Effects of various cations on separation of the two photochemical systems by digitonin treatment

Abstract

The effects of various cations were investigated during separation of the two photochemical systems of photosynthesis by digitonin treatment of spinach chloroplasts. Satisfactory separation was obtained only when an appropriate concentration of cations was present in the treatment medium; optimum concentrations for divalent cations (Mg 2+, Ca 2+, Ba 2+, Mn 2+) were 3–5 mM; for monovalent cations (Na +, K +, NH 4 +), 50 mM. The modes of action of the salts ( e.g. MgCl 2) were investigated. The presence of the cations in the digitonin treatment mixture was an essential factor for separation of the two photochemical systems. Similar effects of cations were also observed when chloroplasts were disrupted in a French pressure cell. The effects of various salts and of light on the lamellar structure of the chloroplasts were investigated. There was no direct relationship between the electron microscopic changes of the chloroplast ( i.e. presence or absence of stacking of lamellae) and the separation of the two photochemical systems in the digitonin treatment.