Oligosaccharins and Pectimorf® Stimulate Root Elongation and Shorten the Cell Cycle in Higher Plants

The aim was to test promotive effects of oligosaccharins on root growth and development at the root apical meristem and the cell cycle using the model systems, Arabidopsis thaliana and the tobacco (Nicotiana tabacum) BY-2 cell line. Arabidopsis was grown on medium supplemented with 0.1 mg L−1 oligoxyloglucan (OX), 10 mg L−1 Pectimorf® (P) or 0.5 mg L−1 indole butyric acid (IBA). Primary root length, number of lateral root primordia, root apical meristem (RAM) length and epidermal cell length were recorded. Three genotypes were used: wild type (WT) and transgenic lines expressing either Schizosaccharomyces pombe (Sp) cdc25 or over-expressing(oe) Arath;WEE1. All treatments promoted primary root elongation but repressed lateral root production. Only P had a clear positive effect on meristem length whereas all other genotype × treatment interactions showed shorter RAMs. Whilst IBA, OX and P induced an increase in cell length in Spcdc25, the same treatments caused a significant decrease in WEE1 oe . Mitotic indices were also significantly higher in roots treated with oligosaccharins suggesting a shortening of the cell cycle. This hypothesis was tested in the BY-2 cell line. Both OX and P shortened the cell cycle exclusively through a shortening of G1 whilst mitotic cell size remained constant between treatments. In conclusion, both OX and P do indeed stimulate growth and shorten the cell cycle in higher plants and at the cellular level are able to reverse large and small cell size phenotypes normally exhibited by WEE1 oe and Spcdc25 genotypes, respectively.