PLANT CELL WALL NANO-SCALE STRUCTURE AND ITS IMPLICATION IN DETERMINING ORGANIC MATTER RECALCITRANCE IN SOIL AND BIOFUEL PRODUCTION

The work presented in this PhD Thesis aims to investigate the nature of the recalcitrance of plant tissues, i.e the natural resistance of plant cell walls to biodegradation, because despite extensive researches, a purely mechanistic root to recalcitrance phenomenon is still missing. The work started from the idea that biochemical catalyses are limited in their actions because of the complex macroscopic and, above all, microscopic structures of cell wall, that limit mass transportation. The studies were conducted by taking in consideration the role of recalcitrance in two specific contexts. The first context is strongly related to soil because of the important role of recalcitrance in short-term soil organic matter turnover as condition for the maintenance of soil quality. The results indicated that the nature of recalcitrance is greatly dependent upon the ultra-structural distribution of macromolecules characterizing plant tissues. In particular, we showed that the ultra-structure of plant cell wall influenced its degradability in soil and that physical structure at nanometer scale (i.e micropore surface area) constitutes an important factor in determining the biochemical recalcitrance. Secondly, we studied the nature of recalcitrance related to enzymatic hydrolysis of cellulose to produce glucose for biofuel production. The results, in agreement with those reported in the first part of work, indicated that recalcitrance was due to the three-dimensional (3D) structure of the cell wall that determines the presence of microporous “sheath” structure and therby modulating enzymes penetration in the cell wall.