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

2. 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

3. 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

4. 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

5. Do plants have benefits from isoprene synthesis?

6. 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

7. 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

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

9. 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

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

11. Isoprene accumulates at the center of the bilayer

12. Isoprene induces order of the alkyl tails of phospholipids

14. 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