Arabidopsis, a Model to Study Biological Functions of Isoprene Emission?

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Abstract
The volatile hemiterpene isoprene is emitted from plants and can affect atmospheric chemistry. Although recent studies indicate that isoprene can enhance thermotolerance or quench oxidative stress, the underlying physiological mechanisms are largely unknown. In this work, Arabidopsis (Arabidopsis thaliana), a natural nonemitter of isoprene and the model plant for functional plant analyses, has been constitutively transformed with the isoprene synthase gene (PcISPS) from Grey poplar (Populus x canescens). Overexpression of poplar ISPS in Arabidopsis resulted in isoprene-emitting rosettes that showed transiently enhanced growth rates compared to the wild type under moderate thermal stress. The findings that highest growth rates, higher dimethylallyl diphosphate levels, and enzyme activity were detected in young plants during their vegetative growth phase indicate that enhanced growth of transgenic plants under moderate thermal stress is due to introduced PcISPS. Dynamic gas-exchange studies applying transient cycles of heat stress to the wild type demonstrate clearly that the prime physiological role of isoprene formation in Arabidopsis is not to protect net assimilation from damage against thermal stress, but may instead be to retain the growth potential or coordinated vegetative development of the plant. Hence, this study demonstrates the enormous potential but also the pitfalls of transgenic Arabidopsis (or other nonnatural isoprenoid emitters) in studying isoprene biosynthesis and its biological function(s).