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Planta (2010) 232:533543DOI 10.1007/s00425-010-1196-8
ORIGINAL ARTICLE
Regulation of plasma membrane aquaporins by inoculation with a Bacillus megaterium strain in maize (Zea mays L.) plants under unstressed and salt-stressed conditions
Adriana Marulanda Rosario Azcn
Franois Chaumont Juan Manuel Ruiz-Lozano Ricardo Aroca
Received: 7 April 2010 / Accepted: 9 May 2010 / Published online: 25 May 2010 Springer-Verlag 2010
Abstract It is documented that some plant-growth-promoting rhizobacteria (PGPR) enhance plant salt tolerance. However, as to how PGPR may inXuence two crucial components of plant salt tolerance such as, root hydraulic characteristics and aquaporin regulation has been almost unexplored. Here, maize (Zea mays L.) plants were inoculated with a Bacillus megaterium strain previously isolated from a degraded soil and characterized as PGPR. Inoculated plants were found to exhibit higher root hydraulic conductance (L) values under both unstressed and salt-stressed conditions. These higher L values in inoculated plants correlated with higher plasma membrane type two (PIP2) aquaporin amount in their roots under salt-stressed conditions. Also, ZmPIP1;1 protein amount under salt-stressed conditions was higher in inoculated leaves than in non-inoculated ones. Hence, the diVerent regulation of PIP aquaporin expression and abundance by the inoculation with the B. megaterium strain could be one of the causes of the diVerent salt response in terms of root growth, necrotic leaf area, leaf relative water content and L by the inoculation treatment.
Keywords Aquaporins Maize PGPR
Root hydraulic conductance Salt stress
Abbreviations
L Root hydraulic conductancePGPR Plant-growth-promoting rhizobacteria PIP Plasma membrane aquaporins
Introduction
Plants in nature interact with several beneWcial soil micro-organisms, which improve plant stress tolerance (Aroca and Ruiz-Lozano 2009a; Ryan et al. 2009). Among such micro-organisms, plant-growth-promoting rhizobacteria (PGPR) are one of the most studied (Dimkpa et al. 2009; Lugtenberg and Kamilova 2009). PGPR can be classiWed as extracellular bacteria (existing in the rhizosphere, on the rhizoplane, or in spaces between cells) and intracellular bacteria (mainly N2 Wxing bacteria) (Gray and Smith 2005). The action mechanisms of PGPR can be divided also into direct and indirect ones. Direct mechanisms include N2 Wxation, soil mineral solubilization, production of plant-growth-promoting substances (auxins, cytokinins or gibberellins), and reduction of ethylene levels, among others. Indirect mechanisms include favoring colonization by other beneWcial soil microorganisms, as mycorrhizal fungi, and repressing the growth of plant pathogenic microorganisms (Vessey...