A Physiological Comparison of the Symbiotic AlgaPlatymonas Convolutaeand its Free-Living Relatives

Abstract

Studies of the uptake of radioactive carbohydrates by cultures of Platymonas convolutae, the symbiotic alga from Convoluta roscoffensis, have revealed that this alga is very much less permeable to these compounds than free-living members of the same genus. Its extremely low permeability to glucose is shared by the Prasinocladus spp. and Pyramimonas spp. investigated. It is suggested that this effect is due to a permeability barrier as P. convolutae has an active hexokinase. Both P. convolutae and Platymonas tetrathele, the type species of the genus, can metabolize a wide range of organic nitrogen compounds as sole nitrogen sources. P. convolutae contains uricase and the specific activity of this enzyme increases threefold when uric acid is the sole nitrogen source. Relatively little photosynthate is released to the medium by these algae. Although mannitol is the major soluble carbohydrate, it is not released to the medium, but lactic acid is found in both algae and media. Daughter cells of P. convolutae stay for a much longer time within the parent theca than those of other members of this genus. The significance of these observations is discussed in relation to the symbiotic habit of the alga.

Proposal for an Abridged Nitrogen Turnover Cycle in Certain Marine Planktonic Systems Involving Hypoxanthine-Guanine Excretion by Ciliates and their Reutilization by Phytoplankton

“…1) and is estimated to be at least 100-times less soluble (Pfleiderer, 1963). Although we have not examined guanine in our surveys, other investigations have shown it to support generally good growth of a cryptomonad (Antia and Chorney, 1968), 2 prasinophycean (Gooday, 1970) and 6 chlorophycean flagellates (Droop, 1961). We are thus led to infer that both hypoxanthine and guanine are ecologically realistic N-sources for phototrophic Growth Period (days) Fig.…”

“…The utilization of various purines as nitrogen source for phototrophic growth of marine microalgae is now well established for species from numerous taxa (Droop, 1955(Droop, , 1961Guillard, 1963;Van Baalen and Marler, 1963;Antia and Chorney, 1968;Gooday, 1970;Turner, 1970;Kapp et al, 1975;Mahoney and McLaughlin, 1977). Whereas uric acid was the most widely tested purine in these investigations, Antia and Landymore (1974) cautioned that the chemical instability of this purine and its close relative, xanthine, in seawater could give false results if the algae were utilizing one or more decomposition products instead of the intact purines.…”

Uptake rates of various nitrogen sources by nitrate-grownTetraselmis (Platymonas) striata

“…Shah & Syrett (1984) found that the growth of T. subcordiformis on hypoxanthine was similar to that on urea, nitrate or ammonium. Gooday (1970) found that Tetraselmis tetrathele grown on xanthine or hypoxanthine gave 40 and 20% respectively of the growth rate on nitrate. Initial uptake rates for the amino acids were inadequate for normal growth but most were greatly increased after a period of 1-3 h. North & Stephens (1971) showed that Tetraselmis could accumulate amino acids from very dilute solutions and that much higher rates of uptake were found in nitrogen deficient cells.…”

Oceanic mixotrophic flatworms

“…2a, b); in this subgenus protrusions of the nucleus enter the pyrenoid (Hori et al 1983). Prasinophyte endosymbionts occur in C. roscoffensis (Keeble & Gamble 1907, Oschman & Gray 1965, Gooday 1970, Holligan & Gooday 1975, Douglas 1983, 1985 and C. psammophila (Sarfatti & Bedini 1965), 2 l~ttoral species. The endosymbiotic algal cells in our specimens lacked thecae and flagella; loss of these organelles also occurs in endosymbionts of C. roscoffensis (Douglas 1983).…”