Increased Thermostability of Thylakoid Membranes in Isoprene-Emitting Leaves Probed with Three Biophysical Techniques    

Abstract

Three biophysical approaches were used to get insight into increased thermostability of thylakoid membranes in isoprene-emittingplants.Arabidopsis (Arabidopsis thaliana) plants genetically modified to make isoprene and Platanus orientalis leaves, in which isoprene emission was chemically inhibited, were used. First, in the circular dichroism spectrum the transition temperature of the main band at 694 nm was higher in the presence of isoprene, indicating that the heat stability of chiral macrodomains of chloroplast membranes, and specifically the stability of ordered arrays of light-harvesting complex IIphotosystem II in the stacked region of the thylakoid grana, was improved in the presence of isoprene. Second, the decay of electrochromic absorbance changes resulting from the electric field component of the proton motive force (DA 515 ) was evaluated following single-turnover saturating flashes. The decay of DA 515 was faster in the absence of isoprene when leaves of Arabidopsis and Platanus were exposed to high temperature, indicating that isoprene protects the thylakoid membranes against leakiness at elevated temperature. Finally, thermoluminescence measurements revealed that S 2 Q B 2 charge recombination was shifted to higher temperature in Arabidopsis and Platanus plants in the presence of isoprene, indicating higher activation energy for S 2 Q B 2 redox pair, which enables isoprene-emitting plants to perform efficient primary photochemistry of photosystem II even at higher temperatures. The data provide biophysical evidence that isoprene improves the integrity and functionality of the thylakoid membranes at high temperature. These results contribute to our understanding of isoprene mechanism of action in plant protection against environmental stresses.

Knocking Down of Isoprene Emission Modifies the Lipid Matrix of Thylakoid Membranes and Influences the Chloroplast Ultrastructure in Poplar

“…Indeed, with circular dichroism spectroscopy, it has been shown that isoprene deficiency inhibits the formation of the chirally organized macrodomains. This effect in turn decreases the thermal stability of thylakoid membranes (Velikova et al, 2011). We also observed the significant downregulation of the cytochrome b 6 f complex in NE lines (Velikova et al, 2014), which might inhibit the production of ATP in isoprene-suppressed plants.…”

“…One of the proposed biological functions of isoprene is the stabilization of thylakoid membrane structures through modification of the lipid environment and organization of the pigment-protein complexes in thylakoid membranes (Velikova et al, 2011). Indeed, several clear alterations were evident in thylakoid membrane lipids and fatty acid composition due to the translational suppression of isoprene synthase activity in poplar plants.…”

“…Thermoluminescence data demonstrated that the position of the main peak (QB peak; Sane, 2004) was upshifted approximately 10°i n isoprene-emitting (IE) plants, suggesting modifications in the lipid environment due to the presence of isoprene in heterologous Arabidopsis (Arabidopsis thaliana) plants expressing the isoprene synthase gene from poplar (Populus spp.). It was also shown that isoprene improves the stability of PSII light-harvesting complex II (LHCII) through the modification of pigment-protein complex organization in thylakoid membranes (Velikova et al, 2011). Moreover, we recently showed that knocking down isoprene emission in poplar remodels the chloroplast proteome (Velikova et al, 2014).…”

“…The isoprene impact on thylakoid intactness and functionality has been assessed using different biophysical techniques (Velikova et al, 2011). Thermoluminescence data demonstrated that the position of the main peak (QB peak; Sane, 2004) was upshifted approximately 10°i n isoprene-emitting (IE) plants, suggesting modifications in the lipid environment due to the presence of isoprene in heterologous Arabidopsis (Arabidopsis thaliana) plants expressing the isoprene synthase gene from poplar (Populus spp.).…”

“…Different approaches and techniques have been used to determine whether and how the cost of this expensive carbon emission is matched by the accomplishment of the physiological function in planta. It has been shown that isoprene might quench and/or regulate reactive oxygen and nitrogen species formation (Behnke et al, 2010a;Velikova et al, 2012), thereby indirectly providing a general antioxidant action (for review, see Vickers et al, 2009;Loreto and Schnitzler, 2010) and stabilizing thylakoid membrane structures due to the lipophilic properties of this molecule (Sharkey et al, 2001;Velikova et al, 2011).…”