Effect of putrescine on the conversion of protocorm-like bodies of Dendrobium officinale to shoots

The addition of 1.5 mM putrescine to the culture medium facilitated the conversion of protocorm-like bodies (PLBs) of Dendrobium officinale to shoots. The administration of 1.0 mM of the polyamine inhibitor, alpha-DL-difluoromethylarginine, decreased the conversion of PLBs to shoots. Compared to the control, the PLBs treated with 1.5 mM putrescine had higher levels of total intracellular free polyamines. The enhanced conversion of PLBs to shoots following the addition of putrescine was accompanied by an increase in the ratio of total cytokinins (CTKs) to indole-3-acetic acid (IAA). Analysis of enzyme activities indicated that the increased endogenous level of total CTKs driven by putrescine was associated with the inhibition of CTK decomposition by CTK oxidase, while the decreased endogenous level of IAA was associated with the promotion of IAA decomposition by IAA oxidase. In addition, putrescine increased the ratio of reduced glutathione to oxidized glutathione in the conversion process of PLBs to shoots.