Salinity induced changes in the chloroplast proteome of the aquatic pteridophyte <Emphasis Type="Italic">Azolla microphylla</Emphasis>

The growth of the nitrogen fixing aquatic pteridophyte Azolla microphylla is severely affected by salinity. Salinity exposure (0.5%) resulted in significant reduction in chlorophyll a and b content, altered chl a/b ratio and photosynthetic efficiency (Fv/Fm). Chloroplasts maintain photosynthesis but are highly sensitive to salinity stress. Chloroplast proteins extracted from A. microphylla was separated by two-dimensional electrophoresis (2DE) and approximately 200 proteins were observed on each gel. Forty two differentially expressed protein spots were detected and out of this 17 could be identified through MALDI-TOF-MS/MS analysis. Out of the 17 identified proteins, 15 were found to be down regulated and 2 proteins were up regulated. Most of the down regulated proteins were associated with Calvin cycle, ATP synthesis, oxygen evolution, photosystem I and ROS scavenging. The results show changes in proteome dynamics of the chloroplasts of A. microphylla and such changes may lead to reduction in growth and metabolism. The primary target of salinity in A. microphylla is photosynthesis and the changes in the proteome dynamics of the chloroplasts lead to reduced growth.