Bundle sheath cells of small veins in maize leaves are the location of uptake from the xylem

Rb+ as a tracer for K+ was used to test the hypothesis that uptake of K+ fr om xylem vessels of small veins into the symplast of maize leaves occurs at the xylem/bundle sheath cell interface. 22.5 min after immersing cut leave s into 20 mM RbCl+1 mM KCI, Rb+ appeared in the cells of the leaves. Sectio ns of these leaves were freeze-dried. In cryo-thin sections (5 mum), Rb-85( +) and K-41(+) content was determined by laser microprobe mass analysis wit h a large resolution of about 1 mum. Determining the ratio of Rb-85(+) to K -41(+) in the cell walls and cytosols of bundle sheath cells, mesophyll cel ls, and in the cells between the xylem elements resulted in the following p icture: In small veins, Rb+ entered the symplast directly at the xylem/bund le sheath cell interface.