Biostimulant activity of two protein hydrolyzates in the growth and
nitrogen metabolism of maize seedlings

Andrea Ertani, Luciano Cavani, Diego Pizzeghello, Elena Brandellero, Adriano Altissimo, Claudio Ciavatta, and Serenella Nardi

J. Plant Nutr. Soil Sci. 2009, 000, 1–8

Two protein-hydrolyzate-based fertilizers (PHFs), one from alfalfa (AH) and one from meat flour
(MFH), were studied chemically and biologically. AH and MFH revealed a different degree of
hydrolysis and a different amino acid composition. The biostimulant activity was investigated
using two specific and sensitive bioassays of auxins and gibberellins. Extracts of AH and MFH
elicited a gibberellin-like activity and a weak auxin-like one. To improve our understanding of the
biostimulant activity, AH and MFH were supplied to maize plants and their effect on growth and
nitrate metabolism was studied. Both PHFs increased root and leaf growth and induced morphological changes in root architecture. Besides, the treatments increased nitrate reductase (NR)
and glutamine synthetase (GS) activities, suggesting a positive role of the two hydrolyzates in
the induction of nitrate conversion into organic nitrogen. Moreover, treatments enhanced GS1
and GS2 isoforms in maize leaves. The latter isoform, amounting to 5- to 7-fold the level of the
former, appears to be a superior form in the assimilation of ammonia. The high NR and GS activities together with the high induction of GS isoforms indicate a stimulatory effect of the two PHFs
on the assimilation of nitrate. In addition, a role of amino acids and small peptides of the two
PHFs is suggested in the regulation of the hormone-like activity and nitrogen pathway.


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