Progressive loss of organogenic totipotency appears to be a common event in long-term plant tissue eultme. This loss of totipotency, which has been proposed to be a typical trait of plant neoplastic progression, is compared to some mechanisms thai occur during the establishment of animal differentiation-resistant cancer lines in ~itro. Evidence is presented that alteration in DNA methylation patterns and expression of genes occur during long-term callus culture. An effect of the auxin, 2,4-dichlorophenoxyacetic acid, in the progressive methylation, is moreover suggested. Methylation of genes relevant to cell differentiation and progressive elimination of ceils capable of differentiation is proposed as being responsible for this progressive loss of organogenic potential. Finally, the epigenetie alteration (DNA methylation) that occurs during prolonged periods of culture may induce other irreversible genetic alterations that uhimately make the loss of totipotency irreversible.

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Lignosulfonates (LIGNs), low-cost by-products from the paper industry, are already commercialized as fertilizers; they stimulate both vegetative and reproductive growths and fructification. LIGNs have been tested in in vitro cultures and here too, they improve shoot growth and vigor, and rooting of various plant materials. This study aimed at to extend the in vitro application of LIGNs at different developmental stages in order to increase the productivity of systems generating vitroplants. The present results showed the beneficial effects of various LIGN applications on growth of a tropical orchid, Phalaenopsis, multiplication of Saintpaulia ionantha and rooting of poplar and Sequoiadendron sempervirens shoot cuttings. One of the most interesting observations was the stimulating effect of Ca-chelated LIGN on growth of Phalaenopsis and on rooting of Sequoiadendron. The significant and reproducible effects of LIGNs at several steps of micropropagation of different plant materials represent a potential tool to improve quality without embarrassing sideeffects.

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