Water-Soluble Lignins from Different Bioenergy Crops Stimulate the Early Development of Maize (Zea mays, L.)

Abstract

Abstract:The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by 31 P-NMR and 13 C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S-and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries.

Quantitative Structure-Activity Relationship of Humic-Like Biostimulants Derived From Agro-Industrial Byproducts and Energy Crops

“…Finally, CAR favored the largest coleoptile length, followed by MG and AD, whereas BYP 1, BYP 2, RIP, and LIM had the least effect. As for the other parameters, EUC addition did not significantly affected plant development compared to the control (Table 1) (Savy et al, 2015a).…”

“…Briefly, an alkaline 2% H 2 O 2 (v/v) aqueous solution (pH 11.6) was added to the lignocellulosic substrates and stirred overnight at 323 K. The mixture was then centrifuged (15,400 RCF x 20 min) and the supernatant dialyzed (1 kDa cut-off dialysis tubes) against deionized water, freeze-dried, and stored in dried conditions for further analyses. The amount of inorganic compounds in the HLS was previously showed to be negligible, i.e., the biostimulant effect observed is conceivably related only to the organic molecules they contained (Savy and Piccolo, 2014;Savy et al, 2015aSavy et al, , 2017b. HLS obtained from cardoon, eucalypt, poplars from Ripiti and Limatola, miscanthus, giant reed and the two biorefinery wastes will be referred to as CAR, EUC, RIP, LIM, MG, AD, BYP 1, and BYP 2, respectively.…”

“…Prior to run the PLS regression, the biological data were normalized with respect to the control mean for each specific experiment, which was set to 100. Furthermore, the models were built by selecting the treatment means that in most cases provided the longest value for the length of primary root, lateral seminal roots, total root system or coleoptile (Savy et al, 2015a(Savy et al, , 2016a(Savy et al, , 2017b. The dataset consisted of a matrix (8 × 20) with the HLS in columns and spectral data or biological parameters in rows.…”

“…For example, the positive bioactivity of HLS isolated by modifying the lignin contained in several agricultural residues or biorefinery wastes have been ascertained on maize (Zea mays L.) germination and early growth (Savy et al, 2015a(Savy et al, , 2016a(Savy et al, , 2017b. Although such HLS materials were not found to significantly promote seed germination percentage, a positive dose-dependent elongation of primary and lateral seminal roots, as well as of coleoptile, was recorded.…”

“…In this work, we derived a QSAR for HLS extracted from lignin-rich agricultural and biorefinery residues, by applying PLS regression to a dataset retrieved from previously published articles, in which both the chemical structure and the biological activity of such plant enhancers were reported (Savy and Piccolo, 2014;Savy et al, 2015aSavy et al, , 2016aSavy et al, , 2017b. In particular, HLS were chemically characterized by both solid-state 13 C-CPMAS and liquid-state 31 P NMR spectroscopy, whereas the HLS bioactivity was evaluated toward maize germination and early growth.…”