 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 496 DOI: 10.1002/jpln.201000075 J. Plant Nutr. Soil Sci. 2011, 174, 496–503 Phenol-containing organic substances stimulate phenylpropanoid metabolism in Zea mays Andrea Ertani 1 , Michela Schiavon 1 , Adriano Altissimo 2 , Clizia Franceschi 3 , and Serenella Nardi 1 * 1 Department of Agricultural Biotechnology, University of Padova, Agripolis, viale dell’Università 16, 35020 Legnaro, Italy 2 Landlab Associated Office, via Quintarello 12/A, 36050 Quinto Vicentino, Vicenza, Italy 3 R&S ILSA S.p.A., via Quinta Strada 28, 36071 Arzignano, Vicenza, Italy Abstract Intensive land use may affect soil properties (e.g., decreased soil organic matter [SOM] content) and, consequently, reduce crop yields considerably. One way of counteracting the loss of SOM and stimulating plant productivity could be the use of organic residues from agro-industrial pro- cesses as bioactive products. The present study was focused on the possible effects of phenol- containing organic substances derived from agro-industrial by-products on maize (Zea mays L.) metabolism in a pot experiment. Plants were grown for 12 d in a nutrient solution in the absence (control) or in the presence of either a cellulosolitic dry apple hydrolyzate (AP) or a dry blueberry cool extract (BB) applied at two rates (0.1 and 1 mL L –1 ). Both products increased root and leaf biomass and led to higher concentrations of macronutrients in the plant tissue. AP and BB also had a positive impact on nitrogen (N) metabolism stimulating the activity and gene expression of phenylalanine ammonia-lyase, a key enzyme of the phenylpropanoid pathway. Furthermore, both products increased leaf concentrations of phenols (+ 28% and 49% for AP and BB, respec- tively) and flavonoids (+ 22% and 25% for AP and BB, respectively). From our results it can be assumed that residues from agro-industry may be successfully used as bioactive products in agriculture to increase plant yield and resistance to stress conditions. Key words: bioactive substances / flavonoids / gene expression / phenols / phenylalanine ammonia-lyase (PAL) Accepted March 21, 2011 1 Introduction The intensive cultivation of land (e.g., monocropping, soil til- lage) might affect soil quality due to a reduced content of soil organic matter (SOM; Francioso et al., 2000). To counteract SOM losses and improve crop yields, the application of man- ure or other organic amendments to soils has been progres- sively introduced in agricultural practices (Glaser et al., 2002). The addition of selected organic residues from agro- industry to soil is a further strategy to increase SOM and, at the same time, presents a solution for reducing organic- waste disposal (Akavia et al., 2009). Agro-industrial residues often contain bioactive molecules, including antioxidants (Schieber et al., 2001; Balasundram et al., 2005), which could be exploited by farmers to improve crop productivity (da Silva et al., 2008). In such a case, these components can be referred to as biostimulant compounds. Basically, biostimu- lants function as positive growth regulators at low doses by enhancing plant nutrition and metabolism (Chen et al., 2003; Schiavon et al., 2008, 2010; Ertani et al., 2009; Khan et al., 2009). Furthermore, the use of such compounds might lead to reduced nitrogen-application levels (Russo and Berlyn, 1991) and increase the resistance of plants to multiple abio- tic-stress factors such as heat, drought, and salinity (de Vas- concelos et al., 2009). Biostimulants are commercially avail- able in different formulations and are generally classified into three major groups on the basis of their original matrix: humic substances, marine bioactive substances, and amino acid– containing products (Kauffman III et al., 2007). Although several authors have reported the beneficial effects of biostimulants on plants (Chen et al., 2003; Parrado et al., 2008; Ertani et al., 2009; Rayorath et al., 2008; Schiavon et al., 2008, 2010), the physiological and molecular mechan- isms through which such compounds act are to a certain degree unknown. Schiavon et al. (2008) showed that an alfalfa-based biostimulant promoted plant growth and nitro- gen assimilation by inducing a tightly coordinated regulation of the carbon and nitrogen metabolic pathways at the level of both gene expression and enzyme activity. Another recent study suggests that active molecules in biostimulants could enhance plant defense against stress through the induction of secondary metabolism, leading to the synthesis of pheno- lics (Schiavon et al., 2010). Therefore, a pot trial with maize was conducted to test the performance of a cellulosolitic dry apple hydrolysate (AP) and a dry blueberry cool extract (BB) on plant growth and on nitro- gen and phenylpropanoid metabolic pathways. * Correspondence: Dr. S. Nardi; e-mail: serenella.nardi@unipd.it