Influence of a Bacillus sp. on physiological activities of two arbuscular mycorrhizal fungi and on plant responses to PEG-induced drought stress

Abstract

The effects of bacterial inoculation (Bacillus sp.) on the development and physiology of the symbiosis between lettuce and the arbuscular mycorrhizal (AM) fungi Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe and Glomus intraradices (Schenck and Smith) were investigated. Plant growth, mineral nutrition and gas-exchange values in response to bacterial inoculation after PEG-induced drought stress were also evaluated. In AM plants, inoculation with Bacillus sp. enhanced fungal development and metabolism, measured as succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) activities, more than plant growth. Under non-stressed conditions, G. intraradices colonization increased all plant physiological values to a higher extent when in dual inoculation with the bacterium. Under stress conditions, the bacterium had an important stimulatory effect on G. intraradices development. Under such conditions, the effects of the bacterium on photosynthetic rate, water use efficiency (WUE) and stomatal conductance of lettuce plants differed with the fungus species. Plant-gas exchange was enhanced in G. intraradices- and reduced in G. mosseae-colonized plants when co-inoculated with Bacillus sp. Thus, the effects of each fungus on plant physiology were modulated by the bacterium. Stress was detrimental, particularly in G. intraradices-colonized plants without the bacterium, reducing intra and extraradical mycelium growth and vitality (SDH), as well as plant-gas exchange. Nevertheless, Bacillus sp. inoculation improved all these plant and fungal parameters to the same level as in non-stressed plants. The highest amount of alive and active AM mycelium for both fungi was obtained after co-inoculation with Bacillus sp. These results suggest that selected free-living bacteria and AM fungi should be co-inoculated to optimize the formation and functioning of the AM symbiosis in both normal and adverse environments.

Salinity-resistant plant growth promoting rhizobacteria ameliorates sodium chloride stress on tomato plants

“…Treatment with NT1 shows lower sodium uptake by plants, whereas high sodium retention in soil reveals that, although plants took up sodium along with other nutrients, PGPR retained most of the sodium in soil thereby lowering the deleterious effects of Na ' accumulation in plants. Similar reports were also quoted by Han and Lee (2005) as well as Vivas et al (2003) where they mentioned that the presence of PGPR strains could improve production of plant growth regulators and thus enhance plant growth by reducing toxic ion uptake and the formation of stress-specific proteins in plants.…”

“…This result is in accordance with our results where an increase in root length, shoot length, the number of leaves and lateral root count of tomato when inoculated with C4 and T15 under salt stress was observed. Vivas et al (2003) also reported enhanced root and shoot growth of lettuce when inoculated with Bacillus spp. under dry salt stress conditions.…”

Comparative transcriptome analysis of the lichen-forming fungus Endocarpon pusillum elucidates its drought adaptation mechanisms

“…The artificial desiccation treatment was performed on the isolated lichen-forming fungus using polyethylene glycol (PEG), which is a non-permeable osmolyte and can create a severe water deficit [23]. The PEG-induced drought stress was used to investigate the drought-resistant of plants and fungi [24,25]. The mycobiont was desiccated under the condition of cultured in the medium containing 20% PEG for 3 weeks.…”

Rhizosphere and endophytic bacteria for induction of salt tolerance in gladiolus grown in sodic soils

“…This reduction in weight of plants under stress may be due to the inhibition or hydrolysis of reserved food and its translocation to growing shoot portion (Singh et al 2008). The increase in root or corm character in microbial inoculated plants was witnessed earlier by Vivas et al (2003) in lettuce inoculated with Bacillus spp. under salt stress.…”