How do galactoglucomannan oligosaccharides regulate cell growth in epidermal and cortical tissues of mung bean seedlings?

Biologically active galactoglucomannan oligosaccharides (GGMOs) alone or in combination with IBA stimulate primary root elongation and inhibit hypocotyl elongation in mung bean (Vigna radiata (L.) Wilczek) seedlings. For a more detailed view of GGMOs effect in these processes, the present work is focused on cell growth in selected tissues (epidermis and primary cortex) and on xylem formation. The GGMOs effect on tissue level has not been studied so far. The results show that GGMOs-induced stimulation of primary root growth is mainly caused by enhancing cell elongation (and in less extent by cell production rate) in all tissues observed. Xylem elements were formed at longer distance from the root tip than in the control. In hypocotyl GGMOs reduced cell elongation. IBA in roots caused decrease of cell elongation and cell production rate and acceleration of xylem maturation; in hypocotyls IBA strongly stimulated cell elongation. Application of GGMOs with IBA resulted in increase of cell elongation, cell production rate and delay of xylem maturation in roots. In GGMOs + IBA treated hypocotyls, cell length was decreased to 50% compared to IBA. Based on our results it can be concluded that GGMOs induced elongation growth in mung bean seedlings was caused by increased cell production rate and cell elongation and was accompanied with delay of xylem maturation.