Uptake and metabolic effects of salicylic acid on the pulvinar motor cells of Mimosa pudica L.

In this paper, the salicylic acid (o-hydroxy benzoic acid) (SA) uptake by the pulvinar tissues of Mimosa pudica L. pulvini was shown to be strongly pH-dependent, increasing with acidity of the assay medium. This uptake was performed according to a unique affinity system (Km = 5.9 mM, Vm = 526 pmol mgDW−1) in the concentration range of 0.1-5 mM. The uptake rate increased with increasing temperature (5-35 °C) and was inhibited following treatment with sodium azide (NaN3) and carbonyl cyanide m-chlorophenylhydrazone (CCCP), suggesting the involvement of an active component. Treatment with p-chloromercuribenzenesulfonic acid (PCMBS) did not modify the uptake, indicating that external thiol groups were not necessary. KCl, which induced membrane depolarization had no significant effect, and fusicoccin (FC), which hyperpolarized cell membrane, stimulated the uptake, suggesting that the pH component of the proton motive force was likely a driving force. These data suggest that the SA uptake by the pulvinar tissues may be driven by two components: an ion-trap mechanism playing a pivotal role and a putative carrier-mediated mechanism. Unlike other benzoic acid derivatives acting as classical respiration inhibitors (NaN3 and KCN), SA modified the pulvinar cell metabolism by increasing the respiration rate similar to CCCP and 2,4-dinitrophenol (DNP). Furthermore, SA inhibited the osmoregulated seismonastic reaction in a pH dependent manner and induced characteristic damage to the ultrastructural features of the pulvinar motor cells, particularly at the mitochondrial level.