Differences in the Structural Chemical Composition of the Primary Xylem of Cactaceae: A Topochemical Perspective

Abstract

The xylem of Cactaceae is a complex system with different types of cells whose main function is to conduct and store water, mostly during the development of primary xylem, which has vessel elements and wide-band tracheids. The anatomy of primary xylem of Cactaceae has been widely studied, but little is known about its chemical composition. The aim of this study was to determine the structural chemical composition of the primary xylem of Cactaceae and to compare it with the anatomy in the group. Seeds from eight cacti species were used, representing the Pereskioideae, Opuntioideae, and Cactoideae subfamilies. Seeds were germinated and grown for 8 months. Subsequently, only the stem of the seedling was selected, dried, milled, and processed following the TAPPI T-222 om-02 norm; lignin was quantified using the Klason method and cellulose with the Kurshner–Höffer method. Using Fourier transform infrared spectroscopy, the percentage of syringyl and guaiacyl in lignin was calculated. Seedlings of each species were fixed, sectioned, and stained for their anatomical description and fluorescence microscopy analysis for the topochemistry of the primary xylem. The results showed that there were significant differences between species (p < 0.05), except in the hemicelluloses. Through a principal component analysis, it was found that the amount of extractive-free stem and hot water-soluble extractives were the variables that separated the species, followed by cellulose and hemicelluloses since the seedlings developed mainly parenchyma cells and the conductive tissue showed vessel elements and wide-band tracheids, both with annular and helical thickenings in secondary walls. The type of lignin with the highest percentage was guaiacyl-type, which is accumulated mainly in the vessels, providing rigidity. Whereas in the wide-band tracheids from metaxylem, syringyl lignin accumulated in the secondary walls S2 and S3, which permits an efficient flow of water and gives the plant the ability to endure difficult conditions during seedling development. Only one species can be considered to have paedomorphosis since the conductive elements had a similar chemistry in primary and secondary xylem.

Distribution and Chemical Composition of Lignin in Secondary Xylem of Cactaceae

“…Other compounds were detected by this technique located in the phellem of C. pentandra ( Figure S2 , C ), the presence of channels with autofluorescent compounds in blue and green tones corresponded to terpenes and flavonoids, [16] whose presence in the cortex has been reported for this species [34] . Finally, the fluorescence emission in cyan tones of starch granules in P. chrysacanthus was similar to that reported by Maceda et al [13] . in seedlings of L. lychnidiflora , therefore, the combination of this conventional staining method with epifluorescence allowed to identify the presence of starch granules in plant tissues.…”

“…Epifluorescence microscopy: The fluorescence of the analyzed tissues can vary depending on the sample preparation such as pH or concentration of the reagents, the thickness of the tissue, the presence or absence of autofluorescence of the components, the interaction between dyes, and the excitation wavelengths. [14,16] Therefore, in order to make qualitative comparisons of the different species analyzed, this staining was based on the results obtained by De Micco and Aronne [15] and Maceda et al [13] with safranin O/fast green combined with epifluorescence microscopy, as mentioned below.…”

“…When comparing epifluorescence with bright-field microscopy (Figure 2 -4), the results obtained with the safranine O/fast green staining method were of better quality and allowed to identify in detail the differences in the composition of the xylem cells, similar to that reported by different authors. [13,15,30] De Micco and Aronne [15] proposed that the use of safranin O/fast green staining allowed the detection of both the fluorescence of lignin caused by the staining and its autofluorescence, blue tones were related to the presence of syringyl/guaiacyl, while tones close to red could be related to the presence of guaiacyl. [15] Similarly, Bond et al [17] mentioned that fluorescence emission caused by safranin O staining occurred in the range of 488 to 568 nm and Angeles et al [30] detected the lignin fluorescence in the range of 505 to 530 nm with the same staining method.…”

“…The first studies on the chemical composition of Cactaceae stems focused on Opuntia ficus-indica due to its importance in human consumption, [10] as fodder, [11] and more recently, its potential in the paper industry. [12] The chemical composition of secondary [4,5] and primary xylem [13] has been calculated for some species belonging to Pereskioideae, Opuntioideae, and Cactoideae subfamilies.…”

Anatomy, Flow Cytometry, and X-Ray Tomography Reveal Tissue Organization and Ploidy Distribution in Long-Term In Vitro Cultures of Melocactus Species

“…Wide-band trachieds are a special type of tracheid with no perforations on their walls but instead possessing rigid secondary thickening bands ( Mauseth, 1999 ). A region of WBTs was reported in several species of cacti, including in Melocactus zehntneri and Melocactus bahiensis ( Mauseth et al, 1995 ; Mauseth and Plemons-Rodriguez, 1997 ; Mauseth, 1999 ; Stone-Palmquist and Mauseth, 2002 ; Arruda et al, 2004 ; Mauseth, 2004 ; Arruda et al, 2005 ; Mauseth, 2006 ; Melo-de-Pinna et al, 2006 ; Vázquez-Sánchez et al, 2007 ; Arruda and Melo-de-Pinna, 2010 ; Terrazas et al, 2016 ; Reyes-Rivera et al, 2018 ; Maceda et al, 2019 ). The paucity of support elements ( i.e.…”