Photorespiration in diatoms

Abstract

Cylindrotheca fusiformis is shown to be able to convert glycolate to glycerate via tartronic semialdehyde as well as by the better known route involving transamination to glycine. Enzymes related to photorespiration were compared in light-dark synchronized cultures of C. fusiformis kept in continuous light in a complete synthetic seawater medium or starved for nitrogen or silicon. Glycolate oxidation remained constant throughout the cell cycle and was unaffected by starvation. Transamination of glyoxylate was stimulated by light, inhibited during nitrogen starvation, and dramatically stimulated by reintroduction of nitrate to the medium. Glyoxylate carboligase was also stimulated by light and inhibited during nitrogen-starvation but only partially recovered activity after reintroduction of nitrate.

A Model for Carbohydrate Metabolism in the Diatom Phaeodactylum tricornutum Deduced from Comparative Whole Genome Analysis

“…The specificity factor (τ) of Rubisco, a measure of its ability to discriminate CO 2 from O 2 , is considerably higher in diatoms than in cyanobacteria and green algae (reviewed in [50] ) suggesting a lower rate of O 2 fixation in diatoms than observed in members of the green lineage. This is supported by studies showing photorespiratory activity in diatoms at a reduced rate than expected from studies with higher plants [51] – [54] .…”

“…Both predicted carboligases appear to have chloroplast transit peptides, but the evidence is weak and therefore targeting of glyoxylate carboligase remains uncertain in both diatoms. The presence of glyoxylate metabolism is supported by an early study of Paul and Volcani [51] showing that the activity of glyoxylate carboligase in the diatom Cylindrotheca fusiformis is affected by light intensity. These data suggest that similar to cyanobacteria, diatoms combine C2 and glyoxylate/glycerate pathways to metabolize 2-phosphoglycolate back to the Calvin cycle.…”

A new calcium binding glycoprotein family constitutes a major diatom cell wall component.

“…14C-Labelling of cell wall components during valve formation If a diatom culture is incubated in growth medium without any added silicon, cells stop growing within 12 h. The synchronous formation of new hyothecae can be induced by resupplying the medium with silicate (Paul and Volcani, 1976). Within 8 h after addition of silicate, the daughter cells separate, each provided with a complete wall.…”

Hydroxymethylsilanetriol – A Simple Analog of Silicic Acid

“…In evaluating the effect of silicon containing species, 0.5 ml of stock solution was added to 50 ml of medium resulted in 10 ppm of Si present. The media of Paul and Volcani [22,23] as modified by Guilard "f/2" [24] was employed. The compounds were mixed (HCl last) and stirred for 20 min.…”

“…Cylindrotheca fusiformis was established in silicon deficient cultures in polycarbonate bottles as previously described [32,33]. Sodium metasilicate and hydroxymethylsilanetriol were freshly prepared as 3.5 mM stock solutions and then introduced to the silicon The following compounds were screened in synchronous cultures of C. fusiformis: acetoxymethyltriethoxysilane, sodium carboxyethylsiliconate, sodium hydroxymethylsiliconate, and hydroxymethyltriethoxysilane.…”