Arsenate Impact on the Metabolite Profile, Production, and Arsenic Loading of Xylem Sap in Cucumbers (Cucumis sativus L.)

Arsenic uptake and translocation studies on xylem sap focus generally on the concentration and speciation of arsenic in the xylem. Arsenic impact on the xylem sap metabolite profile and its production during short term exposure has not been reported in detail. To investigate this, cucumbers were grown hydroponically and arsenate (As(V)) and DMA were used for plant treatment for 24 h. Total arsenic and arsenic speciation in xylem sap was analyzed including a metabolite profiling under As(V) stress. Produced xylem sap was quantified and absolute arsenic transported was determined. As(V) exposure had a significant impact on the metabolite profile of xylem sap. Four m/z values corresponding to four compounds were up-regulated, one compound down-regulated by As(V) exposure. The compound down-regulated was identified to be isoleucine. Furthermore, As(V) exposure had a significant influence on sap production, leading to a reduction of up to 96% sap production when plants were exposed to 1000 μg kg(-1) As(V). No difference to control plants was observed when plants were exposed to 1000 μg kg(-1) DMA. Absolute arsenic amount in xylem sap was the lowest at high As(V) exposure. These results show that As(V) has a significant impact on the production and metabolite profile of xylem sap. The physiological importance of isoleucine needs further attention.