The Effect of Isoprene on the Properties of Spinach Thylakoids and Phosphatidyicholine Liposomes

Abstract

Isoprene is emitted from the leaves of some plants. It was recently reported that exogenous isoprene delays the onset of leaf damage during controlled increases in leaf temperature (Singsaas et al. Plant Physiology 115: 1413-1420 [1997]171J). Thylakoid membranes are presumed to be the site of action based upon isoprene's hydrophobicity, production in chloroplasts, and effect upon chlorophyll fluorescence at high temperatures. In an attempt to discern the mechanistic basis for isoprene's thermoprotective role, we studied the effect of exogenous isoprene on the peroxidation, permeability, and stability of spinach thylakoids and phosphatidylcholine liposomes. Isoprene, supplied at either 18 or 21 p1 L_l, had no effect upon the rate of liposome peroxidation in the presence of a hydroxyl radical-generating system. Isoprene also did not affect liposome peroxidation at high temperatures. Neither the proton permeability of thylakoids nor the leakage of a fluorescent probe from liposomes was influenced by exogenous isoprene, when measured at several temperatures. Isoprene did not affect the stability of thylakoid membrane proteins during a temperature increase, as shown by differential scanning calorimetry. Therefore, despite the use of a variety of techniques to investigate fundamental membrane parameters, we were unable to demonstrate an effect of isoprene.

The Sesquiterpenes(E)-ß-Farnesene and (E)-α-Bergamotene Quench Ozone but Fail to Protect the Wild Tobacco Nicotiana attenuata from Ozone, UVB, and Drought Stresses

“…The enhanced growth of isoprene-emitting A . thaliana plants under heat stress [ 61 ], and the lack of isoprene-mediated thermoprotection in either isolated membranes [ 62 ] or leaf discs [ 63 ], would be consistent with the hypothesis that terpenes ameliorate stress by activating within-plant signaling cascades rather than by direct reaction with oxidants. Because of their reactive nature, sesquiterpenes might influence hydrogen peroxide signaling [ 8 ] or prime responses to further stress in neighboring cells, organs or individuals in a phenomenon analogous to volatile-mediated induction of herbivore resistance [ 70 ].…”

“…mays [ 24 ]. Isoprene supplementation did not enhance redox status or membrane integrity of isolated Spinacea olearacea thylakoids [ 62 ] or increase thermotolerance in leaf discs of four isoprene-emitting species [ 63 ], but these papers did not test whole-plant responses. In our experiments, we used intact plants producing endogenous sesquiterpenes at the high end of natural levels, but still observed no protective effects.…”

Isoprene: New insights into the control of emission and mediation of stress tolerance by gene expression

“…Recent studies have shown that isoprene is present at very low concentration in chloroplastic membranes (0.0044 mol% isoprene under physiological conditions) and is therefore presumed to be insufficient to affect membrane dynamics or to be an efficient sink for ROS (Harvey et al, ). In addition, leaf discs fumigated with isoprene do not exhibit thermal protection (Logan, Anchordoquy, Monson, & Pan, ; Logan & Monson, ). Therefore, new hypotheses have been put forward to explain how isoprene protects plants from biotic and abiotic stresses.…”