Effects of CO2 enrichment and drought pretreatment on metabolite responses to water stress and subsequent rehydration using potato tubers from plants grown in sunlit chambers.

Experiments were performed using naturally sunlit Soil-Plant-Atmosphere Research chambers that provided ambient or twice ambient CO2. Potato plants were grown in pots that were water sufficient (W), water insufficient for 12-18 days during both vegetative and tuber development stages (VR), or water insufficient solely during tuber development (R). In the ambient CO2 treatment, a total of 17 and 20 out of 31 tuber metabolites differed when comparing the W to the R and VR treatments, respectively. Hexoses, raffinose, mannitol, branched chain amino acids, phenylalanine and proline increased, although most organic acids remained unchanged or decreased in response to drought. Osmolytes, including glucose, branched chain amino acids and proline, remained elevated following 2 weeks of rehydration in both the ambient and elevated CO2 treatments, whereas fructose, raffinose, mannitol and some organic acids reverted to control levels. Failure of desiccated plant tissues to mobilize specific osmolytes after rehydration was unexpected and was likely because tubers function as terminal sinks. Tuber metabolite responses to single or double drought treatments were similar under the same CO2 levels but important differences were noted when CO2 level was varied. We also found that metabolite changes to water insufficiency and/or CO2 enrichment were very distinct between sink and source tissues, and total metabolite changes to stress were generally greater in leaflets than tubers.