Published in International Journal of Plant Sciences, Volume 164, Issue 1, January 1, 2003, pages 53-60. Copyright © 2003 University Of Chicago Press. The definitive version is available at http://dx.doi.org/10.1086/344554.
NOTE: At the time of publication, the author Charles A. Knight was not yet affiliated with Cal Poly.
Evolutionary variation for accumulation of small heat shock protein (sHsp) may contribute to thermal niche differentiation between species. Here we examine temperature and time-course-dependent variation for sHsp accumulation in a recently diverged pair of Encelia raised in a common environment: Encelia farinosa, common in the Mojave desert, and Encelia californica, which is found along the cool coastal bluffs of southern North America. Both species exhibit peak sHsp accumulation at 42oC. Encelia californica accumulated greater levels of sHsp at temperatures below 42oC, while E. farinosa had greater levels above 42oC. Encelia farinosa accumulates sHsp at temperatures up to 45oC, while E. californica does not synthesize sHsp above 44oC. Both species accumulated significant levels of sHsp while maintaining photosynthetic electron transport Fv/Fm, but above the temperatures that elicited peak sHsp expression, levels of sHsp and Fv/Fm declined in parallel to zero. Encelia californica accumulated greater levels of sHsp more rapidly than E. farinosa following a 15 min, 42oC heat treatment; however, E. farinosa maintained greater Fv/Fm at all time points. Our results indicate that there are significant differences between Encelia species for sHsp accumulation but that these results depend on the duration, magnitude, and recovery time following temperature stress.