Transport and assimilation of inorganic carbon by Lichina pygmaea under emersed and submersed conditions

• Published in: The New phytologist Vol. 114; no. 3; pp. 407 - 417
• Main Authors: Raven, J.A, Johnston, A.M, Handley, L.L, Mcinroy, S.G
• Format: Journal Article
• Language: English
• Published: Oxford, UK Cambridge University Press 01.03.1990; Blackwell Publishing Ltd; Blackwell
• Subjects: Algae; bicarbonates; Biological and medical sciences; Carbon dioxide; carbonate dehydratase; carbonic anhydrase; CO2 compensation partial pressure; compensation point; Cyanobacteria; C‐isotope ratios; dark fixation; diurnal variation; Fundamental and applied biological sciences. Psychology; gas exchange; inorganic carbon concentrating mechanism; inorganic C‐concentrating mechanism; intertidal environment; Lichens; Metabolism; net assimilation rate; nutrient uptake; oxygen; Photosynthesis; Photosynthesis, respiration. Anabolism, catabolism; Physiology; Plant physiology and development; Plants; Ravens; Sea water; seawater; Thallus; titratable acidity; Scotland; Assimilation; Littoral zone; Scanning electron microscopy; Carbon dioxide; Ecophysiology; Carbon; Hydrogencarbonates; Carbonic anhydrase; Ultrastructure; Lichenes; Gas exchange; Photosynthesis; Thallophyta; Adaptation; CO2 compensation partial pressure; photosynthesis; carbonic anhydrase; pH; lichens; C-isotope ratios; inorganic C-concentrating mechanism
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.1990.tb00408.x

Photosynthetic O2evolution by the upper littoral lichen, Lichina pygmaea (Lightf.) C.Ag., under light-saturated conditions at 5⚬C is saturated by the 2 mol m-3inorganic C found in seawater at pH 8.0. Photosynthesis is not reduced when pH is increased to pH 9.4, and is slightly reduced at pH 10.0, when submersed in seawater with 2 mol m-3inorganic C. The rate of photosynthesis at pH 10 greatly exceeds the rate of uncatalysed conversion of HCO3 -. It is concluded that HCO3 -is used in photosynthesis. Since extracellular carbonic anhydrase is present, it is possible that CO2enters the photobiont (Calothrix) cells even during HCO3 -use. pH drift experiments support the notion of HCO3 -use. Emersed photosynthesis at 5⚬C is more than half-saturated by 35 Pa (normal atmospheric) CO2; the light- and CO2-saturated emersed photosynthetic rate is not significantly different from the light and inorganic C-saturated photosynthetic rate when submersed. Inorganic C diffusion from the thallus surface to the photobiont needs, at least under some conditions, carbonic anhydrase activity which permits HCO3 -fluxes to supplement CO2movement. The CO2compensation partial pressure at 5⚬C is 0.83 Pa, i.e. at the low range of values found for terrestrial cyanobacterial lichens. Dark14C-inorganic C assimilation when submersed is a small fraction of the dark respiratory rate, consistent with the observed absence of diel CAM-like variation in intracellular titratable acidity. The high value (-11.5 per mil) of δ13C, the low CO2compensation partial pressure, and the relatively high affinity for inorganic C, are consistent with the operation of an inorganic C concentrating mechanism such as occurs in free-living cyanobacteria and probably occurs in terrestrial cyanobacterial lichens and in most intertidal algae.