A key challenge for plant growth is global water shortage, limiting crop yields already today in more than 70% of arable lands. The drought limitations further gain in importance in the near future as agricultural activities expand to less fertile areas to satisfy growing demands for food. Accordingly, novel solutions for plant survival and growth under restricted water availability are of central significance in contemporary plant science. Rhizobacterial ability to increase plant growth and provide protection to various pathogens has been frequently reported and applied in agricultural systems. Relatively few reports have been published on the bacterial ability to induce drought stress tolerance. Application of the isolates to-gether with novel technologies for their monitoring can contribute to solving food security issues in the changing climates

Behers, Lawrence

Timmusk, Salme

English

Salme Timmusk

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Irrigation & Drainage Systems Engineering

Rhizobacterial Application for Sustainable Water Management on the Areas of Limited Water Resources

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1   Enhancing drought tolerance in crops Rhizobacterial application for sustainable water management on the areas of limited water resources   Salme Timmusk1 and Lawrence Behers2 1 Dept. of Forest Mycology and Plant Pathology, Uppsala BioCenter, SLU, Sweden  2Novawest Communications, Tucson, Arizona, USA *Correspondence Salme Timmusk, Dept. of Forest Mycology and Plant Pathology, Uppsala BioCenter, SLU  Box 7026 SE-75007 E-mail: salme.timmusk@slu.se  Published 2012 in Irrigation & Drainage System Engineering 2168-9768-1-e111 Abstract A key challenge for plant growth is global water shortage, limiting crop yields already today in more than 70% of arable lands. The drought limitations further gain in importance in the near future as agricultural activities expand to less fertile areas to satisfy growing demands for food. Accordingly, novel solutions for plant survival and growth under restricted water availability are of central significance in contemporary plant science. Rhizobacterial ability to increase plant growth and provide protection to various pathogens has been frequently reported and applied in agricultural systems. Relatively few reports have been published on the bacterial ability to induce drought stress tolerance. Application of the isolates to-gether with novel technologies for their monitoring can contribute to solving food security issues in the changing climates.  Keywords: Abiotic stress, Plant Growth Promoting Rhizobacteria, ACC deaminase, Bacterial Bio-films  The world population is predicted to in-crease beyond 8 billion by 2030, implying major challenges for the agricultural sector to secure food availability(1). A key chal-2  lenge for plant growth is global water shortage which limits crop yields already today. As the drought limitations gain in importance in the near future the agricul-tural activities must expand to less fertile areas to satisfy growing demands for food (2). During the next years, many countries will experience water problems—shortages, poor water quality, or floods—that will increase regional tensions. By 2030, available fresh water will not keep up with the demand, and without more effi-cient management of our water resources, the problems we now encounter will hinder food production in key countries. This is a global problem for food markets and the associated economic growth. Due to devel-oping economic pressures, North Africa, the Middle East and South Asia will face dramatic challenges in dealing with water problems (3). Because of depleted and con-taminated surface water supplies, many of these countries have resulted in over pump-ing the groundwater to satisfy growing food demands, which has resulted in a seri-ous threat to food security, thereby risking social turmoil i.e. loss in agricultural jobs, significantly stressing the economy. A strong correlation exists between water supplies for agriculture and  GDP. Approx-imately 70% of the global fresh water sup-ply is used in agriculture, creating a great opportunity and potential for technology to provide solutions in order to effectively use the available water (3). Several breeding and genetic engineering strategies have been proposed to increase the ability of plants to tolerate stress in or-der to find practical solutions. Past efforts to improve plant tolerance have has been slower than expected owing to the genetic complexity of stress responses. At the same time the resources already present in natu-ral, complex self-regulating systems i.e. the underground resources of the plant rhizo-sphere offer new opportunities for agricul-tural biotechnology (4, 5). The very first report on plant drought toler-ance enhancement by plant growth promot-ing rhizobacteria (PGPR) was published in Uppsala, Sweden (6) Fig.1. It was shown that  Arabidopsis thaliana inoculated with PGPR  Paenibacillus polymyxa B2 could survive drought stress remarkably longer compared to the untreated control plant. The report was followed by Prof. Glick group in Canada (7). Research is being conducted for the mechanisms behind the observed plant drought stress tolerance enhancement in order to find possibilities for economically efficient rhizobacterial applications for plant drought tolerance enhancement. It has been shown that cer-tain PGPR enhance plant stress tolerance through 1-aminocyclopropane-1-carboxylate deam-inase (ACCd) and provide significant protection 3  to a wide range of plant species from the dam-age caused by various abiotic stress conditions (8). ACC breakdown and ethylene synthe-sis inhibition by ACCd decreases the dam-age of various stress situations by enhanc-ing homeostasis  in and around the plant root, especially at early stages of stress exposure. Hence ACCd can be considered one of the signalling compounds mediating plant basic stress tolerance. The  ACCd containing and biofilm producing bacteria which show the best drought tolerance en-hancing  ability excrete the ’matrix’ to pro-vide a buffer against the environment (4, 9) (Fig.2). The dense biofilm matrix, limits diffusion of compounds secreted by root bacteria and are therefore concentrated at the root surface where they are most likely to affect plant growth (4). Our experiments show that bacteria can engineer their own microenvironment in a form of porous ex-tracellular matrix mixed soil particles. The environment immediately interacts with plant root providing buffered and predicta-ble hydration and transport properties (10). The extracellular matrix producing Paeni-bacillus sp. strains significantly increased soil aggregation in comparison to the strains with limited matrix production (Timmusk manuscript in preparation). The matrix may also contribute to mechanical stability of the biofilm and interact with other macromolecules and low molecular mass solutes, providing a multitude of mi-croenvironments within the biofilm. Cur-rently many of these effects can only be speculated. We keep highlighting themes regarding the nature and diversity of the bacterial isolate biofilms and elucidate their potential protecting plants against drought stress. The underground resources of plant rhizo-sphere could provide insights associated with global water shortage and climate change. So far, these resources have been neglected to a large extent, but hopefully with the help of new technologies we will be able to understand and employ the natu-ral potential of biofilms for our agro-ecosystems.  References  1.  J. P. Smol, Climate Change: A planet in flux. Nature 483, S12 (Mar 1, 2012). 2.  J. A. Foley et al., Solutions for a cultivated planet. Nature 478, 337 (Oct 20, 2011). 3.  M. N. Pieters, M. Bakker, W. Slob, Reduced intake of deoxynivalenol in The Netherlands: a risk assessment update. Toxicology letters 153, 145 (Oct 10, 2004). 4. S.  Timmusk et al., Bacterial distribution in the rhizosphere of wild barley under contrasting microclimates. PLoS ONE 6(3): e17968. doi:10.1371/journal.pone.0017968 (2011). 5.  J. Yang, J. W. Kloepper, C. M. Ryu, Rhizosphere bacteria help plants tolerate abiotic stress. Trends in plant science 14, 1 (Jan, 2009). 6.  S. Timmusk, E. G. Wagner, The plant-growth-promoting rhizobacterium Paenibacillus polymyxa induces changes in Arabidopsis thaliana gene expression: a possible connection between biotic and abiotic stress responses. Mol Plant Microbe Interact 12, 951 (Nov, 1999). 7.  S. Mayak, T. Tirosh, B. R. Glick, Plant growth-promoting bacteria that confer resistance to water stress in tomatoes and peppers. Plant Sci 166, 525 (2004). 8.  J. Duan, K. M. Muller, T. C. Charles, S. Vesely, B. R. Glick, 1-aminocyclopropane-1-4  carboxylate (ACC) deaminase genes in rhizobia from southern Saskatchewan. Microb Ecol 57, 423 (Apr, 2009). 9.  S. Timmusk, N. Grantcharova, E. G. Wagner, Paenibacillus polymyxa invades plant roots and forms biofilms. Appl Environ Microbiol 71, 7292 (Nov, 2005). 10.  S. Timmusk, E. Nevo, in Bacteria in agrobiology (vol 3) : Plant nutrient management, D. K. Maheshwari, Ed. (Springer Verlag, Berlin, 2011).                                           Figure 1. Enhancement of plant drought tolerance by Paenibacillus polymyxa.  P. polymyxa B2 inoculated plants (A) survived drought stress two weeks longer than untreated control plants (B). Image after three day  drought exposure is shown. Plants were grown and inoculated and subsequently ex-posed to drought stress as described by Timmusk and Wagner (1999).  5     Figure 2. Typical pattern of P. polymyxa  colonization and biofilm formation on plant roots. Scanning electron microscopy (SEM) micrographs of colonized roots.  Studies in the controlled system after two hours of colonization (A, C, E) and in non-sterile soil assays  after one week of colonization (B, D, F). Plants were grown and inoculated as described by Timmusk et al.2005. Images were taken from the root tips (A, B, C and D) and from tip-distal regions (E and F) Timmusk et al.2005. 

1-aminocyclopropane-1-4 carboxylate (ACC) deaminase genes in rhizobia from southern Saskatchewan.

Bacterial distribution in the rhizosphere of wild barley under contrasting microclimates.

Climate Change: A planet in flux.

Foley et al., Solutions for a cultivated planet.

Paenibacillus polymyxa invades plant roots and forms biofilms.

Plant growthpromoting bacteria that confer resistance to water stress in tomatoes and peppers. Plant Sci 166,

Reduced intake of deoxynivalenol in The Netherlands: a risk assessment update. Toxicology letters 153,

Rhizosphere bacteria help plants tolerate abiotic stress.

The plant-growthpromoting rhizobacterium Paenibacillus polymyxa induces changes in Arabidopsis thaliana gene expression: a possible connection between biotic and abiotic stress responses.

Rhizobacterial application for sustainable water management on the areas of limited water resources

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Rhizobacterial application for sustainable water management on the areas of limited water resources

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