PLANT STRESS IN VITRO: THE ROLE OF PHYTOHORMONES

Genetic and morphological abnormalities that arise in in vitro culture are most likely the result of oxidative stress. Several factors induce stress in plant tissue cultures namely: the treatment of the mother plant, explant excision, the composition of the medium, the atmosphere in the vessel and the growth room environment. An imbalance in phytohormones in the media, particularly auxins and cytokinins, is an important source of stress and has been linked to hyperhydricity, somaclonal variation, recalcitrance and habituation. All of these abnormalities are potentially very costly to the plant breeding industry. This requires a better understanding of factors that contribute to these phenomena. While certain treatments are known to induce these abnormalities, the mechanisms whereby they act are still largely unresolved, particularly in the case of phytohormones.