Choride as a beneficial macronutrient in plants: biological functions and regulation

1. Background and Objectives: In the agronomic context, chloride (Cl-) has been generally considered a toxic anion rather than a plant nutrient (Brumós et al, 2010). However we have recently shown that, in addition to an essential micronutrient, Cl- is a beneficial macronutrient (Franco-Navarro et al, 2016). Under non-saline conditions (1-5 mM), Cl- specifically stimulates higher leaf cell size and leads to a moderate increase of plant fresh and dry biomass mainly due to higher shoot expansion. Chloride plays specific roles in regulating leaf osmotic potential and turgor, allowing plants to improve leaf water balance parameters. In addition, Cl- regulates water relations at the whole plant level through reduction of plant transpiration. This is a consequence of a lower stomatal conductance, which results in lower water loss and greater photosynthetic and integrated water-use efficiency (Franco-Navarro et al, 2016). 2. Material and Methods: Tobacco plants were predominantly used for physiological measurements; Arabidopsis thaliana plants were used for the molecular characterization of genes involved in Cl- transport. Physiological methods used in this work include quantification of: nutrients content; plant biomass; anatomic parameters (leaf area, leaf cell size and density, chloroplast size and density and stomatal opening); water parameters (water content, relative water content, succulence, water potential, osmotic potential, turgor and water use efficiency); photosynthetic parameters (photosynthetic rate, stomatal conductance, intrinsic WUE and mesophyll conductance to CO2). Molecular methods used in this work include: tissue and cell-specific expression pattern of the candidate gene determined in transgenic lines of Arabidopsis thaliana expressing the chimeric GUS::GFP gene marker under the control of the gene promoter; gene expression response to abiotic stress and nutritional treatments quantified by Quantitative Real Time-PCR (qPCR); and phenotype of the homozygous mutant line (growth, shoot Cl- content and xylem sap Cl- concentration). 3. Results: The following open questions about chloride accumulation at macronutrient levels will be addressed: i) are Cl--treated plants more resistant to water deficit?; ii) why photosynthetic rate is not reduced as a result of lower stomatal conductance?; iii) why nitrate assimilation is not adversely affected?; iv) How is Cl- accumulation and Cl-/NO3- interaction regulated at the molecular level? 4. Conclusions: We propose that the abundant uptake and accumulation of Cl- responds to adaptive functions improving water homeostasis, drought tolerance, and nitrate- and carbon-use efficiency in plants. Brumós et al. (2010). Plant Cell Env, 33. Pages 2012-2027. Franco-Navarro et al. (2016) J Exp Bot, 67. Pages 873-891.

Bibliographic Details

Main Authors:	Franco-Navarro, Juan D., Cubero Font, Paloma, Rosales Villegas, Miguel Á., Rivero, Carlos, Díaz-Rueda, P., Espartero, Joaquín, Colmenero Flores, José M.
Other Authors:	European Commission
Format:	comunicación de congreso biblioteca
Published:	Sociedad Española de Fisiología Vegetal 2016-09-25
Online Access:	http://hdl.handle.net/10261/158847 http://dx.doi.org/10.13039/501100000780 http://dx.doi.org/10.13039/501100004837
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