Cellulose in secondary xylem of Cactaceae: crystalline composition and anatomical distribution

Abstract Cellulose is the main polymer that gives strength to the cell wall and consists of crystalline-microfibrils and amorphous-matrix cellulose located in the primary and secondary cell walls of the plants. In the Cactaceae family, there are studies on the composition of lignin but not on the crystallinity of cellulose. Therefore, the objective of his work is to analyze the crystallinity composition and distribution of cellulose in the cells of the xylem tissue. Twenty-five species of Cactaceae were collected, dried, and milled. The extractives were removed until obtaining extractive-free wood. Subsequently, cellulose was purified, readings with Fourier transform infrared spectroscopy were made, the crystallinity indexes were calculated and statistical analyzes were performed to identify differences between species. In addition, for the anatomical analysis of wood, stem sections for each plant were fixed, cut, and stained with safranin O / fast green to observe under epifluorescence microscopy. The results showed that crystalline cellulose ratios had statistically significant differences between Echinocereus pectinatus and C. pallida. All cacti species had a higher proportion of crystalline cellulose in the Total crystalline index and Hydrogen bond intensity except for E. pectinatus in the latter. The fluorescence emission of cellulose in all species was red, the distribution of cellulose in non-fibrous species was in the primary wall; while in the fibrous species, the distribution was in the internal walls and the pits. The high percentages of crystalline cellulose may be related to its distribution in the non-lignified parenchyma and primary walls of tracheary elements with helical or annular thickenings of non-fibrous species, possibly offering structural rigidity and as part of the defense system against pathogens.