Acclimation to low water potential in potato cell suspension cultures leads to changes in putrescine metabolism

Changes in levels and biosynthesis of di- and polyamines are associated wit h stress responses in plant cells. The involvement of these molecules was i nvestigated here in cultured potato (Solanum tuberosum L.) cells grown in m edium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin, and acclimated or not to low water potential. The diamine (putrescine) and polyamine (spermidine and spermine) status in cells gradually acclimated t o increasing concentrations (up to 20 %, w/v) of polyethylene glycol (PEG) Mr 8000, was compared with that of unacclimated cells abruptly exposed (sho cked) or not (controls) to 20 % (w/v) PEG. After a 72-h subculture, the fre e and perchloric acid (PCA)-soluble conjugated di- and polyamine pattern in acclimated cells was not dramatically different from that of controls, but PCA-insoluble conjugated putrescine was 14-fold higher than in controls. I n shocked cells, a strong reduction in free putrescine and spermidine/sperm ine titres occurred. Arginine (ADC, EC 4.1.1.19) and ornithine (ODC, EC 4.1 .1.17) decarboxylase activities were not substantially altered in shocked c ells compared with controls, while in PEG-acclimated cell populations they increased about 3-fold, both in the soluble and particulate fractions. S-Ad enosylmethionine decarboxylase (SAMDC, EC 4.1.1.21) and diamine oxidase (DA O, EC 1.4.3.6) activities followed a similar pattern to each other in that their activities were enhanced 2- and 3-fold, respectively, in acclimated c ells over unacclimated controls. Ethylene production was also enhanced in a cclimated cells. These results indicate that, with respect to di- and polya mines, acquired tolerance to low water potential in potato cells leads prin cipally to changes in putrescine biosynthesis and conjugation which may be involved in ensuring cell survival. (C) 2000 Editions scientifiques et medi cales Elsevier SAS.