Symbiotic effectiveness and response to mannitol-mediated osmotic stress of various chickpea–rhizobia associations

Abstract

Thirty-six symbiotic associations involving six chickpea cultivars against six rhizobial strains were evaluated for symbiotic performance and responses to osmotic stress applied by mannitol (50 mM) in aerated hydroponic cultures. Analyses in different symbioses were focused on biomass production, nodulation, nitrogen fixation, and their modulation under osmotic stress conditions, as well as expression of nodular antioxidant enzymes. Mesorhizobium ciceri reference (835) and local (CMG6) strains, as well as the local (C 11 ) M. mediterraneum allowed the best symbiotic efficiency for all chickpea cultivars. The osmotic stress induces severe decrease ranging 30-50% in aerial biomass and 50-70% for nitrogen fixation. Nevertheless, plants inoculated with M. ciceri (835) and M. mediterraneum (C 11 ) preserve a relatively high growth (4 g plant -1 ) with nitrogen-fixing activity (25 lmols h -1 plant -1 ). The bacterial partner was the most important factor of variance of the analysed parameters in osmotic stress or physiological conditions where it gets to 60-85%. The strains allowing the best competent symbioses were proposed for field assays. Under osmotic stress, nodular peroxidase (POX) and ascorbate peroxidase (APX) activities were significantly enhanced. The increase of POX and APX was inversely correlated with the inhibition of aerial biomass production (p = 0.05) and nitrogen-fixing capacity (p = 0.01), suggesting a protective role of these enzymes in nodules. Superoxide dismutase (SOD) was also activated in stressed nodules. However, the spectacular decrease in catalase (CAT) activity discounts its involvement in osmotic stress response.

Plant Hydroponic Cultivation: A Support for Biology Research in the Field of Plant-Microbe-Environment Interactions

“…Among the different hydroponic media assessed in our experiments, the liquid medium (table 1) associated to artificial aeration (400 ml/min/plant) seems been the adequate medium for a maximum plant biomass production, mainly when plant are cultivated in symbiosis with nitrogen fixing bacteria (Mhadhbi et al, 2004, 2008, 2009, 2010. This system presents more advantages "vigorous and clean biological material" due to the absence of support which make easier the physiological, biochemical and molecular analyses performed on root parts.…”

“…Composition of the nutrient solution could be adjusted according to specific needs of plant species. Indeed, our experience with legumes plants showed that composition of nutrient solution allowing optimal plant growth for some grain legume species (Common bean, Chickpea) (Vadez et al, 1996, Jebara et al, 2001, Mhadhbi et al, 2004, 2008 could be modified for concentration of some elements to be adequate for others legume species (Medicago truncatula, Medicago sativa) (Mhadhbi et al, 2005). Control of mineral elements concentrations and forms could be previously adjusted.…”

“…Measure of fixed nitrogen is performed by different methods: (i) Khjeldal method which determine the quantity of nitrogen within tissues after plant harvest, there for it is a destructive method, (ii) monitoring fixed nitrogen using N 15 isotope which require radioactivity manipulation and so special equipments, care and spaces, (iii) An "In Situ, In Vivo" method using acetylene (C 2 H 2 ) as structural analogue of molecular nitrogen (N 2 ) and the result of reaction is ethylene (C 2 H 4 ) easily determined using gas chromatograph (Hardy et al, 1968). It is an estimative method with limits due to the inhibition of nitrogense enzyme by acetylene (Minchin et al, 1983) but simple and effective mainly for comparative studies (Mhadhbi et al, 2005(Mhadhbi et al, , 2008.…”

Enhancement of nodulation by some arid climate strains of Rhizobium leguminosarum biovar trifolii using protoplast fusion

“…Nodulation production and the efficiency of the symbiotic relation with leguminous depends on many factors (Valdenegro et al 2001;Ö güt et al 2005;Sivaramaiah et al 2007;Mcneil and Materne 2007;Mhadhbi et al 2008). Examination of the structure of large Rhizobium populations in soil, and how it is influenced by the host and environment has been possible only with the development of molecular and computational tools (Thies et al 2001;Hirsch et al 2003;Graham 2008).…”

“…Nodulation and N 2 fixation in symbiosis require compatibility between the host and microorganism, appropriate soil environment for the exchange of signals that precede infection (Hirsch et al 2003;Graham 2008), availability of nutrients and the coinoculation with other plant growth-promoting rhizobacteria or biocontrol fungi (Valdenegro et al 2001;Ö güt et al 2005;Sivaramaiah et al 2007). The infection process and the achievement of high nodule occupancies could fail due to a number of reasons including a lack of or inappropriate strains of rhizobia, failure of the plant to invest in the symbiosis, or through altered metabolism due to environmental condition such as osmotic stress (Mcneil and Materne 2007;Mhadhbi et al 2008).…”