Light stress study on in vitro photoautotrophic cultures. Application to the search of mutants

Light stress applied on a photoautotrophic ce11 suspension of Euphorbia characias leads to inhibition of photosynthesis. The examination of the effects of O₂ concentration and methyl viologen showed a limited implication of the superoxide radical. Moreover, photoinhibition occurs at non saturating light suggesting a major contribution of the donor side of the photosystem II. In long term, the energetic deficit induced by the prolonged photosynthesis photoinhibition results in a catabolic pathway that leads, in the absence of tissue cooperation, to the death of the cells. This work was used to establish on Solanum tuberosum a strategy for the in vitro selection of variants modified in their response to light stress. Photoautotrophic protocols were developed for the culture and regeneration of callus derived from protoplast as we11 as for the culture of a regenerating cell suspension. A light stress screening procedure under 2% CO₂ was applied on the photosynthetically active callus derived from these two systems. In the regenerated plants, several physiological variants have been obtained, some of them showing different levels of photoinhibition under air or under 2% CO₂ when compared to the wild type; most of the regenerated plants do not exhibit the higher photoinhibition which is observed, under 2% CO₂, in the wild type. The effects of high CO₂ and light in the screening procedure are discussed. (author)