Disruption of the Plasma Membrane Integrity by Cholesterol Depletion Impairs Effectiveness of TRH Receptor-Mediated Signal Transduction via Gq/G11α Proteins

We monitored the radioligand-binding characteristics of thyrotropin-releasing hormone (TRH) receptors, functional activity of G_q/11α proteins, and functional status of the whole signaling cascade in HEK293 expressing high levels of TRH receptors and G₁₁α. Our analyses indicated that disruption of plasma membrane microdomains by cholesterol depletion did not markedly influence the binding parameters of TRH receptors, but it altered efficacy of signal transduction. The functional coupling between TRH receptor and G_q/11α was assessed by agonist-stimulated [³⁵S]GTPγS binding, and results of these measurements pointed out to significantly lower potency of TRH to mediate G protein activation in the plasma membrane fraction isolated from cholesterol-depleted cells; there was a shift in sensitivity by one order of magnitude to the higher concentrations. A markedly lower sensitivity to stimulation with TRH was also observed in our experiments dealing with determination of hormone-induced Ca²⁺ response. These data suggest that the intact structure of plasma membranes is an important optimum signal transduction initiated by TRH receptors and mediated by G_q/11α proteins.     

Effects of an experimental drought on the functioning of a cacao agroforestry system,Sulawesi, Indonesia

Agroforestry systems may play a critical role in reducing the vulnerability of farmers' livelihood to droughts as tree‐based systems provide several mechanisms that can mitigate the impacts from extreme weather events. Here, we use a replicated throughfall reduction experiment to study the drought response of a cacao/Gliricidia stand over a 13‐month period. Soil water content was successfully reduced down to a soil depth of at least 2.5 m. Contrary to our expectations we measured only relatively small nonsignificant changes in cacao (?11%) and Gliricidia (?12%) sap flux densities, cacao leaf litterfall (+8%), Gliricidia leaf litterfall (?2%), soil carbon dioxide efflux (?14%), and cacao yield (?10%) during roof closure. However, cacao bean yield in roof plots was substantially lower (?45%) compared with control plots during the main harvest following the period when soil water content was lowest. This indicates that cacao bean yield was more sensitive to drought than other ecosystem functions. We found evidence in this agroforest that there is complementary use of soil water resources through vertical partitioning of water uptake between cacao and Gliricidia. This, in combination with acclimation may have helped cacao trees to cope with the induced drought. Cacao agroforests may thus play an important role as a drought‐tolerant land use in those (sub‐) tropical regions where the frequency and severity of droughts is projected to increase.