63
are well known, and coloured products (Cristofalo e~ al., 1962) as
well as surface-active compounds (Wilson and Collier, 1972) are among
the more exotic exudates of microscopic algae.
Certain organic phosphorus compounds are also involved in some form
of rapid excretion and uptake by phytoplankton (Lean and Nalewajko,
1976). In addition several enzymes such as a a-glucosidase (Mayer,
1976) as well as lipids (Billmire and Aaronson, 1976) must be regarded
as real excretion compounds having important functions in the metabolism and reproduction of algae.
Compounds possibly involved in massive excretion which may play a
significant role in the energy flow in lakes and oceans are above all
the carbohydrates and to some extent glycollate, amino acids and peptides. The concentration of certain carbohydrates, especially polysaccharides, found in culture media may be quite impressive. Myklestad
and Haug (1972) detected 40 mg polysaccharide per liter while Moore
and Tischer (1964) as well as Marker (1965) reported values corresponding to 500 mg/l. The highest concentrations were always found in old
cultures in some stress situation. Very often old cultures (and algal
populations in general) are not only old but also starved, and it is
difficult to separate the influence of these two factors on the excretion process.
In the 1970's Myklestad and Haug started a series of investigations
on the excretion of carbohydrates by marine diatoms and paid special
attention to the influence of the major nutrient salts on this process.
Much of our knowledge of the influence of nitrate and phosphate on
excretion of carbohydrates by marine phytoplankton originate in these
studies which will be treated in some detail in the following.
During
their investigation of the effect of nutrient composition and concentration in the growth medium on the chemical composition of the diatom
Chavtoc.eJr.O.6 a66-i.nl.6 Myklestad and Haug (1972) observed that the main
production of extracellular polysaccharide followed a period of rapid
increase in the cellular content of storage carbohydrates. The latter
started when the medium became nitrate depleted and the cells were in
the stationary phase. The release of extracellular polysaccharide was
enhanced by a high proportion of nitrate to phosphate in the medium.
(Fig. 1).
are well known, and coloured products (Cristofalo e~ al., 1962) as
well as surface-active compounds (Wilson and Collier, 1972) are among
the more exotic exudates of microscopic algae.
Certain organic phosphorus compounds are also involved in some form
of rapid excretion and uptake by phytoplankton (Lean and Nalewajko,
1976). In addition several enzymes such as a a-glucosidase (Mayer,
1976) as well as lipids (Billmire and Aaronson, 1976) must be regarded
as real excretion compounds having important functions in the metabolism and reproduction of algae.
Compounds possibly involved in massive excretion which may play a
significant role in the energy flow in lakes and oceans are above all
the carbohydrates and to some extent glycollate, amino acids and peptides. The concentration of certain carbohydrates, especially polysaccharides, found in culture media may be quite impressive. Myklestad
and Haug (1972) detected 40 mg polysaccharide per liter while Moore
and Tischer (1964) as well as Marker (1965) reported values corresponding to 500 mg/l. The highest concentrations were always found in old
cultures in some stress situation. Very often old cultures (and algal
populations in general) are not only old but also starved, and it is
difficult to separate the influence of these two factors on the excretion process.
In the 1970's Myklestad and Haug started a series of investigations
on the excretion of carbohydrates by marine diatoms and paid special
attention to the influence of the major nutrient salts on this process.
Much of our knowledge of the influence of nitrate and phosphate on
excretion of carbohydrates by marine phytoplankton originate in these
studies which will be treated in some detail in the following.
During
their investigation of the effect of nutrient composition and concentration in the growth medium on the chemical composition of the diatom
Chavtoc.eJr.O.6 a66-i.nl.6 Myklestad and Haug (1972) observed that the main
production of extracellular polysaccharide followed a period of rapid
increase in the cellular content of storage carbohydrates. The latter
started when the medium became nitrate depleted and the cells were in
the stationary phase. The release of extracellular polysaccharide was
enhanced by a high proportion of nitrate to phosphate in the medium.
(Fig. 1).