In Vitro Physiological Studies of Crocus sativus Development

Some likely stresses encountered by plants are flooding and water/soil contamination by heavy metals. Oxygen deprivation by flooding, commonly known as hypoxia-anoxia, induces profound changes in cellular metabolism and poses a significant threat to plant survival. Heavy metal contamination results in similar adverse effects. Evidence has accumulated on the involvement of reactive oxygen species (ROS) in the anoxic and in the heavy metal toxicities. Roots and corms being among the plant organs most directly exposed to these stresses, we investigated the effect of hypoxia/anoxia, as well as that of heavy metals, on enzymatic activities in Crocus sativus corms, with emphasis on ROS scavenging enzymes. The morphology of corms exposed to hypoxia/anoxia or to heavy metals was also examined. Catalase, peroxidases (ascorbate, lignin, guaiacol and ABTS peroxidases) and polyphenol oxidase activity was investigated in corms cultivated in liquid medium in the presence of ambient (normoxia) and reduced (hypoxia/anoxia) oxygen levels. In normoxia, the activities of ascorbate and ABTS peroxidases as well as that of polyphenol oxidase were stimulated. In dormant corms placed under hypoxia/anoxia, only the activities of catalase and guaiacol peroxidase were stimulated, with the highest stimulation observed for catalase. In corms cultivated for three days before hypoxia/anoxia, the activities of all ROS scavenging enzymes studied were increased with the highest increase still observed for catalase, followed by lignin and guaiacol peroxidases, then scorbate and ABTS peroxidases. The activity of catalase, o-dianisidine peroxidase and superoxide dismutase, investigated in corms cultivated in liquid medium supplemented with increasing Cu2+ concentrations was stimulated, with a peak at 0.3 mM Cu2+ for catalase and at 1.2 mM for superoxide dismutase. Thus hypoxia/anoxia altered the balance between ROS scavenging enzymes with a dependence on the time of onset of hypoxia/anoxia. Selected Cu2+ concentrations stimulated differentially ROS scavenging enzymes activity while excess Cu2+ inhibited them.