Ecological and Physiological Aspects of Endosymbiosis
311
(Muscatine et al. 1984) to 20% (Zvalinski et al. 1980; Davies 1984). Lower
numbers were obtained by calculation from the ratios of biomasses of
zooxanthellae and polyps, while the higher ones by direct measurements of
respiration in isolated zooxanthellae; around 3-5Jlg02h-1106 cells
(Edmunds and Davies 1986). From the latter data it could be deduced that
the ratio of their gross photosynthesis to respiration (Pt/Mz) should be
around 5-10. But the specific growth rate in zooxanthellae is very low,
being evaluated as between 0.003-0.01 day-l (Muscatine 1983; Wilkerson et
al. 1983; Edmunds and Davies 1986). Their own energy expenditures are
also low, between 10-15%. The rest of their photosynthesis production is
translocated to their host polyps.
The assimilation of CO2 by their photosynthesis proceeds via the "C3 "
cycle with the participation of the ribulose diphosphate carboxylase (Benson
et al. 1978), with the posibility of involvement of the "C4"-cycle with
participation of phosphoenolpyruvate carboxylase (Trench and Blanck 1987).
Being within the polyps, zooxanthellae probably have photorespiration, thus
enhancing the net production of their photosynthesis (Muscatine 1980).
Among the primary products of their photosynthesis are drates, phosphoglyceric acid, several simple amino acids and various lipids (von Holt and von
Holt 1968; Trench 1974; Patton et al. 1977). About 50% of assimilates are
soon transformed into alcohol-soluble lipid fraction (Schmitz and Kremer
1977). As regards the nutrients supply of zooxanthellae, they use the salts of
phosphorus and nitrogen, formed during heterotrophic metabolism in tissues
of the polyp, also using those directly consumed by corals from the sea
water (Webb and Wiebe 1978; Muscatine et al. 1984; Sorokin 1990c). In
cultures they use inorganic nutrients (D'Elia et al. 1983). Over 70-80% of
organic P and N produced by zooxanthellae they translocate to the host
polyps, providing them with the bulk of the amino acids necessary for
growth (Burris 1983; Muscatine et al. 1984; Wafar et al. 1985).
Thus the symbiosis of polyps and zooxanthellae is based upon their
mutualistic metabolic relationships (Muscatine 1974; Lewis 1981b). Three
main forms of such relationships could me mentioned: (1) translocation of
assimilates by zooxanthellae to the host; (2) consumption of inorganic
nutrients - products of metabolism of host cells by zooxanthellae; and (3)
acceleration of calcification in corals, which is definitely coupled with the
photosynthesis of their symbionts. The host polyp stimulates the
translocation of the main portion of autotrophic production by
zooxanthellae. The zooxanthellae freshly isolated from coral of Tridacna
tissues excrete over 60% of their photosynthates (Muscatine 1967; von Holt
and von Holt 1968), but the addition of tissue homogenate of polyps again
restores this process (Trench 1979). The main product thus excreted by the
isolated zooxanthellae was glycerine plus some amounts of alanine glucose
and organic acids (Trench 1971; Goreau et al. 1973). 14C-acetate, which was
added to the suspension of isolated zooxanthellae in light, is rapidly
assimilated and transformed into the lipid fraction (Patton and Burris 1983).
311
(Muscatine et al. 1984) to 20% (Zvalinski et al. 1980; Davies 1984). Lower
numbers were obtained by calculation from the ratios of biomasses of
zooxanthellae and polyps, while the higher ones by direct measurements of
respiration in isolated zooxanthellae; around 3-5Jlg02h-1106 cells
(Edmunds and Davies 1986). From the latter data it could be deduced that
the ratio of their gross photosynthesis to respiration (Pt/Mz) should be
around 5-10. But the specific growth rate in zooxanthellae is very low,
being evaluated as between 0.003-0.01 day-l (Muscatine 1983; Wilkerson et
al. 1983; Edmunds and Davies 1986). Their own energy expenditures are
also low, between 10-15%. The rest of their photosynthesis production is
translocated to their host polyps.
The assimilation of CO2 by their photosynthesis proceeds via the "C3 "
cycle with the participation of the ribulose diphosphate carboxylase (Benson
et al. 1978), with the posibility of involvement of the "C4"-cycle with
participation of phosphoenolpyruvate carboxylase (Trench and Blanck 1987).
Being within the polyps, zooxanthellae probably have photorespiration, thus
enhancing the net production of their photosynthesis (Muscatine 1980).
Among the primary products of their photosynthesis are drates, phosphoglyceric acid, several simple amino acids and various lipids (von Holt and von
Holt 1968; Trench 1974; Patton et al. 1977). About 50% of assimilates are
soon transformed into alcohol-soluble lipid fraction (Schmitz and Kremer
1977). As regards the nutrients supply of zooxanthellae, they use the salts of
phosphorus and nitrogen, formed during heterotrophic metabolism in tissues
of the polyp, also using those directly consumed by corals from the sea
water (Webb and Wiebe 1978; Muscatine et al. 1984; Sorokin 1990c). In
cultures they use inorganic nutrients (D'Elia et al. 1983). Over 70-80% of
organic P and N produced by zooxanthellae they translocate to the host
polyps, providing them with the bulk of the amino acids necessary for
growth (Burris 1983; Muscatine et al. 1984; Wafar et al. 1985).
Thus the symbiosis of polyps and zooxanthellae is based upon their
mutualistic metabolic relationships (Muscatine 1974; Lewis 1981b). Three
main forms of such relationships could me mentioned: (1) translocation of
assimilates by zooxanthellae to the host; (2) consumption of inorganic
nutrients - products of metabolism of host cells by zooxanthellae; and (3)
acceleration of calcification in corals, which is definitely coupled with the
photosynthesis of their symbionts. The host polyp stimulates the
translocation of the main portion of autotrophic production by
zooxanthellae. The zooxanthellae freshly isolated from coral of Tridacna
tissues excrete over 60% of their photosynthates (Muscatine 1967; von Holt
and von Holt 1968), but the addition of tissue homogenate of polyps again
restores this process (Trench 1979). The main product thus excreted by the
isolated zooxanthellae was glycerine plus some amounts of alanine glucose
and organic acids (Trench 1971; Goreau et al. 1973). 14C-acetate, which was
added to the suspension of isolated zooxanthellae in light, is rapidly
assimilated and transformed into the lipid fraction (Patton and Burris 1983).