Changes in endogenous hormones and oxidative burst as the biochemical basis for enhanced shoot organogenesis in cold-treated Saussurea involucrata explants

A low temperature treatment significantly improved shoot morphogenesis of Saussurea involucrata Kar. et Kir leaf explants. The biochemical mechanisms underlying the cold-induced shoot organogenesis were investigated by measuring endogenous plant growth hormones, peroxide radicals, and superoxide dismutase (SOD) activity in the cold-treated leaf explants compared to controls. The ratio of zeatin (ZT) to indole-3-acetic acid (IAA) significantly increased in leaf explants subjected to a 5-day treatment at 4 °C compared to controls. The accumulation of O ₂ ·⁻ also rapidly increased in response to cold treatment, and then decreased as SOD activity catalyzed the dismutation of O ₂ ·⁻ to molecular oxygen and H₂O₂; this resulted in a significant increase in H₂O₂ concentrations in the cold-treated explants. We propose that a combination of the increased ZT/IAA ratio and H₂O₂ concentration is the basis for the enhanced shoot morphogenesis in response to cold treatment. These results provide a starting point for an improved understanding of the biochemical mechanisms underlying cold-induced shoot organogenesis of this unique plant species.