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EFFECTS OF ENVIRONMENTAL FACTORS ON PHOTOSYNTHESIS PATTERNS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE). II. EFFECT OF OXYGEN 1
Author(s) -
Beardall John,
Morris Ian
Publication year - 1975
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.1975.tb02807.x
Subject(s) - phaeodactylum tricornutum , photorespiration , photosynthesis , biology , biochemistry , ribulose , glycine , rubisco , light intensity , biophysics , botany , diatom , amino acid , physics , optics
SUMMARY Oxygen inhibited the rate of light‐saturated photosynthesis of the marine diatom Phaeodactylum tricornutum Bohlin. However, inhibition could only be detected with O 2 concentrations approaching 100%. Atmospheric concentrations of O 2 (21%) had little effect on photosynthesis. In this, Phaeodactylum more closely resembles the so‐called C‐4 plants which show low rates of photorespiration. The results presented here agree with others in showing increased O 2 inhibition at reduced bicarbonate concentrations. The biochemical mechanism of photorespiration in Phaeodactylum appears to be similar to that reported for other photosynthetic systems. The activity of ribulose‐1,5 diphosphate (RuDP) carboxylase in cell‐free extracts was also inhibited, by oxygen. Inhibition by O 2 was optimal at pH 9.2 as was the RuDP‐dependent O 2 uptake. RuDP carboxylase/oxygenase ratios decreased with increasing pH and were greater in cells grown at lower light intensities. Carboxylase levels were less affected by the light intensity for growth than were the levels of the oxygenase. Short‐term incorporation of NaHCO 3 ‐ 14 C by cells grown at high light intensities showed increased labelling of glycolate and glycine plus serine under O 2 compared with nitrogen. There was a concomitant decrease in the radioactivity found in phosphoglyeric acid (PGA) and sugar phosphates in the presence of O 2 . The effects of O 2 on the short‐term pattern of photosynthesis were less marked when the alga was previously grown at low light intensities.