Effects of an Alfalfa Protein Hydrolysate on the Gene Expression and Activity of Enzymes of the Tricarboxylic Acid (TCA) Cycle and Nitrogen Metabolism in Zea mays L.

Abstract

The effects through which an alfalfa protein hydrolysate (EM) possessing gibberellin- and auxin-like activity may promote plant nitrogen (N) nutrition have been investigated in Zea mays L. Treatment with 0.01 or 0.1 mg L(-1) EM for 48 h resulted in enhanced plant growth and leaf sugar accumulation. Concomitantly, the level of nitrates decreased, whereas total N percentage was unchanged. The activity of a number of enzymes involved in carbon (C) metabolism (malate dehydrogenase, MDH; isocitrate dehydrogenase, IDH; citrate synthase, CS) and N reduction and assimilation (nitrate reductase, NR; nitrite reductase, NiR; glutamine synthetase, GS; glutamate synthase, GOGAT; aspartate aminotransferase, AspAT) was significantly induced by EM supply to plants, and the transcription pattern of MDH, IDH, CS, and NR strongly correlated with data of enzyme activity. The transcript accumulation of asparagine synthetase (AS) was also induced by EM in the roots. The results suggest that EM might promote nitrogen assimilation in plants through a coordinate regulation of C and N metabolic pathways and open the way for further research on protein hydrolysates as a valid tool to improve N use efficiency and, as a consequence, to reduce the intensive use of inorganic N fertilizers in agriculture.

Agricultural uses of plant biostimulants

“…(Kunicki et al 2010) and Gajc-Wolska et al (2012) found no effect of Aminoplant (Siapton) on yield of spinach (Spinacia oleracea) and endive (Chicorium pumilum), respectively, in field trials and (Grabowska et al 2012) showed an effect on carrot (Daucus carota) yield only for one variety in one year of three years of field trials and soluble sugars and carotenoids increased and nitrate content decreased in Aminoplant-treated carrot roots relative to the control in one year of two field trials. An alfalfa hydrolysate increased leaf growth, foliar sugar content and decreased nitrate content of hydroponically-grown maize plants (Schiavon et al 2008) and in more recent studies, enhanced short-term growth of hydroponically-grown maize in the absence and presence of salt stress (NaCl) (Ertani et al 2013b). It also increased K + content of leaves in the absence of NaCl and in the presence of NaCl, enhanced Na + and decreased K + contents in roots and leaves (Ertani et al 2013b).…”

“…Maini (2006) summarized the early literature showing enhanced activity of NAD-dependent glutamate dehydrogenase, nitrate reductase and malate dehydrogenase in maize following application of Siapton. These results were expanded upon by (Schiavon et al 2008) who showed that an alfalfa protein hydrolysate applied to hydroponically-grown maize increased the activity of three enzymes in the tricarboxylic acid cycle (malate dehydrogenase, isocitrate dehydrogenase and citrate synthase) and five enzymes involved in N reduction and assimilation (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase and aspartate aminotransferase). Increased gene expression of the three TCA cycle enzymes, nitrate reductase and asparagine synthetase was confirmed by RT-PCR in the roots following application of alfalfa hydrolysate.…”

“…Protein hydrolysates are prepared by enzymatic, chemical or thermal hydrolysis of a variety of animal and plant residues, including animal epithelial or connective tissues (Cavani et al 2006;Ertani et al 2009Ertani et al , 2013aGrabowska et al 2012;Kauffman et al 2007;Kunicki et al 2010;Maini 2006;Morales-Payan and Stall 2003), animal collagen and elastine (Cavani et al 2006), carob germ protein (Parrado et al 2008), alfalfa residue (Schiavon et al 2008;Ertani et al 2009Ertani et al , 2013b, wheat-condensed distiller solubles (García-Martínez et al 2010 Protein/peptide and free amino acid contents of the hydrolysates vary in these preparations in the range of 1-85 % (w/w) and 2-18 % (w/w), respectively. The major amino acids include alanine, arginine, glycine, proline, glutamate, glutamine, valine and leucine (Parrado et al 2008;Ertani et al 2009;García-Martínez et al 2010).…”

“…For example, in addition to proteins, peptides and free amino acids, carob germ extract hydrolysate contained fats, carbohydrates, macro and micronutrient elements and at least six phytohormones, while an animal-based product, Siapton had a similar profile of proteins, amino acids, fats and macro and micronutrients, but lacked carbohydrates and phytohormones (Parrado et al 2008). An alfalfa hydrolysate was high in free amino acids (1.9 % w/w) and also contained macro and micronutrient elements and auxin-and gibberellin-like activities based on a bioassay (Schiavon et al 2008). (Ertani et al 2013a) reported the presence of triacontanol and IAA, both plant growth regulators, in the same alfalfa hydrolysate product and endogenous IAA in a meat hydrolysate (Ertani et al 2013b).…”

“…The application of new analytical and molecular tools and carefully controlled studies are providing further insight into the composition of protein hydrolysates and evidence for their ability to stimulate plant growth and enhance resistance to a variety of abiotic stresses (Schiavon et al 2008;Ertani et al 2013a, b;Corte et al 2014). Studies with individual amino acids found as components of hydrolysate preparations lend further support to these claims and offer insights into their activity as signaling molecules, regulators of C and N metabolism, and inducers of plant defense responses to stress (Sharma and Dietz 2006;Forde and Lea 2007;Ahmad et al 2013;Liang et al 2013).…”