Chloride Nutrition: Impact in Plant Development and Water Relations

Abstract

Although Cl- has been characterized as a micronutrient, we have observed that when available in the millimolar range (e.g. 1-5 mM), higher plants accumulate Cl- to levels that are typical of the content of a macronutrient (Plant Cell Env. 2010, 33: 2012-27). Since this requires a considerable cost of energy, we speculate whether Cl- might play a poorly understood function in plants when accumulated to macronutrient levels. Given that Cl- is a major osmotically active solute in the plant vacuole, we propose that this element improves osmoregulatory and plant water relation mechanisms. To elucidate this hypothesis, tobacco plants were grown for 9 weeks with a basal nutrient solution (BS) and subjected to different treatments: 5 mM Clsolution (Cl); 5 mM NO3- (N); and 5 mM SO4 2- and PO33- (SP). Compared to BS and SP plants, chloride nutrition in the millimolar range promoted plant growth in terms of dry weight and total leaf area. This, together with the observation that Cl- was preferentially included in growing and reproductive organs, suggested a role in plant development. In addition, compared to BS, SP and N plants, Cl plants exhibited the best water parameters.