Involvement of lignin deposition and cell wall degradation in stem senescence of Chinese flowering cabbage during storage.

Chinese flowering cabbage is susceptible to leaf yellowing, however, little is known about stem senescence after harvest. Herein, changes in the microstructures, lignin and cell wall polysaccharide contents, and expression of their corresponding genes during the stem senescence of Chinese flowering cabbage were investigated. Anatomical and chemical analyses revealed that an increase in cell wall thickness was accompanied by lignin deposition around the vascular cells in the stem. Concurrently, the collapse of parenchyma cells developed gradually, which was probably related to the degradation of cell wall polysaccharides including pectin, hemicellulose, and cellulose, among others. The outer stem tissues, including epidermal cells to vascular cells, could be directly peeled, and the middle of the stem was found to contain prominent parenchyma cells as pith tissues. Activity of lignin biosynthesis-related enzymes of phenylalanine ammonia lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD), and the expression of their corresponding genes BrPAL2/3/6, Br4CL1/4...