Effect of a Peat Humic Acid on Morphogenesis in Leaf Explants of Pyrus communis and Cydonia oblonga. Metabolomic Analysis at an Early Stage of Regeneration

Plant regeneration is a critical step in most in vitro breeding techniques. The present paper studies the 21 effects of a low-molecular-weight humic acid (HA) on morphogenesis from pear and quince leaf 22 explants. Variable HA amounts [0 (control), 1, 5, 10 and 20 mg C L-1] were added to the regeneration 23 media. A dose-response effect was observed in pear for root and shoot production; it was improved at 24 HA 1 mg C L-1 and considerably reduced at the highest amounts. HA was, instead, ineffective in 25 quince. The 1H HR-MAS NMR analyses of calli in the induction phase showed more evident 26 metabolite (asparagine, alanine and γ-amino butyric acid) signals in quince than pear. The assignment 27 of overlapped signals in both genotypes were supported by the 2D NMR analyses. Spectroscopic 28 characterization suggested also an enhancement of asparagine contents in morphogenic calli of pear 29 with respect to the control and higher HA amount treatments.