Paclobutrazol and xanthan gum involvement in proliferation and stress response of ornithogalum dubium houtt. bud clusters cultured in bioreactors

Scaling-up in bioreactors and reduction in manual handling provide an efficient and economic system for micro-propagation of bulb and corn plants. Liquid medium and continuous aeration-circulation induce mechanical and oxidative stress often resulting in hyperhydricity. Growth retardants, inhibitors of Gibberellin (GA) synthesis and changes in medium viscosity were studied to reduce shoot and leaf growth, induce nodular clusters and enhance proliferation in bioreactor cultured Ornithogalum dubium. Plant propagules were initiated from agar established leaf and inflorescence explants from flowering plants, in the presence of 8.9 μM BA and 0.54 μM NAA. Regenerated buds were subcultured to liquid shake cultures with 2.5 μM PAC, in 250 ml flasks with 80 ml medium for further multiplication. The buds proliferated and formed shoot clusters and were transferred to 1.5 1 airlift bioreactors with 1.2 1 medium resulting in a 4 fold biomass increase after 32 days and a 10 fold increase after 50 days. PAC, ranging from 0.5 μM to 5.0 μM was added to liquid cultured O. dubium clusters. The level of 2.5 μM PAC was found as most effective in inhibiting leaf expansion and shoot malformations in bioreactors. It enhanced meristematic cluster formation, increased bud proliferation along with bulblet initiation. Addition of 0.5% w/v XAN, a polymer that increased medium viscosity of the PAC medium, further reduced abnormal morphology. PAC and XAN lowered enzyme activity of the Ascorbate-Glutathione cycle after the second week of O. dubium bud clusters in bioreactors. Growth retardants and medium viscosity improved shoot structure and function, reduced stress response thus providing O. dubium plants with initial bulblets for ex vitro transplanting and improved survival.