PARADOXICAL RESULTS IN THE ANALYSIS OF HYPERHYDRIC TISSUES CONSIDERED AS BEING UNDER STRESS: QUESTIONS FOR A DEBATE

Abstract

Summary. Hyperhydric malformations affecting shoots under micropropagation, a phenomenon called vitrification or hyperhydricity, appear as resulting from an unability of the organs to adapt completely their whole defense battery composed of enzymes against activated oxygen species and of soluble reductants, in front of several simultaneous stresses due to in vitro culture conditions. Two different types of calli, habituated to both auxins and cytokinins, show typical characteristics of hyperhydricity. Although they appear to be protected against deleterious reactions generated by stresses, behaviour in darkness instead of light and several biochemical features prone for the calli still being tissues under permanent stress. Paradoxical results unexplained by literature data lead to a reappraisal of fundamental questions related to stresses, especially in relation to hyperhydricity and habituation. Key words: defense enzymes, habituation, hyperhydricity, plant tissue cultures, stress Paradoxical results in the analysis of hyperhydric tissues... Hyperhydric malformations as a response to stress conditions The term vitrification, recently rebaptized hyperhydricity (Debergh et al., 1992), encompasses a teratological process occurring during the in vitro multiplication of