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Kuznetsov, V. V. and Shevyakova, N. I. 1997. Stress responses of tobacco cells to high temperature and salinity. Proline accumulation and phosphorylation of polypeptides. -Physiol. Plant. 100: 320-326.Stress responses to high temperatures (35^8°C) and salinity (170-340 mM NaCl) and thermotolerance were investigated for the salt-sensitive wild type and the salt-tolerant NfEj-l strain of Nicotiana sylvestris L. using suspension-cultured cells. Under saline conditions, NjEs-l strain cells accumulated proline, polyamine (putrescine and spermidine) and betaine in contrast to wild-type cells. The simultaneous treatment of salt-tolerant cells with high temperature (40°C) and NaCl (170 or 340 mM) resulted in a transient overproduction of proline accompanied by an increase in their thermotolerance. At the high temperature, the synthesis of polypeptides and the accumulation of heat shock protein HSP70 mRNA were not affected by salinity. The higher thermotolerance of the NaCl-tolerant cells could not be related to osmoprotecting sugar-starch interconversions but could rather be associated with selective phosphorylation of several polypeptides (23)(24) 27,(31)(32) 47 kDa) pdor to the accumulation of proline. The possible role of polyamines and polypeptide phosphorylation in this respect is discussed.

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Among metals, Ni has been indicated as one of the most dangerous for the environment, and plants exposed to this metal are frequently reported to undergo a severe stress condition. In this work, the tolerance responses to different Ni concentrations at physiological and biochemical levels were evaluated in Amaranthus paniculatus L., a plant species previously characterised for their ability to phytoremove Ni from metal-spiked water. Results indicated a good metal tolerance of this plant species at environmentally relevant Ni concentrations, while clear symptoms of oxidative damages were detected at higher Ni concentrations, both in roots and leaves, by measuring lipid peroxide content. At the photosynthetic level, pigment content determination, chlorophyll fluorescence image analysis and gas-exchange parameter measurements revealed a progressive impairment of the photosynthetic machinery at increasing Ni concentrations in the solution. Regarding biochemical mechanisms involved in antioxidative defence and metal binding, antioxidative enzyme (ascorbate peroxidase, APX; catalase, CAT; guaiacol peroxidase, GPX; superoxide dismutase, SOD) activity, polyamine (PA) content, polyamine oxidase (PAO) activity and organic acid (OA) content were differently affected by Ni concentration in the growth solution. A role for GPX, SOD, PAs, and oxalic and citric acid in Ni detoxification is suggested. These results can contribute to elucidate the tolerance mechanisms carried out by plants when facing environmentally relevant Ni concentrations and to identify some traits characterising the physiological and biochemical responses of Amaranthus plants to the presence and bioaccumulation of Ni.

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