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.