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 O2 2 also rapidly increased in response to cold treatment, and then decreased as SOD activity catalyzed the dismutation of O2 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.
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