ISOPRENE - A possible mechanism by which plants protect themselves from thermal shock Magdalena Siwko

Building unit of biomolecules, such as hormones, chlorophyll, fragrances, natural rubber The highest rate of emission in woody plants, e.g. oaks, poplars Atmospheric chemistry (generate large amounts of O3, forms secondary organic aerosols ISOPRENE Global isoprene emission from plants is ~ 5x1014 g C year-1 The most common volatile hydrocarbon Isoprene synthases: a) thylakoid-bound lumenal protein, b) free soluble synthase

ISOPRENE 2-methyl-1,3-butadiene Highly volatile, boiling point 34°C Reactive, capable of polymerizing Insoluble in water <1 mg/ml Soluble in non-polar solvents 100 mg/ml Blue haze

During acute increases in temperature: isoprene production in plants rises dramatically No isoprene storage in leaves synthesized de novo 5%-50% photosynthetic carbon converted to isoprene

Do plants have benefits from isoprene synthesis?

The thermotolerance hypothesis - Sharkey&Singsaas, 1997 Isoprene enhances hydrophobic interactions in the thylakoid membrane protecting the photosynthetic system from thermal damage including: Formation of non-lamellar structures. Fragmentation of membrane-protein complexes

Systems Different concentrations of isoprene - 20 mol% (16 isoprene:64 DMPC) - 43mol% (48 isoprene:64 DMPC) Reference system: pure DMPC bilayer Hydration level: 20 SPC water/lipid Range of temperatures: 303K, 323K, 333K, 343K, 353K Simulation time: 90 ns

Spontaneous bilayer formation 0 ns 5 ns SPC DMPC 20 ns 30 ns 40 ns

Parameterization of the isoprene molecule 500 isoprene molecules Density: calc. 680,6 kg/m3 exp. 681 kg/m3 Heat of vaporization H: calc. 27 kJ/mol exp. 24 kJ/mol

Diffusion of isoprene into the bilayer 0 ns 2 ns 20 ns 50 ns

Isoprene accumulates at the center of the bilayer

Isoprene induces order of the alkyl tails of phospholipids

Conclusions Isoprene enhances the packing of lipid tails Isoprene partitions into the center of the bilayer inducing an order of the lipid tails counteracting the effect of an increase in temperature The dynamics of the tails is not affected Isoprene protects against thermal shock by maintaining constant level of membrane fluidity