Cellular debris, not mucilage polysaccharides, dominate extracts of Plantago ovata and Plantago lanceolata calli grown in vitro

Mucilage is a hydrophilic mixture of polysaccharides produced by seeds of many species, and used in research, industrial processes and as human health supplements. As such, demand often outweighs supply. In recent years, several researchers have reported that mucilage can be produced efficiently from in vitro-cultured calli as a direct plant-less alternative to seed mucilage; however, this mucilage has not been rigorously characterised. Here we replicate previously published culturing and extraction procedures and couple them with compositional analysis to determine whether the mucilage produced from Plantago ovata and P. lanceolata calli are similar to seed mucilage. Our monosaccharide profiling and microscopy show that, while calli derived from either seedling hypocotyls or roots yield more material than seeds using the same extraction techniques, the majority of extract mass is cellular debris. Debris polysaccharide composition was significantly different to seed mucilage from both species. Plant tissue culture as an alternative source of high yields of useful mucilage polysaccharides, at least by these and similar methods, is likely to not be possible.