Research articleSalinity induced physiological and biochemical changes in the freshly separated cyanobionts of Azolla microphylla and Azolla caroliniana
Introduction
The free floating aquatic fern Azolla has the ability to fix atmospheric nitrogen due to the presence of symbiotic association with the nitrogen fixing cyanobacterium Anabaena azollae (Peters, 1978). Because of the high rates of nitrogen fixing potential the system is considered to be economically important (Stewart et al., 1987). The Azolla-Anabaena system is unique and has great agronomic significance due to high productivity, nitrogen fixation and photosynthesis. Singh (1989) highlighted the importance of Azolla as biofertilizer in rice cultivation. Besides the traditional use as biofertilizer the plant has several other uses such as green manure, fish and animal feed, water purifier and hydrogen gas producer (Wagner, 1997).
Increasing soil salinity is however, serious impediment in the popularization of this system as biofertilizer. There are several reports on the impact of salinity on Azolla and free living cyanobacteria (Rai and Rai, 1999, Masood et al., 2006, Rai et al., 2014). However, there have been no attempts to understand the effect of salinity on the physiological and biochemical response of the cyanobionts. On the other hand, the salinity tolerance mechanism in free living cyanobacteria has been worked out in considerable detail (Moisander et al., 2002, Chris et al., 2006, Srivastava et al., 2005, Srivastava et al., 2008). Pabby et al. (2003) isolated the cyanobionts from different strains of Azolla and characterized them physiologically. Understanding the physiological response of the cyanobiont to salinity is therefore important to unravel the salinity tolerance mechanism operating in this system. This will further pave way for the intervention of advanced molecular biological tools to work out the mechanisms operating under salinity stress conditions in the cyanobionts. Therefore in the present study the physiological and biochemical response of freshly separated cyanobionts from two different species of Azolla viz. Azolla microphylla and Azolla caroliniana exposed to salinity was studied.
Section snippets
Cellular constituents and nitrogenase activity of freshly separated cyanobionts
The freshly separated cyanobionts from A. microphylla and A. caroliniana showed contrasting pattern with respect to the cellular constituents (Fig. 1a&b). Cyanobionts of A. caroliniana showed much drastic reduction in the content of chlorophyll (P > 0.05) as compared to A. microphylla. Compared with the control, the observed decrease in the chlorophyll content was 23.1 and 38.9% in the cyanobionts of A. microphylla and A. caroliniana, respectively. On the other hand cellular constituents such
Discussion
Increasing soil salinity is a serious threat to agriculture and according to a report 50% loss of land has been predicted by the year 2050 (Wang et al., 2003). In such a scenario organisms capable of sustainable nitrogen fixation may also be adversely affected. Due to nitrogen fixing potential Azolla is used in tropical rice fields as biofertilizer. Masood et al. (2006) has already reported the adverse influence of salinity on the growth of Azolla plants. However, no attempts have been made to
Conclusion
Our results offer new insights regarding the response of freshly isolated cyanobionts of A. microphylla and A. caroliniana to salinity. This first hand information demonstrates significant differences with respect to the physiological attributes, antioxidant enzymes, nitrogen fixation and regulation of ion fluxes in the cyanobionts probably due the differences in the adaptive responses. The observations suggest that the response of the freshly separated cyanobiont from salt stressed Azolla
Plant material, growth conditions and salinity treatment
Azolla microphylla and Azolla caroliniana plants maintained at the Centre for Conservation Utilization Blue Green algae, Indian Agricultural Research Institute, New Delhi was used for the experiments. Plants were grown in Espianase and Watanabe medium (Espianase and Watanabe, 1976) without nitrogen containing NaCl (90 mM) for 9 days. The temperature was maintained at 30 ± 2 °C with a light intensity of 3–5 Klux and a light/dark cycle of 10/14 h. Five gram (5 g) of fresh biomass was inoculated in
Author contribution
GA and PWR planned the experiments and provided intellectual inputs for the work. RKY conducted the experiments and KNT helped in conducting the experiments and recording data. EV helped in the statistical analysis of the data.
Conflict of interest
None.
Acknowledgement
We are grateful to Indian Agricultural Research Institute and the Indian Council for Agricultural Research, New Delhi for facilities and encouragement.
References (56)
Catalase in vitro
Methods Enzymol.
(1984)- et al.
NaCl induced Proline accumulation counteract the effect of UV-B in a cyanobacterium Cylindrospermum sp
Environ. Exp. Bot.
(2006) - et al.
Antioxidant responses of rice seedlings to salinity stress
Plant Sci.
(1998) - et al.
Salt induced lipid changes in Catharanthus roseus cultured cell suspensions
Phytochemistry
(2004) - et al.
Analysis of stress responses in the cyanobacterial strains Synechococcus sp. PCC 7942, Synechocystis sp. PCC 6803, and Synechococcus sp. PCC 7418: osmolyte accumulation and stress proteins synthesis
J. Plant Physiol.
(1999) Absorption of light by chlorophyll solutions
J. Biol. Chem.
(1941)- et al.
Differential response of antioxidant enzymes to salinity stress in two varieties of Azolla (Azolla pinnata and Azolla filiculoides)
Environ. Exp. Bot.
(2006) Symbiotic associations
Methods Enzym.
(1988)- et al.
Physiological characterization of the cultured and freshly isolated endosymbionts from different species of Azolla
Plant Physiol. Biochem.
(2003) - et al.
Effect of NaCl on growth, nitrate uptake and reduction and nitrogenase activity of Azolla pinnata-Anabaena azollae
Plant Sci.
(2003)
Comparative proteomics unveils cross species variations in Anabaena under salt stress
J. Proteom.
Growth and cellular ion content of a salt-sensitive symbiotic system Azolla pinnata–Anabaena azollae under NaCl stress
J. Plant Physiol.
Salt stress responses of higher plants: the role of proton pumps and Na+/H+ antiporters
J. Plant Physiol.
Recombinant glycinebetaine improves metabolic activities, ionic balance and salt tolerance in diazotrophic fresh water cyanobacteria
Algal Res.
Salinity stress induced proteins in two nitrogen-fixing Anabaena strains differentially tolerant to salt
J. Bacteriol.
Official Methods of Analysis
Rapid determination of free proline for water stress studies
Plant Soil.
Salt adaptation of the eyanobacterium Synechococcus 6311 growing in a continuous culture (turbidostat)
Pl. Physiol.
Proteomic analysis of the cyanobacterium of the Azolla symbiosis: identity, adaptation, and NifH modification
J. Experi. Bot.
Mineral Nutrition of Plants: Principles and Perspectives
Salinity tolerance in halophytes
New Phytol.
Superoxide dismutase 1. Occurrence in higher plants
Plant Physiol.
Osmotic stress induced changes in germination, growth and soluble sugar contents of Sorghum bicolor (L.) Moench seeds under various abiotic stresses
Plant Physiol.
Alterations of protein synthesis in the cyanobacterium Syechoystis sp. PCC 6803 after a salt shock
J. Gen. Microbiol.
Sodium sensing induces different changes in free cytosolic calcium concentration and pH in salt tolerant and sensitive rice (Oryza sativa) cultivars
J. Plant Physiol.
A hydroponic rice seedling culture model system for investigating proteome of salt stress in rice leaf
Electrophoresis
The role of calcium in the regulation of membrane and cellular growth processes under salt stress
Cited by (11)
Diversity and regulation of symbiotic nitrogen fixation in plants
2023, Current BiologySalinity Induced Alterations in the Growth and Cellular Ion Content of Azolla caroliniana and Azolla microphylla
2023, Journal of Plant Growth RegulationA comprehensive study on the assessment of chemically modified Azolla pinnata as a potential cadmium sequestering agent
2023, International Journal of Experimental Research and ReviewA Review on the Use of Azolla Meal as a Feed Ingredient in Aquatic Animals' Diets
2023, Aquaculture ResearchMicroalgae for saline wastewater treatment: a critical review
2020, Critical Reviews in Environmental Science and Technology