International Journal of Horticulture, 2025, Vol.15, No.5, 218-233 http://hortherbpublisher.com/index.php/ijh 221 3 Cell Wall Structure and Texture Formation 3.1 Composition of cell wall polysaccharides: cellulose, hemicellulose, pectin Cellulose, hemicellulose and pectin each play their own role in the sugarcane cell wall, and together determine the mechanical properties and degradability of the cell wall. The cellulose content directly affects the stiffness of the stalk - the more and denser the cellulose microfibrils, the greater the tensile and shear strength of the cell wall, and the tougher and harder the tissue is to chew (Liu et al., 2024). Hemicellulose (mainly arabinoxylan) fills the pores between cellulose microfibrils and cross-links with them. Its presence increases the rigidity of the cell wall, but also reduces the degradation efficiency of the fiber in chemical pretreatment and enzymatic hydrolysis. Lignin is deposited on the cellulose-hemicellulose network, making the cell wall hydrophobic and stronger, and plays a "gluing" and reinforcement role on the cell wall (Buckeridge et al., 2019). The degree of lignification of sugarcane stalks gradually increases during maturity, and the wall thickness increases. Although this improves the ability to resist lodging, it increases the chewing resistance of the stem meat fiber. Therefore, sugarcane is usually harvested at the right time of maturity when lignification is not too serious, so as to take into account both sugar content and texture (Chen et al., 2022). Pectin in the primary wall also affects the softness of the texture. Pectin is composed of polygalacturonic acid as the main chain, and its degree of esterification and cross-linking determines the hardness of the middle layer of the cell wall: highly methylated pectin chains are soft and sticky, which is conducive to intercellular adhesion; after demethylation by pectin methylesterase, pectin is easily cross-linked with calcium ions to form an "egg box" structure, making the middle layer hard and brittle. Some fresh sugarcane varieties may have a higher degree of pectin methylation, so the intercellular binding force is moderate, and it is neither too loose nor too hard and brittle when chewing. These hypotheses still need further experimental verification, but from the research on other fruit tissues, pectin modification does play an important role in the softness and hardness of the taste (Tipu and Sherif, 2024). 3.2 Lignin biosynthesis and its influence on chewing resistance Lignin content is considered to be one of the key factors affecting the chewing difficulty of sugarcane stalks. High-fiber and high-lignin stalks are often thick and hard, making them difficult to chew and break; while low-lignin tender stalks are easy to chew into dregs. Plants enhance mechanical strength to resist adverse environments by regulating the content of cellulose, hemicellulose and lignin in cell walls. Comparisons between sugarcane varieties show that fiber content (mainly representing the total amount of cellulose and lignin) is significantly positively correlated with stalk toughness, that is, varieties with high fiber content have harder stalks, more chewy and less likely to be chewed. Therefore, reducing lignin synthesis is a potential way to improve the texture of sugarcane. Genetic engineering intervention has proved this: using site-directed mutagenesis technology to knock out the key gene caffeic acid-O-methyltransferase (COMT) in sugarcane lignin synthesis can reduce the lignin content of transgenic sugarcane by about 20%, while increasing the sugar accumulation level, and even increasing the enzymatic saccharification rate of fiber raw materials by more than 40%. More importantly, this lignin-reduced sugarcane mutant did not show obvious growth defects or yield reduction in the field, indicating that moderate reduction of lignin can soften the stem without compromising the mechanical strength of the plant, providing a genetic target for improving the texture of sugarcane (Kannan et al., 2018). In addition to regulating lignin content through genetic means, agricultural measures can also affect the degree of stem lignification. For example, silicon can be deposited in the cell wall of sugarcane stems to form siliceous bodies, thereby improving the lodging resistance and insect resistance of the stems. Adding silicon fertilizer often makes the stem wall thicker and harder, which is beneficial for sugarcane but not for the texture of fresh sugarcane, and needs to be weighed in cultivation (Wang et al., 2020). Reducing the relative content of lignin and cellulose and optimizing the composition of cell walls are one of the important ideas for improving the chewability of sugarcane. In actual breeding, by screening materials with weaker lignin synthesis or using molecular means to inhibit the expression of some lignin pathway genes, new sugarcane varieties with softer fibers and easier chewing may be obtained.
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