Drought affects carbon partitioning into volatile organic compound biosynthesis in Scots pine needles

The effect of drought on the interplay of processes controlling carbon partitioning into plant primary and secondary metabolisms, such as respiratory CO2 release and volatile organic compound (VOC) biosynthesis, is not fully understood. To elucidate the effect of drought on the fate of cellular C sources into VOCs vs CO2, we conducted tracer experiments with (CO2)-C-13 and position-specific C-13-labelled pyruvate, a key metabolite between primary and secondary metabolisms, in Scots pine seedlings. We determined the stable carbon isotope composition of leaf exchanged CO2 and VOC. Drought reduced the emission of the sesquiterpenes alpha-farnesene and beta-farnesene but did not affect C-13-incorporation from C-13-pyruvate. The labelling patterns suggest that farnesene biosynthesis partially depends on isopentenyl diphosphate crosstalk between chloroplasts and cytosol, and that drought inhibits this process. Contrary to sesquiterpenes, drought did not affect emission of isoprene, monoterpenes and some oxygenated compounds. During the day, pyruvate was used in the TCA cycle to a minor degree but was mainly consumed in pathways of secondary metabolism. Drought partly inhibited such pathways, while allocation into the TCA cycle increased. Drought caused a re-direction of pyruvate consuming pathways, which contributed to maintenance of isoprene and monoterpene production despite strongly inhibited photosynthesis. This underlines the importance of these volatiles for stress tolerance.

Automated summary

The study found that drought has effects on carbon partitioning and volatile organic compound synthesis in Scots pine seedlings, reducing the emission of certain sesquiterpenes but not affecting carbon incorporation. Additionally, drought resulted in a re-direction of pyruvate to secondary metabolism pathways, maintaining isoprene and monoterpene production.