Alleviation of NaCl toxicity in the cyanobacterium Synechococcus sp.
PCC 7942 by exogenous calcium supplementation
Arun K. Mishra
Received: 21 July 2017 /Revised and accepted: 19 January 2018 / Published online: 15 February 2018
Springer Science+Business Media B.V., part of Springer Nature 2018
Salinity (NaCl) is one of the major problems associated with irrigated agricultural lands, especially rice fields. Being the common
inhabitants of rice fields, cyanobacteria frequently experience high concentration of NaCl which in turn causes cellular damage.
Therefore, mitigation of NaCl stress in cyanobacteria, plant growth-promoting microorganisms, is of utmost importance. The
present study was designed to investigate the role of calcium in the alleviation of NaCl stress-induced cellular in Synechococcus
sp. PCC 7942. The cyanobacterium was subjected to sub-lethal concentration of NaCl (800 mM) with and without the supple-
mentation of calcium (1 mM CaCl
) for 8 days. The results showed a drastic reduction in growth due to excess NaCl, but
supplementation of CaCl
reduced the salt stress damage and partially restored growth. Application of calcium increased pigment
contents, photosynthetic efficiency, antioxidative enzyme activity, osmolyte contents and reduced the intracellular sodium ion
concentration, MDA content, electrolyte leakage and free oxygen radical generation. Furthermore, proteins involved in photo-
synthesis, respiration, ATP synthesis and protein synthesis along with two hypothetical proteins were also observed to be
upregulated in the cyanobacterium in presence of calcium. Furthermore, proteins related to oxidative stress defence, nitrogen
metabolism, carbohydrate metabolism, fatty acid metabolism and secondary metabolism were found to be upregulated by several
fold. Therefore, our study suggests that calcium suppresses salt toxicity in Synechococcus sp. PCC 7942 by restricting the entry of
into the cell, increasing osmolyte production and upregulating defence-related proteins.
Synechococcus sp. PCC 7942
Salt stress is one of the most common environmental problems
of recent times and is associated with irrigated agricultural
lands, especially rice fields. Almost 7% of the world’stotal
arable land and 20% of the irrigated agricultural land are affect-
ed by salt stress (Rai et al. 2014; Arora 2017). Moreover, it has
been estimated that more than 50% of the total arable land
would be salinized by the year 2050 (Jamil et al. 2011).
Therefore, increasing rate of soil salinization is of major con-
cern and is a serious threat to the growth of soil microbes
residing in the irrigated agricultural lands. Cyanobacteria, the
common residents of such irrigated farmable lands, form a
diverse group of highly specialized bacteria capable of
performing oxygenic photosynthesis. They are prokaryotes
and considered as the ancestors of eukaryotic algae and higher
plants (Xiao et al. 2012). Effects of salt stress have already been
studied in a number of cyanobacterial species (Allakhverdiev
et al. 2000) and it has been observed that salinity causes ionic
imbalances, hampers photosynthesis, creates oxidative stress
and disturbs other important metabolic processes
(Allakhverdiev et al. 2000;Sudhiretal.2005). Adverse effects
of salinity on the protein profile also have been reported in
cyanobacteria (Fulda et al. 2006; Huang et al. 2006).
Although salinity exposure causes numerous disorders in
cyanobacteria at the physiological, biochemical and molecular
levels, all of them exhibit equal adverse effects under salt stress.
Furthermore, the extent of salt tolerance may vary within
cyanobacterial genera and species due to variations in their
morphological as well as genomic properties (Golubic 1980;
Stal 2007). It has been shown by Rai et al. (2014) that three
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10811-018-1410-9) contains supplementary
material, which is available to authorized users.
* Arun K. Mishra
Laboratory of Microbial Genetics, Department of Botany, Banaras
Hindu University, Varanasi 221005, India
Journal of Applied Phycology (2018) 30:1465–1482