Poster: Temperature Responses

Abs # 182: Thermoadaptation of barley aleurone layer ER membrane function and fluidity to heat shock temperature

Presenter:	Brodl, Mark R., mbrodl@trinity.edu
Authors	Brodl, Mark R. (A)   Rosenblum, Joshua M. (A)
Affiliations:	(A): Trinity University

In heat-shocked (HS) barley aleurone layers (BALs), co-translational translocation of proteins into the ER lumen is significantly less efficient than in non-HS BALs. However, when the assay temperature is raised from 25 to 30C, ER derived from HS BALs are at least as efficient at translocation as nonheat-shocked controls. Previous thin layer chromatographic studies of ER phospholipids have shown that HS increases the level of fatty acid saturation, and electron-spin resonance (ESR) studies have shown that this HS-induced increase in saturation reduces the fluidity of the ER. According to the principle of homeoviscous adaptation, this is an adaptive response, for this increase in membrane viscosity will counter the fluidizing effects of heat, maintaining proper function of integral membrane proteins. In this study we used fluorescence polarization and wheat germ-based in vitro translation/translocation assays to monitor the fluidity and function of heat-adapted BAL ER. Our data show that when BALs are heat adapted by prolonged exposure (18 h at 40C), gradual "ramping" (2.5C increase every 30 or 60 minutes) to heat shock temperature (40C), or, warm pre-incubations preceding HS (30-34C rather than 25C), ER transport efficiency is comparable to that of non-HS ER when the assays are performed at warmer temperatures. Furthermore, fluorescence polarization data confirm ESR results, and we are extending our studies to heat adapted samples. Our studies provide insights about the range of heat adaptability in the secretory process that will be useful in breeding or engineering heat-tolerant crops.