Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942 exhibit dissimilar tolerance to Cr(VI) witha tenfold difference in their EC50 value for Cr(VI). This contrasting tolerance was attributed to the difference in theability to transport Cr(VI) and to detoxify ROS. The present study used biochemical assays and chlorophyllfluorescence to investigate the effect of growth with Cr(VI) on photosynthesis in the two cyanobacteria. Inabsence of Cr(VI), all the measured parameters viz., rates of CO2 fixation, PSII and PSI activities were higher inSynechocystis in comparison to Synechococcus, suggesting intrinsic differences in their photosynthesis. Growthin the presence of Cr(VI) reduced the pigment content and photosystems’ activities in both cyanobacteria. It wasfurther observed that photosynthetic functions were more adversely affected in Synechocystis in comparisonto Synechococcus, in spite of exposure to tenfold lower Cr(VI) concentration. The effective quantumyield of PSIIand PSI obtained by chlorophyll fluorescence measurements increased in the presence of Cr(VI) in Synechococcuswhereas it decreased in Synechocystis. However, the overall CO2 fixation remained unchanged. These resultsindicated that, in addition to the intrinsic difference in photosynthetic rates, the two cyanobacteria exhibit differentialmodulation of photosynthetic machinery upon Cr(VI) exposure and Synechococcus could adapt betterit’s photosystems to counter the oxidative stress.
Volume 46, 2020
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode