Time-dependent changes in the in vitro effects of sodium chloride on photosynthetic electron transport of isolated chloroplasts

The effects of a wide concentration range of NaCl and sorbitol on three photosynthetic electron transport reactions of Pisum sativum L. cv. Feltham First chloroplasts were examined as a function of time from thylakoid membrane isolation. Rates of electron flow from water to diaminodurene (DAD) and ferricyanide were determined polarographically, whilst photoreduction of 2,6-dichlorophenolindophenol (DCPIP) was monitored spectrophotometrically. Assay of thylakoids immediately after isolation showed that the rate of photoreduction of all three electron acceptors decreased with increasing salt concentration. However, 100 min after leaf homogenisation the response pattern of ferricyanide and DCPIP photoreduction to increasing NaCl, but not increasing sorbitol concentration, became significantly modified. This was not the case for DAD photoreduction. The results are discussed in relation to the assessment of the possible effect of salinity on photosynthetic electron transport in vivo.