Absorption of Copper, Zinc, and Manganese by Sugarcane Leaf Tissue

The absorption of Cu(2+), Zn(2+), and Mn(2+) by leaf tissue of 4-month old sugarcane plants (Saccharum officinarum L., var. H53-263) has been investigated. After the "apparent free space" fraction was desorbed, the absorption of Cu(2+), Mn(2+), and Zn(2+) yielded a curve typical of many ion uptake processes when measured as a function of the external concentration. However, only 1 absorption mechanism was evident for each cation. The pH optimum for Cu(2+) and Zn(2+) uptake was 5.0 to 6.0, whereas that for Mn(2+) absorption was 4.5 to 6.0. Absorption was competitively inhibited by H(+), and this inhibition was reversible when 0.5 mm Ca(2+) was present. Cu(2+) and Zn(2+) were absorbed through the same carrier sites, as concluded from their mutually competitive activities. Mn(2+) was absorbed through a second, independent mechanism. Uptake of each cation was strongly inhibited by uncouplers of oxidative phosphorylation, by Amytal and Nembutal(2), by 5 x 10(-2)m succinate, and by ADP and P(i). Absorption of Cu(2+), Zn(2+), and Mn(2+) was concluded to be coupled to oxidative phosphorylation, and specifically to energy-conservation Site I.