Der Einfluß unterschiedlicher NaCl-Konzentrationen auf die Atmung der einzelligen Alge Platymonas subcordiformis Hazen

Cytological evidence for cytoplasmic volume control inPlatymonas subcordiformisafter osmotic stress

“…5). This explains the physiological observations of a severe inhibition of photosynthesis (Kirst, 1975) while respiration is stimulated (Kirst & Keller, 1976) at this stage. A swelling of the chloroplast resulting in disorientation of the thylakoid structure has also been described in Dunaliella salina (Trezzi et al, 1965) after a decrease in external osmolarity.…”

“…In P. subcordiformis this is achieved by control of internal concentrations of ions (K + , Na"^ and CI") and the organic solute mannitol (Kirst, 1977b). However, in contrast to wall-less micro-algae like Poteriochromonas malhamensis (synonym: Ochromonas) (Kauss, 1974) and Dunaliella parva (Ben Amoz, 1974;Rabinowitch, Grover & Ginzburg, 1975), in which an almost complete control of the cell volume was Correspondence: G, O, Kirst, Institut fiir Botanik der TH Darmstadt, SchnittspahnstraBe 3-5, D-6100 Darmstadt, FRG, 0140-7791/81/1200-0455502.00 © 1981 Blackwell Scientific Publications observed, the volume recovery of Platymonas subcordiformis is incomplete, especially after large hypoosmotic stresses (Kirst, 1977a), During the adaptation process following hypoosmotic shocks a temporary inhibition of CO2-fixation is observed (Kirst, 1975) whereas respiration is stimulated; only extreme hypo-osmotic shocks lead to a short-lived reduction in the rate of respiration (Kirst & Keller, 1976). Such changes in physiological behaviour might originate from changes in the ultrastructure of the algal cells.…”

Physics of Turgor- and Osmoregulation

“…Single cells without walls (4,59) or with very elastic walls (40) or organic scales (68,72) shrink and swell very rapidly (within seconds) and markedly if they are exposed to hypertonic or hypotonic solutions. In the subsequent second phase, which is generally characterized by a substantially longer time constant (minutes and hours), a reverse volume regulation is observed which may lead to a close readjustment to the original volume .…”