosis (Schroder et aI. 1986).
The cell wall phase again consists of two fractions, one being the aqueous
phase and the other being a fibrillar cellulose skeleton (the proper cell
wall; see below). The cell wall is thus a "continuous, more or less tough
integument ... , formed mainly by a fibrillar framework within which the
interstices are filled with an amorphous material" (Colvin 1981) and an
aqueous medium.
The cell wall was long considered to be a dead compartment of minor
importance and its only significance was seen in the stabilization of the plant
cells. Yet it has been recognized and it is now generally accepted that the
plant cell wall is a "living" reaction room with vital functions (Varshney and
Varshney 1985; Pfanz and Oppmann 1991; Grignon and Sentenac 1991;
Pfanz et aI. 1992). The different functions are: (1) The cell wall is a rigid
cytoskeleton that allows plant growth up to heights of 100m and more. All
the "naked" protoplasts are embedded in, and surrounded by the cell wall,
and there is tight contact between the plasmalemma and the apoplastic
solution. The cell wall protects the pro top lasts from mechanical injuries like
abrasion, desiccation, ultraviolet radiation or excessive light, etc. (Colvin
1981). (2) The apoplast of roots and leaves is the very first target for