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.

Effect of Osmotic Stress on Photosynthesis Studied with the Isolated Spinach Chloroplast

“…However, uncouassay media 4, to -20.7 bars (0.67 M pled electron flow through PSII and PSI were not inhibited at s can be considered as moderate and reaction medium sorbitol concentrations of 0.67 M with either on, respectively, relative to the range of broken or intact chloroplasts. It is not clear why whole chain is studies (4,5,9,17,19,20,26). electron flow is inhibited in intact chloroplasts while partitioned lated chloroplast as determined by the flow through either photosystem was not found to be adversely cted by reaction medium osmolarity affected in our work.…”

“…in chioroplasts of one of two species tested (26 (9), is about twice that found for coupled and uncoupled whole chain electron transport at this osmoticum concentration (Fig 1; Table I), implying that there are mediating mechanisms other than noncyclic photophosphorylation and photochemical production of NADPH by which osmotic potential adversely affects PGA reduction.…”

“…Only minimal inhibition of coupled DCIP reduction with decreasing assay medium 4,, was reported by Potter and Boyer (19) with isolated chloroplasts; the rate between 0 and approximately -8 bars was optimal and was inhibited by 13% at -16 bars and by 16% at -24 bars. Wignarajah and Baker (26) found no osmotic inhibition of coupled electron flow through PSII (DCIP reduction) in lysed chloroplasts isolated either from Pisum sativum or Atriplex tripolium. Coupled electron flow through PSI (MV reduction) was inhibited 45% at 0.8 M mannitol when compared to a control rate measured in 0.3 M mannitol in P. sativum, but no osmotic inhibition of PSI activity ofA.…”

“…tripolium chloroplasts was found in their study. Finally, Kaiser et al (9) reported that electron transport to MV in the intact chloroplast was not affected by osmotic stress between -10 and -25 bars.The in vitro stress effects of reaction medium 4, on chloroplastic photochemical activity have been monitored hitherto either with broken chloroplast preparations (4,5,20,26) or with intact preparations containing a significant proportion of broken chloroplasts (9, 19). The interposition of the chloroplast envelope might afford the thylakoids responding to the imposition of osmotic stress an environment closer to that in situ.…”

Some considerations of and perspectives in coastal ecology

“…Comparison of halophytes with ecologically and/or evolutionary unrelated glycophytes (Wignarajah & Baker, 1981;Vakhmistrov et al, 1982;Ownbey & Mahall, 1983) as well as shortterm experiments on the effects of sodium chloride on growth (Erdei & Kuiper, 1979), enzymatic activities (Binet, 1976), and synthesis of specific metabolites (Gorham et aL, 1981;Goas et aL, 1982), have produced a mass of data, but underestimated the final aim of an organism: its contribution to the following generation. Why do halophytes sometimes have a higher demand for sodium chloride for optimal enzymatic activity (Cavalieri & Huang, 1977) or/and growth (Tiku, 1976)?…”