Abundance of mixed linkage glucan in mature tissues and secondary cell walls of grasses.

(1,3; 1,4)-β-D-glucan, also known as mixed linkage glucan (MLG), is a polysaccharide that in flowering plants is unique to the cell walls of grasses and other related members of Poales. MLG is highly abundant in endosperm cell walls, where it is considered a storage carbohydrate. In vegetative tissues, MLG transiently accumulates in the primary cell walls of young, elongating organs. In evolutionary distant species such as Equisetum, MLG accumulates predominantly in old tissues in the stems. Similarly, we have recently shown that rice accumulates a large amount of MLG in mature stems, which prompted us to re-evaluate the hypothesis that MLG is solely related to growth in grass vegetative tissues. Here, we summarize data that confirms the presence of MLG in secondary cell walls and mature tissues in rice and other grasses. Along with these results, we discuss additional evidence indicating a broader role for MLG than previously considered.