Seasonal variation in heat shock proteins Hsp70 and Hsp90 expression in an exposed and a shaded habitat of Iris pumila.

Seasonal variation in heat shock proteins Hsp70 and Hsp90 expression was studied in the leaves of two naturally growing Iris pumila populations, one inhabiting an open dune site, and the other the understorey of a Pinus silvestris stand. The Hsps were quantified by an immunoblotting procedure. The level of the Hsps was found to vary significantly both across seasons and between habitats. The mean Hsp70 concentration was significantly greater at the open area than in the woodland understorey, reaching its maximum in the summer, especially in plants experiencing full sunlight. Two Hsp90 isoforms, referred to as Hsp90a (86 kDa) and Hsp90b (84 kDa), were detected. At both habitats, the level of Hsp90a was highest in autumn, that of Hsp90b in spring, whereas both of them reached a nadir in summer. Throughout the growing season, the relative abundance of Hsp90b was higher in plants growing under vegetation canopy in comparison to those inhabiting the open dune site. An inverse relationship between the phenotypic variation in specific leaf area and the level of Hsp90b over seasons at both habitats was observed, suggesting the role of this protein in buffering phenotypic variation in the wild.

Mercury influences rat liver tyrosine aminotransferase activity and induction by dexamethasone.

The effects of mercury (Hg) on basal and dexamethasone-induced tyrosine aminotransferase (TAT) activity in rat liver were studied. Comparison of TAT activity after in vitro and in vivo mercury application revealed the influence of the metal only when applied in vivo, suggesting that the effects are expressed at the level of TAT gene transcription. Intraperitoneal administration of mercury at 1, 2 or 3 mg Hg kg(-1) b.w. 4 h before decapitation was shown to stimulate the basal activity of TAT. The most prominent increase was observed 4 h after the metal administration. When applied at 1 and 2 mg Hg kg(-1) b.w. mercury was also shown to reduce partially the extent of the enzyme induction by dexamethasone, which was injected intraperitoneally at 5 mg kg(-1) b.w. 5 h before death. The highest dose of mercury (3 mg Hg kg(-1) b.w.) almost completely abolished the dexamethasone effect. The finding that mercury increases basal activity of the enzyme while decreasing its induction by dexamethasone suggests that stimulatory effects of this metal on TAT activity are probably mediated by factors other than glucocorticoids.