Growth and biochemical responses of jojoba (Simmondsia chinensis (Link) Schneid) explants cultured under mannitol-simulated drought stress in vitro

Jojoba explants were cultured under four levels of mannitol (control plus 50, 100, 250 and 500mM mannitol)-induced osmotic stress during the proliferation stage in vitro. Explants grown under control condition exhibited the highest growth, while the more severe the stress was, the lower was the growth of explants. Electrolyte leakage, lipid peroxidation, H2O2 content and proline concentration were highest and relative water content lowest under the highest level of osmotic stress. Concentration of phenolic compounds (total phenolic compounds, o-diphenols and flavanols, as well as protocatechuic, vanillic, p-coumaric and ferulic acids and rutin), putrescine and total polyamines decreased with increasing stress level. Mannitol, glucose and pinitol concentrations increased, whereas that of inositol decreased with increasing stress level. Explants were transferred to the rooting stage, separately per stress treatment. Explants grown under stress conditions during the proliferation stage exhibited lower rooting percentage than controls, as the stress became more severe, the lower was the rooting response. Jojoba tolerated osmotic stress to some extent (till 100-250mM mannitol), exhibiting sufficient growth rate and good rooting response as well as low oxidative damage (based on electrolyte leakage and lipid peroxidation indices).