Soluble sugars maintain redox homeostasis and accelerate the growth of cultured Malva neglecta cells under 2D-clinorotation

Abstract

In addition to their nutritional role, carbohydrates play essential roles in metabolism, growth, development, and response to the environment. In the present study, the effects of clinorotation on structural and soluble sugar metabolism and the redox system were investigated in cultured Malva neglecta cells. A rapidly growing cell line was established from leaf explants of M. neglecta on a solidified LS medium, and the cells were exposed to 2D-clinostat for 7 days. Clinorotation significantly increased monosaccharide content, including glucose, fructose, rhamnose, mannose, and xylose, while reducing sucrose levels compared to control groups. The activities of pectin methylesterase (PME) and β-1, 3-glucanase increased, whereas those of covalently wall-bound peroxidase (CPO) and polyphenol oxidase (PPO) decreased. This reduction, along with a decrease in callose, cellulose, and phenolic acid content, likely accelerated cell growth by reducing cell wall crosslinking and stiffness. The content of reactive oxygen/nitrogen species i.e., hydrogen peroxide (H₂O₂), hydroxyl radical (^.OH), and nitric oxide (NO) radicals significantly decreased in response to clinorotation compared with 1g-grown cells. Hierarchical cluster analysis revealed a strong negative correlation between NO and catalase (CAT) activity. The observed decrease in these oxidants can be attributed, at least in part, to the increased content of soluble sugars through the oxidative pentose-phosphate pathway or tricarboxylic acid cycle (TCA), and more significantly, to the enhancement of catalase activity and flavonoid content.