Plant growth stimulation in Prunus species plantlets by BTH or OTC treatments under in vitro conditions.

The effects of benzothiadiazole (BTH) and L-2-oxothiazolidine-4-carboxylic acid (OTC) on the growth and viral content of micropropagated, Plum pox virus (PPV)-infected peach [(Prunus persica (L.) Batsch] 'GF305' plantlets were analyzed. Low BTH and OTC concentrations resulted in a significant increase in the growth of GF305 peach and plum plants, with greater effects in PPV-infected than in healthy GF305 peach plantlets. Neither BTH nor OTC reduced the virus content. In fact, the highest growth and viral contents coincided, especially with the 10 μM BTH treatment. Differing effects on the antioxidative metabolism of PPV-infected GF305 peach plantlets were observed, depending on the compound and the concentration used: BTH decreased GSH, whereas OTC increased it. In PPV-infected plants, the 50 μM OTC treatment produced a decrease in ascorbate peroxidase, catalase, and glutathione peroxidase, but an increase in superoxide dismutase. However, BTH produced a rise in peroxidase activity. Both 10 μM BTH and 50 μM OTC produced H₂O₂ accumulation that was correlated with the histochemical detection of H₂O₂ by 3,3'-diaminobenzidine staining. PPV infection induced NPR1 expression and a synergistic effect occurred in the presence of 50 μM OTC, since this compound produced an up-regulation of NPR1 in both healthy and PPV-infected GF305 peach plantlets. The results showed that GSH, as previously suggested, and/or H₂O₂ could be involved in the regulation of NPR1 expression. Globally, the results show that both OTC and BTH improved the vigor of Prunus species, including peach and plum, under in vitro conditions, producing positive effects on growth, antioxidative metabolism and NPR1 expression. All of these improvements could be critical for more successful ex vitro acclimatization as well as for improved responses to different stresses.