Abstract

INTRODUCTION Barley (Hordeum vulgare) is highly consumed due to energetic and nutritional content, including phenolic compounds with antioxidant action (Newman and Newman 2006). However, the acidic conditions of soils and presence of toxic aluminum (Al) are important growth-limiting factors for plants (Cartes et al., 2012). It has been demonstrated that silicon (Si) attenuates Al toxicity, as well promotes the production of phenolic compounds, such as lignin (Maksimovic et al., 2007). The aim of this research was to evaluate Si uptake, lignin accumulation and yield at different growth stages of barley under Al stress. METHODS A field experiment was conducted on an acid Andisol of Southern Chile by using barley (cv. Sebastian and Scarlet) fertilized with Si at increasing doses (0, 250, 500 mg Si/kg soil) in combination of lime supply (0 or 1000 mg CaCO3/kg). At harvest, yield parameters, Si and Al concentration of shoots were determined on samples in three different growth stages (tillering, anthesis and mature grain). In addition, changes in lignin accumulation in leaves of both cultivars were visualized by laser scanning confocal microscopy (CLSM) for all vegetative stage. RESULTS AND DISCUSSION Silicon accumulation in the shoots has been related to a number of factors (transpiration,growth duration, growth rate) but root uptake ability is the most important factor for determining Si accumulation in the shoots (Takahashi et al., 1990). In our study, Si concentration in plants increased progressively when Si was applied and even more in combination with lime in the most vegetative stages. The highest Si concentrations were presented at the last vegetative stage (mature grain). Moreover, the Si concentration in grains is increased in both cultivars when Si was applied alone or in combination with lime with respect to control. However, Al concentration in shoots was decreased in Si and Si-lime treatment in all vegetative stages. In the other hands, Sebastian grain yield was increased by Si application independent from dose and combination with lime. Nevertheless, only Scarlet grain yield was increased 500 kg ha-1 Si was applied. Conversely, protein was decreased by either Si or Si-lime treatment in both cultivars compared with control. Lignin is a phenolic polymer usually derived from phenylalanine. It serves as a matrix of some plant cell walls, providing stiffness and compressive strength (Boerjan et al., 2003). Some studies in plants treated with different Si sources have demonstrated a Si-relieving effect due to stimulation of lignin production under stress conditions (Filha et al., 2011; Zhang et al. 2013). In our study, lignin content displayed by Sebastian and Scarlet cultivars was different for the three harvest times (tillering, anthesis and madure grain), with a higher accumulation in the state of madure grain. On the other hand, both cultivars had higher lignin content in leaves of plants fertilized with Si (250 or 500 kg ha-1), which was even more evident in the combined treatment with lime. This is the first work to study the effect of Si in different growth stages and grains of plants on Al stress. Therefore more studies are need to clarify the information. CONCLUSIONS Silicon supply increased Si concentration in plants of barley cultivars, whereas Al concentration in plants was diminished by Si application, thus attenuating Al toxicity in barley, improving lignin accumulation and yield parameters. ACKNOWLEDGEMENTS FONDECYT projects 1120901 and 1161326, and Convenio de Desempeño Doctoral Scholarship.