Response of NaCl-adapted and unadapted Azolla pinnata Anabaena azollae complex to salt-stress: Partial photosynthetic processes and respiration

Chi a and b content in adapted complex, Azolla pinnata-Anabaena azollae was almost unchanged in response to 60 mM NaCl, while the values changed in th e unadapted complex, resulting in an altered chi a/b ratio of the latter. S alinity increased the photosynthetic O-2 evolution in unadapted as well as adapted complex. However, the stimulation was rapid in the unadapted comple x and reached its optimum within 12 h, whereas a gradual increase was evide nt in the adapted complex. Exposure of the unadapted complex to 60 mM NaCl resulted in enhanced PS II (27%) and PSI (10%) electron transport activity, while a decrease of 45% was evident in the whole chain activity. The compl ex adapted to 60 mM NaCl showed a reduction of 22% in PSI electron transpor t activity relative to that of the control, but appeared to adjust the PSII and whole chain electron transport activity. The effect of NaCl on in vitr o electron transport activity showed that the PSII electron transport activ ity was most sensitive to NaCl, followed by PSI and cyt b6-f activity. A mo derate salinity of 20 mM NaCl was found stimulatory to PSI electron transpo rt activity. The unadapted complex stressed with NaCl respired at higher ra tes in comparison to the control and the adapted complex incubated in the p resence of NaCl.