Abstract
BackgroundCyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; however, increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields. Plant growth regulators play beneficial role in combating the negative effects induced by heavy metals in photoautotroph. Current study evaluates the potential role of indole acetic acid (IAA; 290 nm) and kinetin (KN; 10 nm) on growth, nitrogen metabolism and biochemical constituents of two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 exposed to two concentrations of chromium (CrVI; 100 μM and 150 μM).ResultsBoth the tested doses of CrVI declined the growth, ratio of chlorophyll a to carotenoids (Chl a/Car), contents of phycobiliproteins; phycocyanin (PC), allophycocyanin (APC), and phycoerythrin (PE), protein and carbohydrate associated with decrease in the inorganic nitrogen (nitrate; NO3— and nitrite; NO2—) uptake rate that results in the decrease in nitrate and ammonia assimilating enzymes; nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT) except glutamate dehydrogenase (GDH). However, exogenous supplementation of IAA and KN exhibited alleviating effects on growth, nitrogen metabolism and exopolysaccharide (EPS) (first protective barrier against metal toxicity) contents in both the cyanobacteria, which probably occurred as a result of a substantial decrease in the Cr uptake that lowers the damaging effects.ConclusionOverall result of the present study signifies affirmative role of the phytohormone in minimizing the toxic effects induced by chromium by stimulating the growth of cyanobacteria thereby enhancing its ability as bio-fertilizer that improved fertility and productivity of soil even in metal contaminated condition.
Highlights
Cyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields
Earlier reports indicated that biochemical constituents such as protein and carbohydrate were negatively affected by Cr stress [18, 19], beside this, EPS which is the polymer of carbohydrates and act primarily as a protective barrier against heavy metal stress were found to decline under Cr stress
Growth Result pertaining to growth of tested cyanobacteria i.e. Nostoc muscorum ATCC 27893 and Anabaena sp
Summary
Cyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields. Cyanobacteria exclusively mediate the nitrogen fixation in form of ammonia (NH4+) thereby enhance the fertility of paddy fields and act as bio-fertilizer [7, 8] They are potent sources of carbohydrates, lipids, phenolics, vitamins, amino acids and sugars that directly or indirectly enhance the crop yield [9]. Chromium (Cr) induces negative effects on the growth of micro-flora associated with paddy fields, by obstructing their physiological and biochemical processes as studied by other workers in Oscillatoria, Nostoc and Haematococcus [10,11,12]. Chromium significantly declined the inorganic nitrogen uptake associated with decreased nitrogen and ammonia assimilating enzymes (NR, NiR, GS and GOGAT) except GDH (involved in alternative pathway of NH4+ assimilation) [17]. Earlier reports indicated that biochemical constituents such as protein and carbohydrate were negatively affected by Cr stress [18, 19], beside this, EPS which is the polymer of carbohydrates and act primarily as a protective barrier against heavy metal stress were found to decline under Cr stress
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