Abstract
Problem statement: The chitosan derivatives promote diverse defensive responses in plants, which are affected by chitosan chemical fea tures and concentration. Glucanase (EC 3.2.1.6), Phenylalanine Ammonia-Lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.6) are key enzymes in tobacco defense responses. Thus, the aim of this study was to know the behavior of their enzymatic activity in leaves and roots of whole tob acco plants, previously elicited with chitosan derivatives of different molecular weight and acety lating degree. Approach: 25 day-old tobacco plants were treated with three chitosan derivatives (CH- 6 3, CH-88 and OLG) of different chemical features. True leaves and roots were sampled after three, six , nine and 12 days post-treatment for further evaluation of the enzymatic activities. Results: Chitosan treatments increased the activity of all three studied enzymes depending on the concentration and chemical feature of the derivative. The highest enzymatic activities with polymers occurred at 1 g L -1 while the oligochitosan mixture achieved good enzymatic levels as compared to controls from 0.1 g L -1 onwards. The Degree of Acetylation (DA) affected PAL activity; a more acetylated polymer in duced a higher activity than a less acetylated one. However, the low levels of acetylation favored POD activity. The systemic induction of enzymatic activities was detected in leaves of treated plants after root application. The effect of the acetylat ion degree was systemically transmitted to the leaves b y POD, but not by PAL activity; so the transmission of the acetylating degree influence beyond the tiss ue directly elicited by chitosan polymer depended o n each enzymatic response tested. Conclusion: This study proved that various chitosan derivative s induced and raised lasting β-1,3-glucanase, PAL and POD activities in tobacco l eaves and roots as local or systemic responses, which could lead to th e accumulation of secondary metabolites and formation of barriers that all together enhance pla nt resistance against pathogens.
Highlights
Plants respond to pathogen attack with a complex set of preformed structures and inducible reactions
Defensive enzymes induced in roots and leaves of tobacco plants treated by chitosan derivatives of different molecular weight and acetylating degree
No enzymatic activity different from control was obtained with any of the tested concentrations from the less acetylated polymer, which proves an effect of the acetylating degree in favor of more activity increments with the more acetylated polymer in roots (Fig. 2)
Summary
Plants respond to pathogen attack with a complex set of preformed structures and inducible reactions. The inducible reactions require the perception of primary signal molecules from plant and fungal cell wall released in the pathogenesis process and recognized by plant cell membranes. This recognition triggers a wide range of plant enzymatic and chemical arsenal that attacks and degrades pathogen cell wall, removing. Sci., 4 (3): 192-200, 2009 oligosaccharides from this structure The recognition of these exogenous oligosaccharides by the plant is known to amplify defensive signals as well as the number and magnitude of its responses against the pathogen[1,2]
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