Salt induced responses of chloroplast activities in species of differing salt tolerance. Photosynthetic electron transport in Aster tripolium and Pisum sativum

Abstract

A comparative study was made of the effects of high concentrations of NaCl, KCl and MgCl2 on two electron transport reactions of thylakoids isolated from a mesophyte, Pisum sativum and a halophyte, Aster tripolium. The rate of photosystem I mediated electron transport from reduced N, N, N′, N′‐tetramethyl‐p‐phenylenediamine (TMPD) to methyl viologen was determined polarographically, and photosystem II mediated electron flow from water to 2,6‐dichlorophenolindophenol (DCPIP) was monitored spectrophotometrically. The response of photosystem II to increasing in vitro salt concentrations was similar for thylakoids isolated from both A. tripolium and P. sativum, but differences in the response of photosystem I to salinity changes were observed for the two species. Increasing NaCl, KCl and MgCl2 concentrations produced similar patterns of response of photosystem I activity in P. sativum thylakoids, whilst for A. tripolium KCl induced a completely different response pattern compared to NaCl and MgCl2. The salinity of the culture medium in which A. tripolium was grown also had an effect on both the absolute in vitro activities of photosystems I and II and their response to changes in salt concentration of the reaction media.