Aluminum (Al) toxicity is one of the main growth and yield limiting factors for barley grown on acid soils. Silicon (Si) ameliorates Al toxicity as well as it promotes the phenolic compounds production that have antioxidant or structural role. We evaluated the time-dependent kinetics of Al and Si uptake and the impact of Si on the production of antioxidant- or structural- phenols in barley cultivars at the short-term. Two barley cultivars with contrasting Al tolerance (Hordeum vulgare ‘Sebastian’, Al tolerant; and H. vulgare ‘Scarlett’, Al sensitive), exposed to either −Al (0 mM) or +Al (0.2 mM) nutrient solutions without Si (−Si) or with 2 mM (+Si) were cultured for 48 h. Aluminum and Si concentration decreased in plants at all harvest times when Al and Si were simultaneously supplied; this effect was more noticeable in ‘Scarlett’. Nevertheless, Si influenced the antioxidant system of barley irrespective of the Al tolerance of the cultivar, decreasing oxidative damage and enhancing radical scavenging activity, the production of phenolic compounds, and lignin accumulation in barley with short-term exposure to Al.

Silicon (Si) exerts beneficial effects in mitigating aluminum (Al) toxicity in different plant species. These include attenuating oxidative damage and improving structural strengthening as a result of the increased production of secondary metabolites such as phenols. The aim of this research was to evaluate the effect of Si on phenol production and composition in two barley cultivars under Al stress. Our conceptual approach included a hydroponic experiment with an Al-tolerant (Sebastian) and an Al-sensitive (Scarlett) barley cultivar treated with two Al doses (0 or 0.2 mM of Al) and two Si doses (0 or 2 mM) for 21 days. Chemical, biochemical and growth parameters were assayed after harvest. Our results indicated that the Al and Si concentration decreased in both cultivars when Al and Si were added in combination. Silicon increased the antioxidant activity and soluble phenol concentration, but reduced lipid peroxidation irrespective of the Al dose. Both barley cultivars showed changes in culm creep rate, flavonoids and flavones concentration, lignin accumulation and altered lignin composition in Si and Al treatments. We concluded that Si fertilization could increase the resistance of barley to Al toxicity by regulating the metabolism of phenolic compounds with antioxidant and structural functions.

No abstract

Although silicon (Si) and lignin are accumulated on plant cell walls and both confer resistance to multiple biotic and abiotic stresses [1,2], the impact of Si on lignin production in plants grown under phosphorus (P) stress still remains unknown. We evaluated the effect of Si on the lignin accumulation pattern and expression of lignin biosynthesis-related genes in wheat plants grown at different P levels. Two wheat cultivars differing in tolerance to P deficiency (Púrpura-sensitive and Fritz-tolerant) were hydroponically grown in a continuously aerated nutrient solution, as proposed by [3]. Ten days later, plants were treated with P (0, 0.01 or 0.1 mM) in combination with Si (0, 1 or 2 mM). Twenty-one days after the initiation of treatments, plants were harvested and lignin concentration, the lignin distribution pattern and the gene expression of phenylalanine ammonia lyase (TaPAL) and cinnamyl alcohol dehydrogenase (TaCAD) were analyzed in shoots. The lignin concentration of both wheat cultivars did not vary at different P doses; nevertheless, 2 mM Si increased lignin accumulation mainly at either 0 mM P (cv. Púrpura) or 0.01 mM P (cv. Fritz), with a more noticeable effect in Púrpura than in Fritz. This increase was in agreement with the stronger intensity of Safranine O staining observed after Si was added to both cultivars grown at sufficient or deficient P levels and supports previous findings showing the alleviative role of Si by increasing lignin production under stressful conditions [4,5,6,7,8]. Such an effect may be related to either increased hydrogen peroxide production or peroxidase activity in cell walls, as well as to the modulation of the activity and/or gene expression of some key enzymes involved in lignin biosynthesis. In this way, we also found that Si induced the expression of lignin biosynthesis genes. The up-regulation of TaPAL was detected in cv. Púrpura grown at low P levels, with a further increase observed in plants treated with Si. Similar to Si addition to P-stressed plants of cv., Fritz caused a 1.5-fold increase in the transcript level of TaPAL. Similarly, the expression level of TaCAD increased 1.7-fold as a result of the Si supply to both cultivars grown at low P. Overall, our results show that Si induced the biosynthesis of lignin in shoots of wheat plants grown under P stress. Acknowledgments. FONDECYT Regular Project N° 1201257 and FONDECYT Postdoctoral Project N° 3200901.

No abstract