Effects of exogenous salicylic acid on Impatiens walleriana L. grown in vitro under polyethylene glycol-imposed drought

We describe the responses of Impatiens walleriana to polyethylene glycol (PEG)-induced physiological drought and the potential of exogenous salicylic acid (SA) as stress-ameliorating agent. Impatiens shoot culture was established on 16 different media containing 0-3% PEG and 0-3 mM SA. After prolonged drought (60 days), water relation parameters, oxidative stress indicators, and growth responses of the shoots to PEG and/or SA were recorded. PEG reduced growth, fresh weight, the number of developed leaves and shoots (proliferation rate, PR), relative water content, and chlorophyll content. PEG increased leaf water loss (LWL) and caused accumulation of proline, H2O2, and malondialdehyde. The activities of catalase, superoxide dismutase, and peroxidase were increased in response to PEG in a dose-dependent manner, with specific peroxidase isoforms induced by drought. Exogenous SA counteracted the effects of PEG on growth, physiological and biochemical parameters, except on proline accumulation. SA was particularly effective in enhancing PR, preserving LWL, and protecting photosynthetic pigments and membranes from oxidative damage. Proline accumulation was strongly enhanced by both PEG and SA. SA had differential effects on different peroxidase isoforms. SA may be safely used in 2-3 mM concentration for drought protection of Impatiens with no negative effects