Page 190 - The Biochemistry of Inorganic Polyphosphates

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Peculiarities of polyphosphate metabolism
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8.12.4 The Effects of P i Limitation and Excess
Many algae were shown to accumulate and store large amounts of PolyPs when grown
under conditions of unlimited available P i , namely Scenedesmus (Rhee, 1973), Cosmarium
(Elgavish et al., 1980), Chlorella (Miyachi and Tamiya, 1961) and Heterosigma (Watanabe
et al., 1987; 1988; 1989). Overbeck (1961, 1962) showed that Scenedesmus quadricauda
was able to accumulate excessive amounts of PolyPs in the dark when grown on a phoshate-
containing medium after P i starvation. In other words, he demonstrated that algae, like
heterotrophs, display a hypercompensation (phosphate overplus) effect.
It is probable that PolyP in algae can play the role of phosphorus reserve, as in other
organisms. It was observed that the granules disappeared from the vacuoles of Scenedesmus
quadricauda under phosphate starvation (Voˇr´ıˇsek and Zachleder, 1984). If Chlorella was
growninthelightandonaP i -containingmedium,itdidnotutilizePolyPfornucleicacidsyn-
thesis, although such utilization occurred under P i starvation (Baker and Schmidt, 1964a,b).
The results of Lundberg et al. (1989) concerning P i uptake and storage demonstrated
that PolyP formed the main P i store in the marine macroalga Ulva lactuca. The short-chain
‘NMR-visible’ PolyP in this alga was synthesized when the organism was grown in seawater
supplemented by P i , and utilized to support the growth when the organism was transferred
to a P i -deficient medium. However, this organism might possess another P i storage pool,
namely an amorphous calcium phosphate in the cell wall (Weich et al., 1989).
The effect of starvation and the subsequent addition of phosphate-containing medium
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on phosphorus-containing compounds was studied by P NMR spectroscopy of perchloric
acid extracts and intact cells of Heterosigma akashiro (Watanabe et al., 1987, 1888, 1989).
The PolyP content and chain length decreased under starvation and rapidly increased on P i
restoration in the medium (Table 8.8).
This phenomenon, known as ‘luxury storage’, is important for development of the algae
population under P i -starved conditions, while the P i concentrations in the coastal zones are
influenced by such factors as land run-off and wastewaters. When the phosphate concen-
tration in the water becomes low, the PolyP store may be used for further synthesis. The
alga Heterosigma akashiro has a specific feature in its phosphate metabolism during its
vertical migrations in natural sea water (Watanabe et al., 1987) and under simulation of
such migrations in a (laboratory) tank (Watanabe et al., 1988). At night, this alga migrated
to the lower phosphate-rich water layer and took up P i , which is used for elongation of
the PolyP chains. In the daytime, the alga migrated to the P i -depleted surface water and

Table 8.8 Some phosphate compounds in extracts from the algae Heterosigma akashiro
under P i starvation and restoration (Watanabe et al., 1987).

Sugar P P i ATP PolyP PolyP PolyP average
−1
Conditions/time (%) (%) (%) (%) (fmol cell ) chain length
Starvation 33.5 21.5 5.6 5.8 76 10
2 h after P i addition 12.1 10.9 7.4 43.7 108 14
1 d after P i addition 9.0 9.5 — 59.1 222 20
3 d after P i addition 9.2 8.4 — 63.3 185 17